Citation
Rhodium and Iridium Complexes Supported by Chelating Bis-N-Heterocyclic Carbene Ligands

Material Information

Title:
Rhodium and Iridium Complexes Supported by Chelating Bis-N-Heterocyclic Carbene Ligands Design, Synthesis, and Catalytic Investigation
Creator:
Lowry, Roxy
Place of Publication:
[Gainesville, Fla.]
Publisher:
University of Florida
Publication Date:
Language:
english
Physical Description:
1 online resource (187 p.)

Thesis/Dissertation Information

Degree:
Doctorate ( Ph.D.)
Degree Grantor:
University of Florida
Degree Disciplines:
Chemistry
Committee Chair:
Veige, Adam S.
Committee Members:
Abboud, Khalil A.
Scott, Michael J.
Wagener, Kenneth B.
Hagelin-Weaver, Helena E.
Graduation Date:
8/8/2009

Subjects

Subjects / Keywords:
Carbenes ( jstor )
Catalysis ( jstor )
Catalysts ( jstor )
Crystals ( jstor )
Imidazoles ( jstor )
Ligands ( jstor )
Molecular structure ( jstor )
Protons ( jstor )
Rhodium ( jstor )
Room temperature ( jstor )
Chemistry -- Dissertations, Academic -- UF
carbene, conjugate, heterocyclic, rhodium
Genre:
Electronic Thesis or Dissertation
born-digital ( sobekcm )
Chemistry thesis, Ph.D.

Notes

Abstract:
RHODIUM AND IRIDIUM COMPLEXES SUPPORTED BY CHELATING BIS-N-HETEROCYCLIC CARBENE LIGANDS:DESIGN, SYNTHESIS, AND CATALYTIC INVESTIGATION Eighty-five percent of all industrial chemical processes occur catalytically. The world?s expanding appetite for mass production of exotic chemicals necessitates the design and application of enhanced catalysts. To optimize catalytic materials, the detailed relationships between catalyst architecture and reactivity must be determined. Although for many ligand families these relationships are well understood, novel catalysts require in depth empirical investigation to determine these connections. The design of a novel di-N-heterocyclic carbene family of ligands in reported herein. These C2 symmetric ligands are based on the rigid 9,10-dihydro-9,10-ethanoanthracene backbone and designed for utilization in chiral catalysis. Thorough investigation into the relationships between the ligand?s structure and the architecture of the resulting rhodium and iridium catalysts directed the design of three generations of our novel ligand family. The first generation, trans?1,1'?[ 9,10?dihydro?9,10?ethanoanthracene?11,12?diyldimethanediyl]bis(benzylimidazole) bis(triflouromethansulfonate) [DEAM?BI](OTf)2 (2-1), is too flexible to enforce a rigid chiral pocket about a metal center under catalytic conditions. The constrained second generation ligands, trans-1,1'-(9,10-dihydro-9,10-ethanoanthracene-11,12-diyl)di(3-methyl-imidazol-3-ium) diiodide [DEA-MI](I)2 (3-3) and trans-1,1-(9,10-dihydro-9,10-ethanoanthracene-11,12-diyl)di(3-methyl-benzimidazol-3-ium) diiodide [DEA-MBI](I)2 (3-4), produce complexes with rigid chiral pockets. However, the small variation between the two ligands produces a large alteration in the catalytic activity of the resulting complexes. In an attempt to further increase the enantiocontrol displayed by these compounds small alterations were made to produce the third generation of ligands, trans-1,1'-(9,10-dihydro-9,10-ethanoanthracene-11,12-diyl)di(3-isopropyl-imidazol-3-ium) diiodide [DEA-iPrI](I)2 (4-1), trans-1,1-(9,10-dihydro-9,10-ethanoanthracene-11,12-diyl)di(3-isopropyl-benzimidazol-3-ium) diiodide [DEA-iPrBI](I)2 (4-2), trans-1,1-(9,10-dihydro-9,10-ethanoanthracene-11,12-diyl)di(3-methyl-tolylimidazol-3-ium) diiodide [DEA-MTI](I)2 (4-6), trans-1,1-(9,10-dihydro-9,10-ethanoanthracene-11,12-diyl)di(3-isopropyl-tolylimidazol-3-ium) diiodide [DEA-iPrTI](I)2 (4-7). Catalytic investigation of the asymmetric 1,4-addition of aryl boronic acids to cyclic enones is accomplished for the constrained catalysts 3-8 [rhodium(I) trans?9,10?dihydro?9,10?ethanoanthracene?9,10?bis(1?methylbenzimidazolidine?2?ylidene) cyclooctadiene iodide], 3-9 [rhodium(I) trans?9,10?dihydro?9,10?ethanoanthracene?9,10?bis(1?methylimidazolidine?2?ylidene) cyclooctadiene iodide], and 4-8 [rhodium(I) trans?9,10?dihydro?9,10?ethanoanthracene?9,10?bis(1?isopropylimidazolidine?2?ylidene) cyclooctadiene iodide]. ( en )
General Note:
In the series University of Florida Digital Collections.
General Note:
Includes vita.
Bibliography:
Includes bibliographical references.
Source of Description:
Description based on online resource; title from PDF title page.
Source of Description:
This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Thesis:
Thesis (Ph.D.)--University of Florida, 2009.
Local:
Adviser: Veige, Adam S.
Electronic Access:
RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2010-08-31
Statement of Responsibility:
by Roxy Lowry.

Record Information

Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
Copyright Lowry, Roxy. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
Embargo Date:
8/31/2010
Resource Identifier:
489203792 ( OCLC )
Classification:
LD1780 2009 ( lcc )

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188. S. Oi, M. Moro, S. Ono and Y. Inoue, Chem. Lett., 1998, 27, 83.

189. T. Hayashi and M. Ishigedani, J. Am. Chem. Soc., 2000, 122, 976.

190. S. Oi, M. Moro, H. Ito, Y. Honma, S. Miyano and Y. Inoue, Tetrahedron, 2002, 58, 91.

191. M. Dziedzic, M. Malecka and B. Furman, Org. Lett., 2005, 7, 1725.

192. S. Oi, Y. Honma and Y. Inoue, Org. Lett., 2002, 4, 667.

193. T. Hayashi, N. Tokunaga, K. Yoshida and J. W. Han, J. Am. Chem. Soc., 2002, 124,
12102.

194. N. Tokunaga, K. Yoshida and T. Hayashi, Proc. Natl. Acad. Sci. USA, 2004, 101, 5445.

195. K. C. Nicolaou, W. Tang, P. Dagneau and R. Faraoni, Angew. Chem. Int. Ed., 2005, 44,
3874.

196. N. Miyaura and Z. Suzuki, Chem. Rev., 1995, 95, 2457.

197. D. G. Hall, ed., Boronic Acids: Preparation and Applications in Organic Synthesis and
Medicine, Wiley-VCH, Weinheim, 2005.

198. M. Sakai, H. Hayashi and N. Miyaura, Organometallics, 1997, 16, 4229.

199. Y. Takaya, M. Ogasawara, T. Hayashi, M. Sakai and N. Miyaura, J Am. Chem. Soc.,
1998, 120, 5579.

200. T. Hayashi, M. Takahashi, Y. Takaya and M. Ogasawara, J. Am. Chem. Soc., 2002, 124,
5053.

201. N. Miyaura, Bull. Chem. Soc. Jpn., 2008, 81, 1543.

202. A. Kina, H. Iwamura and T. Hayashi, J. Am. Chem. Soc., 2006, 128, 3904.

203. B. P. Morgan and R. C. Smith, J. Organomet. Chem., 2008, 693, 11.

204. T. Gendrineau, O. Chuzel, H. Eijsberg, J.-P. Genet and S. Darses, Angew. Chem. Int. Ed.,
2008, 47, 7669.

205. W.-C. Yuan, L.-F. Cun, A.-Q. Mi, Y.-Z. Jiang, L.-Z. Gong and W.-C. Yuan, Tetrahedron,
2009, 65, 4130.

206. R. Mariz, X. Luan, M. Gatti, A. Linden and R. Dorta, J Am. Chem. Soc., 2008, 130, 2172.

207. R. Shintani, Y. Ichikawa, K. Takatsu, F.-X. Chen and T. Hayashi, J. Org. Chem., 2009, 74,
869.

208. R. Jana and J. A. Tunge, Org. Lett., 2009, 11, 971.









step in this procedure is the formation of a diacid chloride. To avoid formation of a dicarboxilic

acid by hydrolysis, the reaction procedure was slightly modified.162 Both (R,R)- and (S,S)-3-1

are available through resolution of diastereotopic salts formed from (S)- and (R)-mandelic acid,

respectively.155 The enantiopurity of chiral 3-1 was tested by gas chromatography (Section

3.2.1) and found to be no less than 95% enantiopure.

The synthesis of diimidazolium salt [DEA-MI](I)2 (3-3) was accomplished by adaptation

of a known procedure for generating monoimidazoles (Figure 3-2).163, 164 The procedure was

found to form an equimolar mixture of the desired diimidazole 3-2 and an imidazole-amine. The

products are separated and purified by repeated column chromatography. Subsequent formation

of 3-3 required alkylation of 3-2 by heating with methyliodide in dry acetonitrile over two days.

A 1H NMR spectrum of [DEA-MI](I)2 (3-3) revealed a singlet at 3.82 ppm and is assigned

to the methyl protons. The imidazolium proton (NCHN) is located downfield at 8.93 ppm and

the olefinic protons of the heterocycle appear as a multiple at 7.67 ppm and as a doublet of

doublets at 6.60 ppm (J= 1.5 Hz). Noteworthy in the 13C 1H} spectrum of 3-3 is the

imidazolium carbon (NCHN), which appears downfield at 136.8 ppm.

Figure 3-3 illustrates the procedure used to synthesize the related dibenzimidazolium

derivative. The benzimidazole was constructed using a modified procedure for the conversion of

a primary amine into the corresponding benzimidazole.143 Reaction of diamine 3-1 with two

equivalents of 2-fluoronitrobenzene in DMF followed by precipitation via water addition results

in the formation of the brilliant orange dinitroamine. Initially, the dinitroamine was reduced with

H2 (1 atm over Pd/C) to yield the tetraamine after seven days. However, upon further

investigation it was determined that the reaction could be accomplished overnight at 40 bar H2

pressure.165 The reaction endpoint is signaled by dissipation of the brilliant yellow-orange color









the spectra of 2-3 excluding a few key features. Although 2-3 and 2-5 are structurally similar,

altering the metal center results in a slight variation in geometry, thus altering the exact location

of corresponding resonances. The major alteration in NMR spectra is seen in thel3C{1H} NMR.

Instead of the doublets in the 13C 1H} NMR spectrum of 2-3, the iridium bound carbons resonate

as singlets at 179.4 and 176.5 ppm. Unlike 103Rh, the predominant iridium isotopes, 191Ir and

193Ir, have quadrapolar nuclei with spin of 3/2 thereby negating M-C spin-spin coupling in the

spectra of both 2-5 and 2-6.

2.4 X-ray Structural Analysis and Comparisons

To obtain a more complete understanding of molecules 2-1 through 2-6 a structural study

was performed by single-crystal X-ray diffraction. Solid-state investigations of these molecules

allow comparison of structural variations between analogs.

2.4.1 Comparison of Organic Precursors 2-1 and 2-2.

Suitable crystals for X-ray diffraction studies of both 2-1 and 2-2 were obtained by

diffusion crystallization. Compound 2-1 crystallizes by diffusion of pentane into an ethanol

solution containing the salt, and crystals of the free dicarbene are similarly grown by diffusion of

pentane into a saturated benzene solution of 2-2. Figure 2-8 displays the solid-state structure of

the dicationic imidazolium salt 2-1 and the neutral free di-carbene 2-2.

The asymmetric unit of 2-1 contains one ligand molecule and two triflate anions in a

monoclinic space group. Investigation of the packing structure suggests an intermolecular

attraction between the olefin of the cationic imidazole and the electron-rich aryl ring of its

neighboring molecule. The shortest distance between the carbons of the olefin and aryl ring is

3.72 A and the distance between the olefin and the plane of the aromatic ring is 3.42 A. Unlike

2-1, the neutral free di-carbene 2-2 crystallizes in an orthorhombic crystal system with no

discernible intermolecular attractions.





















































145 140 135 130 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20
Chemical Shift (ppm)
Figure A-30. 13C NMR of N,N'-bis(4-aminotolyl)-9,10-dihydro-9,10-ethanoanthracene- 1,12-diamine (4-4).


II


I I I I I I I I I I


I


I I I I







































i!r 1"1 lrr ,,,lI i i,, l ii ij r j I i 1 i 1 I r '1 l i i i [ ', i ,1 j,,' iIi', iI l ', 1" II ii, i r ', ,,i i ii I' ''i rii j ri '' ,' r p "I rll[ i' iirii ,'i I ,' i I l lllFl '! II, 1" r I Il, I llll 'l r,'l I' 'll ll ,ll 'll "1 I r '\


145 140 135 130 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20
Chemical Shift (ppm)
Figure A-32. 13C NMR 1,1'-(9,10-dihydro-9,10 -ethanoanthracene- 11,12-diyl)di(1H-tolylimidazole) (4-5).


156


1111 1 1 I 1 11J I I I I


1


I I J, 1, 111 1, 11


I ,1


I I I I r ,









catalyst to increase the rate of a reaction in a cyclic manner thereby requiring far less than

stoichiometric amounts of the material.

The appeal of catalysis does not end with its ability to increase the rate of a reaction. The

non-stoichiometric nature of a catalytic cycle makes it an incredibly efficient and atom-economic

process. Not only can a catalyst reduce a reaction's activation barrier, quite often it can be

designed to do this selectively, facilitating the formation of only the desired product, thereby

reducing the amount of any undesired product to minute quantities. This catalytic selectivity is

of great importance, particularly when applied to the synthesis of chiral organic compounds.

1.2 Chiral Catalysis

The word 'chiral' refers to the asymmetry of an object and is derived from the Greek term

for hand.1 A chiral object cannot be superimposed on its mirror image much like your right

hand cannot be superimposed on your left. In chemistry, a chiral molecule and its mirror image

are termed as enantiomers, or optical isomers.11 First discovered by Jean-Baptiste Biot in

1815,12, 13 a solution containing a (+) enantiomer rotates the angle of plane polarized light

clockwise. The opposite holds true for the (-) enantiomer.11 The term chirality was first defined

by Lord Kelvin14 but Louis Pasteur is credited with much of the work regarding the molecular

origins of the phenomenon.15

The importance of molecular chirality is particularly noticeable in biological systems. The

helical architecture of DNA and RNA is determined by the chiral sugar molecules from which

they are composed. The shape of these oligonucleotides determines their biological reactivity.16

Similarly the absolute configuration of hormones, antibodies, enzymes, and receptors plays a

very important role in biological processes.17 These molecules are not only chiral but exist in

our body as only one of two possible enantiomers. In fact, the human body is said to be

homochiral because proteins are composed exclusively of L-amino acids and the backbones of















/-, ,
KV^ \^ R


Figure 1-8. Common N-heterocyclic carbenes; imidazolylidene, benzimidazolylidene,
imidazolinylidene, triazolinylidene.


RN NR


/ \
R-N' \ N R
+B^S


Rl--N N ,









LIST OF TABLES


Table page

2-1 Selected bond lengths (A) and angles () for complex 2-1................................................60

2-2 Selected bond lengths (A) and angles () for complex 2-2................................................61

2-3 Selected bond length (A) and angles () for complex 2-3............................................. 61

2-4 Selected bond length (A) and angles () for complex 2-4 ............................................. 62

2-5 Selected bond lengths (A) and angles (0) for complex 2-5................................................62

2-6 Selected bond length (A) and angles (0) for complex 2-6 ............................................. 63

2-7 Initial catalytic hydroformylation results utilizing complex 2-3...................................63

3-1 Selected bond length (A) and angles () for complex 3-5 .................................................. 88

3-2 Selected bond length (A) and angles () for complex 3-6 .................................................. 88

3-3 Selected bond lengths (A) and angles () for complex 3-7............................................... 89

3-4 Selected bond lengths (A) and angles () for complex 3-8............................................... 89

3-5 Comparison of measured and calculated bond lengths (A) and angles (0) for 3-8 ..........90

3-6 Comparison of bond lengths (A) and angles (0) for calculated structures 3-8-calc and
3-9-calc. .......... .. ........................ ....... ... .. 90

4-1 Selected bond lengths (A) and angle () for calculated structures 3-8-calc and 4-10-
calc. ................................... ....... ... .. 104

5-1 Optimization of catalytic conjugate addition involving compound 3-8. .......................... 119

5-2 Form ation of 5-1 catalyzed by 3-8, 3-9, and 4-8 ................................................................ 119

5-3 Formation of 5-2 catalyzed by 3-8, 3-9, and 4-8..........................................................120

5-4 Formation of 5-3 catalyzed by 3-8, 3-9, and 4-8..........................................................120

5-5 Formation of 5-4 catalyzed by 3-8, 3-9, and 4-8..........................................................120

5-6 Formation of 5-5 catalyzed by 3-8, 3-9, and 4-8..........................................................120

5-7 Formation of 5-6 catalyzed by 3-8, 3-9, and 4-8..........................................................120









(CD3)2SO. However, the imidazolium salt resonances are clearly present in the 1H NMR

spectrum. The diagnostic broad imidazolium resonance is displayed at 9.64 ppm, and the aryl

protons span a relatively large range from 7.17 to 9.16 ppm. The bridge and bridgehead protons

both resonate as doublets at 6.75 (J 1.9 Hz) and 4.96 ppm (J=2.1 Hz) respectively. The

isopropyl methine septet overlaps slightly with the bridgehead proton at 4.90 ppm (J=6.7 Hz)

and is coupled to the isopropyl groups which appear at 1.6 ppm (J=J 6.7 Hz).

Attempts to form the rhodium monomeric compound were unsuccessful. [Rh(COD)C1]2

was initially utilized as the rhodium source to maintain similar structures throughout the family

of Rh complexes. When initial synthesis of the monomer failed, substitution of the dimeric

rhodium starting material with the monomeric cationic rhodium source, Rh(NBD)2BF4, was

attempted. However, isolation of monomeric compound was unsuccessful and investigation of

the crude reaction mixture by solution state analysis revealed no sign of a monomeric species.

Formation of a monomeric complex from ligand 4-7 should be thermodynamically feasible,

considering the similarity of the equilibrium geometries for 3-8 and 4-10 and the formation of

the isopropyl substituted complex 4-9.

4.4 Conclusions

The four new ligands described in this chapter present alterations to the architectures of 3-3

and 3-4 to increase the definition of the chiral pocket. Ligands 4-1 and 4-2 represent an increase

in the N-substituent' s size. The reduced yields associated with synthesizing the corresponding

monometallic complexes 4-8 and 4-9 are likely the result of negative steric interactions between

the isopropyl N-substituents. Increasing the size of the substituents on the imidazole by placing a

methyl group in the meta-position does not appear to alter the calculated equilibrium geometry of

the resulting metal complex but combining the two alterations precludes the formation of a

monometallic rhodium complex.



















































136 128 120 112 104 96 88 80 72
Chemical Shift (ppm)
Figure A-24: 13C NMR spectrum of(+/-) [DEA-iPrl][I]2 (4-1) in (CD3)2SO.


64 56 48 40 32 24 16 8


gww









LIST OF REFERENCES

1. T. H. Maugh II, Science, 1983, 219, 474.

2. M. J. Krische, Tetrahedron, 2005, 61, 6169.

3. K. Kolasinski, Surface Science: Foundations of Catalysis and Nanoscience, John Wiley &
Sons, Chichester, 2002.

4. A. P. Kieboom, J. Moulijn, P. W. N. M. V. Leeuwen and R. A. V. Santen, in Catalysis: An
Integrated Approach, eds. R. A. Van Santen, P. W. N. M. Van Leeuwen, J. A. Moulijn and
B. A. Averill, Elsevier Science, Amsterdam, Editon edn., 2000.

5. J. Tyndall, Catalysis Letters, 2000, 67, 5.

6. S. K. Ritter, Chemical & Engineering News, 2008,
http://pubs.acs.org/cen/coverstory/86/8633cover3box2.html, Accessed 6/18/2009.

7. B. Cornils and W. A. Herrmann, Journal of Catalysis, 2003, 216, 23.

8. E. Morales, The North American Catalysis Society, http://www.nacatsoc.org/default.asp,
Accessed 5/1/2009.

9. B. Bosnich, ed., Asymmetric Catalysis, Martinus Nijhoff Publishers, Dordrecht / Boston /
Lancaster, 1986.

10. G. K. Boreskov, Heterogeneous, Nova Publishers, 2003.

11. F. D. Gunstone, Guidebook to stereochemistry, Longman Group Limited, New York,
1975.

12. J. B. Biot, Bull. Soc. Philomath., 1815, Paris, 190.

13. J. B. Biot, Bull. Soc. Philomath., 1816, Paris, 125.

14. P. Cintas, Angew. Chem. Inter. Ed., 2007, 46, 4016.

15. G. B. Kauffman and R. D. Myers, Chem. Educator, 1998,
http://chemeducator.org/bibs/0003006/00030257.htm, Accessed 6/21/2009.

16. R. Corradini, S. Sforza, T. Tedeschi and R. Marchelli, Chirality, 2007, 19, 269.

17. R. Crossley, Tetrahedron, 1992, 48, 8155.

18. J. L. Bada, Nature, 1995, 374, 594.

19. D. L. Nelson and M. M. Cox, Principles ofBiochemistry, 4th edn., W. H. Freeman and
Company, New York, 2005.
















































9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5
Chemical Shift (ppm)
Figure A-14: H NMR spectrum of 1,1-(9,10-dihydro-9,10-ethanoanthracene-11,12-diyl)di(3-methyl-1H-benzimidazol-3-ium)
diiodide (3-4) in (CD3)2SO.



138










iridium complexes. Chapter 5 will describe the catalytic application of this new ligand family to

the 1,4-addition of aryl boronic acids to cyclic enones.



/ ,\_
/ \







\AGZ

Reaction Coordinate
Figure 1-1. Reaction coordinate diagram for catalyzed (solid) and uncatalyzed (dotted)
reactions.



A X+Y Z

X+Cat.+ Y XCat,+Y( I)
B XCat. -Y XCat.Y (2)
XCat.Y Z + Cat. (3)

X+Cat.+Y XCat.+Y
XCat. Y Z I Cat.

X + 2Cat. + Y XCat. + YCat.
D
XCat. YCat. Z + 2Cat.

Figure 1-2. Generalized mechanisms for A) uncatalyzed reaction B) catalyzed reaction in Figure
1-1 C) single reagent activation catalysis D) catalyzed reaction with intermolecular
reaction.











Table 3-3. Selected bond lengths (A) and angles (0) for complex 3-7
3-7


Bond lengths











Angles

Torsion Angles


Rhl-C17
Rh2-C25
N1-C17
N2-C17
N3-C25
N4-C25
C18-C23
C26-31
Rhl-Cll
Rh2-C12
N1-C17-N2
N3-C25-N4
N1-C16-C15-N3


2.012(2)
2.002(2)
1.374(3)
1.353(3)
1.365(3)
1.358(3)
1.398(3)
1.400(3)
2.3828(6)
2.3626(7)
106.0(2)
106.2(2)
98.3(2)


Table 3-4. Selected bond lengths


(A) and angles (0) for complex 3-8
3-8


Bond lengths








Angles


Torsion Angles
Distance


Rh-C23
Rh-C31
N1-C23
N2-C23
N3-C31
N4-C31
C25-C30
C17-C22
C23-Rh-C31
N1-C23-N2
N3-C31-N4
N1-C15-C16-N3
Rhl-C16


2.033(4)
2.051(5)
1.365(5)
1.375(5)
1.370(5)
1.347(5)
1.376(6)
1.397(6)
84.14(17)
104.7(4)
105.9(4)
68.8(5)
3.033(4)









Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

RHODIUM AND IRIDIUM COMPLEXES SUPPORTED BY CHELATING BIS-N-
HETEROCYCLIC CARBENE LIGANDS:
DESIGN, SYNTHESIS, AND CATALYTIC INVESTIGATION

By

Roxy Joanne Lowry

August 2009

Chair: Adam S. Veige
Major: Chemistry

Eighty-five percent of all industrial chemical processes occur catalytically. The world's

expanding appetite for mass production of exotic chemicals necessitates the design and

application of enhanced catalysts. To optimize catalytic materials, the detailed relationships

between catalyst architecture and reactivity must be determined. Although for many ligand

families these relationships are well understood, novel catalysts require in depth empirical

investigation to determine these connections.

The design of a novel di-N-heterocyclic carbene family ofligands in reported herein.

These C2 symmetric ligands are based on the rigid 9,10-dihydro-9,10-ethanoanthracene

backbone and designed for utilization in chiral catalysis. Thorough investigation into the

relationships between the ligand's structure and the architecture of the resulting rhodium and

iridium catalysts directed the design of three generations of our novel ligand family. The first

generation, trans-1,1'-[ 9,10-dihydro-9,10-ethanoanthracene- 11,12-

diyldimethanediyl]bis(benzylimidazole) bis(triflouromethansulfonate) [DEAM-BI](OTf)2 (2-1),

is too flexible to enforce a rigid chiral pocket about a metal center under catalytic conditions.

The constrained second generation ligands, trans-1,1'-(9,10-dihydro-9,10-ethanoanthracene-











o l.17')A
r 22(1) L3/6(2)A .
iC .125(2)p ,102) (1 )CR
-N" 105(2 N L45(2)A
125(1)" \ / 1.45(3)A
12 3(3)
1.40(3)A
I41(4)A

Figure 2-10. Average bond angles and length of free NHCs (top) and M-NHCs(bottom)
reprinted with permission from E.Baba et al. Inorganica Chimica Acta 2005, 358,
2870.


N ('30
/ 8


C40 ( 39







ie,


C26 Cc37
SC33


( C..0 0



-C4


Figure 2-11. Molecular Structure of 2-4 (left) and 2-6 (right) with ellipsoids drawn at 50%
probability and hydrogens removed for clarity.



Table 2-1. Selected bond lengths (A) and angles (0) for complex 2-1


Bond lengths







Angles

Torsion Angles


C18-C19
C29-C30
N3-C31
N3-C29
N3-C28
N4-C31
N4-C30
N1-C20-N2
N3-C31-N4
C28-C15-C16-C17


C48


cs-%


1.343(4)
1.344(3)
1.328(3)
1.374(3)
1.473(3)
1.330(3)
1.369(3)
108.8(2)
107.9(2)
119.1(2)


c
Q
('2,
C21

C4,




('39
Xl^k

O)


F
rbLP~~


Q




























IR-Thnihdaltdnid" I hili i.r ni.-


Figure 1-3. Structures of(R) and (S)-Carvone (left) and (R)- and (S)-Thalidomidec (right).


BNAP


t-B u-
Mclkl'[hus Bislxa7nXlinil

Figure 1-4. Selected privileged ligands from T.P. Yoon and E. N. Jacobsen, Science, 2003, 299,
1691. Reprinted with permission from AAAS.


R-Cuone S-Curvyont


TADDOI.cTe









2.4.3 Bimetallic Complexes Lu-DEAM-BY] [M(COD)CI]2 2-4 and 2-6

Figures 2-5 and 2-7 display the X-ray crystal structures of bimetallic complexes 2-4 and 2-

6. Similar to the monometallic compounds, the bimetallic compounds form crystal lattices with

similar structures. Both molecules crystallize in the P1 space group and form triclinic crystal

systems.

The solution state assignment of C2 symmetry for the dinuclear complexes is retained in

the solid-state structures. The C2 axis bisects the C15-C16 bond, passing through the center of

the DEA backbone. The two neutral M(I) centers are bridged by the chiral ligand, each NHC

acting as a monodentate ligand in a distorted square planar coordination sphere that includes a

chloride and a chelating COD. The NHC moieties are parallel to each other but face opposite

directions, situating the metal centers directly above opposing backbone aryl rings.

The absence of strain from chelation permits M-CNHC bond lengths (2.021(5)A Rhl-C20,

2.024(5)A Rh2-C31, and 2.033(3)A for both Irl-C20 and Ir2-C31) that correspond to reported

literature values.124 The similarities also extend to the N-CNHC distances and N-C-N angles.

(Table 2-4 and 2-6) The large torsion angles of ZC28-C15-C16-C17 of 125.2(5) and 125.5(3)

for 2-4 and 2-6, respectively, again signify the flexibility of the ligand.

2.5 Initial Catalytic Testing

The monometallic Rh complex (-)2-3125 was investigated toward the hydroformylation of

styrene, vinyl acetate, and allyl cyanide (Table 2-7) by Dr. Muhammad T. Jan.126 It was noted

that the catalysis gave relatively high yields but lacked any significant enantiocontrol. In our

laboratory, related catalysts were being investigated toward the hydrogenation oftrans-

methylstilbene and methyl-2-acetamidoacrylate, the hydroformylation of styrene, and the

hydrogen transfer from 2-propanol to methyl ketones.127 These studies yielded two important









APPENDIX A
NUCLEAR MAGNETIC RESONANCE









Rhodium 1,4-addition ofboronic acids to cyclic enones has become a benchmark reaction

for a variety of ligands to test their capability towards asymmetric induction.23-210 Utilization of

NHC ligands is fairly rare in rhodium catalyzed conjugate additions. Monodentate

paracyclophane-substituted NHCs reported by Andrus et al.211'212 were found to provide high

yields and asymmetric induction utilizing 2 mol% [Rh(acac)(C2H4)2] at 600C in THF/water. The

best e.e. was produced by the paracyclophane with a bulky ortho-methoxyphenyl substituent.

Moderate to high enantioselectivities have also been achieved using a bidentate

diphenylphosphino-NHC rhodium complex synthesized by Helmchen and coworkers.213

Recently, Douthwaite et al. reported the synthesis of a rhodium catalyst supported by a chiral

NHC-phenoxyimine ligand.214 The complex was found to be active towards conjugate addition

but with no enantioselectivity.

NHCs have found more extensive application in copper215-217 based 1,4-addition to enones.

The first asymmetric copper conjugate additions utilizing NHCs were reported by Alexakis215

and Roland216 in 2001. Each reported similar C2 symmetric saturated imidazole ligands in the

addition of diethylzinc to 2-cyclohexen-1 -one mediated by Cu(OTf)2 with a maximum e.e. of

50% reported by Alexakis. Several groups have reported fair e.e.s, ranging from the 27%

initially reported by Roland to 93% reported by Alexakis218 and Mauduit.219 The Hoveyda group

recently reported addition of dialkylzinc reagents to P-substituted cyclic enones catalyzed in situ

using a chiral silver-NHC and Cu(OTf)2.220, 221 The addition produced quaternary stereogenic

centers with yields ranging from 67-98% and e.e.s as high as 97%.

In comparison to the prolific success of rhodium and copper catalyzed conjugate additions,

palladium catalyzed 1,4-additions are uncommon.222226 Recently, Min Shi reported the first

palladium(II) catalyzed 1,4-addition using a chelating bis-NHC ligand.113 The bis-NHC ligand is



















I_ -


Hernnrmn


Manldlir


Phll
- Intchentl


-N



Hulim


lerrmnanin

Ph Pli

l ci


N'
ja-


f l.i


Ieyoi


K' AWu

HR R
DI)mthwnite


- Ph,,-,

Ioin l

H e P .


'-Io

I ruwJLI
Rqnbonh1L


J V

R 'r Pr, Cnli Pt l
Duulhraic


Ar 2.4.6-Mc1CHj
2.6 'Pr'4,] I1
-n mon llo










i I


~" \-A

R -'Bu, bL, Cy.
'Pt, (1I hih"
Burgeas


Nl 'R




R = 'Bu. 2.-'Pr3C(,H
RIlTI IO


N19p



2ru


s M rh 2n
osc c yo
i% I
(,. 41t G t
%lnrAhd1


CN



Mlarsnll


R' R:

^R -o, 'I' I I t-





Sailu Vetg



Figure 2-1. Examples of chelating NHCs. 104-113, 115, 120, 127, 129-147


nmtr2e

Umhiree


























To Faye J. Bell my hero, my best friend, and my grandmother; she taught me to love with
unfaltering resolve, live with unimaginable passion, and to follow my dreams
Rest in Peace










Table 2-4. Selected bond length (A) and angles (0) for complex 2-4
2-4


Bond lengths


Rhl-C20
Rh2-C31
N1-C20
N1-C18
N1-C17
N2-C20
N2-C19
N2-C21
C18-C19
C29-C30
Rh2-C12
Rhl-Cll
N1-C20-N2
N3-C31-N4
C17-C16-C15-C28


Angles


Torsion Angle


2.021(5)
2.024(5)
1.364(6)
1.368(6)
1.463(6)
1.362(6)
1.376(6)
1.460(6)
1.354(7)
1.340(7)
2.3741(15)
2.3622(15)
104.5(4)
103.1(4)
125.2(5)


Table 2-5. Selected bond lengths (A) and angles (0) for complex 2-5
2-5


Bond lengths


Ir-C20
Ir-C31
N1-C18
N1-C20
N1-C17
N2-C20
N2-C19
N2-C21
C20-Ir-C31
N1-C20-N2
N3-C31-N4
C17-C16-C15-C28
Irl-C15


Angles


Torsion Angle
Distance


2.031(9)
2.059(8)
1.382(10)
1.351(10)
1.467(10)
1.361(10)
1.375(11)
1.469(10)
91.2(3)
103.7(7)
104.1(7)
96.2(8)
3.345(8)




































2009 Roxy Joanne Lowry









useful to substitute the dimeric [Rh(COD)Cl]2 with the monometallic, cationic Rh(NBD)2BF4

precursor. Formation of a silver salt from ligand 4-2 that could be used for transmetallation

could also increase the yield of monometallic complex 4-9.

Alternative ligand structures (Figure 6-1) could be used to increase the definition of the

chiral pocket. However, caution must be taken to avoid the design of overly hindered ligands

that favor the formation of bimetallic complexes. The addition of a methyl substituent in the

ortho position (6-1) should lead to a very rigid monometallic complex if it can be formed. Ortho

substitution ofa fluoro substituent should induce less steric inhibition to monometallic complex

formation; however, synthetic procedures required to form this ligand are more complex than for

6-1 and the electronic interaction between the fluoro substituent and the aryl backbone may also

preclude monometallic catalyst synthesis. Although the meta methyl substituent did not alter the

structure of the monometallic catalyst (4-6), introduction of a significantly bulky substituent in

this position (6-3 R = t-Bu or biphenyl) should alter the structure.

The unsaturated imidazole complexes 3-9 and 4-1 do not appear to be promising in high

temperature catalysis. However, they should present much higher enantioselectivities if utilized

at room temperature. An alternative structure 6-4 is proposed whereby the bulk of the backbone

is increased. Substitution of glyoxal with an alkyl substituted dione, such as butane-2,3-dione,

would introduce alkyl groups on the back of the imidazole.

The stability of the rhodium and iridium complexes reported herein has allowed the

structural investigation of a series of di-NHC ligands. Although structural knowledge is vastly

important in catalytic investigation, the stability of these complexes is likely the source of the

observed sluggish reactivity. Formation of metal complexes containing labile co-ligands should

allow the formation of electron-rich metal centers capable of a high degree of enantioselectivity.









3.3.5 X -ray A analysis of D EA -M bBY (3-5) ....................................................................78
3.3.6 X-ray Analysis of Bimetallic Complexes [/,-DEA-MY][Rh(NBD)I]2 (3-6)
and [l-DEA-MBY][Rh(COD)Cl]2 (3-7-COD) ............................................. 79
3.3.7 Structural Analysis of Monometallic Complexes [(DEA-MBY)Rh(COD)]I
(3-8) and [(DEA-M Y)Rh(COD)]I (3-9) .............. ................ .............. ........ 80
3.4 Conclusions ................................................................ 82

4 THIRD GENERATION CATALYSTS ............................................................................. 91

4.1 Introduction ........................................ ...................... 91
4 .2 E xperim mental Section ....................................................................... ... ... ............. . 9 1
4.2.1 Synthesis of Trans-1,1'-(9,10-Dihydro-9,10-Ethanoanthracene-11,12-
Diyl)di(3-Isopropyl-1H-Imidazol-3-Ium) Diiodide [DEA-iPrI](I)2 (4-1).........91
4.2.2 Synthesis of Trans-1,1-(9,10-Dihydro-9,10-Ethanoanthracene-l 1,12-
Diyl)di(3 -Isopropyl-1H-Benzimidazol-3 -lum) Diiodide [DEA-iPrBI](I)2
(4 -2 ) ................. ............................. .............. ... ............. 9 2
4.2.3 Synthesis of N,N'-bis(4-Nitrotolyl)-9,10-Dihydro-9,10-Ethanoanthracene-
1 1,12 -D iam in e (4 -3 ) ................................................................................... ... 9 2
4.2.4 Synthesis of N,N'-bis(4-Aminotolyl)-9,10-Dihydro-9,10-Ethanoanthracene-
11,12-D iam ine (4-4) .................................................................................. ........ 93
4.2.5 Synthesis of Trans-1,1'-(9,10-Dihydro-9,10-Ethanoanthracene-11,12-
D iyl)di(1H -Tolylim idazole) (4-5) ................................................ ................. 94
4.2.6 Synthesis of Trans-1,1-(9,10-Dihydro-9,10-Ethanoanthracene-l 1,12-
Diyl)di(3-Methyl-1H-Tolylimidazol-3-Ium) Diiodide [DEA-MTI](I)2 (4-
6 ) ................... .. ..... ... .............. ... ............... ........ .................. . 9 4
4.2.7 Synthesis of Trans-1,1-(9,10-Dihydro-9,10-Ethanoanthracene-l 1,12-
Diyl)di(3-Isopropyl-1H-Tolylimidazol-3-Ium) Diiodide [DEA-iPrTI](I)2
(4 -7) .................. .................................................... ..... ..... ........ ........... .9 5
4.2.8 Synthesis of Rhodium(I) Trans-9,10-Dihydro-9,10-Ethanoanthracene-
9,10-bis( -Isopropylimidazolidine-2-Yli dene) Cyclooctadiene Iodide,
[(DEA-iPrY)Rh(COD)]I (4-8) ................................... .... .................... 95
4.2.9 Synthesis of Rhodium(I) Trans-9,10-Dihydro-9,10-Ethanoanthracene-
9,10-bis(1-Isopropylbenzylimidazolidine-2-Ylidene) Cyclooctadiene
Iodide, [(DEA-iPrBY)Rh(COD)]I (4-9)........................................................96
4.2.10 Synthesis of Rhodium(I) Trans-9,10-Dihydro-9,10-Ethanoanthracene-
9,10-bis(1-Methyltolylimidazolidine-2-Ylidene) Cyclooctadiene Iodide,
[(DEA-MTY)Rh(COD)]I (4-10) ............... .. ..................98
4.3 R results and D discussion ........................................................................................ 99
4.3.1 Synthesis and Characterization of [DEA-iPrI](I)2 (4-1) and [(DEA-
iP rY )R h(C O D )]I (4 -8)................................................... ................................. 99
4.3.2 Synthesis and Characterization of [DEA-iPrBY](I)2 (4-2), [DEA-MTY](I)2
(4-6), [DEA-iPrTY](I)2 (4-7) and the Corresponding Monometallic
Rhodium Complexes [(DEA-iPrBY)Rh(COD)]I (4-9) and [(DEA-
M TY )Rh(CO D )]I (4-10) ................... ......................................... ............... 100
4.4 Conclusions ........ ....................................... ................ 103









substituents (4-8) does not appear to have a significant effect on the chiral induction ability of the

unsaturated imidazole complex.

A catalytic cycle (Figure 5-2) is proposed based on mechanistic and kinetic studies

accomplished by Hayashi et al.202 and Miyaura.189 The precatalyst I is activated by loss of COD

forming a solvated species II. As reported for the BINAP system by Hayashi, our catalyst

system may be capable of forming a dimeric complex III. From the active catalyst species II

transmetallation of the aryl boronic acid via the transition state IV produces the phenyl

compound V. Subsequent insertion of the olefin is accomplished through a diastereomeric

transition state VI. This transition state is responsible for determining the enantiotopic identity

of the product and forming the oxa-7T-allyl-Rh species VII that is then hydrolyzed to form the

product.

The most enantioselective catalyst, 3-8, was utilized to optimize the conditions for

asymmetric conjugate addition (Table 5-1). Many unrelated catalysts have been reported to

achieve high yields and enantioselectivities at room temperature,28 but our system requires

temperatures well above 70 C. As was discovered with the original Rh(acac)binap system,

dissociation of COD is believed to necessitate these high temperatures as well as the long

reaction times. Attempts to replace the COD ligand by utilization of alternative rhodium

precursors or by ligand substitution were unsuccessful or led to catalyst degradation.

The reaction conditions found to produce the highest yield and enantiomeric excesses

utilized 10/1 dioxane:methanol at 800C with 0.5 equivalents of base and 3 mol% catalyst over 24

hrs for addition of phenyl boronic acid to 2-cyclohexen-1 -one. The addition ofo-tolylboronic

acid to 2-cyclohexen-l-one was found to achieve the same level of enantiopurity utilizing 4/1

dioxane:methanol and 1.5% of(R,R)-3-8. For the addition of phenylboronic acid, the (S,S)




































I.


152 144 136 128 120 112 104 96 88 80 72 64 56 48 40
Chemical Shift (ppm)
Figure A-28. 13C NMR of N,N'-bis(4-nitrotolyl)-9,10-dihydro-9,10-ethanoanthracene- 1,12-diamine (4-3).


32 24 16 8


I1 11 I I


7 '711 r7r"Ir
I I II
111MI1111777


1 1 I


1


I I


I I

















































192 184 176 168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24
Chemical Shift (ppm)
Figure A-39. 13C NMR spectrum of(+/-) Rhodium(I) trans-9,10-dihydro-9,10-ethanoanthracene-9,10-bis(l-
isopropylbenzimidazolidine-2-ylidene cyclooctadiene iodide, [(DEA-iPrBY)Rh(COD)]I (4-9) in CDC13.


163









Both M(I) ions sit in a slightly distorted square-planar coordination sphere. The NHCs

occupy cis coordination sites opposite a chelated 1,5-cyclooctadiene (COD). Examination of the

molecular structure suggests chelation forces the ligand to adopt a strained geometry. The

dihedral angles ZC28-C15-C16-C17 of 95.8(2) for 2-3 and 96.2(8) for 2-5 are significantly

smaller than those for the organic precursor molecules 2-1 and 2-2. Although ligand bite angles

correspond to values expected for square planar complexes (ZC20-Rh-C31 of 89.93(8) and

ZC20-Ir-C31 of 91.2(3)), conformational strain is evident by unsymmetrical NHC-M bonds.

This feature is significant in the solid state structure of Rh(I) compound 2-3. One NHC-M bond

length, C31-Rh, is 2.037(2) A corresponding closely to the average M-NHC bond length found

in the Cambridge Structural Database by Baba et. al.124 The second Rh-NHC bond is longer at

2.068(2) A for C20-Rh, well over the 30 significance factor. Although the trend appears to

continue in 2-5 the difference lies within the error of the data (2.031(9)A for Ir-C20 and

2.059(8)A for Ir-C31).

As previously discussed, binding of NHCs to metal centers is believed to be highly

electrostatic in nature, allowing the NHC to retain much of its free carbene character.

Supporting this assertion, the N-C-N bond lengths and angles of 2-3 and 2-5 correspond closely

to those noted for free carbene 2-2. Figure 2-10 displays average metric parameters for NHC-M

species and their free carbene precursors.124 The ZN-C-N of 2-2 is slightly smaller than in the

metal complexes whereas the ZN-C-N of the imidazolium salt (2-1) is approximately 5 broader

than in 2-3 or 2-5. The N-Ccarbene bond lengths of each chelate complex resemble the slightly

longer bonds of compound 2-2 rather than those of 2-1 (Tables 2-1, 2-2, 2-3, and 2-5).









relationship between phosphine topology and catalytic reactivity has facilitated semi-rational

design of phosphine based ligands. In an attempt to compare the steric demand of NHCs with

phosphines and to establish a guiding principle for NHC ligand design, Nolan et. al. defined the

steric parameter, percent volume buried (%VBur).79'80 Situating the NHC or phosphine 2 A from

the metal center, the %VBur is determined by the percent of a sphere of radius 3 A consumed by

the ligand in question. The authors concede that this method does not explain all of the steric

demands of an NHC ligand. While it is a good beginning in describing symmetrical

monodentate NHCs, this method does not account for rotation around the M-NHC bond or

define the steric demand of unsymmetrical or chelating NHCs.

1.3.5 M-NHC Bonding

The popularity of NHC ligands is due in part to their compatibility with a large variety of

TM species37 60 as well as main group elements.81 This compatibility sets these heterocycles

apart from the other members of the carbene family of ligands. Schrock carbenes (or

alkylidenes) are nucleophilic, triplet ground state carbenes that form covalent interactions with

high oxidation state TM species.82 Fischer carbenes are electrophilic, singlet carbenes that

require stabilization through 7t-backbonding from an electron-rich metal center. Although NHCs

were once considered Fisher type carbenes,82 their versatility and ability to act as ancillary

ligands established them as an independent classification within the carbene family. NHC-M

bonding is considered electrostatic in nature and consists primarily of strong G-donation from the

carbene to a metal center. NHC-M bonds are best described as single or dative bonds.83 The

carbene center does not require 7t-backbonding from the metal center due to the stabilizing

effects of the carbene's a-nitrogen substituents. The empty p, orbital is available for

backdonation but the relative i7-bonding ability of NHCs is controversial and certainly dependent









11,12-diyl)di(3-methyl-imidazol-3-ium) diiodide [DEA-MI](I)2 (3-3) and trans-1,1-(9,10-

dihydro-9,10-ethanoanthracene- 11,12-diyl)di(3-methyl-benzimidazol-3-ium) diiodide [DEA-

MBI](I)2 (3-4), produce complexes with rigid chiral pockets. However, the small variation

between the two ligands produces a large alteration in the catalytic activity of the resulting

complexes. In an attempt to further increase the enantiocontrol displayed by these compounds

small alterations were made to produce the third generation of ligands, trans-1,1'-(9,10-dihydro-

9,10-ethanoanthracene-11,12-diyl)di(3-isopropyl-imidazol-3-ium) diiodide [DEA-iPrI](I)2 (4-1),

trans-1,1 -(9,10-dihydro-9,10-ethanoanthracene-l 1,12-diyl)di(3-isopropyl-benzimidazol-3 -ium)

diiodide [DEA-iPrBI](I)2 (4-2), trans-1,1-(9,10-dihydro-9,10-ethanoanthracene-1 1,12-diyl)di(3-

methyl-tolylimidazol-3-ium) diiodide [DEA-MTI](I)2 (4-6), trans-1,1 -(9,10-dihydro-9,10-

ethanoanthracene-11,12-diyl)di(3-isopropyl-tolylimidazol-3-ium) diiodide [DEA-iPrTI](I)2 (4-

7).

Catalytic investigation of the asymmetric 1,4-addition of aryl boronic acids to cyclic

enones is accomplished for the constrained catalysts 3-8 [rhodium(I) trans-9,10-dihydro-9,10-

ethanoanthracene-9,10-bis(1-methylbenzimidazolidine-2-ylidene) cyclooctadiene iodide], 3-9

[rhodium(I) trans-9,10-dihydro-9,10-ethanoanthracene-9,10-bis(1-methylimidazolidine-2-

ylidene) cyclooctadiene iodide], and 4-8 [rhodium(I) trans-9,10-dihydro-9,10-

ethanoanthracene-9,10-bis(1-isopropylimidazolidine-2-ylidene) cyclooctadiene iodide].









3.2 Experimental Section

3.2.1 GC Analysis of Chiral 9,10-Dihydro-9,10-Ethanoanthracene-11,12-Diamine (3-1)

Synthesis ofracemic and enantioenriched diamine 3-1 was achieved via literature

methods.154, 155 Resolved diamine 3-1 was then dissolved in CH2C12 and a few drops of

trifluoroacetic anyhydride were added. The solution was concentrated and dissolved in acetone.

Enantiopurity of(R)-3-1 and (S)-3-1 was measured by gas chromatography. Column: Chirasil

Val; oven temperature: start 1000C for 2 min, increase by 100C/min until 1800C, hold for 20

min. tR: (S,S): 22.4 min; (R,R): 25.1 min. All samples were found to be greater than or equal to

95% enantiomerically pure.

3.2.2 Synthesis of Trans-l,l'-(9,10-Dihydro-9,10-Ethanoanthracene-11,12-Diyl)di(1H-
Imidazole)
(3-2)

Glyoxal (6 mL of 40% aqueous solution, 2 equiv., 51.6 mmol) was added to a methanol

solution (40 mL) containing diamine 3-1 (6.1 g, 25.8 mmol). The solution immediately turned

bright yellow and became warm, forming a light yellow precipitate. The mixture was stirred for

16 h. Additional MeOH (40 mL) was added, followed by solid NH4C1 (5.52 g, 4 equiv., 103.4

mmol) and formaldehyde (7.7 mL of 37% solution in water, 4 equiv., 103.4 mmol). The

resulting mixture turned dark orange and was heated at reflux for 4 h. Phosphoric acid (7.1 mL

of 85% solution in water, 4 equiv., 103.4 mmol) was added slowly and the resulting mixture was

heated at reflux for 16 h. The mixture was cooled to room temperature and volatiles were

removed. Dichloromethane was added and the mixture was basified to pH 14 with 2.5 M NaOH

solution. The organic extract was dried over sodium carbonate, filtered, and concentrated to a

sticky red oil consisting of roughly a 1:1 mixture of the desired diimidazole 3-2 and a partially

reacted monoimidazole/amine compound.103 Diimidazole 3-2 was isolated by flash column

chromatography using 5% MeOH in CHC13 as the eluent. Chromatography produced pure 3-2 as

66






























Figure 4-9. Overlay of the calculated structure [(DEA-MBY)Rh(COD)]I 3-8-calc and [(DEA-
MTY)Rh(COD)]I 4-10-calc. The side-view (left) displays the similarity of the two
structures as does the top-view (right) with the backbone removed for clarity.



Table 4-1. Selected bond lengths (A) and angle (0) for calculated structures 3-8-calc and 4-10-
calc.


3-8-calc


4-10-calc


Distances











Angles



Torsion Angle
Distances


Rh-C31
Rh-C23
N2-C24
N4-C32
N2-C23
N1-C23
N4-C31
N3-C31
C16-H16
C31RhC23
N1C23N2
N3C31N4
N1-C15-C16-N3
Rh-H16
C36-C4


2.052
2.068
1.468
1.466
1.384
1.395
1.372
1.391
1.097
85.3
105.2
106.0
70.36
2.298
4.238


Rh-C31
Rh-C23
N2-C24
N4-C32
N2-C23
N1-C23
N4-C31
N3-C31
C16-H16
C31RhC23
N1C23N2
N3C31N4
N1-C15-C16-N3
Rh-H16
C36-C4


2.054
2.07
1.468
1.466
1.383
1.394
1.371
1.392
1.096
85.3
105.2
105.9
70.34
2.295
4.226









A-39 13C NMR spectrum of (+/-) Rhodium(I) trans-9,10-dihydro-9,10-
ethanoanthracene-9,10-bis(1-isopropylbenzimidazolidine-2-ylidene cyclooctadiene
iodide, [(DEA-iPrBY)Rh(COD)]I (4-9) in CDC13 ......................................................... 163

A-40 1H NMR spectrum of (+/-) Rhodium(I) trans-9,10-dihydro-9,10-
ethanoanthracene-9,10-bis(1-methyltolylimidazolidine-2-ylidene cyclooctadiene
iodide, [(DEA-M TY)Rh(COD)]I (4-10) in CDC13. .................................... ............... 164

A-41 13C NMR spectrum of (+/-) Rhodium(I) trans-9,10-dihydro-9,10-
ethanoanthracene-9,10-bis(1-methyltolylimidazolidine-2-ylidene cyclooctadiene
iodide, [(DEA-M TY)Rh(COD)]I (4-10) in CDC13. .................................... ............... 165









cyclooctadiene ring to the aryl ring below shows a more than 0.5 A increase in the size of the

chiral pocket for 3-9-calc relative to 3-8-calc. The largest difference between the two structures

is the 100 expansion of the torsion angle N1-C15-C16-N3 for 3-9.

3.4 Conclusions

This chapter presented the structural analysis of the mono- and bimetallic Rh(I) complexes

supported by the two second-generation C2-symmetric chelating di-N-heterocyclic carbene

ligands based upon a trans-ethanoanthracene backbone. The direct attachment of the NHC units

to the DEA backbone reduced the size of the chiral pocket and increased the definition. A

mixture of X-ray diffraction data and computational ground state configurations allowed

comparison of the two structures of the monometallic Rh(I) compounds, suggesting that the bulk

of the benzimidazole actually serves to increase the definition of the chiral pocket.




F ^ (A720 f


First Gcncratiun


3N /-N
(\ 1Ny
\N-N


/ 21


Second Generation


Figure 3-1. First and second generation ligand architectures.

82









2 .3 R esu lts an d D iscu ssion ........................ ....... ................................................................. 4 7
2.3.1 Preparation and Solution State Analysis of [DEAM-BI](OTf)2 (2-1)........... 47
2.3.2 Preparation and Solution State Analysis of [DEAM-BY] (2-2) ...........................48
2.3.3 Preparation and Solution State Analysis of [(DEAM-BY)Rh(COD)]OTf (2-
3) ................... ............. ......................................... 49
2.3.4 Preparation and Solution State Analysis of [,-DEAM-BY][Rh(COD)Cl]2 (2-
4 ) ................. ........ ............ ..... ................... ................................. ......... 5 0
2.3.5 Preparation and Solution State Analysis of [(DEAM-BY)Ir(COD)]OTf (2-5)
and [/,-D EAM -BY ][Ir(COD )Cl]2 (2-6) .............................................................. 50
2.4 X-ray Structural Analysis and Comparisons................................................................ 51
2.4.1 Comparison of Organic Precursors 2-1 and 2-2. ................................................51
2.4.2 Monometallic [(DEAM-BY)M(COD)]OTf 2-3 and 2-5.................................... 52
2.4.3 Bimetallic Complexes [u-DEAM-BY][M(COD)C1]2 2-4 and 2-6..................... 54
2 .5 Initial C atalytic T estin g .............................................. ................................................... 54
2.6 Conclusions ................................................................ 55

3 SECOND GENERATION DI-NHC CATALYSTS148........................................ ............... 64

3 .1 In tro d u ctio n ........................................................................................................................... 6 4
3 .2 E x perim mental S section ........................................ ...... .......... ................................. 66
3.2.1 GC Analysis of Chiral 9,10-Dihydro-9,10-Ethanoanthracene-l 1,12-Diamine
(3 -1) ...................... .. ... ........... .. .. .......... .. ........... ................ 6 6
3.2.2 Synthesis of Trans-1,1'-(9,10-Dihydro-9,10-Ethanoanthracene- 11,12-
D iyl)di(1H -Im idazole) (3-2) ................................................ .......... .................. 66
3.2.3 Synthesis of Trans-1,1'-(9,10-Dihydro-9,10-Ethanoanthracene-11,12-
Diyl)di(3-Methyl-1H-Imidazol-3-lum) Diiodide [DEA-MI](I)2 (3-3).............. 67
3.2.4 Synthesis of Trans-1,1-(9,10-Dihydro-9,10-Ethanoanthracene- 11,12-
Diyl)di(3-Methyl-lH-Benzimidazol-3-Ium) Diiodide [DEA-MBI](I)2 (3-
4) ................... ..... ........................ ... ..................................... 68
3.2.5 Synthesis of Trans-9,10-Dihydro-9,10-Ethanoanthracene-9,10-(1-
Methyl)Bibenzimidazole), DEA-MbBY (3-5).............................................. 68
3.2.6 Synthesis of [a-DEA-MY][Rh(NBD)I]2 (3-6) as a Mixture with 3-9................69
3.2.7 Synthesis of [/-DEA-MBY][Rh(diene)Cl]2 (3-7) as a Mixture with 3-8 ..........70
3.2.8 Synthesis of the Rhodium(I) Trans-9,10-Dihydro-9,10-Ethanoanthracene-
9,10-bis(l-Methylbenzimidazolidine-2-Ylidene) Cyclooctadiene Iodide,
[(DEA-MBY)Rh(COD)]I (3-8) ......... .............. ........... ... ......... ...... 71
3.2.9 Synthesis of Rhodium(I) Trans-9,10-Dihydro-9,10-Ethanoanthracene-
9,10-bis(l-Methylimidazolidine-2-Ylidene Cyclooctadiene Iodide,
[(D EA-M Y )R h(CO D )]I (3-9) ........................................ ....... ........ ....... 72
3 .3 R esu lts an d D iscu ssion ............ ............................ .................................... .......................7 3
3.3.1 Constrained Precursors [DEA-MI](I)2 (3-3) and [DEA-MBI](I)2 (3-4) ..............73
3.3.2 Synthesis and Characterization of DEA-MbBY (3-5)..................................... 75
3.3.3 Synthesis and Characterization of [/-DEA-MY][Rh(NBD)I]2 (3-6) and [pu-
DEA-MBY][Rh(COD)Cl]2 (3-7-COD).............................. ............... ......76
3.3.4 Synthesis and Characterization of [(DEA-MBY)Rh(COD)]I (3-8) and
[(D E A -M Y )R h(C O D )]I (3-9) ......... ................ .................. ................. ..... 77






















































8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5
Chemical Shift (ppm)
Figure A-17: 1H NMR spectrum of [/-DEA-MY][Rh(NBD)I]2 (3-6) as a mixture with 3-9 in C6D6.




























144 136 128 120 112 104 96 88 80 72
Chemical Shift (ppm)
Figure A-34. 13C NMR spectrum of (+/-) [DEA-MTI][I]2 (4-6) in (CD3)2SO


64 56 48 4(


32 24 16


II


0


1111111lHi lll I I 11 i 1 111111Ilii lij









share common design features including C2 symmetry, multiple and strong metal-ligand bonds,

and rigid structures. C2 symmetry, first introduced to chiral catalysis by Kegan's diop ligand,33'

34 is attractive because it reduces the number of reaction pathways by cutting in half the possible

catalyst/substrate arrangements.35 Rigid and robust ligands are important for creating a durable

complex and retaining the structure of the catalyst's chiral environment. Multiple and strong

bonds between the metal and the ligand further stabilize the complex. Stability of the complex

and the topology surrounding the chiral coordination center plays a central role in determining

the enantiopurity of a product in an asymmetric catalytic reaction.

Two "privileged ligands", BINAP and MeDuPhos, are members of the organophosphorous

family of ligands, commonly termed "phosphines". Introduced to organometallic chemistry by

F.G. Mann,36 phosphines are strong o-donor/weak i7-acceptor ligands that support a large variety

of reactive and selective transition metal catalysts. The overwhelming success of phosphine

based ligands in homogeneous catalysis has led many to consider the entire class as "privileged"

ligands; however, these ligands suffer some disadvantages including air-sensitivity, oxidative

degradation, and toxicity,37 as well as difficulty associated with independent modulation of their

electronic and steric parameters.38 N-heterocyclic carbenes (NHCs) are closely related to

phosphines in regards to their electronic donation to a metal center, but are different in their

steric topology and do not suffer the same disadvantages in catalytic reactions. As part of the

carbene family, they were once considered to be too reactive to be utilized as ancillary ligands.

The following sections of this chapter will outline the characteristics of these carbenes that

permit them to support some of the most stable TM complexes in use today. Subsequent

chapters will describe the utilization of this coordinating moiety in a novel chiral ligand family

and utilization of these ligands in asymmetric rhodium catalysis.









1.3 N-Heterocyclic Carbenes


1.3.1 Early History

The stability ofN-heterocyclic carbenes provides one of the few members of the carbene

family capable of functioning as a spectator ligand. Isolation of such a stable carbene was

unimaginable until the early 1960s when Wanzlick proposed the formation of a

diaminocarbene.39-42 He attempted the synthesis of a stable singlet carbene from 1,3-diphenyl-2-

trichloromethylimidazolidene but was unable to isolate the proposed species, obtaining only its

dimer enetetraamine. He was never able to establish the existence of a stable free carbene prior

to coordination. However, later that decade Wanzlick43 and Ofele44 independently reported the

first metal complexes supported by diaminocarbene ligands (Figure 1-5). Excluding an

extensive investigation into the coordination chemistry of related enetetraamines (Figure 1-5) by

Lappert,45 46 research involving these elegant compounds was nonexistent throughout the 1970s

and 80s. In 1991, a renaissance of chemistry involving NHC compounds was initiated by the

isolation of a stable crystalline NHC by Arduengo.47'48 Investigations of NHC coordination

chemistry, catalytic properties, and particularly the steric and electronic characteristics

responsible for the stability of these "diradicals" were immediately launched and continue to be

the subject of an overwhelming number ofj journal and review articles,38'49-62 and books.37'63

1.3.2 Carbene Geometry

Carbenes are neutral divalent carbons in which four of the six valence electrons are

contained in bonding orbitals. They were first proposed by Hermann and Geuther in 1855 as

reactive diradical (triplet ground state) intermediates.64 It was almost 100 years later that

Lennard-Jones and Pople used computational evidence to suggest the accessibility of two

different ground states;65' 66 the non-bonding electrons could occupy the same orbital with

antiparallel spins (singlet ground state) or two different orbitals with parallel spins (triplet).









KN(TMS)2 to generate the corresponding enetetramine and free di-NHC, respectively, followed

by addition of metal substrate. The complexes were obtained as mixtures with the corresponding

mononuclear species which complicated analysis (Figure 3-5). The molecular structures of 3-6

and 3-7-COD were confirmed by single-crystal X-ray crystallography and are presented in

Figures 3-8 and 3-9.

3.3.4 Synthesis and Characterization of [(DEA-MBY)Rh(COD)]I (3-8) and [(DEA-
MY)Rh(COD)]I (3-9)

Treatment of the dibenzimidazolium salt 3-4, at -35 C, with 2.1 equiv. of KN(TMS)2

followed by 0.5 equiv. of [Rh(COD)Cl]2 in THF, resulted in precipitation of crystalline yellow 3-

8 in 53% yield (Figure 3-6). The absolute assignment of each proton and carbon is accomplished

by gDQCOSY, gHMBC, and NOESY two-dimensional NMR techniques. Similar to compound

2-3, in solution the chelated complex 3-8 displays C1 symmetry. The low symmetry is

demonstrated by nonequivalent methyl resonances observed at 4.46 ppm and 3.95 ppm. A

distinct but unexpected doublet is observed downfield at 9.26 ppm (J= 10 Hz). Using two-

dimensional NMR analysis this proton was assigned to one of the aliphatic protons on the bridge.

It is coupled to the other bridge proton that resonates upfield, at 4.36 ppm (J=10.2 Hz). In the

1H NMR spectrum of monometallic complex 2-3 the aliphatic bridge protons are also separated

(by 3 ppm) but the most downfield proton appears at 4.40 ppm. The unusual position of the

resonance at 9.26 ppm suggested that the bridge proton is in very close proximity to the rhodium

center.

The formation of chelate species 3-8, rather than a bridging 2:1 complex, does not conflict

with the studies presented earlier that suggested a ligand with a two carbon linker should form a

bridging species. As stated previously, deprotonation of 3-4 results in formation of enetetramine

3-5, thereby positioning the two heterocycle moieties in close proximity, akin to a









85. M. T. Lee and C. H. Hu, Organometallics, 2004, 23, 976.

86. X. L. Hu, I. Castro-Rodriguez and K. Meyer, J. Am. Chem. Soc., 2004, 126, 13464.

87. W. A. Herrmann and C. Kocher, Angew. Chem. Int. Ed., 1997, 36, 2163.

88. M. Nichues, G. Erker, G. Kehr, P. Schwab, R. Frohlich, O. Blacque and H. Berke,
Organometallics, 2002, 21, 2905.

89. X. Hu, I. Castro-Rodriguez, K. Olson and K. Meyer, Organometallics, 2004, 23, 755.

90. X. Hu, Y. Tang, P. Gantzel and K. Meyer, Organometallics, 2003, 22, 612.

91. M. Srebro and A. Michalak, Inorg. Chem., 2009, 48, 5361.

92. N. M. Scott, R. Dorta, E. D. Stevens, A. Correa, L. Cavallo and S. P. Nolan, J. Am. Chem.
Soc., 2005, 127, 3516.

93. R. Dorta, E. D. Stevens and S. P. Nolan, J. Am. Chem. Soc., 2004, 126, 5054.

94. K. Getty, M. U. Delgado-Jaime and P. Kennepohl, J. Am. Chem. Soc., 2007, 129, 15774.

95. E. N. Jacobsen, A. Pfaltz and H. Yamamoto, eds., Comprehensive Asymmetric Catalysis I,
Springer-Verlag, Berlin Heidelberg, 1999.

96. M. F. Lappert, J. Organomet. Chem., 1988, 358, 185.

97. P. L. Arnold and S. Pearson, Coord. Chem. Rev., 2007, 251, 596.

98. D. Pugh and A. A. Danopoulos, Coord. Chem. Rev., 2007, 251, 610.

99. V. P. W. Bohm, T. Weskamp, C. W. K. Gstottmayr and W. A. Herrmann, Angew. Chem.
Int. Ed., 2000, 39, 1602.

100. J. Huang, H. J. Schanz, E. D. Stevens and S. P. Nolan, Organometallics, 1999, 18, 2370.

101. L. H. Gade and S. Bellemin-Laponnaz, Coord. Chem. Rev., 2007, 251, 718.

102. 0. Kihl, Chem. Soc. Rev., 2007, 36, 392.

103. R. J. Lowry, M. K. Veige, O. Clement, K. A. Abboud, I. Ghiviriga and A. S. Veige,
Organometallics, 2008, 27, 5184.

104. C. M. Zhang and M. L. Trudell, Tetrahedron Lett., 2000, 41, 595.

105. D. S. Clyne, J. Jin, E. Genest, J. C. Gallucci and T. V. RajanBabu, Org. Lett., 2000, 2,
1125.

106. L. G. Bonnet, R. E. Douthwaite and R. Hodgson, Organometallics, 2003, 22, 4384.









mmol). The resulting bright orange mixture was heated at 65 OC for 18 h. The mixture was

cooled to room temperature and 50 mL of water was added. The resulting bright orange

precipitate was isolated by filtration and washed with water producing 2.09 g of crude product

(92% yield). Dinitro 4-3 was purified by stirring in boiling EtOH (10 mL/g) for 30 min. After

cooling to 0 OC, the orange solid was filtered and finally washed with cold EtOH; yield 1.03g

(45%). 1HNMR (300 MHz, CDC13) 6 ppm: 8.05 (d, J= 8.8 Hz, 2H, Ar), 7.94 (d, J= 8.8 Hz,

2H, NH), 7.42 7.49 (m, 4H, Ar), 7.28 7.34 (m, 4H, Ar), 6.50 (s, 2H, Ar), 6.42 6.49 (m, 2H,

Ar), 4.49 (d, J= 2.9 Hz, 2H, bridge CH), 3.75 3.84 (br m, 2H, bridgehead CH), 2.05 (s, 6CH3).

13C NMR (75 MHz, CDC13) 6 ppm: 147.9 (C, Ar), 143.5 (C, Ar), 139.7 (C, Ar), 138.4 (C, Ar),

127.4 (C, 2Ar), 126.9 (C, 2Ar), 126.1 (C, Ar), 124.7 (C, Ar), 117.7 (C, Ar), 114.4 (C, Ar), 61.3

(bridge CH), 49.4 (bridgehead CH), 21.8 (CH3). HRMS (APCI-TOF) calculated (found) for

C30H26N404 (M+H)+ 507.2021 (507.2062).

4.2.4 Synthesis of N,N'-bis(4-Aminotolyl)-9,10-Dihydro-9,10-Ethanoanthracene-1l,12-
Diamine (4-4)

Pd/C (10 wt%, 50% wet; 310 mg) was added to a solution of dinitro 4-3 (1.027 g, 27.2 mmol)

in CH2C2 (25 mL) and MeOH (10 mL). The resulting mixture was stirred under H2 (40 atm) for

12 hr and then filtered through Celite to remove the Pd/C. The filtrate was concentrated to

afford 4-3 as a brown solid; yield 900 mg (99%). 1HNMR (300 MHz, CDC13) 6 ppm: 7.30 7.42

(m, 4 H, Ar), 7.15 7.26 (m, 4 H, Ar), 6.62 6.75 (m, 4 H, Ar), 6.52 6.62 (m, 2 H, Ar), 4.44 (s,

2 H, bridgehead CH), 3.56 3.90 (br s, 6 H, NH2/NH), 3.53 (s, 2H, bridge CH), 3.46 (s, MeOH),

2.26 (s, 6 H, CH3). 13C NMR (75 MHz, CDC13) 6 ppm: 141.6 (s, Ar), 139.52 (s, Ar), 135.7 (s,

Ar), 126.6 (s, Ar), 126.3 (s, Ar), 126.2 (s, Ar), 124.4 (s, Ar), 120.4 (s, Ar), 117.5 (s, Ar), 116.9

(m, Ar), 116.9 (s, Ar), 113.4 (s, Ar) 62.1 (s, bridge C), 48.7 (s, bridgehead C), 21.0 (s, CH3).

HRMS (APCI-TOF) calculated (found) for C28H27N4 (M+H) 447.2543 (447.2557).

93









typically activated by reaction with protonated solvents, forming a Rh-OH or Rh-OMe complex

depending on the solvent mixture. Under these conditions, base is not strictly required but does

have a strong accelerating effect.201

Kinetic studies by Hayashi et al.202 on the Rh-BINAP system revealed transmetallation as

the rate limiting step (rls). These studies also uncovered the formation of a homochiral dimer

that is inactive towards catalysis, but its position prior to the rls means that the equilibrium

constant between monomer and dimer can influence the overall rate of the reaction. The reaction

was found to be first order overall and half-order in catalyst. Interestingly, Hayashi also

discovered a negative non-linear effect between the enantiopurity of the ligand and the e.e. of the

product.

Subsequent to transmetallation, transient coordination of the enone to the metal center is

followed by insertion of the enone into the rhodium-aryl bond. In asymmetric reactions, the

product's stereochemistry is determined by this diastereomeric transition state.28 When (S)-

BINAP is used as the chiral control the (S)-product is formed suggesting approach of the enone

from its 2si face. Insertion of the enone forms an oxa-7t-allylrhodium species which is then

hydrolyzed yielding the product and the catalytically active L*Rh-OH species.

In the initial mechanistic studies, NMR experiments revealed that all of the individual

steps could be accomplished at 250C.200 However, catalytic reactions starting from

Rh(acac)(binap) required temperatures well above 600. The tightly bound acetylacetonato (acac)

ligand was found responsible for the high temperature requirement. Temperature and time

requirements were drastically reduced when the acac ligand was replaced with a hydroxyl (OH)

group.









149. R. H. Crabtree, J. Organomet. Chem., 2006, 691, 3146.


150. J. A. Mata, A. R. Chianese, J. R. Miecznikowski, M. Poyatos, E. Peris, J. W. Faller and R.
H. Crabtree, Organometallics, 2004, 23, 1253.

151. C. H. Leung, C. D. Incarvito and R. H. Crabtree, Organometallics, 2006, 25, 6099.

152. Y. A. Wanniarachchi, M. A. Khan and L. M. Slaughter, Organometallics, 2004, 23, 5881.

153. S. Burling, L. D. Field, H. Li, B. A. Messerle and R. Turner, Eur. J. Inorg. Chem., 2003,
3179.

154. B. M. Trost, D. L. Van Vranken and C. Bingel, J. Am. Chem. Soc., 1992, 114, 9327.

155. E. Fox, A. Gerlach, I. C. Lennon, G. Meek and C. Praquin, Sylihe/i 2005, 19, 3196.

156. C. L. Lee, W. Yang and R. G. Parr, Phys. Rev. B., 1988, 37, 785.

157. T. H. Dunning Jr. and P. J. Hay, in Methods ofElectronic Structure Theory, ed. H. F.
Schaefer III, Plenum Press, New York, Editon edn., 1977, vol. 2.

158. P. J. Hay and W. R. Wadt, J. Chem. Phys., 1985, 82, 270.

159. P. J. Hay and W. R. Wadt, J. Chem. Phys., 1985, 82, 284.

160. P. J. Hay and W. R. Wadt, J. Chem. Phys., 1985, 82, 299.

161. Gaussian 03, Revision E.O1,M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M.
A. Robb, J. R. Cheeseman, J. A. Montgomery, T. Vreven Jr., K. N. Kudin, J. C. Burant, J.
M. Millam, S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N.
Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J.
Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E.
Knox, H. P. Hratchian, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, P. Y. Ayala,
K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich,
A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari, J.
B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov,
G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A.
Al-Laham, C. Y. Peng, A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W.
Chen, M. W. Wong, C. Gonzalez and J. A. Pople, Gaussian, Inc., Wallingford CT, 2004.

162. In order to avoid formation of the diacid, the water used in Lennon et al.'s reaction of the
diacid chloride was replaced with N,N-dimethyl formamide.

163. A. A. Gridnev and I. M. Mihaltseva, Synth. Commun., 1994, 24, 1547.

164. J. P. Liu, J. B. Chen, J. F. Zhao, Y. H. Zhao, L. Li and H. B. Zhang, Synthesis, 2003, 2661.

165. Hydrogenation was accomplished in a steel Parr Instruments autoclave.











-- 2 I


1 / \ 2,1 K NI M'S,,
1/2 Rh[(COD)CIJ2
THF




Figure 4-6. Synthesis of [(DEA-iPrBY)Rh(COD)]I 4-9.


7-21


S2.1 KN(TMS)h
N a
1/2 Rhr(COD)C]l2
Fig 4 -7if[ A-THF
Figure 4-7. Synthesis of [(DEA-MTY)RhCOD)] 4-10.


Figure 4-7. Synthesis of [(DEA-MTY)Rh(COD)]J 4-10.


N Rh


4-10
S,0 ^-


C24W


*I


Figure 4-8. Calculated structure for [(DEA-MTY)Rh(COD)] 4-10.


71'


1


`i










B-l

B-2

B-3

B-4

B-5

B-6

B-7

B-8

B-9

B-10


Crystal

Crystal

Crystal

Crystal

Crystal

Crystal

Crystal

Crystal

Crystal

Crystal


data, structure

data, structure

data, structure

data, structure

data, structure

data, structure

data, structure

data, structure

data, structure

data, structure


solution and refinement for 2-1.

solution and refinement for 2-2.

solution and refinement for 2-3.

solution and refinement for 2-4.

solution and refinement for 2-5.

solution and refinement for 2-6.

solution and refinement for 3-5.

solution and refinement for 3-6.

solution and refinement for 3-7.

solution and refinement for 3-8.


................ ................... ...... 16 6

................ ................... ...... 16 7

................ ................... ...... 16 8

................ ................... ...... 16 9

................ ................... ...... 17 0

.................... .................. ....... 17 1

................ ................... ...... 172

................ ................... ...... 17 3

................ ................... ...... 174

................ ................... ...... 17 5









2.2.8 X-ray Crystallography

Data were collected by Dr. Khalil A. Abboud at 173 K using a Siemens SMART

PLATFORM equipped with a CCD area detector and a graphite monochromator utilizing MoKa

radiation (X = 0.71073 A). Cell parameters were refined using up to 8192 reflections. A full

sphere of data (1850 frames) was collected using the co-scan method (0.30 frame width). The

first 50 frames were re-measured at the end of data collection to monitor instrument and crystal

stability (maximum correction on I was < 1 %). Absorption corrections by integration were

applied based on measured indexed crystal faces.

The structures were solved by direct methods in SHELXTL6119, and refined using full-

matrix least squares. The non-H atoms were treated anisotropically, whereas the hydrogen atoms

were calculated in ideal positions and were riding on their respective carbon atoms.

Crystallographic data and structure refinement details for all compounds are listed in appendix B.

2.3 Results and Discussion

2.3.1 Preparation and Solution State Analysis of [DEAM-BI](OTf)2 (2-1)

Figure 2-2 illustrates the synthesis of compound 2-1. The ditriflate is synthesized

according to a literature procedure reported by Zsolnai et al.118 A straightforward substitution

reaction is used to replace the trifluoromethane sulfonyl (OTf) with 1-benzylimidazole, a

commercially available substrate. Unlike other derivatives of 2-1, such as the

methylimidazolium salt [DEAM-MBI](OTf)2,120 2-1 does not precipitate from the reaction

medium. After solvent removal, the isolated white solid is used without further purification. If

desired, sonication in ethyl acetate or crystallization via diffusion of pentane into ethanol

solution followed by filtration provides analytically pure compound.

A 1H NMR spectrum of 2-1 reveals a signature downfield imidazolium proton resonance

(NCHN) at 9.27 ppm. Coupling between the imidazolium proton and the imidazole olefinic
47




















































7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5
Chemical Shift (ppm)
Figure A-10: 1H NMR spectrum of(+/-) [(DEAM-BIY)Ir(COD)]OTf(2-5) in CD2C12.



134









versa.58, 150-153 The commonly accepted reactivity patterns for chelating bis-NHCs are as

follows:

1. When small alkyl N-substituents are used, the linker length has a strong effect on the
mode of coordination.150

2. Small linkers (1 or 2 units) favor a bridging mode due to negative steric interactions of
the N-substituents with co-ligands. Chelating species can be formed when the co-ligands
on the metal are small or the complex is capable of forming an octahedral geometry.

3. Longer linkers ( >3 units) favor chelation unless the steric bulk of the nitrogen
substituents is sufficiently large (ex. t-butyl).58

4. Systems that do not involve halogenated compounds (from the metal or imidazole salt)
typically favor formation of chelating cationic complexes. Halogen abstraction (by use
of a silver salt) can also promote chelate formation.151

These results suggest that a di-NHC ligand with a linker of 2 units and small N-methyl

substituent should favor a bridged 2:1 complex. Ligand architectures containing short linkers

typically force both bulky azole rings into the crowded x,y-plane of the metal complex. In these

cases, bulky co-ligands (e.g. COD or NBD) promote the formation of bridging complexes to

circumvent overcrowding in the x,y-plane. Longer linkers allow orientation of the bulky azole

plane along the z-axis thereby allowing chelation without steric crowding. As will be discussed

later, the second-generation ligand backbone, although only two carbon units link the azole rings,

fortuitously allows the azole ring to orient along the z-axis.

This chapter will describe the synthesis of monometallic and bimetallic complexes

supported by the constrained second-generation ligands, 1,1'-(9,1 0-dihydro-9,10-

ethanoanthracene- 11,12-diyl)di(3 -methyl-1H-imidazol-3 -ium) diiodide [DEA-MI](I)2 (3-3) and

1,1'-(9,1 0-dihydro-9,1 0-ethanoanthracene-l 1,12-diyl)di(3 -methyl-1H-benzimidazol-3 -ium)

diiodide [DEA-MBI](I)2 (3-4).












DEA

GDP

NHC

Ditriflate


COD

TMS

Ea

TM

e.e.

B3LYP

LANL2DZ

ECP

RMSD

Acac

Dppb

rls

gDQCOSY

gHMBC

NOESY


LIST OF ABBREVIATIONS

9,10-dihydro-9,10-ethanoanthracene

gross domestic product

N-heterocyclic carbene

(+/-) 9,10-dihydro-9,10-ethanoanthracene- 11,12-diyldimethanediyl
bi s(trifluoromethanesulfonate)

1,5-cyclooctadiene

trimethylsilylamide

energy of activation

transition metal

enantiomeric excess

Becke 3 term with Lee, Yang, Parr exchange hybrid functional

Los Alamos National Laboratory 2 double-C

effective core potential

root mean square deviation

acetylacetonate

(diphenylphosphino)butane

rate limiting step

gradient double-quantum filtered correlation spectroscopy

gradient heteronuclear multiple bond coherence

nuclear Overhauser effect spectroscopy









107. W. L. Duan, M. Shi and G. B. Rong, Chem. Commun., 2003, 2916.

108. M. Shi and W.-L. Duan, Appl. Organometal. Chem., 2005, 19, 40.

109. Q. Xu, W.-L. Duan, Z.-Y. Lei, Z.-B. Zhu and M. Shi, Tetrahedron, 2005, 61, 11225.

110. T. Chen, J. J. Jiang, Q. Xu and M. Shi, Org. Lett., 2007, 9, 865.

111. T. Zhang, M. Shi and M. Zhao, Tetrahedron, 2008, 64, 2412.

112. W. Wang, T. Zhang and M. Shi, Organometallics, 2009, 28, 2640.

113. T. Zhang and M. Shi, Chem. Eur. J., 2008, 14, 3759.

114. G. Ma, T. Zhang and M. Shi, Org. Lett., 2009, 11, 875.

115. Q. Xu, X. Gu, S. J. Liu, Q. Y. Dou and M. Shi, J. Org. Chem., 2007, 72, 2240.

116. Either the Pd(II) iodide, Pd(II) acetate, or Pd(II)trifluoroacetate

117. Several ligands were reported with similar BINAM-bis(benzimidazole) or H8-BINAM-
bis(benzimidazole) backbones, ligand variation was through alteration of N-substituents.

118. K.-L. Gibis, G. Helmchen, G. Huttner, L. Zsolnai and J. O. C., 181, J. Organomet. Chem.,
1993, 445, 181.

119. SHELXTL6; Bruker-AXS, Madison, WI, (2000).

120. M. S. Jeletic, I. Ghiviriga, K. A. Abboud and A. S. Veige, Organometallics, 2007, 26,
5267.

121. Z. Shi andR. P. Thummel, J. Org. Chem., 1995, 60, 5935.

122. D. Bourissou, O. Guerret, F. P. Gabbai and G. Bertrand, Chem. Rev., 2000, 100, 39.

123. H. M. Tuononene, R. Roesler, J. L. Dutton and R. J. Ragogna, Inorg. Chem., 2007, 46,
10693.

124. E. Baba, T. R. Cundari and I. Firkin, Inorg. Chem. Acta, 2005, 358, 2867.

125. All chiral versions are prepared in the same manner as the racemic excluding resolution
procedures of the reported ligand.

126. R. J. Lowry, M. T. Jan, K. A. Abboud, I. Ghiviriga, and A. S. Veige, Polyhedron in press,
2009..

127. M. S. Jeletic, M. T. Jan, I. Ghiviriga, K. A. Abboud and A. S. Veige, Dalton Trans., 2009,
2764.



















































9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0
Chemical Shift (ppm)
Figure A-19: 1HNMR spectrum of(+/-) Rhodium(I) trans-9,10-dihydro-9,10-ethanoanthracene-9,10-bis(1-
methylbenzimidazolidine-2-ylidene cyclooctadiene iodide, [(DEA-MBY)Rh(COD)]I (3-8) in CDC13.



143


1.5 1.0
















F
F 0
F t
S-


2.1 eq I-benzylimidazole
DME, A 2h


Figure 2-2. Synthesis of [DEAM-BI](OTf)2 (2-1)









N 2 O
2 / 2.1 eq KN{TM%1.. Till
-35C-R I, 2 hrs


Figure 2-3. Synthesis of DEAM-BIY (2-2)


72 0Tf


1) 2.1 eq KN(TMS)2,
-100"C, Ti IF
2) 1.2 eq [Rh(COD)CI];,
-100T, Tl]IF


Figure 2-4. Synthesis of [(DEAM-BY)Rh(COD)]OTf (2-3)


-2 0]f


SOTI









41. H. W. Wanzlick and H. J. KLEINER, Angew. Chem., 1961, 73, 493.

42. H. W. Wanzlick, Angew. Chem. Int. Ed., 1962, 1, 75-80.

43. H. W. Wanzlick, H. -J. Schonherr, Angew. Chem. Int. Ed. Engl., 1968, 7, 148.

44. K. J. Ofele, Organomet. Chem., 1968, 12, 42.

45. D. J. Cardin, B. Cetinkaya, M. F. Lappert, L. Manojlovic-Muir, Chem. Commun., 1971,
400.

46. M. F. Lappert, J. Organomet. Chem., 2005, 690.

47. A. Arduengo, M. Kline, J. C. Calabrese, F. Davidson, J. Am. Chem. Soc., 1991, 113, 9704.

48. A. J. Arduengo, R. L. Harlow and M. Kline, J. Am. Chem. Soc., 1992, 113, 361.

49. D. Enders, O. Niemeier and A. Henseler, Chem. Rev., 2007, 107, 5606.

50. V. Cesar, S. Bellemin-Laponnaz and L. H. Gade, Chem. Soc. Rev., 2004, 33, 619.

51. F. E. Hahn and M. C. Jahnke, Angew. Chem. Int. Ed., 2008, 47, 3122.

52. W. A. Herrmann, Angew. Chem. Int. Ed., 2002, 41, 1290.

53. H. Clavier and S. P. Nolan, Annu. Rep. Prog. Chem., Sect. B, 2007, 103, 193.

54. R. E. Douthwaite, Coord. Chem. Rev., 2007, 251, 702.

55. S. Diez-Gonzalez and S. P. Nolan, Coord. Chem. Rev., 2007, 251, 874.

56. J. M. Praetorius and C. M. Crudden, Dalton Trans., 2008, 4079.

57. J. A. Mata, M. Poyatos and E. Peris, Coord. Chem. Rev., 2007, 251, 841.

58. M. Poyatos, J. A. Mata and E. Peris, Chem. Rev., 2009.

59. 0. Schuster, L. Yang, H. G. Raubenheimer and M. Albrecht, Chem. Rev., 2009, ASAP.

60. P. L. Arnold and I. J. Casely, Chem. Rev., 2009, ASAP.

61. C. Samojlowicz, M. Bieniek and K. Grela, Chem. Rev., 2009, ASAP.

62. P. De Fremont, N. Marion and S. P. Nolan, Coord. Chem. Rev., 2008, 253, 862.

63. S. P. Nolan, ed., N-heterocyclic Carbenes in Synthesis, Wiley-VCH, Weinheim, Germany,
2006.

64. P. De Fremont, N. Marion and S. P. Nolan, Coord. Chem. Rev., 2009, 253, 862.









55.6 (COD-CH), 53.5 (COD-CH), 52.2 (CH2), 50.8 (CH2), 48.5 (CHCHCH2), 39.3 (CCHC),

33.9 (COD-CH2), 31.9 (COD-CH2), 30.4 (COD-CH2), 28.0 (grease), 27.7 (COD-CH2). Anal

Calc. for Ir2C54H56N4C12: C, 53.32%; H,4.64%; N,4.61% Found: C, 51.528%; H,4.077%; N,

4.890. MS(TOF-ESI+):Calc. for [C54H58N4lr2C1 ]+: m/z 1183.967 (M-C1) found m/z

1183.3595. The molecular structure determined by X-ray crystallography is displayed in Figure

2-11, crystals were grown by diffusion of pentane into a THF solution contianing the compound

and a small amount of benzene.

2.2.7 Catalytic Hydroformylation

The hydroformylation experiments were carried out in a 100 mL stainless steel Parr reactor

heated in a sand bath. The reactor was charged with 50 mg of the substrate, 0.1 mol% of the bis-

carbene rhodium complex (2-3) and 1.5 mL of solvent. Before starting the catalytic reactions,

the charged reactor was purged three times with 10-20 bar of syngas (CO/H2 = 1/1) and then

pressurized to 100 bar. The reaction mixture was stirred at 800 rpm at 50 OC for the appropriate

reaction time (typically 24h). Once complete, the reactor was cooled to room temperature, the

pressure was reduced to 1.0 bar in a well-ventilated hood, and the reaction mixture was collected

in a vial. The reaction mixtures were analyzed directly without further purification. The %

conversion and regioselectivity were determined by 1H NMR spectroscopy and gas

chromatography. The enantiomeric purity was determined by GC using Supelco' s Beta Dex 225

column. Temperature program: 100 C for 5 min, then 4 C/min to 160 C. Retention times: 4.8

min for vinyl acetate, 11 (S) and 12.8 (R) min for the enantiomers of methyl 2-methyl-3-

oxopropanoate (branched regioisomer), 16 min for methyl 4-oxobutanoate (linear regioisomer), 9

min for styrene, 18 (S) and 18.2 (R) min for the enantiomers of 2-phenylpropanal (branched

regioisomer), and 22 min for 3-phenylpropanal (linear regioisomer).


























































8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5
Chemical Shift (ppm)
Figure A-27. H NMR of N,N'-bis(4-nitrotolyl)-9,10-dihydro-9,10-ethanoanthracene-11,12-diamine (4-3).



151


3.0 2.5 2.0









Table B-3. Crystal data, structure solution and refinement for 2-3-CH2C12.
identification code rxl
empirical formula C48 H48 C12 F3 N4 03 Rh S
formula weight 991.77
T(K) 173(2)
X(A) 0.71073
crystal system Monoclinic
space group P2(1)/n
a (A) 9.8237(13)
b(A) 18.047(3)
c(A) 24.957(3)
a (deg) 90
/ (deg) 92.909(2)
y (deg) 90
V(A3) 4418.9(10)


Z
pcalcd (Mg mm 3)
crystal size (mm3)
abs coeff (mm-1)
F(000)
0 range for data collection
limiting indices
no. ofreflns called
no. ofind reflns (Rint)
completeness to 0 = 27.490
absorption corr
refinement method
data / restraints / parameters
R1,a wR2b [I > 20]
R1,a wR2b (all data)
GOFc on F2
largest diff. peak and hole


4
1.491
0.16x 0.16x 0.10
0.615
2040
1.39 to 27.500
-12 29619
10128 (0.0483)
0.997
Integration
Full-matrix least-squares on F2
10128 / 1 / 570
0.0359, 0.0988 [8286]
0.0459, 0.1024
1.077
0.801 and -1.078 e.A-3


a R1 = I||Fo |IFe||/|Fol. b wR2= ((w(Fo2 Fc2)2)/((F2)2))1/2. c GOF = ( w(Fo2
Fc2)2/(n ))1/2 where n is the number of data andp is the number of parameters refined.









LIST OF FIGURES


Figure page

1-1 Reaction coordinate diagram for catalyzed and uncatalyzed reactions............................ 32

1-2 Generalized mechanisms for A) uncatalyzed reaction B) catalyzed reaction C) single
reagent activation catalysis D) catalyzed reaction with intermolecular reaction ..............32

1-3 Structures of(R) and (S)-Carvone and (R)- and (S)-Thalidomidec .................................. 33

1-4 Selected privileged ligands ......... ... ............ ................. ......................... ......................... 33

1-5 Wanzlick's and Ofele' sNHC complexes and Lappert's enetetraamine ...........................34

1-6 Relative influence of geometric and electronic effects on the energy gap between o
and p, orbitals ......................... ................. ..................................34

1-7 Resonance structures of NH C. ................................................. ............................... 34

1-8 Com m on N -heterocyclic carbenes ................................................ .......................... 35

2-1 E xam ples of chelating N H C s ....................................... .................................................. 56

2-2 Synthesis of [DEAM -BI](OTf)2 (2-1)............................. .......................... 57

2-3 Synthesis of DEAM-BIY (2-2)...... .................................................... ................ 57

2-4 Synthesis of [(DEAM-BY)Rh(COD)]OTf (2-3).............................................................57

2-5 Synthesis of [/,-DEAM-BY][Rh(COD)Cl]2 (2-4) ................ ................................ 58

2-6 Synthesis of [(DEAM-BY)Ir(COD)]OTf (2-5)................. ......................................58

2-7 Synthesis of [/,-DEAM-BY][Ir(COD)Cl]2 (2-6)............................................................58

2-8 X -ray Crystal Structure of 2-1 and 2-2 ........................................ ......................... 59

2-9 M olecular Structure of 2-3 and 2-5 .......................... ......... .......................... ................. 59

2-10 Average bond angles and length of free NHCs and M-NHCs ..................... ............ 60

2-1 1 M molecular Structure of 2-4 and 2-6 ........................ ........................................................ 60

3-1 First and second generation ligand architectures. ................................................... 82

3-2 Synthesis of [D EA -M I](I)2 (3-3).................................................................................... 83

3-3 Synthesis of [D E A -M B I](I)2 (3-4) ............... ......................... ........................................... 83












7Z


c2"22
".3 ^


C9) CIO
Figure 3-7. Molecular structure of 3-5 from the side (left) and top (right) view. Ellipsoids are
drawn at the 50% probability level.








I C22 NI









CIO C9
Figure 3-8. Molecular structure of compound 3-6. Ellipsoids are drawn at the 50% probability
level.


I




,6


0 16









6 ppm: 145.5 and 138.28 (NCCHCHCHCHCN), 144.0 and 139.2 (N-C=C-N), 127.4 (C, Ar),

126.9 (C, Ar), 126.4 (C, Ar), 123.9 (C, Ar), 122.8 (C=C), 121.5 (C, Ar), 119.8 (C, Ar), 109.1 and

106.9 (NCCHCHCHCHCN), 65.9 (NCHCHC), 46.6 (NCHCHC), 36.2 (NCH3). MS(DIP-CI):

Calc. for [C32H26N4]: m/z 466.5564 [M+], found m/z 466.2157. The molecular structure of 3-5

as determined by X-ray crystallography is displayed in Figure 3-7, crystals were grown by a

diffusion of ether into a THF solution containing the compound.

3.2.6 Synthesis of Lu-DEA-MY] [Rh(NBD)I]2 (3-6) as a Mixture with 3-9

At -35 C, KN(TMS)2 (46 mg, 0.23 mmol) in 3 mL dry THF was added dropwise to a

suspension of 3-3 (76 mg, 0.12 mmol) in THF (3 mL). The reaction mixture was then stirred for

45 min while warming to room temperature. After cooling the mixture to -35 OC, it was added

dropwise to a cold solution of [Rh(NBD)2]BF4 (100 mg, 0.27 mmol) in THF (3 mL). This

mixture was allowed to stir at room temperature for 2.5 h before the solvent was removed in

vacuo. The resulting residue was triturated with Et20 (2x3 mL) and pentanes (2x3 mL). After

drying overnight, the residue was taken up in pentanes, filtered and then washed with Et20 and

extracted into benzene. The solvent was removed, producing a yellow/orange solid (53 mg). A

1H NMR spectrum of the solid revealed 25 mol% of 3-9 was present as an impurity that could

not be removed. H NMR (300 MHz, C6D6) 6 ppm: 7.85 (d, JHH = 7.1 Hz, 2ArH), 6.86 7.11

(m, 6ArH), 6.41 (s, bridge H), 5.91 (d, JHH = 1.7 Hz, NCHCHN), 5.77 (d, JHH = 1.7 Hz,

NCHCHN), 5.48 (s, 2bridgehead H), 5.19 (br s, 2NBD-CH), 5.05 (br s, 2NBD-CH), 3.38 (br s,

2NBD-CH), 3.28 (s, 6CH3), 3.12 (d, JHH = 2.3 Hz, 2NBD-CHCHCH) 2.89 (br. s., 2NBD-CH)

1.64 (d, JHH = 2.5 Hz, 2NBD-CHCHCH) 0.96 (m, 4NBD-CH2). The molecular structure 3-6 as

determined by X-ray crystallography is displayed in Figure 3-8, crystals were grown by diffusion

of ether into a THF solution containing the compound.
























































E .Z"1 ~ I 1 I I
216 208 200 192 184 176 168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48
Chemical Shift (ppm)
Figure A-4: 13C NMR spectrum of(+/-) DEAM-BIY (2-2) in C6D6.



128


























































9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0
Chemical Shift (ppm)
Figure A-23: 1H NMR spectrum of(+/-) [DEA-iPrI][I]2 (4-1) in (CD3)2SO.


35 30 25 20 15 10 05






































184 176 168 160 152 144 136 128 120 112 104 96 88 80 72
Chemical Shift (ppm)
Figure A-6: C NMR spectrum of(+/-) [(DEAM-BIY) Rh (COD)] OTf(2-3) in CDC13.


64 56 48 40 32 24 16


I 1 ,1


I


pjjjr
1177


' I I I II


i


I









enantiomer of the ligand produces (S)-5-1 and the (R,R) enantiomer forms (R)-5-1, suggesting a

similar pattern of chiral induction to that reported for the privileged (S,S)-BINAP ligand.28

Omission of base or utilization of pyridine led to no product formation and substituting

potassium hydroxide with potassium carbonate led to reduced yields and e.e.. Altering the

solvent mixture to THF/Methanol had little effect but did lead to a small decrease in e.e. and

attempting the reaction in pure methanol drastically increased the yield but produces no e.e.

suggesting catalyst degradation. Typical solvent mixtures for rhodium catalyzed conjugate

addition reactions include water to facilitate hydrolysis and formation of the final product.

However, substitution of methanol with deionized, degassed water reduced e.e. measurements

from 82% to 5% under the same reaction conditions. Loss of enantioselectivity may be due to

water facilitated dissociation of the chiral backbone or formation of dimer III. To completely

remove water from the system, anhydrous methanol was utilized, leading to a slight decrease in

both yield and enantiocontrol suggesting a fine balance between catalyst activation and

degradation by protonated solvents.

Investigation of chiral catalysis utilizing a variety of other boronic acids (Tables 5-2

through 5-7) leads to several conclusions. Comparison of the catalytic runs involving 4-

methoxyboronic acid and 4-fluoroboronic acid suggest transmetallation is facilitated by electron

donating substituents. 4-methoxyboronic acids produced significant yields after only 14 hours,

as the fluoro analog required 24 hrs and produced lower yields for 3-8 and 3-9. Utilization of o-

tolylboronic acid allowed for increased steric bulk about the chiral pocket during the olefin

insertion step. This was expected to increase the enantiomeric excess produced particularly for

the more flexible catalysts 3-9 and 4-8 by affecting the structure of diastereotopic transition state

VI. The close proximity of the methyl group to the metal center could serve to further define the









chiral pocket, affecting the approach and insertion of the olefin. The e.e.s produced by these

reactions are higher than those obtained utilizing phenylboronic acid, but this affect is not

drastic. For 4-8 the increase in e.e. is small but the yield is drastically reduced, inferring that the

isopropyl group may hinder the overlap between hindered aryl substituents and the enone in the

transition state VI. Comparison of reactions forming 3-phenylcyclopentanone (5-6) with those

forming the much bulkier 3-(1-naphthalenyl)-cyclohexanone (5-3) (Tables 5-4 and 5-7) show

that the more flexible catalysts 3-9 and 4-8 produce higher yields when the size of the boronic

acids is increased. However, the more constrained catalyst 3-8 produces small amounts of bulky

5-3 but large amounts of the relatively small 5-6.

5.4 Conclusions

Catalytic trials involving catalyst 2-3, 3-8, 3-9, and 4-8 display the large variation in

catalytic behavior that can emanate from relatively small alterations in ligand structure. The

significant increase in the enantioselectivity of catalyst 3-8 is assigned to an increase in the size

of the imidazole, an area that is not typically associated with catalytic behavior. These findings

further support the assertion that the purely rational design of catalyst should not be attempted

before empirical investigation can be accomplished.

R R

1.Rh H





R= Me or I
Figure 5-1. Transmetallation of aryl substituents to rhodium catalysts.









temperature. Mononuclear salt 2-5 formed as an orange precipitate, was isolated by filtration

and washed with THF (2 mL) and Et20 (5 mL) to remove excess base. The metal complex was

extracted from any remaining starting materials with CH2C2 and upon solvent removal was

isolated as a brilliant orange powder; yield 57 mg (48%). H NMR (300 MHz, CDC13) 6 ppm:

7.51 (1H, d, J 2.0 Hz, NCHCHN), 7.47 7.55 (1H, m, Ar), 7.29 7.45 (6H, m, Ar), 7.17 7.26

(5H, m, Ar), 7.07 7.17 (2H, m, Ar), 6.84 6.95 (2H, m, Ar), 6.81 (2H, d, J 2.0 Hz, NCHCHN),

6.71 (1H, d, J=2.0 Hz, NCHCHN), 6.58 6.67 (2H, m, Ar), 6.55 (1H, d, J=2.0 Hz, NCHCHN),

5.83 (2H, d, J 15.9 Hz, N(HCH)C), 5.31 (2 H, d, J 15.6 Hz, CH(HCH)N), 5.03 (d, J 15.5 Hz,

N(HCH)C), 4.94 (d, J=15.5 Hz, CH(HCH)N), 4.51 (1 H, d, J=1.9 Hz bridgehead H), 4.43 (1 H,

dd, J=13.3, 3.8 Hz, CH(HCH)N), 4.38 (1 H, d, J 1.8 Hz, bridgehead H), 4.07 4.19 (2 H, m,

overlapping CH(HCH)N and COD-CH), 4.02 (1 H, dd, J=14.4, 8.1 Hz, CH(HCH)N), 3.88 3.97

(1 H, m, COD-CH), 3.68 3.77 (1 H, m, COD-CH), 3.58 3.67 (1 H, m, COD-CH), 3.49 (1 H, q,

J=7.0 Hz, ether), 3.19 (2 H, overlapping m and dd, J 14.5, 1.6 Hz, bridge H and CH(HCH)N),

1.89 2.20 (2 H, m, COD-CH2), 1.73 1.88 (3 H, m, bridge H overlapped by COD-CH2), 1.48 -

1.72 (3 H, m, COD-CH2), 1.29 1.48 (1 H, m, COD-CH2), 1.22 (2 H, t, J=7.0 Hz, ether). 13C

NMR (75 MHz, CD2C12) 6 ppm: 179.4 (NCN), 176.5 (NCN), 145.0 (C, Ar), 144.9 (C, Ar), 139.5

(C, Ar), 139.4 (C, Ar), 136.1 (C, Ar), 135.8 (C, Ar), 129.6 (2C, Ar), 129.6 (2C, Ar), 128.8 (C,

Ar), 128.7 (C, Ar), 127.5 (C, Ar), 127.3 (C, Ar), 127.0 (C, Ar), 126.8 (C, Ar), 126.8 (2C, Ar),

126.8 (2C, Ar), 126.2 (C, Ar), 124.7 (NCHCHN), 124.2 (NCHCHN) 123.7 (NCHCHN), 123.7

(NCHCHN), 121.5 (2C, Ar), 79.4 (COD-CH), 77.9 (COD-CH), 77.0 (COD-CH), 73.1 (COD-

CH), 68.3 (THF), 57.4 (CHCH2N), 55.6 (NCH2C), 55.1 (CHCH2N), 54.4 (NCH2C), 49.0

(CCHC), 48.8 (CHCHCH2), 48.2 (CCHC), 47.9 (CHCHCH2), 32.6 (COD-CH2), 32.1 (COD-

CH2), 30.9 (COD-CH2), 30.8 (COD-CH2), 26.1 (THF). Anal. Calc. for Ir C47N4H4603SF3: C,









(overlapping d, J=6.8 Hz, 6 H, NCHCH3). 13C NMR (75 MHz, (CD3)2SO) 6 ppm: 139.3 (2 C,

NCHCHN), 138.3 (s, 2 C, NCHCHN), 135.2 (s, 2 C, NCHN), 128.4 (s, 2 C, Ar), 128.3 (s, 2 C,

Ar), 126.9 (s, 2 C, Ar), 126.6 (s, 2 C, Ar), 121.4 (s, 2 C, Ar), 121.1 (s, 3 C, Ar), 63.5 (s, 2 C,

bridge C), 53.3 (s, 2 C, NCHCH3), 49.5 (s, 2 C, bridgehead C), 22.9 (s, 2 C, NCHCH3), 22.7 (s, 2

C, NCHCH3).

4.2.2 Synthesis of Trans-l,l-(9,10-Dihydro-9,10-Ethanoanthracene-1l,12-Diyl)di(3-
Isopropyl-1H-Benzimidazol-3-Ium) Diiodide [DEA-iPrBI](I)2 (4-2)

Dibenzimidazole103 (900 mg, 2 mmol) was dissolved in anhydrous MeCN (10.0 mL) in a

sealable glass bomb flask. 2-iodopropane (0.82 mL, 4 equiv, 8 mmol) was added, and the vessel

was evacuated and sealed. The flask was shielded from light and heated in a sand bath at 105 C

for 48 h. The mixture was cooled to room temperature and the solid was filtered and washed

with cold MeCN to afford 4-2 as a light beige powder; yield 430 mg (28%). 1H NMR (300 MHz,

(CD3)2SO) 6 ppm: 8.50 (d, J 8.2 Hz, 2 H, Ar), 8.43 (s, 2 H, NCHN), 8.16 (d, J 8.0 Hz, 2 H.

Ar), 7.87 7.96 (m, 2 H, Ar), 7.68 7.86 (m, 4 H, Ar), 7.46 (t, J=7.5 Hz, 2 H, Ar), 7.24 (t, J=7.4

Hz, 2 H, Ar), 7.04 (d, J 7.5 Hz, 2 H, Ar), 6.21 (br. s., 2 H, bridge H), 5.13 (br. s., 2 H,

bridgehead H), 5.02 (spt, J=6.6 Hz, 2 H, NCH(CH3)2), 1.44 (d, J=6.6 Hz, 6 H, NCHCH3), 1.37

(d, J=6.6 Hz, 6 H, NCHCH3). 13C NMR (75 MHz, (CD3)2SO) 6 ppm: 138.7 (s, Ar), 138.7 (s,

NCHN), 138.2 (s, Ar), 138.1 (s, Ar), 131.7 (s, Ar), 130.5 (s, Ar), 128.7 (s, Ar), 128.4 (s, Ar),

127.8 (s, Ar), 127.6 (s, Ar), 126.6 (s, Ar), 115.6 (s, Ar), 114.6 (s, Ar), 61.8 (s, bridge C), 51.3 (s,

NCH(CH3)2), 48.7 (s, bridgehead C), 22.5 (s, CH3), 22.0 (s, CH3).

4.2.3 Synthesis of N,N'-bis(4-Nitrotolyl)-9,10-Dihydro-9,10-Ethanoanthracene-11,12-
Diamine (4-3)

To a solution of diamine 3-1 (1.05 g, 4.5 mmol) in anhydrous DMF (10 mL) was added

anhydrous K2CO3 (1.36 g, 2.2 equiv., 10 mmol) and 3-fluoro-4-nitrotoluene (1.45 g, 2.1 equiv., 9









Table B-6. Crystal data, structure solution and refinement for 2-6C6sH6.
identification code rxl7
empirical formula C60 H64 C12 Ir2 N4
formula weight 1296.45
T(K) 173(2)
S(A) 0.71073
crystal system Triclinic
space group P1
a(A) 13.8318(17)
b (A) 13.9515(17)
c(A) 14.5432(18)
a (deg) 80.640(2)
/ (deg) 70.355(2)
y (deg) 75.494(2)
V(A3) 2549.4(5)
Z 2
pcalcd (Mg mm 3) 1.689
crystal size (mm3) 0.15 x 0.12 x 0.04
abs coeff (mm-1) 5.363
F(000) 1280
0 range for data collection 1.49 to 27.500
limiting indices -17 no. ofreflns called 17315
no. ofind reflns (Rint) 11384 (0.0589)
completeness to 0 = 27.490 97.50%
absorption corr Integration
refinement method Full-matrix least-squares on F2
data / restraints / parameters 11384 / 0 / 613
R1,a wR2b [I > 2c] 0.0293, 0.0760 [9922]
R1,a wR2b (all data) 0.0348, 0.0791
GOFc on F2 1.007
largest diff peak and hole 1.769 and -1.397 e.A-3

" R1 = E||Fo IFc||/|1Fol. b w R = ((w(Fo2 Fc2)2)/(w(Fo2)2))1/2. c GOF = (Y w(Fo2
F2)2/(n ))1/2 where n is the number of data andp is the number of parameters refined.









catalyst. Purified enzymes work well toward these ends27 but are limited by their reaction scope,

cost, and availability of the enzymatic catalysts. Increased understanding of the "black art" of

catalysis has enabled scientists to develop synthetically prepared catalytic species capable of

asymmetric induction. Purely organic compounds have recently gained popularity as catalytic

species because of their low-cost and environmentally friendly nature in relation to many metal

containing compounds.28 However, the unique properties of transition metal complexes have

made them ubiquitous in the field of asymmetric synthesis.

Transition metals (TMs) are unique with regard to their energetically accessible valence d-

orbitals. The number and shape of these partially filled orbitals allow for versatile reactivity.

TMs interact with organic molecules in a covalent, ionic, or dative manner (or a combination

thereof). Exploitation of these interactions can be used to modulate the electronic nature and

topological environment of a TM center via coordinated organic ligands. Ligands can also be

used to increase a compound's stability or its solubility in specific solvents. Although TM

complexes have found application in heterogeneous asymmetric catalysis29 homogeneous

systems are more popular due to their ease of use and investigation. The advantages of

homogeneous TM catalysis are as follows:

1. TM complexes are capable of facilitating reactions that do not occur naturally.

2. The electronic character and steric bulk of organometallic complexes are easily altered by
modification of the supporting ligands.

3. The variety of complexes available permits reactions with substrates that are not
compatible with selective systems such as enzymes.

4. TM complexes are applicable in a larger variety of reaction conditions than enzymes that
require very specific and typically aqueous environments.30

5. Reaction conditions including temperature, solvent mixing, and catalyst/ligand
concentration are more efficiently controlled in solution than in heterogeneous
environments.31









turns bright yellow upon deprotonation. After 1 h the suspension is then cooled again to -1000C.

A cold solution of [Rh(COD)Cl]2 (32 mg, 0.06 mmol) in 3 mL of dry THF was added dropwise

to the salt suspension and allowed to stir overnight. A yellow precipitate formed that was filtered

and washed with THF and diethyl ether to afford 4-9 as a yellow powder; yield 10 mg (10%). 1H

NMR (300 MHz, CDCl3) 6 ppm: 9.45 (d, J=10.3 Hz, 1 H, bridge H), 7.81 (d, J=7.0 Hz, 1 H,

Ar), 7.75 (d, J 7.0 Hz, 1 H, Ar), 7.54 7.65 (m, 3 H, Ar), 7.13 7.54 (m, 9 H, Ar), 7.01 -7.12

(m, 2 H, Ar), 6.22 (spt, J=6.7 Hz, 1 H, overlapping NCH(CH3)2 with COD-CH), 5.21 (s, 1 H,

bridgehead H), 5.17 (s, 1 H, bridgehead H), 5.02 (spt, J=6.7 Hz, 2 H, overlapping NCH(CH3)2

with COD-CH), 4.55 (m, 1 H, COD-CH), 4.43 (dd, J=10.1, 1.0 Hz, 1 H, bridge H), 4.13 (t,

J=6.7 Hz, 1 H, COD-CH), 3.64 3.78 (m, 1 H, COD-CH), 2.69 2.90 (m, 1 H, COD-CH2), 2.51

- 2.66 (m, 1 H, COD-CH2), 2.26 2.51 (m, 3 H, COD-CH2), 1.92 (d, J 6.7 Hz, 3 H), 1.88 2.04

(overlapping m, 1 H), 1.61 (d, J=7.0 Hz, 3 H, NCH(CH3)2), 1.55-1.65 (overlapping m, 2H,

COD-CH2) 1.58 (d, J=6.7 Hz, 3 H, NCH(CH3)2), 1.52 (d, J=7.0 Hz, 3 H, NCH(CH3)2), 1.22 -

1.37 (m, 1 H, NCH(CH3)2). 13C NMR (75 MHz, CDC13) 6 ppm: 191.7 (d, J=54.5 Hz, NCN),

190.8 (d, J 51.5 Hz, NCN), 146.9 (s, Ar), 144.4 (s, Ar), 138.7 (s, Ar), 137.2 (s, Ar), 135.9 (s,

Ar), 133.6 (s, Ar), 133.19 (s, Ar), 132.9 (s, Ar), 128.3 (s, Ar), 128.1 (s, Ar), 127.8 (s, Ar), 127.6

(s, Ar), 127.4 (s, Ar), 127.1 (s, Ar), 124.2 (s, Ar), 124.1 (s, Ar), 124.0 (s, Ar), 123.7 (s, Ar), 123.1

(s, Ar), 122.1 (s, Ar), 113.2 (s, Ar), 113.0 (s, Ar), 112.1 (s, Ar), 111.2 (s, Ar), 94.2 (d, J 8.6 Hz,

COD-CH), 91.9 (d, J8.1 Hz, COD-CH), 89.9 (d, J=7.2 Hz, COD-CH), 89.5 (d, J 6.6 Hz,

COD-CH), 65.3 (s, CHCHN), 62.3 (s, CHCHN), 57.8 (s, NCHCH3), 53.9 (s, NCHCH3), 49.1 (s,

CCHC), 47.9 (s, CCHC), 32.0 (s, COD-CH2), 31.79(s, COD-CH2), 29.4 (s, COD-CH2), 28.7 (s,

COD-CH2), 22.6 (s, NCHCH3), 22.5 (s, NCHCH3), 21.8 (s, NCHCH3), 21.5 (s, NCHCH3).









A-22 13C{1H} NMR spectrum of(+/-) Rhodium(I) trans-9,10-dihydro-9,10-
ethanoanthracene-9,10-bis(1-methylimidazolidine-2-ylidene cyclooctadiene
iodide, [(DEA-MY)Rh(COD)]I (3-9) in CD3C. ................................ ................... 146

A-23 1HNMR spectrum of(+/-) [DEA-iPrI][I]2 (4-1) in (CD3)2SO ................ .............. 147

A-24 13C NMR spectrum of(+/-) [DEA-iPrI][I]2 (4-1) in (CD3)2SO................ ................. 148

A-25 1HNMR spectrum of(+/-) [DEA-iPrBI][I]2 (4-2) in (CD3)2SO ................................... 149

A-26 13C NMR spectrum of(+/-) [DEA-iPrBI][I]2 (4-2) in (CD3)2SO. .................................. 150

A-27 H NMR of N,N'-bis(4-nitrotolyl)-9,10-dihydro-9,10-ethanoanthracene- 1,12-
diam ine (4-3). .............................................................................. 15 1

A-28 13C NMR of N,N'-bis(4-nitrotolyl)-9,10-dihydro-9,10-ethanoanthracene-1 1,12-
diam ine (4-3). .............................................................................. 152

A-29 H NMR of N,N'-bis(4-aminotolyl)-9,10-dihydro-9,10-ethanoanthracene- 1,12-
diam ine (4-4). .............................................................................. 153

A-30 13C NMR of N,N'-bis(4-aminotolyl)-9,10-dihydro-9,10-ethanoanthracene-l 1,12-
diam ine (4-4). .............................................................................. 154

A-31 H NMR 1,1'-(9,10-dihydro-9,10-ethanoanthracene- 1,12-diyl)di(1H-tolylimidazole)
(4-5) ...................... ........................................... 155

A-32 13C NMR 1,1'-(9,10-dihydro-9,10-ethanoanthracene-l 1,12-diyl)di(1H-
toly lim id azo le) (4 -5 ). ............................................... ..................................................... 15 6

A-33 1HNMR spectrum of(+/-) [DEA-MTI][I]2 (4-6) in (CD3)2SO............... ........... 157

A-34 13C NMR spectrum of(+/-) [DEA-MTI][I]2 (4-6) in (CD3)2SO.................................... 158

A-35 1HNMR spectrum of R,R [DEA-iPrTI][I]2 (4-7) in CDC13 ............. .......... ........ 159

A-36 1H NMR spectrum of (+/-) Rhodium(I) trans-9,10-dihydro-9,10-
ethanoanthracene-9,10-bis(1-isopropylimidazolidine-2-ylidene cyclooctadiene
iodide, [(DEA-iPrY)Rh(COD)]I (4-8) in CDC13 ............................... ............... 160

A-37 1H NMR spectrum of (+/-) Rhodium(I) trans-9,10-dihydro-9,10-
ethanoanthracene-9,10-bis(1-isopropylimidazolidine-2-ylidene cyclooctadiene
iodide, [(DEA-iPrY)Rh(COD)]I (4-8) in CDC13................................. ................... 161

A-3 8 H NMR spectrum of (+/-) Rhodium(I) trans-9,10-dihydro-9,10-
ethanoanthracene-9,10-bis(1-isopropylbenzimidazolidine-2-ylidene cyclooctadiene
iodide, [(DEA-iPrBY)Rh(COD)]I (4-9) in CDC13 ......................................................... 162













7 21


4 'PrI, CHICN
105 `C, 2d
aib


Figure 4-3. Synthesis ofligand [DEA-iPrBI](I)2 4-2.


2liN NH,
NH-
H-^^^


p4QOEid
p-T&O~H, fd


2 F


KCO,, DMF
, I8 h


4 Mel, CII CN
105 "C, 2d
-----------,


H,, PdC
CI(1ClW/MeOHll
IN


/-21

Nr



4-6


Figure 4-4. Synthesis ofligand [DEA-MTI](I)2 4-6.


/7n21


N, /J--N
N
N
N ,


4 'Prl, CHICN
105 ~C, 2d
bI-


Figure 4-5. Synthesis ofligand [DEA-iPrTI](I)2 4-7.









3.2.4 Synthesis of Trans-l,l-(9,10-Dihydro-9,10-Ethanoanthracene-1l,12-Diyl)di(3-Methyl-
1H-Benzimidazol-3-Ium) Diiodide [DEA-MBI](I)2 (3-4)

Dibenzimidazole103 (970 mg, 2.2 mmol) was dissolved in anhydrous MeCN (10 mL) in a

glass ampoule fitted with a sealable Teflon stopcock. Mel (0.55 mL, 4 equiv, 8.8 mmol) was

added, and the vessel was evacuated and sealed. The flask was shielded from light and heated in

a sand bath at 105 OC for 48 h. The mixture was cooled to room temperature and the solid was

filtered and washed with cold MeCN to afford 3-4 as a light beige powder; yield 1.05 g (66%).

1HNMR (300 MHz, (CD3)2SO) 6 ppm: 8.85 (s, 2 H, NCHN), 7.99 8.07 (m, 2 H, Ar), 7.82 -

7.92 (m, 4 H, Ar), 7.66 7.77 (m, 4 H, Ar), 7.47 (td, J=7.5, 1.13 Hz, 2 H, Ar), 7.27 (td, J=7.4,

0.99 Hz, 2 H, Ar), 7.15 7.22 (m, 2 H, Ar), 5.99 (s, 2 H, bridge H), 5.16 (s, 2 H, bridgehead H),

3.92 -4.01 (m, 6 H, CH3) 13C NMR (75.3 MHz, (CD3)2SO) 6 (ppm): 140.5 (N=CH-N), 138.5

and 137.5 (C=C), 131.3 and 130.6 (N-C=C-N), 127.8 (C aromatic), 127.7 (C aromatic), 126.8 (C

aromatic), 126.8 (C aromatic), 126.6 (C aromatic), 126.2 (C aromatic), 114.2 and 113.7 (N-

CCHCHCHCHC-N), 61.3 (N-CH-CH-C=), 48.0 (N-CH-CH-C=), 33.8 (N-CH3). HRMS (ESI-

FTICR) calc'd (found) for C32H28IN4 (M-I) 595.1353 (595.1272)..

3.2.5 Synthesis of Trans-9,10-Dihydro-9,10-Ethanoanthracene-9,10-(1-
Methyl)Bibenzimidazole), DEA-MbBY (3-5)

KN(TMS)2 (116 mg 0.58 mmols) in 5 mL of dry THF was added dropwise to a 10 mL

THF solution of 3-4 (200 mg, 0.27 mmol). The reaction was allowed to stir at room temperature

for 3 h and then filtered. Solvent was removed from the filtrate in vacuo to produce a yellow

powder. Excess base was extracted by washing the yellow precipitate with Et20 (10 mL) to

afford 3-5 as a yellow solid; yield 53 mg (40%). 1H NMR (300 MHz, C6D6) 6 ppm: 6.95 (m, 12

H, Ar), 6.77 (dt, J= 7.5, 1.1 Hz, 2 H, Ar), 6.39 (dd, J= 7.5, 1.0 Hz, 2 H, Ar), 4.95 (s, 2 H,

bridgehead CH), 3.40 (s, 2 H, bridgehead CH) 2.63 (s, 6 H, NCH3). 13C NMR (75.3 MHz, C6D6)









CCHCHCHCHC ), 7.46 (dd, J= 6.9, 1.0 Hz, CCHCHCHCHC), 7.11-7.39 (overlapping signals,

5 H, Ar and NCH=CHN), 6.96 (d, J = 2.0 Hz, NCH=CHN), 6.69 (d, J = 1.7 Hz, NCH=CHN),

5.17 (d, J= 1.1 Hz, NCHCHC), 4.87 (overlapping d and m, J= 0.6 Hz, NCHCHC and COD-

CH), 4.15 (m, COD-CH), 4.03 (s, CH3), 3.73 (m, 2COD-CH), 3.64 (s, CH3), 3.62 (dd, J= 1.4

Hz, 15), 2.44- 2.66 (m, 1COD-CH2), 2.18 -2.41 (m, 2COD-CH2), 1.98 -2.17 (m, 1COD-CH2),

1.69 -1.98 (m, 3COD-CH2), 1.47 1.68 (m, 1COD-CH2). 13C NMR (75.3 MHz, CDC13) 6 ppm:

180.1 (1 C, d, JRhC = 54.7 Hz, NCN), 179.3 (1 C, d, Jhc = 52.7 Hz, NCN), 143.7 (C, Ar), 142.6

(C, Ar), 136.9 (C, Ar), 136.1 (C, Ar), 128.6 (C, Ar), 127.8 (C, Ar), 127.7 (C, Ar), 127.4 (C, Ar),

127.2 (C, Ar), 126.9 (C, Ar), 125.1 (C, Ar), 125.0 (NCHCHN), 124.7 (NCHCHN), 123.7

(NCHCHN), 122.4 (C, Ar), 115.9 (NCHCHN), 92.6 (d, Jhc = 8.6 Hz, COD-CH), 88.3 (d, JRhC =

7.4 Hz, COD-CH), 87.9 (d, Jhc = 8.3 Hz, COD-CH), 85.8 (d, JRh = 7.4 Hz, COD-CH), 66.5 (s,

CHCHN), 63.7 (s, CHCHN), 48.5 (s, CCHC), 47.7 (s, CCHC), 40.8 (s, NCH3), 37.5 (s, NCH3),

32.5 (s, COD-CH2), 31.8 (s, COD-CH2), 29.0 (s, COD-CH2), 28.0 (s, COD-CH2). Anal. Calc. for

C32H34N4IRh: C, 54.56%; H, 4.86%; N, 7.95%. Found: C, 54.47%; H, 4.72%; N, 8.25%. The

molecular structure of 3-9 as calculated by ground-state geometry optimization calculations

using the hybrid density functional B3LYP156 with the LANL2DZ157-160 basis set utilizing

effective core potentials (ECP) for the core rhodium electrons is displayed in Figure 3-12.

3.3 Results and Discussion

3.3.1 Constrained Precursors [DEA-MI](I)2 (3-3) and [DEA-MBI](I)2 (3-4)

Synthesis of the constrained 9,10-dihydro-9,10-ethanoanthracene (DEA) ligands requires

assembly of each azole onto the diamine 3-1. Synthesis of 3-1 was achieved using three

different procedures. Initially, 3-1 was synthesized from a di-carboxylic acid via a literature

preparation reported by Trost et al.154 A similar procedure reported by Lennon et al.155 enabled

the formation of 3-1 via a multi-step one-pot synthesis beginning from anthracene. The initial

73









spectrum of [DEA-MTI](I)2 (4-6) relative to [DEA-MBI](I)2 (3-4) is an additional methyl

resonance at 2.45 ppm, corresponding to the methyl substituents on the aryl ring of the

benzimidazole. Solution state analysis of the corresponding monometallic rhodium compound 4-

10 (Figure 4-7) again nearly matches that shown for 3-8, except for two additional methyl

resonances due to Ci symmetry.

During the preparation ofligand 4-6 and the resulting monometallic complex 4-10, a

ground state geometry optimization calculation was performed by adding the methyl substituent

to the benzimidazole of the crystal structure of 3-8 as a starting point. Figure 4-8 displays the

calculated structure of 4-10. Table 4-1 compares selected metric parameters for complexes 3-8-

calc and 4-10-calc, and Figure 4-9 displays an overlay of the two structures, showing that the

complexes are nearly identical, excluding the addition of the methyl group. The choice to

position the methyl group at the meta-position was influenced by the structure of 3-8. In the

constrained monometallic complex, one of the benzylimidazoles sits directly above the

ethanoanthracene backbone at a distance of approximately 3.5 A. Addition of a substituent at the

ortho-position would likely come in very close proximity to the backbone, thereby hindering the

formation of monometallic complexes and promoting the formation of the less desirable

bimetallic complex.

Ligand 4-7 combines both architectural alterations to include isopropyl N-substituents and

methyl groups on the back of the benzimidazole. Only the chiral version of the salt (R,R)-4-7

was synthesized producing a meager 300 mg. The chiral salt is sparingly soluble in CDCl3.

Therefore, to retain the valuable imidazolium salt, CDC13 was utilized as the NMR solvent to

facilitate reisolation of(R,R)-4-7, which is difficult from (CD3)2SO. This precludes direct

comparison with the other imidazolium salt 1H NMR spectra which were all obtained in























































7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0
Chemical Shift (ppm)
Figure A-9: H NMR spectrum of (+/-) [(DEAM-BIY)Ir(COD)]OTf (2-5) in CDC13.



133


3.5 3.0 2.5 2.0 1.5









APPENDIX B
REFINEMENT DATA

Table B-1. Crystal data, structure solution and refinement for 2-1.
identification code rxl4
empirical formula C40 H36 F6 N4 06 S2
formula weight 846.85
T(K) 173(2)
S(A) 0.71073
crystal system Monoclinic
space group P2(1)/c
a(A) 12.5937(8)
b (A) 24.6077(16)
c(A) 12.9797(9)
a (deg) 90
l (deg) 97.815(1)
y (deg) 90
V(A3) 3985.1(5)


Z
pcalcd (Mg mm 3)
crystal size (mm3)
abs coeff (mm-1)
F(000)
0 range for data collection
limiting indices
no. ofreflns called
no. ofind reflns (Rint)
completeness to 0 = 27.490
absorption corr
refinement method
data / restraints / parameters
R1,a wR2b [I > 2]
R1,a wR2b (all data)
GOFc on F2
largest diff. peak and hole


4
1.411
0.29 x 0.26 x 0.22
0.214
1752
1.63 to 24.990
-8 < h < 14, -29 k< 15, -15 <1< 15
12702
6516 (0.0349)
0.93
Integration
Full-matrix least-squares on F2
6516/0/509
0.0467, 0.1194 [5128]
0.0602, 0.1279
1.035
0.411 and -0.361 e.A-3


a R1 = i|Fo IFcI/1Fol. b wR2 = ( (w(Fo2 Fc2)2)/((F2)2))1/2. c GOF = (Y w(Fo2
F2)2/(n ))1/2 where n is the number of data andp is the number of parameters refined.









analysis and X-ray crystal structures is accomplished to lay groundwork for establishing a

relationship between the structure of these unique ligands and their catalytic activity.

2.2 Experimental Section

2.2.1 Synthesis of Trans-l,l'-[ 9,10-Dihydro-9,10-Ethanoanthracene-11,12-
Diyldimethanediyl]bis(Benzylimidazole) bis(Triflouromethansulfonate) [DEAM-
BI](OTf)2 (2-1)

1-Benzylimidazole (3.13 g, 19.8 mmol) was added to a 250 mL flask containing trans-

1,1 '-[9,10-dihydro-9,10-ethanoanthracene-l 1,12-

diyldimethanediyl]bis(trifluoromethanesulfonate)"1 (5.00 g, 9.40 mmol) in dry DME (100 mL).

After refluxing under argon for 2 h, the solvent was removed producing a yellow powder. The

powder was suspended in ethyl acetate and sonicated to produce a white powder which was

isolated by filtration as a white microcrystalline solid; yield 7.63 g (96%). 1H NMR (300 MHz,

(CD3)2SO) 6 ppm: 9.27 (m, 2 H, NCHN), 7.83 (m, 2 H, NCHCHN), 7.78 (m, 2 H, NCHCHN),

7.45-7.51 (m, 8H, Ar), 7.34-7.45 (m, 4H, Ar), 7.31 (m, 2 H, Ar), 7.15-7.23 (m, 4H, Ar), 5.37 -

5.57 (m, 4 H, NCH2C), 4.08 (s, 2 H, bridgehead H), 3.92 (dd, JHH=13.9, 4.2 Hz, 2 H,

CH(HCH)N), 3.62 (dd, JHH=13.7, 8.9 Hz, 2 H, CH(HCH)N), 2.04 2.18 (m, 2 H, bridge H).

13C[1H] NMR (75 MHz, (CD3)2SO) 6 ppm: 142.5 (2C, Ar), 139.3 (2C, Ar), 136.7 (2C, NCHN),

134.8 (2C, Ar), 129.1 (4C, Ar), 128.9 (2C, Ar), 128.4 (4C, Ar), 126.5 (2C, Ar), 126.3 (2C, Ar),

125.7 (2C, Ar), 123.9 (2C, Ar), 123.0 (s, 2C, NCHCHN), 122.6 (s, 2C, NCHCHN), 120.6 (q,

J=322 Hz, -CF3), 52.1 (s, 2C, NCH2C), 51.8 (s, 2C, NCH2CH), 44.3 (s, 2C, bridgehead C), 43.1

(s, 2C, bridge C). MS(HR-ESI+): Calc. for [C40H36N4S206F6]: m/z 869.8450 [M+Na] found

m/z 869.1876. Anal. Calc. for C40H36N4S206F6: C, 56.73%; H, 4.29%; N, 6.62%. Found: C,

56.68%; H, 4.35%; N, 6.50%. The molecular structure of 2-1 determined by X-ray









crystallography is displayed in Figure 2-8, crystals were grown by diffusion of pentane into an

ethanol solution containing the salt.

2.2.2 Synthesis of Trans-l,l'-[9,10-Dihydro-9,10-Ethanoanthracene-11,12-
Diyldimethandiyl] bis(1-Benzylimidazolidine-2-Ylidene), DEAM-BY (2-2)

At -35 C, KN(TMS)2 (395 mg, 1.98 mmol in 5 mL THF) was added to a cold solution of

[DEAM-BI](OTf)2 (2-1) (800 mg, 0.95 mmol) in THF (10 mL). After 1 h, the solution was

allowed to warm to room temperature while stirring. The solvent was then removed in vacuo

producing an orange-yellow powder. After trituration with diethyl ether (2 x 5 mL) and pentanes

(2 x 5 mL) the solid was taken up in pentanes and filtered. The precipitate was then washed with

diethyl ether and extracted with THF. The THF was removed to produce a peach colored

powder; yield 366 mg (71%). 1H NMR (300 MHz, C6D6) 6 ppm: 7.57 (dd, J=7.4, 1.1 Hz, 2H,

Ar), 7.04 7.27 (m, 16H, Ar), 6.47 6.52 (overlapping d, 4H, NCHCHN and NCHCHN), 5.17 (s,

4H, NCH2C), 4.38 (d, J 1.1 Hz, 2H, bridgehead H), 3.77 (dd, J 13.2, 8.4 Hz, 2H, CH(HCH)N),

3.47 (dd, J=13.3, 5.9 Hz, 2H, CH(HCH)N), 2.28 2.39 (m, 2H, bridge H). 1C NMR (75 MHz,

C6D6) 6 ppm: 216.1 (s, NCcarbene N), 144.6 (s, Ar), 141.5 (s, Ar), 139.6 (s, Ar), 129.1 (s, Ar),

128.3 (s, Ar), 126.9 (s, Ar), 126.7 (s, Ar), 126.4 (s, Ar), 124.0 (s, Ar), 120.7 (s, NCHCHN), 119.1

(s, NCHCHN), 55.4 (overlapping singlets, NCH2C & CHCH2N), 47.1 (overlapping singlets,

bridge & bridgehead C). MS(DIP-CI): Calc. for [C38H34N4]: m/z 546.2929 [M]+, found m/z

546.2783. The molecular structure of 2-2 determined by X-ray crystallography is displayed in

Figure 2-8, crystals were grown by a diffusion of ether into a THF solution containing the

compound.









a beige colored solid (1.03 g, 12%). 1H NMR (300 MHz, CDC13) 6 ppm: 7.43 7.50 (m, 2 H,

Ar), 7.22 7.35 (m, 6 H, Ar), 7.08 (t, J 1.1 Hz, 2 H, NCHCHN), 6.92 (t, J 1.1 Hz, 2 H,

NCHCHN), 6.17 (t, J=1.4 Hz, 2 H, NCHN), 4.49 (2 overlapping s, 4 H, bridge and bridgehead

H) 13C NMR (75.3 MHz, CDC13) 6 (ppm): 140.39 (N-CH=N), 138.16 and 136.16 (C=C), 129.79

(C aromatic), 127.67 (C aromatic, overlapping signals), 126.63 (C aromatic), 124.32 (N-

CH=NCH=CH), 117.10 (N-CH=NCH=CH), 64.67 (N-CH-CH-C=), 50.78 (N-CH-CH-C=).

HRMS (CIP-CI) calc'd (found) for C22H19N4 (M+H)+ 339.1610 (339.1649).

3.2.3 Synthesis of Trans-l,l'-(9,10-Dihydro-9,10-Ethanoanthracene-11,12-Diyl)di(3-
Methyl-lH-Imidazol-3-Ium) Diiodide [DEA-MI](I)2 (3-3)

Diimidazole 3-2 (1.0 g, 2.96 mmol) was dissolved in anhydrous MeCN (25 mL) in a glass

ampoule fitted with a sealable Teflon stopcock. Mel (0.74 mL, 4 equiv., 11.8 mmol) was added

and the flask was evacuated then sealed under vacuum. The flask was shielded from light and

was heated in a sand bath at 105 OC for 48 h. The mixture was cooled to room temperature and

the precipitate was filtered and washed with cold MeCN to produce 3-3 as an off-white solid;

yield (1.41 g, 77%). 1HNMR (300 MHz, (CD3)2SO) 6 ppm: 8.93 (br. s, 2 H, NCHN), 7.68 (t,

J=1.7 Hz, 2 H, NCHCHN), 7.62 (d, J=7.1 Hz, 2 H, Ar), 7.33 7.43 (m, 4 H, Ar), 7.23 7.31 (m,

2 H, Ar), 6.60 (t, J 1.5 Hz, 2 H, NCHCHN), 5.48 (br. s, 2 H, bridge H), 5.05 (br. s, 2 H,

bridgehead H), 3.82 (s, 6 H, CH3) 13C NMR (75.3 MHz, (CD3)2SO) 6 (ppm): 139.1 and 137.3

(C=C), 136.7 (N-CH=N), 127.6 (C aromatic), 127.5 (C aromatic), 126.3 (C aromatic), 125.5 (C

aromatic), 123.6 (N-CH=NCH=CH), 119.7 (N-CH=NCH=CH), 63.0 (N-CH-CH-C=), 48.3 (N-

CH-CH-C=), 36.1 (NCH3). HRMS (FIA-ESI) calc'd (found) for C24H24IN4 (M-I) 495.1040

(495.1040).









Table 5-3. Formation of 5-2 catalyzed by 3-8, 3-9, and 4-8
Product Catalyst Solvent Temp C % e.e. Yielda Hours
5-2 (S,S) 3-8 Dioxane/MeOHd 80C 65 18 24
5-2 (S,S) 3-8 Dioxane/MeOH 76b 82 40 24
5-2 (S,S) 3-9 Dioxane/MeOH 80C 20 70 24
5-2 (S,S) 3-9 Dioxane/MeOH 76b 10 22 24
5-2 (R,R) 4-8 Dioxane/MeOH 80C 15d 41 24
5-2 (R,R) 4-8 Dioxane/MeOH 76b 8d 25 24
aIsolated yield after column chromatography b 1.5 mol % catalyst c 3 mol % catalyst dR
enantiomer

Table 5-4. Formation of 5-3 catalyzed by 3-8, 3-9, and 4-8
Product Catalyst Solvent Temp C % e.e. Yielda Hours
5-3 (S,S) 3-8 Dioxane/MeOH 80 NAb 45 24
5-3 (S,S) 3-9 Dioxane/MeOH 80 NAb 83 24
5-3 (R,R) 4-8 Dioxane/MeOH 80 NAb 69 24
a Isolated yield subsequent to column b HPLC/GC method was not found to fully resolve the
enantiomers

Table 5-5. Formation of 5-4 catalyzed by 3-8, 3-9, and 4-8.
Boronic Acid Catalyst Solvent Temp C % e.e. Yielda Hours
5-4 (S,S) 3-8 Dioxane/MeOH 80 NAb 57 14
5-4 (S,S) 3-9 Dioxane/MeOH 80 NAb 98 14
5-4 (R,R) 4-8 Dioxane/MeOH 80 NAb 29 14
aIsolated yield subsequent to column b HPLC/GC method was not found to fully resolve the
enantiomers

Table 5-6. Formation of 5-5 catalyzed by 3-8, 3-9, and 4-8.
Product Catalyst Solvent Temp C % e.e. Yielda Hours
5-5 (S,S) 3-8 Dioxane/MeOH 80 47 45 24
5-5 (S,S) 3-9 Dioxane/MeOH 80 11 65 24
5-5 (R,R) 4-8 Dioxane/MeOH 80 0 71 24
aIsolated yield subsequent to column

Table 5-7. Formation of 5-6 catalyzed by 3-8, 3-9, and 4-8.
Product Catalyst Solvent Temp C % e.e. Yielda Hours
5-6 (S,S) 3-8 Dioxane/MeOH 80 NAb 71 15
5-6 (S,S) 3-9 Dioxane/MeOH 80 NAb 50 15
5-6 (R,R) 4-8 Dioxane/MeOH 80 NAb 22 15
aIsolated yield subsequent to column b HPLC/GC method was not found to fully resolve the
enantiomers

















































7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5
Chemical Shift (ppm)
Figure A-15: H NMR spectrum of(+/-) trans-9,10-dihydro-9,10-ethanoanthracene-9,10-(1-methyl)bibenzimidazole), [(DEA-
MbBY] (3-5) in C6D6.


139











Table 3-5. Comparison of measured and calculated bond lengths (A) and angles (0) for 3-8.
3-8 3-8-calc
Distances Rh-C31 2.051(5) Rh-C31 2.052
Rh-C23 2.033(4) Rh-C23 2.068
N2-C24 1.461(5) N2-C24 1.468
N4-C32 1.467(5) N4-C32 1.466
N2-C23 1.375(5) N2-C23 1.384


Angles



Torsion Angle
Distances


N1-C23
N4-C31
N3-C31
C16-H16
H16-Rh
C4-C36
C31RhC23
N1C23N2
N3C31N4
N1-C15-C16-N3
Rh-H16


1.365(5)
1.347(5)
1.370(5)
1.001
3.033(4)
3.831
84.14(17)
104.7(4)
105.9(4)
68.8(5)
3.033(4)


N1-C23
N4-C31
N3-C31
C16-H16
H16-Rh
C4-C36
C31RhC23
N1C23N2
N3C31N4
N1-C15-C16-N3
Rh-H16


Table 3-6. Comparison of bond lengths (A) and angles ()
3-9-calc.


for calculated structures 3-8-calc and


Calculation
Distances










Angles



Torsion Angle
Distances


3-


Rh-C31
Rh-C23
N2-C24
N4-C32
N2-C23
N1-C23
N4-C31
N3-C31
C16-H16
C31RhC23
N1C23N2
N3C31N4
N1-C15-C16-N3
Rh-H16
C36-C4


8-calc
2.052
2.068
1.468
1.466
1.384
1.395
1.372
1.391
1.097
85.3
105.2
106.0
70.36
2.298
4.238


3-


Rh-C31
Rh-C23
N2-C24
N4-C32
N2-C23
N1-C23
N4-C31
N3-C31
C16-H16
C31RhC23
N1C23N2
N3C31N4
N1-C15-C16-N3
Rh-H16
C36-C4


9-calc
2.053
2.078
1.472
1.47
1.385
1.396
1.375
1.386
1.095
87.1
103.6
104.2
80.64
2.394
4.946


1.395
1.372
1.391
1.097
2.298
4.238
85.3
105.2
106.0
70.36
2.298









cyclohexen-1 -one.183 Since this report, a variety of different ligand architectures have been

found to be highly enantioselective toward this reaction.28' 184-187

Copper based catalysts are typically utilized at low temperatures (often well below 0C)28

to introduce alkyl groups via an organozinc reagent. Rhodium catalysts, on the other hand, can

be used at ambient to high (above 100 C) temperatures with a wide variety of organometallic

reagents,188-195 to introduce alkenyl or aryl substituents. Aryl stannanes,188-191'112

arylsilicon,192,113 aryltitanium,193 194,114 and alkenylzirconium 95,115 reagents have been used as

transmetallating reagents in 1,4-addition reactions. However, the commercial availability and

stability of boronic acids have made them the most popular choice.196' 197

The first rhodium catalyzed 1,4-conjugate addition of aryl and alkenylboronic acids to

enones was reported by Miyaura in 1997.198 In this communication, the authors focused on

acyclic enones with no reported e.e. measurements. Rh(acac)(CO)2/dppb (dppb =

diphenylphosphino butane) was used as the precatalyst and the reaction proceeded at 50 OC in

aqueous solvents with modest yields. A year later, the same authors reported a chiral

application using the bis-phosphine ligand (S)-BINAP as the chiral auxiliary.199 Although two

acyclic enones were investigated, the focus of the paper was addition to 2-cyclohexen-1-one. To

achieve high yields and chiral induction it was necessary for the authors to increase the reaction

temperature to 1000C.

Mechanistic investigation200 of this system revealed transmetallation of the aryl group from

boronic acid to rhodium as the initial catalytic step. Transmetallation occurs via a four centered

transition states shown in Figure 5-1.201 Addition of base is important when utilizing a rhodium

catalyst containing a halogen ligand. The boronic acid is quaternized by the base increasing the

nucleophilicity of the aryl group and facilitating transmetallation. Non-halogenated catalysts are









CHAPTER 2
FIRST GENERATION DI-NHC CATALYSTS

2.1 Introduction

NHC based ligands are quickly becoming common-place in organometallic and inorganic

chemistry.37,63, 97-99 The large dissociation energies associated with most NHC-M bonds make

these molecules particularly useful as ancillary ligands in catalysis. Increasing evidence suggests

NHC supported TM catalysts can surpass well-established phosphine-based systems in both

activity and scope.5 In contrast to phosphines, NHCs do not favor dissociation from metal

centers100 eliminating the need for excess ligand and promoting their utilization toward

asymmetric catalysis.50' 101

Electron rich metal centers supported by chiral NHC ligands have been applied to

hydrogenation, hydrosilylation, olefin metathesis, and a myriad of other chiral transformations.37'

61,63 Monodentate NHCs are undeniably the largest contributors to these catalytic applications

because of their ease of access and modification. However, the stability and rigidity associated

with chelating ligands has led to the design of multidentate NHC ligands. Chelating NHC

ligands can be split into two major categories; "mixed" NHC ligands and pure NHC-based

chelating ligands. "Mixed" NHCs consist of one (or rarely two) NHC moieties and another,

typically more labile, moiety.102 Chelating ligands based purely on NHCs are usually bidentate

but a few tris-NHC58 ligands have been reported. The increased stability of chelating ligands

along with the overwhelming success of chelating bis-phosphines inspired the investigation of

NHC equivalents.

Chiral bidentate NHC ligands can be separated into four distinct categories (Figure 2-1);63

a) bidentate NHCs in which the chiral center is contained on the peripheral N-substituents, b)

bidentate NHCs containing stereogenic centers within the heterocycle, c) bidentate NHCs that









CHAPTER 4
THIRD GENERATION CATALYSTS

4.1 Introduction

Coupling experimental observation with computational analysis has become a vital tool in

the application and optimization of catalytic species. Chapter 3 described the design and

structural analysis of the constrained second-generation ligands. Using gas-phase ground state

optimized geometry calculations it was determined that the steric bulk of the azole backbone

plays a significant role in determining the chiral structure.

To further improve the catalyst design, the ligands reported in chapter 3 were subjected to

architectural modifications (Figure 4-1). Through the slight variation of specific structural

components a more thorough understanding of the relationship between ligand and catalyst

structure is obtained. Independent alteration of the alkyl N-substituents and azole ring size is

accomplished. Formation and structural analysis of C1 symmetric mononuclear rhodium species

from the altered ligands is described.

4.2 Experimental Section

4.2.1 Synthesis of Trans-l,1'-(9,10-Dihydro-9,10-Ethanoanthracene-l1,12-Diyl)di(3-
Isopropyl-1H-Imidazol-3-Ium) Diiodide [DEA-iPrI](I)2 (4-1)

Diimidazole 3-3 (2.34 g, 6.9 mmol) was dissolved in dry MeCN (5 mL) in a sealable

glass flask. 2-iodopropane (2.8 mL, 4 equiv., 27 mmol) was added under argon and the flask

was evacuated then sealed under vacuum. The flask was shielded from light and was heated in a

sand bath at 105 OC for 48 h. The mixture was cooled to room temperature and the precipitate

was filtered and washed with cold MeCN to produce 4-1 as a white solid; yield 1.99 g (43%). 1H

NMR (300 MHz, (CD3)2SO) 6 ppm: 8.82 (s, 2 H, NCHN), 7.86 (t, J=1.8 Hz, 2 H, NCHCHN),

7.64 (d, J=7.1 Hz, 2 H, Ar), 7.19 7.42 (m, 6 H, Ar), 6.78 (t, J 1.8 Hz, 2 H, NCHCHN), 5.61 (s,

2 H, bridgehead H), 5.06 (s, 2 H, bridge H), 4.57 (spt, J=6.5 Hz, 2 H, NCHCH3), 1.40 and 1.39

91








C32

I,





_10 161 .





tl ^H .4' c.ki: .
IfII* '6 *













Figure 3-10. Molecular Structure of 3-8 from a Side-on (Left) and Top View (right). Ellipsoids
are drawn at the 50% probability level.
Q '4 Z '*^ 7
rrP 9-t_ ,,p ^t "'',









found in the asymmetric unit and are related to the opposite enantiomer via an inversion center.

Only one molecule is presented in Figure 3-7, but the metric parameters are similar for all like

species. For example, the C=C double bond for each independent molecule is 1.3426(19) A and

1.3416(19) A, similar to that observed previously for a derivative featuring a two-carbon

expanded ring.120 All four nitrogen atoms are pyramidalized (zC-N-Cavg = 116.07(13)),

indicating significant loss of aromaticity, and representative of an sp3-hybridized nitrogen. In

viewing the molecule from the top (Figure 3-7-B) it is clear the methyl groups are bent out of the

plane created by the four nitrogen atoms. The benzimidazole groups are nearly coplanar,

separated by only 150 resulting in an incredibly small torsion angle ZN1-C16-C15-N3 of 76.6(1).

3.3.6 X-ray Analysis of Bimetallic Complexes Lu-DEA-MY] [Rh(NBD)I]2 (3-6) and u[-DEA-
MBY][Rh(COD)C1]2 (3-7-COD)

Each bimetallic complex features a ligand that bridges two separate distorted square-planar

rhodium centers via a Rh-carbene bond. The coordination spheres are completed by a halide (Cl

,3-7; or I, 3-6) and a chelating diene (NBD, 3-6; and COD, 3-7). As expected, in 3-6 the

average bond distance between the Rh and alkene carbons opposite the Rh-NHC (d(Rh-

CtramNHC) = 2.2125(6) A) are elongated by 0.116(6) A compared to those opposite the I (d(Rh-

CtransI)= 2.097(6) A). The relatively small differences in C-donor strength of

benzimidazolidynes versus imidazolidynes imparts a similar difference (0.109(6) A) in the Rh-

alkene bond in complex 3-7. In fact, the average Rh-NHC bond lengths between 3-6 (d(Rh-

NHCavg = 2.018(4) A) and 3-7 (d(Rh-NHCavg = 2.007(3) A) differ only by 0.011(5) A.

Unfortunately, the variations in trans influences of Cl versus I and NBD versus COD precludes

a meaningful comparison.

Within 3-6 the rhodium iodide bonds are divergent and preserve the ligand C2-symmetry,

whereas in 3-7 the solid-state symmetry is broken by rotation of one Rh-Cl bond inward. The









Table B-7. Crystal data, structure solution and refinement for 2(3-5).
identification code rx08
empirical formula C64 H52 N8
formula weight 933.14
T(K) 173(2)
S(A) 0.71073
crystal system Monoclinic
space group P21/n
a (A) 10.5224(7)
b(A) 38.633(3)
c(A) 11.9173(7)
a (deg) 90
l (deg) 102.497(1)
y (deg) 90
V(A3) 4729.7(5)


Z
pcalcd (Mg mm 3)
crystal size (mm3)
abs coeff (mm-1)
F(000)
0 range for data collection
limiting indices
no. ofreflns called
no. ofind reflns (Rint)
completeness to 0 = 27.490
absorption corr
refinement method
data / restraints / parameters
R1,a wR2b [I > 20]
R1,a wR2b (all data)
GOFc on F2
largest diff. peak and hole


4
1.310
0.19 x 0.19x 0.08
0.078
1968
1.83 to 27.500
-13 32190
10772 (0.0356)
99.00%
Integration
Full-matrix least-squares on F2
10772 / 0 / 651
0.0416, 0.0943 [7390]
0.0695, 0.1028
1
0.200 and -0.212 e.A-3


a R1 = I||Fo |IFe|/|Fol. b wR2 = ((w(Fo2 Fc2)2)/((F2)2))12. c GOF = ( w(Fo2
F2)2/(n ))1/2 where n is the number of data andp is the number of parameters refined.









4.2.10 Synthesis of Rhodium(I) Trans-9,10-Dihydro-9,10-Ethanoanthracene-9,10-bis(1-
Methyltolylimidazolidine-2-Ylidene) Cyclooctadiene Iodide, [(DEA-MTY)Rh(COD)]I
(4-10)

Diimidazolium salt 4-6 (500 mg, 0.66 mmol) was suspended in 5 ml THF and stirred

overnight. At -350C, KN(TMS)2 (279 mg, 1.4 mmol) in 5 mL THF was added dropwise to the

salt suspension and allowed to warm to room temperature and stir for 1 h. After cooling the

solution to -35 C, [Rh(COD)Cl]2 (164 mg, 0.33 mmol) in 3 mL THF was then added dropwise

to the reaction and allowed to stir for 1 h at room temperature. The reaction mixture was

allowed to stir at room temperature overnight and the resulting solid was filtered, washed with

Et20 and extracted with CHC13 to provide [(DEA-MTY)Rh(COD)]I 4-10 as a dark yellow

powder. (113 mg, 20%) H NMR (300 MHz, CDC13) 6 ppm: 9.06 (d, J=9.9 Hz, 1 H, CHCHN),

7.74 (dd, J=7.0, 1.2 Hz, 1 H, Ar), 7.64 (dd, J=7.0, 1.2 Hz, 1 H, Ar), 7.56 (d, J=7.0 Hz, 1 H, Ar),

7.33 7.47 (m, 3 H, Ar), 7.03 7.32 (m, 7 H, Ar), 6.89 (d, J=8.5 Hz, 1 H, Ar), 6.68 (s, 1 H), 5.1

(s, 1H, CCHC) 5.08 (s, 1 H, CCHC), 4.90 5.04 (m, 1 H, COD-CH), 4.39 4.50 (m, 1H, COD-

CH), 4.29 (s, 3 H, NCH3), 4.22 (dd, J=10., 0.80 Hz, 1 H, CHCHN), 4.10 4.19 (m, 1 H, COD-

CH), 3.76 (s, 3 H, NCH3), 3.73 (m, 1 H, COD-CH), 2.46 (s, 3 H, tolyl-CH3), 2.53 (m, 2 H, COD-

CH2), 2.14 (s, 4 H, COD-CH2), 2.14 (s, 3 H, tolyl-CH3), 1.55 1.72 (m, 1 H, COD-CH2), 1.14 -

1.33 (m, 1 H, COD-CH2). 13C NMR (75 MHz, CDC13) 6 ppm: 192.9 (d, JRhC =52.00 Hz, NCN),

190.8 (d, JRhC =52.00 Hz, NCN), 146.7 (Ar), 144.46 (Ar), 138.8 (Ar), 136.2 (Ar), 135.8 (Ar),

134.9 (Ar), 134.4 (Ar), 134.3 (Ar), 134.1 (Ar), 131.7 (Ar), 128.8 (Ar), 128.1 (Ar), 128.0 (Ar),

127.7 (Ar), 127.4 (Ar), 127.2 (Ar), 125.7 (Ar), 124.5 (Ar), 124.1 (Ar), 122.2 (Ar), 111.8

(NCCH), 111.1 (NCCH), 110.8 (NCCH), 110.7 (NCCH), 94.1 (d, JRhC =8.06 Hz, COD-CH),

91.0 (d, JRhC =8.06 Hz, COD-CH), 90.5 (d, JRhC =6.91 Hz, COD-CH), 89.9 (d, JRhC =7.49 Hz,

COD-CH), 65.8 (s, CHCHN), 62.2 (s, CHCHN), 49.1 (s, CCHC), 48.0 (s, CCHC), 39.3 (s,












NH,
11,N -


3-1 -


1. glyoxal, McOH
2. NH4C1, H2CO, A
3. 11,PO,.A
-- : --------p


N N

3-N2
^3- '1-/


N NH2
I NHW


-N / -


;N 21


Mel, CHICN
105 "C, 2d
UP,


Figure 3-2. Synthesis of [DEA-MI](I)2 (3-3)


NH,
HN N2 2


AI




HC(-OE'H),
p-TsOH, 2d


H,, PdC
CIT2C]2'/MeOi
i


F -.1
N

ICO, N DMF
'16h

N-^ p=


4 Mcd, CH4CN
105, C, 2d


\/3-4


Figure 3-3. Synthesis of [DEA-MBI](I)2 (3-4)




\ i=N 21

N N 2. KN(SiMc3)

34 T111



Figure 3-4. Synthesis ofDEA-MBY (3-5)


~~









Table 5-1. Optimization of catalytic coniugate addition involving compound 3-8.


Product
5-1
5-1
5-1
5-1
5-1
5-1
5-1
5-1
5-1
5-1
5-1
5-1
5-1 (leq)
5-1 (2eq)
5-1
5-1
5-1
5-1
5-1
5-1
5-1
5-1


Catalyst
(+/-) 2-5
(+/-) 2-3
(-) 2-3
(+/-) 3-8
(S,S) 3-8
(+/-) 3-8f
(S,S) 3-8
(S,S) 3-8b
(S,S) 3-8c
(S,S) 3-8
(S,S) 3-8
(S,S) 3-8d
(S,S) 3-8
(S,S)3-8
(R,R) 3-8
(R,R) 3-8
(R,R) 3-8
(R,R) 3-8
(S,S) 3-8
(R,R) 3-8
(S,S) 3-8d
(S,S) 3-8d


Solvent
Dioxane/Water
Dioxane/Water
Dioxane/MeOH
Dioxane/MeOH
Dioxane/MeOH
Dioxane/MeOH
Dioxane/MeOH
Dioxane/ MeOH
Dioxane/ MeOH
Dioxane/MeOH
Dioxane/MeOH
Dioxane/MeOH
Dioxane/MeOH
Dioxane/MeOH
THF/MeOH
Dioxane/H20
Dioxane/MeOH (10:1)
Dioxane/MeOH (2:1)
Dioxane/H20 (4:1)
Dioxane/MeOH(4:1)
Dioxane/MeOH (10:1)
Dioxane/anh MeOH (10:1)


aIsolated Yield after column chromatography bPyradine instead of KOH CK2CO3 instead of KOH
d 3 mol% catalyst Isolated after column eR-enantiomer No Base

Table 5-2. Formation of 5-1 catalyzed by 3-8, 3-9, and 4-8.
Product Catalyst Solvent Temp C % e.e. Yielda Hours
5-1 (S,S)3-8 Dioxane/MeOH 75 71 33 24
5-1 (R,R) 3-8 Dioxane/MeOH 80 78b 56 24
5-1 (S,S) 3-9 Dioxane/MeOH 75 6 17 24
5-1 (S,S)3-9 Dioxane/MeOH 82 4 20 23
5-1 (R,R) 3-9 Dioxane/MeOH 82 5b 19 23
5-1 (S,S) 3-9 MeOH 81 0 50 17
5-1 (R,R) 4-8 Dioxane/MeOH 75 5b 13 24
5-1 (R,R) 4-8 Dioxane/MeOH 80 7b 26 24
aIsolated yield after column chromatography bR-enantiomer


Temp C
85
85
82
78
50
80
75
80
80
75
80
80
80
80
80
80
80
80
80
80
80
80


% e.e. Yielda
NA 0
NA 99
0 98
NA 60
NA 0
NA 0
70 25
NA 0
46 30
70 33
69 55
73 72
72 59
57 68
77e 73
5e 82
82e 86
61 70
5 83
78e 56
54 98
43 74


Hours
20
20
18
22
17
17
22
17
17
24
24
24
24
24
24
24
24
24
24
24
24
24









20. J. C. Leffingwell, in Leffingwell Reports Chirality & Bioactivity I.: Pharmacology, Editon
edn., 2003, vol. 3.

21. S. C. Stinson, Chem. Eng. News, 2000, 78, 55.

22. E. J. Ariens, Soudigen, W., Timmermans, P. B. M. W. M., ed., Stereochemistry and
BiologicalActivity ofDrugs, Blackwell Scientific Publications, Oxford, 1983.

23. S. C. Stinson, Chem. Eng. News, 2001, 79, 45.

24. S. C. Stinson, Chem. Eng. News, 2001, 79, 45.

25. B. M. Trost, PNAS, 2004, 101, 5348.

26. E. Fogassy, M. N6gradi, D. Kozma, G. Egri, E. Palovics and V. Kiss, Org. Biomol. Chem.,
2006,4,3011.

27. R. N. Patel, Current Organic Chemistry, 2006, 10, 1289.

28. K. Mikami and M. Lautens, eds., New Fronteirs in Asymmetric Catalysis, John Wiley &
Sons, New Jersey, 2007.

29. M. Lemaire, Pure Appl. Chem., 2004, 76, 679.

30. W. A. Nugent, T. V. RajanBabu and M. J. Burk, Science, 1993, 259, 479.

31. G. W. Parshall, Homogeneous Catalysis: the applications and chemistry of catalysis by
soluble transition metal complexes, John Wiley & Sons, New York, 1980.

32. T. P. Yoon, E. N. Jacobsen, Science, 2003, 299, 1691.

33. T. P. Dang and H. B. Kagan, J. Chem. Soc. Chem. Commun., 1971, 481.

34. H. B. Kagan and T. P. Dang, J. Am. Chem. Soc., 1972, 94, 6429.

35. J. K. Whitesell, Chem. Rev., 1989, 89, 1581.

36. F. Jo6, Aqueous Organometallic Catalysis, Kluwer Academic Publishers, Dordrecht /
Boston/ London, 2001.

37. F. Glorius, ed., N-Heterocyclic Carbenes in Transition Metal Catalysis, Springer-Verlag,
Berlin Heidelberg, 2007.

38. R. H. Crabtree, J. Organomet. Chem., 2005, 690, 5451.

39. H. W. Wanzlick, E. Fjedor and K. H. Jerg, Chem. Ber., 1963, 96, 1208.

40. H. W. Wanzlick and E. Schikora, Angew. Chem., 1960, 72, 494.












































I., 1 1 .


r.,II..II, 111 .............l.. ...................... ii ...... ........ ir 0 .l. .I l u IIS,... ir..rLahI.pt ... 0L. J s ........ a iuidlh.l a M i .............i ........ qr............... .... Ik.... ...L.


!,.r1n~innn.~,nim ru vwunu rnww mu r I'pr


56 48 40 32 24


176 168 160 152 144 136 128 120 112 104 96 88 80 72
Chemical Shift (ppm)
Figure A-13: 13C NMR spectrum of(+/-) (DEAM-BIY)Ir2(COD)2C12 (2-6) in CDC13.


64


,I1I h ', ,


It I ~


il, l ,I









12), 136.6 (s, 30), 136.0 (s, 22), 135.7 (s, 1), 131.6 (s, 25), 128.3 (s, 10), 128.1 (s, 9), 127.7 (s, 4),

127.6 (s, 2), 127.4 (s, 3), 127.0 (s, 11), 124.6 (s, 19), 124.4 (s, 20), 124.1 (s, 8), 123.9 (s, 27),

123.6 (s, 28), 122.2 (s, 5), 111.6 (s, 21), 111.5 (s, 29), 111.4 (s, 26), 110.5 (s, 18), 94.2 (d, JRh =

8.3 Hz, 35), 91.7 (d, JRh = 7.7 Hz, 39), 90.9 (d, JRc = 7.2 Hz, 34), 90.1 (d, JRh = 7.7 Hz, 38),

65.9 (s, 16), 62.3 (s, 15), 49.2 (s, 13), 48.1 (s, 14 ), 39.6 (s, 24), 35.7 (s, 32), 30.9 (s, 37), 30.7 (s,

33), 30.6 (s, 40), 29.8 (s, 36). Numbering correlates to X-ray Crystal structure (Figure 3-10).

Anal. Calc. for C40H38N4IRh plus one molecule CH2C12: C, 55.36%; H, 4.53%; N, 6.30%.

Found: C, 55.06%; H, 4.56%; N, 6.17%. The molecular structure of 3-8 as determined by X-ray

crystallography is displayed in Figure 3-10, crystals were grown by diffusion of ether into a

methylene chloride solution containing the compound. The equilibrium geometry of 3-8 as

calculated by ground-state geometry optimization calculations using the hybrid density

functional B3LYP156 with the LANL2DZ157-160 basis set utilizing effective core potentials (ECP)

for the core rhodium electrons is displayed in Figure 3-11. All calculations reported in this

manuscript were done using the Gaussian161 program.

3.2.9 Synthesis of Rhodium(I) Trans-9,10-Dihydro-9,10-Ethanoanthracene-9,10-bis(1-
Methylimidazolidine-2-Ylidene Cyclooctadiene Iodide, [(DEA-MY)Rh(COD)]I (3-9)

Diimidazolium salt 3-3 (100 mg, 0.16 mmol) was suspended in 3 mL dry THF and stirred

overnight. At -350C, KN(TMS)2 (61 mg, 0.31 mmol) in 3 mL of dry THF was added dropwise

to the salt suspension and allowed to stir at room temperature for 1.5 h. At -35 C a solution

[Rh(COD)Cl]2 (40 mg, 0.08 mmol) in 3 mL of dry THF was added dropwise to the salt

suspension and allowed to stir for 1.5 h. A precipitate formed that was filtered and washed with

Et20 to afford 3-9 as a yellow powder; yield 99 mg (87%). 1H NMR (300 MHz, CDCl3) 6 ppm:

8.23 (dd, J= 7.5, 1.0 Hz, H16), 7.84 (d, J= 1.7 Hz, NCH=CHN), 7.74 (dd, J= 6.4, 1.8 Hz,

CCHCHCHCHC ), 7.58 (dd, J= 6.4, 2.1 Hz, CCHCHCHCHC), 7.52 (dd, J= 7.1, 1.1 Hz,





















































145 140 135 130 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20
Chemical Shift (ppm)
Figure A-26. 13C NMR spectrum of (+/-) [DEA-iPrBI][I]2 (4-2) in (CD3)2SO.



150









5 ASYMMETRIC CONJUGATE ADDITION .............................................................. 108

5 .1 Introdu action ....................................................... 10 8
5 .2 E x perim mental S section .............................................................. .............. ............... ...... 1 12
5.2.1 General Catalytic Procedure ................................ 112
5.2.2 3-Phenylcyclohexanone (5-1) ............ .................................. 112
5.2.3 3-(2-Methylphenyl)-Cyclohexanone (5-2)........ ...........................................113
5.2.4 3-(1-Naphthalenyl)-Cyclohexanone (5-3)..................... ..................... 113
5.2.5 3-(4-Methoxyphenyl)-Cyclohexanone (5-4)............... .... ............... 113
5.2.6 3-(4-Fluorophenyl)-Cyclohexanone (5-5).......................................................114
5.2.7 3-Phenylcyclopentanone (5-6) ...................................... ......................... ......... 114
5 .3 R esu lts an d D iscu ssion ............................................................. ...................................... 114
5 .4 C o n clu sio n s ............... .......................................................................................................... 1 17

6 CONCLUSIONS AND FUTURE DIRECTION....................................... ............... 121

APPENDIX

A NUCLEAR MAGNETIC RESONANCE ................................ 124

B R E FIN E M EN T D A T A ....................................................................................................... 166

L IST O F R E F E R E N C E S .............................................................................. ............................. 176

B IO G R A PH IC A L SK E T C H ...................................................... ............................................... 187




Full Text

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1 RHODIUM AND IRIDIUM COMPLEXES SUPPORTED BY CHELATING BIS -N HETEROCYCLIC CARBENE LIGANDS: DESIGN, SYNTHESIS, AND CATALYTIC INVESTIGATION By ROXY JOANNE LOWRY A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2009

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2 2009 Roxy Joanne Lowry

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3 To Faye J. Bell m y hero, my best friend, and my grandmother ; s he taught me to love with unfaltering resolve, l ive with unimaginable passion, and to follow my dreams Rest in Peace

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4 ACKNOWLEDGMENTS I thank my family for their love and support; m y mother for her logical and sound advice and he r genetic strength of character; m y dad for his compassion and d o ting ; and my brother for his gentle, unassuming, and humble heart. I thank Jason Swails; his patience, affection, and computer skills got me through the last several d ifficult months. I will be forever grateful to Mrs. Vanessa (Thurston) Keck and Dr. Chad E. Mair for their friendship s and particularly their ever -present shoulders during one of the most difficult years of my life. I thank Soumya Sarkar for being my sanity in the laboratory. I acknowledge those people who have aided in aspects of my research; Melanie K. Veige, Dr. Khalil Abboud, and Dr. Ion Ghiviriga Although they are t oo numerous to name personally, I thank all of the wonderful people with whom I have become friends over the last five years. Finally, I thank my advise r, Dr. Adam S. Veige for his advice and instruction

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS .................................................................................................................... 4 LIST OF TABLES ................................................................................................................................ 9 LIST OF FIGURES ............................................................................................................................ 11 LIST OF ABBREVIATIONS ............................................................................................................ 16 ABSTRACT ........................................................................................................................................ 17 CHAPTER 1 GENERAL INTRODUCTION .................................................................................................. 19 1.1 Catalysis Background and Importance ................................................................................ 19 1.2 Chiral Catalysis ..................................................................................................................... 22 1.3 N-Heterocyclic Carbenes ...................................................................................................... 27 1.3.1 Early History ............................................................................................................ 27 1.3.2 Ca rbene Geometry ................................................................................................... 27 1.3.3 Electronic Influences ............................................................................................... 28 1.3.4 NHC Topologies ...................................................................................................... 29 1.3.5 M NHC Bonding ..................................................................................................... 30 1.4 Contribution of This Manuscript .......................................................................................... 31 2 FIRST GENERATION DI -NHC CATALYSTS ...................................................................... 36 2.1 Introduction ........................................................................................................................... 36 2.2 Experimental Section ............................................................................................................ 39 2.2.1 Synthesis of Trans 1,1' [ 9,10 Dihydro 9,10 Ethanoanthracene 11,12 Diyldimethanediyl]bis(Benzylimidazole) bis(Triflouromethansulfonate) [DEAM BI](OT f)2 (2 1) ...................................................................................... 3 9 2.2.2 Synthesis of Trans 1,1' [9,10 Dihydro 9,10 Ethanoanthracene 11,12 Diyldimethandiyl]bis(1 Benzylimidazolidine 2 Y lidene), DEAM BY (2 2) ............................................................................................................................ 40 2.2.3 Synthesis of Rhodium(I) Trans 9,10 Dihydro 9,10 Ethanoanthracene 11,12 bis(1 Benzylimidazolidine 2 Ylidene) Cyclooctadiene Triflate, [(DEAM BY)Rh(COD)]OTf (2 3) ..................................................................... 41 2.2.4 Synthesis of [ 2 DEAM BY][Rh(COD)Cl]2 (2 4) ............................................... 42 2.2.5 Synthesis of Iridium(I) Trans 9,10 Dihydro 9,10 Ethanoanthracene 11,12 bis(1 Benzylimidazolidine 2 Ylidene) Cyclooctadiene Triflate, [(DEAM BY)Ir(COD)]OTf (2 5) ....................................................................... 43 2.2.6 Synthesis of [ 2 DEAM BY][Ir(COD)Cl]2 (2 6) ................................................. 45 2.2.7 Catalytic Hydroformylation .................................................................................... 46 2.2.8 X ray Crystallography ............................................................................................. 47

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6 2.3 Results and Discussion ......................................................................................................... 47 2.3.1 Preparation and Solution State Analysis of [DEAM BI](OTf)2 (2 1) .................. 47 2.3.2 Preparation and Solution State Analysis of [DEAM BY] (2 2) ........................... 48 2.3.3 Preparation and Solution State Analysis of [(DEAM BY)Rh(COD)]OTf (2 3) ............................................................................................................................ 49 2.3.4 Preparation and Solution State Analysis of [ DEAM -BY][Rh(COD)Cl]2 (2 4) ............................................................................................................................ 50 2.3.5 Preparation and Solution State Analysis of [(DEAM BY)Ir(COD)]OTf (2 5) and [ DEAM BY][Ir(COD)Cl]2 (2 6) .............................................................. 50 2.4 X ray Structural Analysis and Comparisons ....................................................................... 51 2.4.1 Comparison of Organic Precursors 2 1 and 2 2. ................................................... 51 2.4.2 Monometallic [(DEAM BY)M(COD)]OTf 2 3 and 2 5 ...................................... 52 2.4.3 Bimetallic Complexes [ DEAM BY][M(COD)Cl]2 2 4 and 2 6 ....................... 54 2.5 Initial Catalytic Testing ........................................................................................................ 54 2.6 Conclusions ........................................................................................................................... 55 3 SECOND GENERATION DI NHC CATALYSTS148............................................................. 64 3.1 Introduction ........................................................................................................................... 64 3.2 Experimental Section ............................................................................................................ 66 3.2.1 GC Analysis of Chiral 9,10 Dihydro 9,10-Ethanoanthracene 11,12Diamine (3 1) ....................................................................................................................... 66 3.2.2 Synthesis of Trans 1,1' (9,10-Dihydro9,10Ethanoanthracene 11,12Diyl)di(1H Imidazole) (3 2) ............................................................................... 66 3.2.3 Synthesis of Trans 1,1' (9,10 Dihydro 9,10-Ethanoanthracene 11,12Diyl)di(3 -Methyl 1H Imidazol 3 Ium) Diiodide [DEA -MI](I)2 (3 3) .............. 67 3.2.4 Synthesis of Trans 1,1 (9,10 Dihydro 9,10-Ethanoanthracene 11,12Diyl)di(3 -Methyl 1H -Benzimidazol 3 Ium) Diiodide [DEA -MBI](I)2 (3 4) ............................................................................................................................ 68 3.2.5 Synthesis of Trans 9,10 Dihydro 9,10 Ethanoanthracene 9,10 (1 Methyl)Bibenzimidazole), DEA MbBY (3 5) ................................................... 68 3.2.6 Synthesis of [ DEA MY][Rh(NBD)I]2 (3 6) as a Mixture with 3 9 ................. 69 3.2.7 Synthesis of [ DEA MBY][Rh(diene)Cl]2 (3 7) as a Mixture with 3-8 ........... 70 3.2.8 Synthesis of the Rhodium(I) Trans 9,10 Dihydro 9,10 Ethanoanthracene 9,10 bis(1 Methylbenzimidazolidine 2 Ylidene) Cyclooctadiene Iodide, [(DEA MBY)Rh(COD)]I (3 8) ................................ .......................................... 71 3.2.9 Synthesis of Rhodium(I) Trans 9,10 Dihydro 9,10 Ethanoanthracene 9,10 bis(1 Methylimidazolidine 2 Ylidene Cyclooctadiene Iodide, [(DEA MY)Rh(COD)]I (3 9) ............................................................................ 72 3.3 Results and Discussion ......................................................................................................... 73 3.3.1 Constrained Precursors [DEA -MI](I)2 (3 3) and [DEA MBI](I)2 (3 4) ............... 73 3.3.2 Synthesis and Characterization of DEA MbBY (3 5) ........................................... 75 3.3.3 Synthesis and Characterization of [ -DEA-MY][Rh(NBD)I]2 (3 6) and [ DEA -MBY][Rh(COD)Cl]2 (3 7 COD) ............................................................... 76 3.3.4 Synthesis and Characterization of [(DEA -MBY)Rh(COD)]I (3 8) and [(DEA MY)Rh(COD)]I (3 9) .............................................................................. 77

PAGE 7

7 3.3.5 X ray Analysis of DEA MbBY (3 5) ..................................................................... 78 3.3.6 X -ray Analysis of Bimetallic Complexes [ DEA -MY][Rh(NBD)I]2 (3 6) and [ DEA-MBY][Rh(COD)Cl]2 (3 7 COD) .................................................. 79 3.3.7 Structural Analysis of Monometalli c Complexes [(DEA -MBY)Rh(COD)]I (3 8) and [(DEA -MY)Rh(COD)]I (3 9) .............................................................. 80 3.4 Conclusions ........................................................................................................................... 82 4 THIRD GENERATION CATALYSTS .................................................................................... 91 4.1 Introduction ........................................................................................................................... 91 4.2 Experimental Section ............................................................................................................ 91 4.2.1 Synthesis of Trans 1,1' (9,10 Dihydro 9,10-Ethanoanthracene 11,12Diyl)di(3 Isopropyl 1 H Imidazol 3 Ium) Diiodide [DEA iPrI](I)2 (4 1) ......... 91 4.2.2 Synthesis of Trans 1,1 (9,10 Dihydro 9,10-Ethanoanthracene 11,12Diyl)di(3 Isopropyl 1H Benzimidazol 3 Ium) Diiodide [DEA -iPrBI](I)2 (4 2) ....................................................................................................................... 92 4. 2.3 Synthesis of N,N' -bis(4 Nitrotolyl) 9,10 Dihydro 9,10 Ethanoanthracene 11,12Diamine (4 3) ............................................................................................. 92 4.2.4 Synthesis of N,N' -bis(4 -A minotolyl) 9,10Dihydro9,10 Ethanoanthracene 11,12Diamine (4 4) ............................................................................................. 93 4.2.5 Synthesis of Trans 1,1' (9,10 Dihydro 9,10-Ethanoanthra cene 11,12Diyl)di(1 H Tolylimidazole) (4 5) ....................................................................... 94 4.2.6 Synthesis of Trans 1,1 (9,10 Dihydro 9,10-Ethanoanthracene 11,12Diyl)di(3 -Methyl 1 H Tolylimidazol 3 Ium) Diiodide [DEA MTI](I)2 (4 6) ............................................................................................................................ 94 4.2.7 Synthesis of Trans 1,1 (9,10 Dihydro 9,10-Ethanoanthracene 11,12Diyl)di(3 Isopropyl 1H Tolylimidazol 3 -Ium) Diiodide [DEA -iPrTI](I)2 (4 7) ....................................................................................................................... 95 4.2.8 Synthesis of Rhodium(I) Trans 9,10 Dihydro 9,10 Ethanoanthracene 9,10 bis(1 Isopropylimidazolidine 2 Ylidene) Cyclooctadi ene Iodide, [(DEA iPrY)Rh(COD)]I (4 8) ........................................................................... 95 4.2.9 Synthesis of Rhodium(I) Trans 9,10 Dihydro 9,10 Ethanoanthracene 9,10 bis(1 Isopropylbenzylimidazolidine 2 Ylidene) Cyclooctadiene Iodide, [(DEA iPrBY)Rh(COD)]I (4 9) ............................................................ 96 4.2.10 Synthesis of Rhodium(I) Trans 9,10 Dihydro 9,10 Ethanoanthracene 9,10 bis(1 Methyltolylimidazolidine 2 Ylidene) Cyclooctadiene Iodide, [(DEA MTY)Rh(COD)]I (4 10) ........................................................................ 98 4.3 Results and Discussion ......................................................................................................... 99 4.3.1 Synthesis and Characterization of [DEA iPrI](I)2 (4 1) and [(DEA iPrY)Rh(COD)]I (4 8) .......................................................................................... 99 4.3.2 Synthesis and Characterization of [DEA iPrBY](I)2 (4 2), [DEA MTY](I)2 (4 6), [DEA iPrTY](I)2 (4 7) and the Corresponding Monometallic Rhodium Complexes [(DEA iPrBY)Rh(COD)]I (4 9) and [(DEA MTY)Rh(COD)]I (4 10) ................................................................................... 100 4.4 Conclusions ......................................................................................................................... 103

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8 5 ASYMMETRIC CONJUGATE ADDITION ......................................................................... 108 5.1 Introduction ......................................................................................................................... 108 5.2 Experiment al Section .......................................................................................................... 112 5.2.1 General Catalytic Procedure ................................................................................. 112 5.2.2 3Phenylcyclohexanone (51) ............................................................................... 112 5.2.3 3(2 Methylphenyl) Cyclohexanone (52) ........................................................... 113 5.2.4 3(1 Naphthalenyl) -Cyclohexanone (5 3) ............................................................ 113 5.2.5 3(4 Methoxyphenyl) Cyclohexanone (54) ........................................................ 113 5.2.6 3(4 Fluorophenyl) -Cyclohexanone (5 5) ............................................................ 114 5.2.7 3Phenylcyclopentanone (5 6) .............................................................................. 114 5.3 Results and Discussion ....................................................................................................... 114 5.4 Conclusions ......................................................................................................................... 117 6 CONCLUSIONS AND FUTURE DIRECTION .................................................................... 121 APPENDIX A NUCLEAR MAGNETIC RESONANCE ............................................................................... 124 B REFINEMENT DATA ............................................................................................................. 166 LIST OF REFERENCES ................................................................................................................. 176 BIOGRAPHICAL SKETCH ........................................................................................................... 187

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9 LIST OF TABLES Table page 2 1 Selected bond lengths () and angles ( ) for complex 2 -1 .................................................. 60 2 2 Selected bond lengths () and angles ( ) for complex 2 -2 .................................................. 61 2 3 Selected bond length () and angles ( ) for complex 2 -3 ................................................... 61 2 4 Selected bond length () and angles ( ) for complex 2 -4 ................................................... 62 2 5 Selected bond lengths () and angles ( ) for complex 2 -5 .................................................. 62 2 6 Selected bond length () and angles ( ) for complex 2 -6 ................................................... 63 2 7 Initial catalytic hydroformylation results utilizing complex 2 -3 ......................................... 63 3 1 Selected bond length () and angles ( ) for complex 3 -5 ................................................... 88 3 2 Selected bond length () and angles ( ) for complex 3 -6 ................................................... 88 3 3 Selected bond lengths () and angles ( ) for complex 3 -7 .................................................. 89 3 4 Selected bond lengths () and angles ( ) for complex 3 -8 .................................................. 89 3 5 Comparison of measured and calculated bond lengths () and angles ( ) for 3 -8 ........... 90 3 6 Comparison of bond lengths () and angles ( ) for calculated structures 3 -8 -calc and 3 -9 -calc .................................................................................................................................. 90 4 1 Selected bond lengths () and angle ( ) for calculated structures 3 -8 -calc and 4 -10calc ....................................................................................................................................... 104 5 1 Optimization of catalytic conjugate addition involving compound 3 -8 .......................... 119 5 2 Formation of 5 -1 catalyzed by 3 -8 3 -9 and 4 -8 ............................................................... 119 5 3 Formation of 5 -2 catalyzed by 3 -8 3 -9 and 4 -8 ................................................................ 120 5 4 Formation of 5 -3 catalyzed by 3 -8 3 -9 and 4 -8 ................................................................ 120 5 5 Formation of 5 -4 catalyzed by 3 -8 3 -9 and 4 -8 ............................................................... 120 5 6 Formation of 5 -5 catalyzed by 3 -8 3 -9 and 4 -8 ............................................................... 120 5 7 Formation of 5 -6 catalyzed by 3 -8 3 -9 and 4 -8 ............................................................... 120

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10 B1 Crystal data, structure solution and refinement for 2 -1 .................................................... 166 B2 Crystal data, structure solution and refinement for 2 -2 .................................................... 167 B3 Crystal data, structure solution and refinement for 2 -3 .................................................... 168 B4 Crystal data, structure solution and refinement for 2 -4 .................................................... 169 B5 Crystal data, structure solution and refinement for 2 -5 .................................................... 170 B6 Crystal data, structure solution and refinement for 2 -6 .................................................... 171 B7 Crystal data, structure solution and refinement for 3 -5 .................................................... 172 B8 Crystal data, structure solution and refinement for 3 -6 .................................................... 173 B9 Crystal data, structure solution and refinement for 3 -7 .................................................... 174 B10 Crystal data, structure solution and refinement for 3 -8 .................................................... 175

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11 LIST OF FIGURES Figure page 1 1 Reaction coordinate diagram for catalyzed and uncatalyzed reactions. ............................. 32 1 2 Generalized mechanisms for A) uncatalyzed reaction B) catalyzed reaction C) single reagent activation catalysis D) catalyzed reaction with intermolecular reaction. .............. 32 1 3 Structures of (R ) and ( S ) Carvone and ( R ) and ( S ) Thalidomide .................................... 33 1 4 Selected privileged ligands .................................................................................................... 33 1 5 Wanzlicks and feles NHC complexes and Lapperts enetetraamine ............................. 34 1 6 Relative influence of geometric and electronic effects on the energy gap between and p orbitals. ........................................................................................................................ 34 1 7 Resonance structures of NHC. .............................................................................................. 34 1 8 Common N-heterocyclic carbenes ........................................................................................ 35 2 1 Examples of chelating NHCs ................................................................................................ 56 2 2 Synthesis of [DEAM -BI](OTf)2 (2 -1 ) ................................................................................... 57 2 3 Synthesis of DEAM -BIY (2 -2 ) .............................................................................................. 57 2 4 Synthesis of [(DEAM BY)Rh(COD)]OTf (2 -3 ) .................................................................. 57 2 5 Synthesis of [ DEAM BY][Rh(COD)Cl]2 (2 -4 ) ................................................................ 58 2 6 Synthesis of [(DEAM BY)Ir(COD)]OTf (2 -5 ) .................................................................... 58 2 7 Synthesis of [ DEAM BY][Ir(COD)Cl]2 (2 -6 ) .................................................................. 58 2 8 X ray Crystal Structure of 2 -1 and 2 -2 ................................................................................. 59 2 9 Molecular Structure of 2 -3 and 2 -5 ....................................................................................... 59 2 10 Average bond angle s and length of free NHCs and M NHCs ............................................ 60 2 11 Molecular Structure of 2 -4 and 2 -6 ....................................................................................... 60 3 1 First and second generation ligand architectures. ................................................................ 82 3 2 Synthesis of [DEA -MI](I)2 (3 -3 ) ........................................................................................... 83 3 3 Synthesis of [DEA -MBI](I)2 (3 -4 ) ........................................................................................ 83

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12 3 4 Synthesis of DEA MBY (3 -5 ) ............................................................................................... 83 3 5 Synthesis of binuclear compounds [ DEA-MY][Rh(NBD)I]2 (3 -6 ) and [ -DEA MBY][Rh(COD)Cl]2 (3 -7 ) as mixtures with 3 -8 and 3 -9 ................................................... 84 3 6 Synthesis of rhodium monomer complexes [(DEA -MBY)Rh(COD)]I (3 -8 ) and [(DEA MY)Rh(COD)]I (3 -9 ). ............................................................................................... 84 3 7 Molecular structure of 3 -5 ..................................................................................................... 85 3 8 Molecular structure of compound 3 -6 ................................................................................... 85 3 9 Molecular structure of 3 -7 ..................................................................................................... 86 3 10 Molecular Structure of 3 -8 ..................................................................................................... 86 3 11 Calculated equilibrium geometries of 3 -8 -calc and 3 -9 -calc ............................................. 87 3 12 Overlay of calculated structures 3 -8 -calc and 3 -9 -calc ....................................................... 87 4 1 Generations of ligands to date. ............................................................................................ 104 4 2 Synthesis of ligand [DEA -iPrI](I)2 4 -1 and [(DEA -iPrY)Rh(COD)]I 4 -8 ....................... 104 4 3 Synthesis of ligand [D EA -iPrBI](I)2 4 -2 ........................................................................... 105 4 4 Synthesis of ligand [DEA -MTI](I)2 4 -6 ............................................................................. 105 4 5 Synthesis of ligand [DEA -iPrTI](I)2 4 -7 ........................................................................... 105 4 6 Synthesis of [(DEA iPrBY)Rh(COD)]I 4 -9 ...................................................................... 106 4 7 Synthesis of [(DEA -MTY)Rh(COD)]I 4 -10. ..................................................................... 106 4 8 Calculated structure for [(DEA MTY)Rh(COD)]I 4 -10. .................................................. 106 4 9 Overlay of the calculated structure [(DEA -MBY)Rh(COD)]I 3 -8 -calc and [(DEA MTY)Rh(COD)]I 4 -10-calc ................................................................................................ 107 5 1 Transmetallation of aryl substituents to rhodium catalysts. .............................................. 117 5 2 Catalytic cycle for the 1,4 addition of boronic acids to cyclic enones. ............................ 118 6 1 Proposed ligand structures for enhanced chiral induction. ................................................ 123 A 1 1H NMR spectrum of (+/ ) [DEAM BI][OTf]2 (2 -1 ) in (CD3)2SO. ................................ 125 A 2 13C NMR spectrum of (+/ ) [DEAM BI][OTf]2 (2 -1 ) in (CD3)2SO. ............................... 126

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13 A 3 1H NMR spectrum of (+/ ) DEAM BIY (2 -2 ) in C6D6. ................................................... 127 A 4 13C NMR spectrum of (+/ ) DEAM BIY (2 -2 ) in C6D6. .................................................. 128 A 5 1H NMR spectrum of (+/ ) [(DEAM BIY) Rh (COD)] OTf (2 -3 ) in CDCl3. ................. 129 A 6 13C NMR spectrum of (+/ ) [(DEAM BIY) Rh (COD)] OTf (2 -3 ) in CDCl3. ................ 130 A 7 1H NMR spectrum of (+/ ) (DEAM BIY)Rh2(COD)2Cl2 (2 -4 ) in CDCl3....................... 131 A 8 13C NMR spectrum of (+/ )(DEAM BIY)Rh2(COD)2Cl2 (2 -4 ) in CDCl3. ..................... 132 A 9 1H NMR spectrum of (+/ ) [(DEAM BIY)Ir(COD)]OTf (2 -5 ) in CDCl3. ...................... 133 A 10 1H NMR spectrum of (+/ ) [(DEAM BIY)Ir(COD)]OTf (2 -5 ) in CD2Cl2...................... 134 A 11 13C NMR spectrum of (+/ ) [(DEAM BIY)Ir(COD)]OTf (2 -5 ) in CD2Cl2 .................... 135 A 12 1H NMR spectrum of (+/ ) (DEAM BIY)Ir2(COD)2Cl2 (2 -6 ) in CDCl3......................... 136 A 13 13C NMR spectrum of (+/ ) (DEAM BIY)Ir2(COD)2Cl2 (2 -6 ) in CDCl3. ...................... 137 A 14 1H NMR spectrum of 1,1 (9,10 dihydro9,10 -ethanoanthracene 11,12-diyl)di(3 methyl 1H -benzimidazol 3 ium) diiodide ( 3 -4 ) in (CD3)2SO. ......................................... 138 A 15 1H NMR spectrum of (+/ ) trans 9,10 dihydro 9,10 ethanoanthracene 9,10 (1 methyl)bibenzimidazole), [(DEA MbBY] (3 -5 ) in C6D6. ............................................... 139 A 16 13C{1H} NMR spectrum of (+/ ) trans 9,10 dihydro 9,10 ethanoanthracene 9,10 (1 methyl)bibenzimidazole), [(DEA MbBY] (3 -5 ) in C6D6. ......................................... 140 A 17 1H NMR spectrum of [ DEA MY][Rh(NBD)I]2 (3 -6 ) as a mixture with 3 9 in C6D6. ..................................................................................................................................... 141 A 18 1H NMR spectrum of [ 2 DEA MBY][Rh(NBD)I]2 (3 -7 -NBD ) as a mixture with 3 8 -NBD in C6D6. .................................................................................................................... 142 A 19 1H NMR spectrum of (+/ ) Rhodium(I) trans 9,10 dihydro 9,10 ethanoanthracene 9,10 bis(1 methylbenzimidazolidine 2 ylidene cyclooctadiene iodide, [(DEA MBY)Rh(COD)]I (3 -8 ) in CDCl3. ........................................................... 143 A 20 13C{1H} NMR spectrum of (+/ ) Rhodium(I) trans 9,10 dihydro 9,10 ethanoanthracene 9,10 bis(1 methylbenzimidazolidine 2 ylidene cyclooctadiene iodide, [(DEA MBY)Rh(COD)]I (3 -8 ) in CDCl3. ........................................................... 144 A 21 1H NMR spectrum of (+/ ) Rhodium(I) trans 9,10 dihydro 9,10 ethanoanthracene 9,10 bis(1 methylimidazolidine 2 ylidene cyclooctadiene iodide, [(DEA MY)Rh(CO D)]I (3 -9 ) in CD3Cl. .............................................................. 145

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14 A 22 13C{1H} NMR spectrum of (+/ ) Rhodium(I) trans 9,10 dihydro 9,10 ethanoanthracene 9,10 bis(1 methylimidazolidine 2 ylidene cyclooctadiene iodide, [(DEA MY)Rh(COD)]I (3 -9 ) in CD3Cl. .............................................................. 146 A 23 1H NMR spectrum of (+/ ) [DEA iPrI][I]2 (4 -1 ) in (CD3)2SO. ....................................... 147 A 24 13C NMR spectrum of (+/ ) [DEA iPrI][I]2 (4 -1 ) in (CD3)2SO. ...................................... 148 A 25 1H NMR spectrum of (+/ ) [DEA iPrBI][I]2 (4 -2 ) in (CD3)2SO. .................................... 149 A 26 13C NMR spectrum of (+/ ) [DEA iPrBI][I]2 (4 -2 ) in (CD3)2SO. ................................... 150 A 27 1H NMR of N,N' -bis(4 -nitrotolyl) 9,10 -dihydro 9,10-ethanoanthracene 11,12diamine ( 4 -3 ). ....................................................................................................................... 151 A 28 13C NMR of N,N' bis(4 -nitrotolyl) 9,10-dihydro 9,10-ethanoanthracene 11,12diamine ( 4 -3 ). ....................................................................................................................... 152 A 29 1H NMR of N,N' -bis(4 aminotolyl) 9,10-dihydro 9,10-ethanoanthracene 11,12diamine ( 4 -4 ). ....................................................................................................................... 153 A 30 13C NMR of N,N' bis(4 aminotolyl) 9,10-dihydro 9,10 ethanoanthracene 11,12diamine ( 4 -4 ). ....................................................................................................................... 154 A 31 1H NMR 1,1' -(9,10-dihydro 9,10-ethanoanthracene 11,12 diyl)di(1 H -tolylimidazole) (4 -5 ). ...................................................................................................................................... 155 A 32 13C NMR 1,1' (9,10-dihydro 9,10 ethanoanthracene 11,12-diyl)di(1 H tolylimidazole) ( 4 -5 ). ........................................................................................................... 156 A 33 1H NMR spectrum of (+/ ) [DEA MTI][I]2 (4 -6 ) in (CD3)2SO ....................................... 157 A 34 13C NMR spectrum of (+/ ) [DEA MTI][I]2 (4 -6 ) in (CD3)2SO ...................................... 158 A 35 1H NMR spectrum of R,R [DEA iPrTI][I]2 (4 -7 ) in CDCl3. ............................................ 159 A 36 1H NMR spectrum of (+/ ) Rhodium(I) trans 9,10 dihydro 9,10 ethanoanthracene 9,10 bis(1 isopropylimidazolidine 2 ylidene cyclooctadiene iodide, [(DEA iPrY) Rh(COD)]I (4 -8 ) in CDCl3. ............................................................. 160 A 37 1H NMR spectrum of (+/ ) Rhodium(I) trans 9,10 dihydro 9,10 ethanoanthracene 9,10 bis(1 isopropylimidazolidine 2 ylidene cyclooctadiene iodide, [(DEA iPrY)Rh(COD)]I (4 -8 ) in CDCl3 .............................................................. 161 A 38 1H NMR spectrum of (+/ ) Rhodium(I) trans 9,10 dihydro 9,10 ethanoanthracene 9,10 bis(1 isopropylbenzimidazolidine 2 ylidene cyclooctadiene iodide, [(DEA iPrBY)Rh(COD)]I (4 -9 ) in CDCl3. .......................................................... 162

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15 A 39 13C NMR spectrum of (+/ ) Rhodium(I) trans 9,10 dihydro 9,10 ethanoanthracene 9,10 bis(1 isopropylbenzimidazolidine 2 ylidene cyclooctadiene iodide, [(DEA iPrBY)Rh(COD)]I (4 -9 ) in CDCl3. .......................................................... 163 A 40 1H NMR spectrum of (+/ ) Rhodium(I) trans 9,10 dihydro 9,10 ethanoanthracene 9,10 bis(1 methyltolylimidazol idine 2 ylidene cyclooctadiene iodide, [(DEA MTY)Rh(COD)]I (4 -10) in CDCl3. ......................................................... 164 A 41 13C NMR spectrum of (+/ ) Rhodium(I) trans 9,10 dihydro 9,10 ethanoanthracene 9,10 bis(1 methyltolylimidazolidine 2 ylidene cyclooctadiene iodide, [(DEA MTY)Rh(COD)]I (4 -10) in CDCl3. ......................................................... 165

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16 LIST OF A BBREVIATIONS DEA 9,10 dihydro 9, 10 ethanoanthracene GDP g ross domestic product NHC N-heterocyclic carbene Ditriflate (+/ ) 9,10 dihydro 9,10 ethanoanthracene 11,12 diyldimethanediyl bis(trifluoromethanesulfonate) COD 1,5 -cyclooctadiene TMS t rimethylsilylamide Ea energy of a ctivation TM transition metal e.e. enantiomeric excess B3LYP Becke 3 term with Lee, Yang, Parr exchange hybrid functional LANL2DZ Los Alamos National Laboratory 2 double ECP e ffective core potential RMSD root mean square deviation Acac acetylacetonate Dppb (diphenylphosphino)butane rls rate limiting step gDQCOSY gradient double -quantum f iltered correlation spectroscopy gHMBC gradient heteronuclear multiple bond c oherence NOESY n uclear Overhauser effect spectroscopy

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17 Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy RHODIUM AND IRIDIUM COMPLEXES SUPPORTED BY CHELATING BIS -N HETEROCYCLI C CARBENE LIGANDS: DESIGN, SYNTHESIS, AND CATALYTIC INVESTIGATION By Roxy Joanne Lowry August 2009 Chair: Adam S. Veige Major: Chemistry Eighty -five percent of all industrial chemical processes occur catalytically The world s expanding appetite for mass production of exotic chemicals necessitates the design and application of enhanced catalysts. To optimize catalytic material s the detailed relationships between cataly s t architecture and reactivity must be determined. Although for many ligand families these relationships are well understood novel catalysts require in depth empirical investigation to determine these connections. The design of a novel di N -heterocyclic carbene family of ligands in reported herein. Thes e C2 symmetric ligands are based on the rigid 9,10 -dihydro 9,10-ethanoanthracene backbone and designed for utilization in chiral catalysis Thorough investigation into the relationships between the ligands structure and the architecture of the resulting rhodium and iridium catalysts directed the design of three generations of our novel ligand family The first generation, t rans1,1' [ 9,10 d ihydro 9,10 ethanoanthracene 11,12 d iyldimethanediyl]bis (benzylimidazole) bis(t rif louromethansulfonate) [DEAM BI](O Tf)2 (2 -1 ), is too flexible to enforce a rigid chiral pocket about a metal center under catalytic conditions. The constrained second generation ligands, trans 1,1' -(9,10-dihydro 9,10-ethanoanthracene -

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18 11,12diyl)di(3 -methyl -imidazol 3 ium) diiodide [DEA -MI ](I)2 (3 -3 ) and trans 1,1 (9,10 dihydro 9,10-ethanoanthracene 11,12 diyl)di(3 -methyl -benzimidazol 3 -ium) diiodide [DEA MBI](I)2 (3 -4 ), produce complexes with rigid chiral pockets. However, the small variation between the two ligands produces a large alteration in the catalytic activity of the resulting complexes. In an attempt to further increase the enantiocontrol displayed by these compounds small alterations were made to produce the third generation of ligands, trans 1,1 (9,10-dihydro 9,10e thanoanthracene11,12d iyl) di (3 -isopropyl -imidazol 3 i um) d iiodide [DEA -iPrI](I)2 (4 -1 ), trans 1,1 (9,10-dihydro 9,10-ethanoanthracene 11,12diyl)di(3 -i so propyl -benzimidazol 3 ium) d iiodide [DEA -iPrBI](I)2 (4 -2 ), trans 1,1 (9,10 dihydro9,10 -e thanoanthracen e 11,12 d iyl) di (3 methyl t olyli midazol 3 -ium) d iiodide [DEA MTI](I)2 (4 -6 ), trans 1,1 (9,10-dihydro 9,10ethanoanthracene 11,12-d iyl)di(3 i sopropyl tolylimidazol 3 ium) d iiodide [DEA -iPrTI](I)2 (4 7 ). Catalytic investigation of the asymmetric 1,4 addition of aryl boronic acids to cyclic enones is accomplished for the constrained catalysts 3 -8 [rhodium(I) trans 9,10 dihydro 9,10 ethanoanthracene 9,10 bis(1 methylbenzimidazolidine 2 ylidene) cyclooctadiene iodide], 3 -9 [rhodium(I) trans 9,10 dihydro 9,10 ethanoanthracene 9,10 bis(1 methylimidazolidine 2 ylidene) cyclooctadiene iodide], and 4 -8 [rhodium(I) trans 9,10 dihydro 9,10 ethanoanthracene 9,10 bis(1 isopropylimidazolidine 2 ylidene) cyclooctadiene iodide].

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19 CHAPTER 1 GENERAL INTRODUCTION Catalysis is leaving the realm of alchemy and entering the field of science. It is still pretty much of an art to design and optimize new catalysts and to improve upon existing catalysts, b ut it is no longer a black art1 claimed Edward Hayes of the National Science Foundation (NSF) in a 1983 Science article. Although t he term catalysis ha d been understood for over 150 years the science behind the phenomenon was just beginning to be uncovered in the late 20th century Even today, the relationship between catalyst structure and function is complex and must be det ermined on a case by case basis. H owever, understanding these fundamental relationships is vital to the optimization of these vastly important materials. 1.1 Catalysis Background and Importance The scientific concept of catalysis began in 1834 when Eilhard Mitscherlich first recorded his observation that certain substances were required for the initiation of specific reactions.2 Within two years, J ns Jakob Berzelius coined the term catalyst to define a substance that participates in a chemical reaction without itself being consumed.3 A n understanding of the foundations of catalysis was just be g inning and a fundamental comprehension was 150 years in the future but the benefits of catalysis had been known for thousands of years. In fact, fermentation, the catalytic formation of ethanol from sugars by yeast is a natural process probably obser ved by humans before recorded history. Industrial application of catalysis also predated its discovery. It was not understood at the time but the production of sulfuric acid in the mid18th century involved oxidation of sulfur dioxide to sulfur trioxid e catalyzed by nitric oxide.4 Many catalytic reactions discovered in the infancy of catalysis are still industrially important today. First investigated in the late 19th century ,5 the Haber -Bosch process is still used to form bulk quantities of ammonia via iron

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20 catalyze d nitrogen fixation Ammonia manufactured by this process is used i n the production of fertilizers vital to food production around the w orld.6 As knowledge regarding catalytic structure and function exp anded so did the industrial exploitation of catalysis In 2003, it was estimated that 85 percent of all chemical processes relied on catalysis .7 T he North American Catalyst Society claim s Catalysis is the key to both life and lifestyle. It is an essential technology for chemical and materials manufacturing, for fuel cells and other energy conversion systems, for combustion devices, and for pollution control systems which greatly impact everyone on our planet 8 Catalytic processes reportedly contribute to over one -third of the GDP globally.8 How does this black art operate ? A catalyst s effect is purely kinetic B y modifying a reactions mechanism a catalyst reduces the energy of activation (Ea) required for conversion into product Figure 1 1 displays the effect of a catalyst on an exothermic reaction in relative energy terms. An uncatalyzed reaction (do tted line) has a large energy barrier to product formation, but a catalyst drastically lowers the overall Ea, shown here through a multi -step reaction (solid line) The overall thermodynamics of the reaction is unchanged. A thermodynamically forbidden reaction cannot be facilitated by a catalys t, but by reducing the energy barrier of an allowed reaction, a catalyst decreases the time required to reach chemical equilibrium. Unlike the original mechanism, the new catalytic mechanism is cyclic The catalyst enters the mechanism as a reactant, performs one, or poss ibly s everal chemical transformation s and is regenerated to start the cycle again Specific m echanistic pathways through which catalysts can act and the possible structures of these species are virtually limitless. Figure 1 2 shows a few general react ion equations These equations represent: a ) an uncatalyzed reaction, b ) the multistep catalytic reaction

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21 correlating to the energy profile in F ig ure 1 1 c ) a mechanism in which one reactant is catalytically activated without directly affecting the other reactant and d) independent activation of both reactants by separate catalytic molecules followed by intermolecular reaction These generalized mechanisms are necessarily s o broad as to be almost useless, and they only serve to group catalysts into relate d categories. Specific mechanistic details including primary and secondary catalyst/substrate and catalyst/reagent interactions are necessary for thorough understanding and optimization of a catalytic system The complicated nature and identity of cataly sts necessitates the empirical examination of each new catalytic system to determine specific structure/function relationships. These studies are import ant because they set the ground work for a semi rational approach to catalyst design. Although today ma ny structure/ function relationships are well understood, the vast array of catalytically active substances as well as the continued production of new species requires continued investigations Defining a catalytic material is complicated by the fact t hat c atalytic activity cannot be assigned as an intrinsic property because of the selectivity of these substances.9 Enzymes, for examples, are only catalytic in regards to specific substrates and reaction conditions. Materials that serve as catalysts are as wide ranging as the reaction s they promote They can consist of homogeneous catalyst s such as acids, bases, and molecular transition metal complexes or heterogeneous metal surfaces and supported materials. I ndustrial ly viable catalysts are even comprise d of a large variety of diverse compositions and chem ical structures, includin g e lemental substances such as metals and activated c arbon ; simple compounds like inorganic salts, sulf ides, and oxides ; as well as more complex enzymatic substrates and organometallic complexes.10 According to Berzeliuss original definition, a catalytic material is anything that affects a reaction without itself being consumed ; however current definitions typically expect a

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22 catalyst to increase the rate of a reaction in a cyclic manner thereby requiring far less than stoichiometric amounts of the materia l The appeal of catalysis does not end with its ability to increase the rate of a reaction. The non -stoichiometric nature of a catalytic cycle makes it a n incredibly efficient and atom -economic process Not only can a catalyst reduce a reactions activation barrier, quite often it can be designed to do this selectively, facilitating the formation of only the desired product thereby reducing the amount of any undesired product to minute quantities This catalytic selectivity is of great importanc e particularly when applied to the synthesis of chiral organic compounds 1. 2 Chiral Catalysis The word c hiral refers to the asymmetry of an object and is derived from the Greek term for hand.11 A chiral object cannot be superimposed on its mirror image much like your right hand cannot be superimposed on your left. In chemistry, a chiral molecule and its mirror image are termed as enantiomers or optical isomers .11 First discovered by Jean Baptiste Biot in 1815,12, 13 a solution containing a (+) enantiomer rotates the angle of plane polarized light clockwise The opposite holds true for the ( ) enantiomer.11 The term chirality was fi rst defined by Lord Kelvin14 but Louis Pasteur is credited with much of the work regarding the molecular origin s of the phenomenon.15 The importance of molecular chirality is particularly noticeable in b iolo gical systems. The helical architecture of DNA and RNA is determined by the chiral sugar molecules from which they are composed. The shape of these oligonucleotides determines their biological reactivity.16 Similarly the absolute configuration of h ormones, antibodies, enzymes, an d receptors play s a very important role in biological processes .17 These molecules are not only chiral but exist in our body as only one of two possible enantiomer s In fact, the human body is said to be homochiral because proteins are composed exclusively of L amino acids and the backbones of

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23 DNA and RNA are c omposed of only the D -enantiomers of sugar molecules .18, 19 These e nantiopure compounds are di a stereoselective reacting with different enantiomers in distinctly different manners E nantiomers can smell and taste different and have dissimilar react ivity as therapeutic agents .20 The enantiomers of carvone have drastically different smells; (S ) -carvone (Figure 1 3 ) smells of caraway but ( R ) -carvone has a distinct spearmint odor.20 A tragic but poignant example of reactivity differences between biologically active enantiomers is that of Thalidomide, a drug prescribed to pregnant women in the 1960s and 70s as a sedative. It w as prescribed as a racemic mixture that was later found to cause birth defects. The teratological (or mutagenic ) effect was caused by (S ) T halidomide (Figure 1 3 ); s adly, recent studies suggest this tragedy could not have been avoided by using enantiopur e ( R ) Thalidomide.20 The actual mutagenesis is caused by the (S ) -enantiomer, but b oth enantiomer s are unstable and epimerize in vivo to form a racemic mixture. Although enantiopurity would not have c ircumvented the Thalidomide calamity, many side -effects can be prevented and overall dr ug activity improved by utilizing enantiopure drugs.17, 21 Biological di a stereoselectivity necessitates access to single enantiomer compounds in the pharmaceutical industry22 but it is also important in the agricultural, fragrance, and flavor industries .23, 24 The importance of chirality in biological system s has also made the natural world the most efficient producer of single enantiomers supplying a limi ted chiral pool23 of enantiopure compounds.25 The classical laboratory approach to obtain an enantiopure compound is by resolving a racemic (50/50) mixture via mechanical or chemical separation techniques .26 The utility of resolution is indisputable; h owever these process es cannot yield more than 50% of the desired product Application of catalysts capable of selective asymmetric synthesis can produc e industrial quantities of the desired enantiomer using relatively small amounts of expensive

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24 catalyst P urified enzymes work well toward these ends27 but are limited by their reaction scope, cost and availability of the enzymatic catalysts. Increased understanding of the black art of catalysis has enabled scientists to develop synthetically prepared catalytic species capable of asymmetric induction Purely o rganic compounds have recently gained popularity as catalytic species because of their low -cost and environmentally friendly nature in relation to many metal con taining compounds .28 However, the unique properties of t ransition metal complexes have made them ubiquitous in the field of asymmetric synthesis Transition metals (TM s ) ar e unique with regard to their energetically accessible valence d orbitals. The number and shape of these partially filled orbitals allow for versatile reactivity. TMs interact with organic molecules in a covalent ionic or dative manner (or a combinatio n thereof) Exploitation of t hese interactions can be used to modulate the electronic nature and topological environment of a TM center via coordinated organic ligands L igands can also be used to increase a compounds stability or its solubility in specific solvents Although TM complexes have found application in heterogeneous asymmetric catalysis29 homogeneous systems are more popular due to their ease of use and investigation. The advantages of homogeneous TM catalysis a re as follows: 1 TM complexes are capable of facilitating reactions that do not occur naturally 2 The electronic character and steric bulk of organometallic complexes are easily altered by modification of the supporting ligands 3 T he variety of complexes avail able permits reactions with substrates that are not compatible with selective systems such as enzymes 4 TM complexes are applicable in a larger variety of reaction conditions than enzymes that require very specific and typically aqueous environments .30 5 Reaction conditions including temperature, solvent mixing, and catalyst/ligand concentration are more efficientl y controlled in solution than in heterogeneous environments.31

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25 In a Science article regarding industrial enantioselective catalysis the authors claim e nantioselective catalysis is bringing about a revolution in asymmetric synthesis. Seldom has there been an area of chemistry where the scientific goals are so challenging, the e conomic benefits so obvious, and the ethical reasons for doing the research so compelling.30 The ability of a tr ansition metal catalyst to preferentially produce one of two chiral p roduc ts is, like catalysis itself, a kinetic phenomenon. Binding of a prochiral substrate to a chiral TM compound forms energetically inequivalent diastereomers. The preferential production of one enantiomer is caused by this energetic imbalance between the two diastereomeric transition states. Large enantiomeric excesses (e e .) can be obtained when the disparity is as small as 3 kcal/mol.9 The absolute configuration of a product molecule is determined during the first irreversib le step in the mechanism that involves a diastereomeric transition state. The reactivity of a complex is typically associated with the identity of the metal center and m odulated by electronic donation or withdrawal by the ligand(s ), but chiral induction is strongly linked to the ligand topology particularly in close proximity to the active site of the catalyst. The configuration of the ligand around the active site is termed the chiral pocket and determines the enantioselectivity of the catalyst T herefore, the design of a chiral ligand is a crucial step in the development of a new catalyst. Specific organic molecules have been established as phenomenal asymmetric induction auxiliaries The selectivity, activity, and catalyst lifetime of TMs suppo rted by these molecules are consistently high over a large range of mechanistically unrelated rea c tions Yoon and Jacobsen summarized these ligands in Science32 describing them as privileged ligands (Figure 1 4 ) The authors do not venture to provide the best architectural features for a chiral ligand but point out that s everal of these prominent ligands

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26 share common design features including C2 symmetry, multiple and strong metal ligand bonds, and rigid structures C2 symmetry first introduced to chiral catalysis by Kegans diop ligand ,33, 34 is attractive because it reduces the number of reaction pathways by cutting in half the possible catalyst/substrate arrangements.35 Rigid and robust ligand s are important for creating a durable complex and retaining the structure of the catalysts chiral environment Multiple and strong bonds between the metal and the ligand further stabilize the complex S tability of the complex and the topology surrounding the chiral coordination center plays a central role in determining the enantiopurity of a product in an a symmetric catalytic reaction T wo privileged ligands, BINAP and MeDuPhos, are members of the organophosphorous family of ligands commonly termed phosphine s Introduced to organometallic chemistry by F.G. Mann,36 p hosphines are strong -donor/weak acceptor ligands that support a large variety of reactive and selective transition metal catalyst s The overwhelming success of phosphine based ligands in homogeneous catalysis has led many to consider the entire class as privileged ligands ; however, these ligands suffer some disa dvantages including air -sensitivity oxidative degradation, and toxicity 37 a s well as difficulty associated with independent modulation of their electronic and steric parameters.38 Nheterocyclic ca rbenes (NHCs) are closely related to phosphines in regards to their electronic donation to a metal center, but are different in their steric topology and do not suffer the same disadvantages in catalytic reactions As part of the carbene family, they were once considered to be too reactive to be utilized as ancillary ligands. The following sections of this chapter will outline the characterist ics of these carbene s that permit them to support some of the most stable TM complexes in use today. Subsequent chapters will describe the utilization of this coordinating moiety in a novel chiral ligand family and utilization of these ligand s in asymmetric rhodium catalysis.

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27 1.3 N -Heterocyclic Carbene s 1.3 .1 Early History The stability of Nheterocycli c carbenes provides one of the few members of the carbene family capable of functioning as a s pectator ligand Isolation of such a stable carbene was unimaginable until the early 1960s when Wanzlick proposed the formation of a diaminocarbene.39 42 He attempted the synthesis of a stable singlet carbene from 1,3 diphenyl 2 trichloromethylimidazolidene but was unable to isolate the proposed species, obtaining only its dimer enetetraamine. He was never able to establish the existence of a stable free carbene prior to coordinati on However, l ater that decade Wanzlick43 and fele44 independently reported the first metal complexes supported by diaminocarbene ligand s (Figure 1 5) Excluding an extensive investigation into the coordination chemistry of related enetetraamine s (Figure 1 5) by Lappert,45, 46 research involving thes e elegant compounds was nonexistent throughout the 1970s and 80s. In 1991, a renaissance of chemistry involving NHC compounds was initiated by the isolation of a stable crystalline NHC by Arduengo .47, 48 Investigation s of NHC coordination chemistry, catalytic properties, and p articularly the steric and electronic characteristics responsible for the stability of t hese diradical s were immediately launched and continue to be the subject of an overwhelming number of journal and review articles ,38, 4962 and books .37, 63 1.3 .2 Carbene G eometry Carbenes are neutral divalent carbons in which four of the six valence electrons are contained in bonding orbitals They were first proposed by Hermann and Geuther in 1855 as reactive diradical (tripl et ground state) intermediates.64 It was almost 100 years later that Lennard Jones and Pople used computational evidence to suggest the accessibility of two different ground states ;65, 66 the non-bonding electrons could occupy the same orbital with a ntiparallel spins (singlet ground state) or two different orbitals with parallel spin s (triplet)

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28 L ocal geometric and electronic factors both play a role in determining t he g round state of a carbene. The local geometry of a carbene carbon can be either be nt or linear A linear geometry favors a triplet ground state due to the two energetically degenerate p orbitals of the sphybridized carbon (Figure 1 6 ). A bent carbene becomes sp2hybridized, stabilizing one of the frontier orbitals, the -orbital, and leaving the p (or p) unaffected. The ground state of a bent species is determined by an energetic competition E lectron -electron repulsion and exchange correlation energies favor a triplet ground state, and i f the energy gap between the frontier orb itals is sufficiently small, these forces will prevail. Hoffman determined that a minimum separation between the frontier orbitals of 2 eV was required to form a singlet ground state carbene .67 The bent geometry of a n NHC carbon creates non -degenerate frontier orbitals F urther stabilization of the carbene, resulting in a singlet ground state, is a result of the electronic influences of the neighboring nitrogen substituents. 1.3 .3 Electronic Influences The nitrogen substituents affect the carbene center th rough i nductive and mesomeric effects increasing the energy difference between the frontier orbitals. Inductively, the two nit rogens are electr on withdrawing ; stabilizing the -orbital and retain ing the electroneutrality of the carbene center. Although the inductive effect is cre dited as the major stabilizing force m esomeric or resonance effects also play a part. E lectron density from the fill ed p -orbitals of the two amino substituents is donated into the empty p orbital of the carbene destabilizing the p orbital and further increasing the HOMO LUMO gap.68, 69 Another factor that may influence the stability of an NHC is aromaticity within the heterocycle.70 The aromatic stabilizat ion of free NHCs is far less pronounced than in benzene or

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2 9 even their imidazole precursors; however, for some systems it may contribute to their thermodynamic stability.71 Isolation of free carbenes from saturated backbone imidazolin 2 ylidenes72 suggests t hat, although some aromatic stabilization may exist, it is not crucial. Designation of NHCs as carbenes has been questioned due to the resonance structures shown in F igure 1 7 If structures A and C contribute heavily to the stability of the carbene th en they should rather be considered ylids However, u pon deprotonation a lengthening of the N Ccarbene bond (1.313(2) 1.341(4) [salt] to 1.363(1) 1.375(2) [free carbene]) and reduction in the N C -N angle (107.6(3) 113.8(2) [salt] to 101.2(2) 102.2(2) [fre e carbene])51 point toward an increase in -bond character supporting the free carbene designation. 1.3 4 NHC Topologies The NHC family include s a variety of heterocyclic structures. The most common NHC ligands are five -membered heterocycles capable of form ing stable free carbenes; imidazolin 2 ylidene, benzimidazol 2 -ylidene, imidazolidin 2 -ylidene, and triazolin 5 -ylidene ( Figure 1 8 ) Stable free carbenes have also been isolated from four ,73 six ,74, 75 and seven -membered76 heterocycles. Excluding the seven-membered heterocycle these molecules are planar with nitrogen substituents that point toward the carbene center. The se peripheral nitrogen -substituents may serve to kinetically stabiliz e some free carben e s but free carbenes with less demanding Nsubstituents have also been isolated.77 The steric influence of an NHC ligand on a coordinated metal center is quite different than that im posed by phosphine s which NHCs were once considered to mimic NHCs have a fanlike or fencelike topology with the nitrogen substitu ents pointing toward the metal center P hosphines on the other hand, are conical and their substituents point away from the coordinated metal The availability of Tolman cone angle parameters78 describing the

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30 relationship between phosphine topology and catalytic reactivity has facilitated semi rational design of phosphine based ligands In an attempt to compare the steric demand of NHCs with phosphines and to establish a guiding principle for NHC ligand design, Nolan et. al. defined the steric parameter percent volume buried (%VBur).79, 80 Situating the NHC or phosp h ine 2 from the metal center, the %VBu r is determined by the percent of a sphere of radius 3 consumed by the ligand in question. The authors concede that this method does not explain all of the steric demands of an NHC ligand. While i t is a good beginning in describing symmetrical monodentate NHCs this method does not account for rotation around the M NHC bond or define the steric demand of unsymmetrical or chelating NHCs. 1.3.5 M -NHC B onding The popularity of NHC ligands is due in part to their compatibility with a large variety of TM species37, 60 as well as main group elements.81 This compatibility sets these heterocycles apart from the other members of the carbene family of ligands. Schrock carbenes (or alkylidenes) are nuc l e ophilic triplet ground state carbenes that form covalent interactions with high oxidation state TM species.82 Fischer carbenes are electrophilic, singlet carb enes that require stabilization through -backbonding from a n electron rich metal center. Although NHCs were once considered Fi sher type carbenes,82 their versatility and ability to act as ancillary ligands established them as a n independent classification within the carbene family. NHC -M bonding i s considered electrostatic i n nature and consists primarily of strong donation from the carbene to a metal center. NHC -M bonds are best described as s ingle or dative bond s .83 The carbene center does not require -backbonding from the metal center due to the stabilizing effects of the carbenes -nitrogen substituents The empty p orbital is available for backdonation but t he relative -bonding ability of NHC s is controversial and certainly dependent

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31 on the metal, co ligands, NHC substituents, and NHC orientation.37, 8486 Various studies have suggested backbonding from the metal contribute s from 0 to 40% of the overall bonding interactions.55, 85, 8791 In high valent early metal complexes NHCs can accept electronic donation from neighboring chloride ligands into the empty p orbital.81 An N HC has also reportedly contributed to bonding through donation to a metal center to stabilize an un saturated 14 -electron complex.92, 93 T he variation in relative electronic donation between di fferent NHC moieties is much smaller than between members of the phosphine family Substi tuent variation directly affects a phosphine ligand s steric bulk and electronic character but variation of peripheral nitrogen substituents has little effect on the electronic character of the carbene center. To vary the donor ability the azole ring must be altered 37 The relative donor ability of different NHCs spans a much smal ler range than phosphine moieties However even these small variations can le a d to large alterations in catalytic behavior.62, 94 1.4 Contribution of This M anuscript Within homogeneous asymmetric TM catalysis, a wide variety of catalysts with impressive reactivities and enantioselectivities have be en developed, but there is still a great need for catalytic investigations toward industrially applicable catalysts, catalytic efficiency, application range, reliability, accessibility of the catalyst, and functional group tolerance.95 Stable, electron rich, and modular spectator ligands that form strong bond s to transition metal complexes, such as NHC ligands, are ideal for application towards these goals In an attempt to contribute to the ever increasing demand for more versatile and active catalysts, our laboratory designed a new family of bidentate chiral bis NHC ligands. This manuscri pt will describe the synthesis, characterization, and structural investigation of this family of ligand s and their rhodium and

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32 i ridium complexes. C hapter 5 will describe the catalytic application of this new ligand family to the 1,4 addition of aryl boron ic acids to cyclic enones. Figure 1 1. Reaction coordinate diagram for catalyzed (solid) and uncatalyzed (dotted) reactions. Figure 1 2. Generalized mechanisms for A) uncatalyzed reaction B) catalyzed reaction in Figure 1 1 C) single reagent activ ation catalysis D) catalyzed reaction with intermolecular reaction.

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33 Figure 1 3. Structures of ( R ) and ( S ) Carvone (left) and ( R ) and ( S ) Thalidomide (right). Figure 1 4. Selected privileged ligands from T.P. Yoon and E. N. Jacobsen, Science 2003, 299, 1691. Reprinted with permission from AAAS.

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34 Figure 1 5. Wanzlicks40 (left) and feles44 (middle) NHC complexes and Lapperts96 enetetraamine (right). Figure 1 6. Relative influence of geometric an d electronic effects on the energy gap between and p orbitals. Figure 1 7. Resonance structures of NHC.

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35 Figure 1 8. Common Nheterocyclic carbenes; imidazolylidene, benzimidazolylidene, imidazolinylidene, triazolinylidene.

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36 CHAPTER 2 FIRST GENERATION DI -NHC CATALYSTS 2.1 Introduction NHC based ligands are quickly becoming common -place in organometallic and inorganic chemistry.37, 63, 9799 The large dissociation energies associated with most NHC -M bo nds make these molecules particularly useful as ancillary ligands in catalysis Increasing evidence suggests NHC supported TM catalysts can surpass well -established p h osphine -based systems in both activity and scope.55 In contrast to phosphines, NHCs do not favor dissociat ion from metal center s100 eliminating the need for excess ligand and promoting their utilization toward asymmetric catalysis.50, 101 Electron rich metal centers supported by chiral NHC ligands have been applied to hydrogenation, hydrosilylation, olefin metathesis, and a myriad of other chiral transformations.37, 61, 63 Monodentate NHCs are u ndeniably the largest contributors to these catalytic applications because of their ease of access and modification H owever, the stability and rigidity associated with chelating ligands has led to the design of multidentate NHC ligands Chelating NHC ligands can be split into two major categories ; mixed NHC ligands and pure NHC based chelating ligands. Mixed NHCs consist of one (or rarely two) NHC moieties and another, typically more labile, moiety .102 Chelating ligands based purely on NHCs are usually bidentate but a few tris NHC58 ligands have been reported. The increased stability of chelating ligand s along with the overwhelming success of chelating bis phosphines inspired the investigation of NHC equivalents. Ch iral b identate NHC ligand s can be separated into four distinct categories (Figure 2 1) ;63 a ) b identate NHCs in which the chiral center is contained on the peripheral N-substituents, b) b identate NHCs containing stereogenic centers within the heterocycle, c) bidentate NHCs that

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37 possess planar chirality, and d ) bidentate NHCs that contain an axis of symmetry. Figure 2 1 displays the imidazole precursors of several members of each class The bis azole ligands reported in this manuscri pt fit within the axially symmetric group The ligands reported herein are C2 symmet ric chelating bis NHC ligands. F igure 2 1 ( d ) displays all of the ligands repor ted to date with similar architectures excluding those reported in the body of this manuscript.103 Many of the catalysts supported by chelating bis NHC ligands display excellent activity but only a few have achieved a high level of enantioselectivity. The first C2 symmetric di NHC ligands were reported within months of each other in 2000. Trudell et al.104 and Rajanbabu et al.105 independently reported the synthesis of binaphthyl based bis NHC complexes Trudells racemic version was reported with a series of other asymmetric bisimidazolium salts used in the palladium -catalyzed coupling of 4-chlorotoluene and phenylboronic acid. Rajanbabu et al. found that their chiral ligand chelated to a Pd(II) center in both trans and cis orientati ons and coordinated to Ni(II) in only the trans orientation. The palladium complexes were applied to the non -stereoselective Heck coupling of ethyl acrylate and halobenzenes. Douthwaite et al .106 were the first to report chiral induction by a C2 symmetric chelating bis NHC in 2003. The bis NHC ligand based on a 1,2 -cyclohexyldiamine backbone was tested towards the Pd (II) asymmetric intramolecular cycliz ation of N (2 -bromophenyl) N -methyl 2 (1 napthyl)propanamide producing only an 18% e e To date, the only high enantioselectivities produced utilizing bidentate chiral di -NHC ligands have been reported by Min Shi et al .107 115 First reported in 2003,107 Min Shis binaphthyl amine -based ligand was found to form a mixture of bridged bi metallic Rh(I) and chelating monometallic Rh(III) complexes. The Rh(III) complex was applied towards the enantioselective hydrosil ylation of methyl ketones, producing yields

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38 rangin g from 82 to 96% and e.e.s as high as 98%. A bimetallic Ir(I) complex supported by the same ligand was reported in 2005 with no mention of the chelating monometallic version or catalytic application.108 Shortly thereafter, Min Shi reported the neutral chelating monometallic Pd(II) complex supported by the same BINAM -based bis benzimidazole.109 Initial catalytic application towards achiral Suzuki coupling of phenylboronic acids to bromobenzene and Heck coupling of aryl halides with butyl acrylate resulted in moderate to high yields for the majority of substrates reported. Analogs of the same bis(NHC) P d(II) complex116 have since been reported to catalyze the oxidative kinetic resolution of alcohols,110 enantioselective allylation of aldehydes,111, 112 and the conjugate addition of arylboronic acids to cyclic enones113 with high enantiocontrol Most recently, Min Shi et al. reported the application of a [Pd(II)(H2O)2]2+ c omplex supported by the same ligand architecture117 to the enantioselective arylation of N tosylarylimines using boronic acids.114 The original Rh(III) complex was also recently reported to produce enantiopure product whe n applied to the hydrosilylation of 3 -oxo 3 arylpropionic acid methyl or ethyl esters.115 The relatively small number of successful asymmetric catalytic applications involving C2 symmetric chelating bis -NHCs should not be taken as an indication of a fundamental flaw i n the ligand concept, but rather as a reflection of the small number of available architectures. Taking this into account and considering the success of the closely related bis -phosphines our laboratory designed a novel C2 sym metric di NHC ligand based on a trans 9,10 dihydro 9, 10 ethanoanthracene (DEA) backbone. This chapter will describe in detail the design and synthesis of one member of the first generation C2 symmetric di NHC ligands DEAM BY ( trans 9,10 dihydro 9, 10 ethanoanthracene 11,12 bis (1 be nzyl) imidaz 2 ylidene) along with the synthesis of mono and bimetallic Rh(I) and Ir(I) complexes. Structural comparison utilizing solution state

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39 analysis and X ray crystal structures is accomplished to lay groundwork for establishing a relationship betwee n the structure of these unique ligands and their catalytic activity. 2.2 Experimental Section 2.2 .1 Synthesis of T rans1,1' [ 9,10 D ihydro 9,10 Ethanoanthracene 11,12 D iyldimethanediyl]bis (Benzyl imidazole) bis(T rif louromethansulfonate) [DEAM BI](OTf)2 (2 -1 ) 1 B enzylimidazole (3.13 g, 19.8 mmol) was add ed to a 250 mL flask containing trans1,1' [9,10 dihydro 9,10 ethanoanthracene 11,12 diyldimethanediyl ]bis(trifluoromethanesulfonate)118 (5.00 g, 9.40 mmol) in dry DME (100 mL). After refluxing under argon for 2 h, the solvent was removed producing a yellow powder. The powder was suspended in ethyl acetate and sonicated to produce a white powder which was isolated by filtration as a white microcrystalline so lid ; y ield 7.63 g (96%). 1H NMR ( 300 MHz, (CD3)2SO ) ppm : 9.27 ( m 2 H, NC H N ), 7.83 ( m 2 H, NC H CHN ), 7.78 ( m 2 H, NCHCH N ), 7.457.51 (m, 8H, Ar ), 7.34 7.45 (m, 4H, Ar ), 7.31 (m, 2 H, Ar ), 7.15 7.23 (m, 4H, Ar ), 5.37 5.57 (m, 4 H, NC H2C), 4.08 (s, 2 H, bridgehead H ), 3.92 (dd, JHH=13.9, 4.2 Hz, 2 H, CH(HCH )N ), 3.62 (dd, JHH=13.7, 8.9 Hz, 2 H, CH(H CH)N ), 2.04 2.18 (m, 2 H, bridge H ). 13C[1H ] NMR (75 MHz, (CD3)2SO ) ppm : 142.5 (2C, Ar ), 139.3 (2C, Ar ), 136.7 (2C, N CHN), 134. 8 (2C, Ar ), 129. 1 (4C, Ar ), 128. 9 (2C, Ar ), 128. 4 (4C, Ar ), 126. 5 (2C, Ar ), 126. 3 (2C, Ar ), 125. 7 (2C, Ar ), 123. 9 (2C, Ar ), 123. 0 (s, 2C, N CHCHN ), 122.6 (s, 2C, NCH CHN), 120.6 (q, J= 322 Hz, CF3), 52.1 (s, 2C, N CH2C), 51.8 (s, 2C, N CH2CH ), 44.3 (s, 2C, bridgehead C), 43.1 (s, 2C, bridge C). MS(HR ESI+): Calc. for [C40H36N4S2O6F6]: m/z 869.8450 [M+Na]+, found m/z 869.1876. Anal. Calc. for C40H36N4S2O6F6: C, 56.73%; H, 4.29%; N, 6.62%. Found: C, 56.68%; H, 4.35%; N, 6.50%. The m olecular structure of 2 -1 determine d by X ray

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40 c rystallography is displayed in F igure 2 8 crystals were grown by diffusion of pentane into an ethanol solution containing the salt 2. 2.2 Synthesis of Trans 1,1 [9,10 Dihydro 9,10 Ethanoanthracene 11,12 D iyldimethandiyl] bis(1 Benzylim idazolidine 2 Y lidene ), DEAM BY ( 2 -2 ) At 35 oC, KN(TMS)2 (395 mg, 1.98 mmol in 5 mL THF) was added t o a cold solution of [DEAM BI](OTf)2 (2 -1 ) (800 mg, 0.95 mmol) in THF (10 mL). After 1 h, the solution was allowed to warm to room temperature while stir ring. The solvent was then removed in vacuo producing an orange -yellow powder. After trituration with diethyl ether (2 x 5 mL ) and pentanes (2 x 5 mL) t he solid was taken up in pentanes and filtered. The precipitate was then washed with diethyl ether and extracted with THF. The THF was removed to produce a peach colored powder ; y ield 366 mg (71%). 1H NMR ( 300 MHz, C6D6) ppm : 7.57 (dd, J= 7.4, 1.1 Hz, 2 H, Ar ), 7.04 7.27 (m, 16H Ar ), 6.47 6.52 ( overlapping d, 4H, NC H CH N and NC H CH N ), 5.17 (s, 4H, NC H2C), 4.38 (d, J= 1.1 Hz, 2H, bridgehead H ), 3.77 (dd, J= 13.2, 8.4 Hz, 2H, CH(HCH )N ), 3.47 (dd, J= 13.3, 5.9 Hz, 2H, CH(H CH )N ), 2.28 2.39 (m, 2H, bridge H ). 13C NMR (75 MHz, C6D6) ppm : 216.1 (s, N Ccarbene N ), 144.6 (s, Ar ), 141.5 (s, Ar ), 139.6 (s, Ar ), 129.1 (s, Ar ), 128.3 (s, Ar ), 126.9 (s, Ar ), 126.7 (s, Ar ), 126.4 (s, Ar ), 124.0 (s, Ar ), 120.7 (s, NCH CH N ), 119.1 (s, N CH CHN ), 55.4 (overlapping singlets, N CH2C & CH CH2N ), 47.1 (overlapping singlets, bridge & bridgehead C). MS(DIP -CI): Calc. for [C38H34N4]: m/z 546.2929 [M]+, found m/z 546.2783. The m olecular structure of 2 -2 determined by X -ray c rystallog raphy is displayed in Figure 2 8 crystals were grown by a diffusion of ether into a THF solution containing the compound

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41 2.2.3 Synthesis of Rhodium(I) Trans 9,10 Dihydro 9,10 Ethanoanthracene 11,12 bis(1 Benzylimidazolidine 2 Y lidene ) Cyclooctadiene T riflate, [(DEAM BY )Rh( COD)]OTf (2 -3 ) a) To a solution of DEAM BIY (2 -2 ) (500 mg, 0.92 mmol) in THF (5 mL ) was added a solution of [Rh( COD )Cl]2 ( 226 mg 0 .458 mmol ) in THF (5 mL). The reaction was stirred for two hours during which time a yellow precipitate formed The precipitate was filtered and washed with cold THF (2 x 3 mL ) to provide [(DEAM BI)Rh( COD )](OTf) (2 -3 ) as a bright yellow solid; y ield 417 mg ( 50%) b) At 100 C, a solution of KN (TMS)2 (50 mg, 0.25 mmol) in dry THF (3mL) was added to a solution of [DEAM BI](OTf)2 (100 mg, 0. 118 mmol) in THF (5 mL ) and allow ed to warm to room temperature while stirring vigorously. After 45 min, the solution was again cooled to 100 C. After 15min, a cold solution of [Rh( COD )Cl]2 ( 28 mg 0 057 mmol ) in THF (5 mL) was added to the mixture and allowed to warm to room tempera ture overnight. The yellow precipitate was collected by filtration, washed with Et2O (10 mL) and THF (2 mL), and dried under high vacuum ; y ield 97 mg (90% ). 1H NMR ( 300 MHz, CDCl3) ppm : 7.78 (d, J= 1.7 Hz, 1H, 18), 7.34 7.58 (4H, 2,5,8,11), 7.28 7.34 (3H, 35,36,37), 7.1 7.25 (7H, 3,4,9,10,24,25,26), 6.88 (overlapping d and m, for d J= 2.0 Hz, 3H, 29,34,38), 6.58 (m, 2H, 23,27), 6.68 (d, J= 1.7 Hz, 1H, 19), 6.56 (d, J= 2.0 Hz, 1H, 30), 5.97 (d, J= 15.9 Hz, 1H, 32J= 15.6 Hz, 1H, 21 5.17 (d, J= 16.1 Hz, 1H, 32), 5.09 (d, J= 16.1 Hz, 1H, 21), 4.69 (dd, J= 13.3, 3.1 Hz, 1H, 17 J= 1.1 Hz, 1H, 14), 4.47 4.58 (m, 1H, 40), 4.43 (d, J= 0.8 Hz, 1H, 13), 4.37 4.45 (m, 1H, 15), 4.27 4.34 (m, 1H, 44), 4.19 4.30 (dd, 1H, 17), 4.01 4.09 (m, 1H, 39), 3.97 (dd, J= 14.0, 7.8 Hz, 1H, 2843), 3.12 (dd, J= 14.2, 2.0 Hz, 1H, 28 ), 1.23 2.39(m, 9H, 16, 41, 42, 45, 46). 13C NMR (75 MHz, CDCl3) ppm : 181.7 (d, JRhC =54.1 Hz, 20), 179.4 (d, JRhC =52.7 Hz, 31), 144.7 (s, 1 ), 144.3 (s, 12), 139.8 (s, 7 ), 138.2 (s, 6 ), 135.9 (s, 33), 135.9 (s,

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42 22), 129.3 (s, 35 & 37), 129.1(s, 24 & 26), 128.3 (s, 36), 128.6 (s, 25), 127. 1 (s, 3 ), 126.9 (s, 10), 126.6 (s, 9 23 & 27), 126.4 (s, 4 ), 126.3 (s, 34 & 38), 126.2 (s, 8 ), 125.7 (s, 5 ), 125.3 (s, 29), 124.8 (s, 18), 124.1 (s, 2 ), 123.4 (s, 11), 121.5 (s, 30 & 19), 92.4 (d, JRhC =8.2 Hz, 40), 90.0 (d, J= 7.3 Hz, 39), 89 1 (d, JRhC =9.6 Hz, 44), 84.8 (d, JRhC =8.2 Hz, 4 3 ), 57. 5 (s 28), 55. 7 (s 21), 55. 4 (s 17), 54 4 ( s 32), 48.4 (s, 14), 48.2 (s, 16), 47.8 (s, 13), 47.7 (s, 15), 32.3 (s, 45), 31.3 (s, 41), 29.4 (s, 42), 29.1 (s, 46). MS(HR ESI+):Calc. for [C47H46N4Rh]+: m/z 757.7874 M+, found m/z 757.2773 Anal. Calc. for C47H46N4SO3F3Rh plus one molecule MeCl: C, 58. 12%; H, 4.87%; N, 5.65%. Found: C, 57.88%; H, 4.834%; N, 5.50%. The m olecular structure determined by X ray crystallography and numbering associated with NMR assignment is displayed in Figure 2 9 crystals were grown by diffusion of ether into a mixed solution of methylene chrloride and benzene containing the compound 2.2.4 Synthesi s of [2 DEAM BY][Rh(COD)Cl]2 (2 -4 ) A solution of KN(TMS)2 (50 mg 0.250 mmol ) in dry THF (5 mL) was added t o a solution of [DEAM BI](OTf )2 (2 -1 ) (100 mg 0.118 mmol ) in THF (5 mL ) at 100 C. After stirring at room temperature for 45 min, the solution was cooled to 100 C and added slowly to a cold solution of [Rh( COD )Cl]2 (58 mg, 0.117 mmol ) in THF (5 mL). The reaction was stirred overnight forming a n orange solution. After the volatiles were removed, the resulting powder was washed with Et2O and extracted with dry THF. The THF was removed and the product was washed with a small amount of Et2O and pentane to reveal a yellow powder; yield 116 mg (94%). 1H NMR (300 M Hz, CDCl3) ppm : 7.49 (2H, d, J= 7.0 Hz, Ar ), 7.29 7.39 (4H, m, Ar ), 7.18 7.26 (8H, m, Ar ), 7.06 7.19 (4H, m, Ar ), 6.90 (2H, J= 1.9 Hz, NC H CHN), 5.88 (2H, d, J= 13.6 Hz, N( H CH)C), 4.77 4.88 (2H, m, COD -CH), 4.57 (2H, d, J= 1.9 Hz, NCHC H N ), 4.56 (2H, d, J= 13.7 Hz, N(HC H )C), 4.42 4.54 (2H, m, COD CH), 4.23 (2H, d, J= 2.8 Hz,

PAGE 43

43 bridgehead H ), 4.10 (2H, overlapping dd J= 12.6 Hz, CH(HCH )N ), 3.57 (2H, dd, J= 13.3, 2.6 Hz, bridge H ), 3.19 3.30 (2H, m, CH(H CH)N ), 2.72 2.84 (2H, m, COD CH), 2.3 9 2.50 (2H, m, COD CH), 2.16 2.34 (2H, m, COD -CH2), 1.89 2.05 (2H, m, COD CH2), 1.56 1.89 (8H, m, COD CH2), 1.33 1.56 (4H, m, COD -CH2). 13C NMR (75 MHz, CDCl3) ppm : 179.5 (d, J= 51.2 Hz, NC N), 142.4 (s Ar ), 142.30 (s Ar ), 136.1 (s Ar ), 130.0 (s Ar ), 128.7 (s Ar ), 128.1 (s Ar ), 126.0 (s Ar ), 125.7 (s Ar ), 125.3 (s Ar ), 124.3 (s Ar ), 120.7 (s N C H=CHN), 119.8 (s N CH= CHN), 98.7 (d, J= 6.6 Hz COD CH ), 98.0 (d, J= 7.2 Hz COD CH ) 68.5 (d, J= 14.3 Hz COD -CH ), 67.4 (d, J= 14.9 Hz COD -CH ), 65.8 (s residual ether ), 56. 1 (s N CH2C), 53.9 (s CH CH2N), 48.6 (s CCH CHCH2), 39.6 (s C CHC), 33.1 (s COD CH2), 31.5 (s COD -CH2), 29.6 (s grease), 29.5 (s COD -CH2), 27.2 (s COD -CH2), 15.2 (s residual ether ). Anal. Calc. for C54H58N4Rh2Cl2 : C, 62.37%; H, 5.62%; N, 5.39%. Found: C, 62.17%; H, 5.57%; N, 5.18 %. MS(HR ESI+):Calc. for [C47H46N4Rh]+: m/z 757.7874 M+, found m/z 757.2773. The m olecular structure determined by X -ray c rystallography is displayed in Figure 2 11, crystals were grow n by diffution of ether into a mixed solution of benzene and THF contining the compound 2. 2.5 Synthesis of Iridium(I) Trans 9,10 Dihydro 9,10 Ethanoanthracene 11,12 bis(1 Benzylimidazolidine 2 Y lidene ) Cyclooctadiene T riflate, [(DEAM BY )Ir(COD)] OTf (2 5 ) Triflate salt 2 -1 (100 mg, 0.118 mmol), KN(TMS)2 (50 mg, 0.25 mmol), and [Ir(COD)Cl]2 (39 mg, 0.058 mmol) were each weighed into separate scintillation vials and suspended in dry THF (5mL). At 100 C, the KN(TMS)2 solution was added dropwise to the salt suspension. The reaction mixture was allowed to warm to room temperature while stirring forming a brilliant yellow color after 45 min. The mixture was again cooled to 100 C followed by drop wise addition of the [ Ir (COD)Cl]2 solution. The reaction was stirred overnight at room

PAGE 44

44 temperature. Mononuclear salt 2 -5 formed as an orange precipitate, was isolated by filtration and washed with THF (2 mL) and Et2O (5 mL) to remove excess base. The metal complex was extracted from any remaining start ing materials with CH2Cl2 and upon solvent removal was isolated as a brill iant orange powder; yield 57 mg (48% ) 1H NMR (300 MHz CDCl3) ppm : 7.51 (1H, d, J= 2.0 Hz, NC H CHN ), 7.47 7.55 (1H, m, Ar ), 7.29 7.45 (6H, m, Ar ), 7.17 7.26 (5H, m, Ar ), 7.07 7.17 (2H, m, Ar ), 6.84 6.95 (2H, m, Ar ), 6.81 (2H, d, J= 2.0 Hz NCHCH N ), 6.71 (1H, d, J= 2.0 Hz, NC H CHN ), 6.58 6.67 (2H, m, Ar ), 6.55 (1H, d, J= 2.0 Hz, NCHC H N ), 5.83 (2H, d, J= 15.9 Hz, N( H CH)C), 5.31 (2 H, d, J= 15.6 Hz, CH(HCH )N ), 5.03 (d, J= 15.5 Hz, N(HC H )C), 4.94 (d, J= 15.5 Hz, CH(HCH )N ), 4.51 (1 H, d, J= 1.9 Hz bridgehead H ), 4.43 (1 H, dd, J= 13.3, 3.8 Hz, CH(HC H )N ), 4.38 (1 H, d, J= 1.8 Hz, bridgehead H ), 4.07 4.19 (2 H, m, overlapping CH(HCH )N and COD CH ), 4.02 (1 H dd, J= 14.4, 8.1 Hz, CH(HC H )N ), 3.88 3.97 (1 H, m, COD CH ) 3.68 3.77 (1 H, m, COD -CH ), 3.58 3.67 (1 H, m, COD CH ), 3.49 (1 H, q, J= 7.0 Hz, ether) 3.19 (2 H, overlapping m and dd, J= 14.5, 1.6 Hz, bridge H and CH(H CH)N ), 1.89 2.20 (2 H, m, COD CH2), 1.73 1.88 (3 H, m, bridge H overlapped by COD -CH2), 1.48 1.72 (3 H, m, COD -CH2), 1.29 1.48 (1 H, m, COD -CH2), 1.22 (2 H, t, J= 7.0 Hz, ether). 13C NMR (75 MHz, CD2Cl2) ppm : 179.4 (N CN ), 176.5 ( N CN ), 145.0 (C, Ar ), 144.9 (C, Ar ), 139.5 (C, Ar ), 139.4 (C, Ar ), 136.1 (C, Ar ), 135.8 (C, Ar ), 129.6 ( 2 C, Ar ), 129.6 ( 2 C, Ar ), 128.8 (C, Ar ), 128.7 (C, Ar ), 127.5 (C, Ar ), 127.3 (C, Ar ), 127.0 (C, Ar ), 126.8 (C, Ar ), 126.8 ( 2 C, Ar ), 126.8 ( 2 C, Ar ), 126.2 (C, Ar ), 124.7 (N CHCHN), 124.2 (NCHCHN) 123.7 (N CH CHN), 123.7 (N CHCH N), 121.5 ( 2 C, Ar ), 79.4 (COD CH), 77.9 (COD CH), 77.0 (COD -CH), 73.1 (COD CH), 68.3 (THF), 57.4 (CH CH2N), 55.6 (N CH2C), 55.1 (CH CH2N), 54.4 (N CH2C), 49.0 (CCHC), 48.8 (CH CH CH2), 48.2 (C CHC), 47.9 (CH CH CH2), 32.6 (COD C H2 ), 32.1 (COD CH2), 30.9 (COD -CH2), 30.8 (COD CH2) 26.1 (THF ). Anal. Calc. for Ir C47N4H46O3SF3: C,

PAGE 45

45 56.67%; H 4.65%; N 5.62 % Found: C, 56.37%; H 4.509%; N 5.452%. MS(TOF ESI+):Calc. for [C46H46N4Ir]+: m/z 847.6958 M+, found m/z 847.3350. The m olecular structure determine d by X ray crystallography is displayed in Figure 2 9 crystals were grown by diffusion of ether into a methylene chloride solution contianing the compound and a small amount of benzene 2.2.6 Synthesis of [2 DEAM BY][Ir(COD)Cl]2 (2 -6 ) Triflate salt 2 -1 (100 mg, 0.118 mmol), KN(TMS)2 (50 mg, 0.25 mmol), and [Ir(COD)Cl]2 (79 mg, 0.117 mmol) were each weighed into separate scintillation vials and suspended in dry THF (4 mL). At 100 C, the KN(TMS)2 solution was added dropwise to the salt suspensions; the reaction mixture was stirred vigorously while warming to room temperature. After 45 min, the mixture was again cooled to 100 C and added dropwise to the [Ir(COD)Cl]2 solution. The reaction was a llowed to warm to room temperature overnight. The solvent was removed and the resulting residue was washed with Et2O (10 mL ) and extracted with THF. THF was removed to reveal the dinuclear, [ 2 DEAM BY][Ir(COD)Cl]2 (2 -6 ) as a yellow solid; yield 71 mg (4 9 % ) 1H NMR (300 MHz, CDCl3) ppm : 7.09 7.58 (18H, m, Ar ), 6.96 (2H, d, J= 2.1 Hz, NC H CHN ), 5.87 (2H, d, J= 13.5 Hz, N(HCH )C), 4.67 (2H, d, J= 1.8 Hz, NCHC H N ), 4.57 (2H, d, J= 13.8 Hz, N(HC H )C), 4.49 (2H, m, COD C H ), 4.24 (2H, d, J= 2.1 Hz, bridgehead H ), 4.08 4.20 (2H, m, COD -CH ), 3.91 4.08 (2H, overlapping dd, CH(H CH)N ), 3.61 (2H, dd, J= 13.8, 1.0, 0.7 Hz, CH(HC H )N ), 3.22 (2H, br. d, J= 10.8 Hz, 6 ), 2.39 2.56 (2H, m, COD CH ), 2.23 (2H, m, COD -CH ), 2.07 2.21 (2H, m, COD CH2 ), 1.90 (2H, m, COD CH2), 1.70 (5H, m, COD -CH2), 1.35 1.51 (2H, m, COD CH2), 1.06 1.35 (5H, m, COD -CH2). 13C NMR (75 MHz, CDCl3) ppm : 177.3 (N CN) 142.1 (C Ar ) 142.0 ( C, Ar ), 136.0 (C Ar ), 129.9 ( C, Ar ), 128.7 (C Ar ), 128.6 (C, Ar ), 128.2 (benzene) 126.0 ( C, Ar ) 125.7 (C, Ar ), 125.1 (C, Ar ) 124.2 ( C, Ar ), 119.9 ( N CH CHN) 119.5 ( NCN CHN) 84.9 ( COD -C H) 83.7 ( COD CH),

PAGE 46

46 55.6 (COD C H) 53.5 ( COD -CH) 52.2 ( CH2), 50.8 ( C H2), 48.5 ( CH CHCH2), 39.3 ( CCHC) 33.9 (COD C H2), 31.9 (COD CH2), 30.4 ( COD CH2), 28.0 (grease ), 27. 7 ( COD -CH2). Anal Calc. for Ir2C54H56N4Cl2: C, 53.32%; H 4.64%; N 4.61% Found: C, 51.528 %; H 4.077%; N 4.890. MS(TOF ESI+):Calc. for [C54H58N4Ir2Cl ]+: m/z 1183.967 (M Cl)+, found m/z 1183.3595. The molecular structure determined by X ray crystallography is displayed in Figure 2 11, crystals were grown by diffusion of pentane into a THF solution contianing the compound and a small amount of benzene 2.2.7 Catalytic H ydroformylation The hydroformylation experiments were carried out in a 100 mL stainless steel Parr reactor heated in a sand bath. The reactor was charged with 50 mg of the substrate, 0.1 mol% of the bis carbene rhodium complex ( 2 -3 ) and 1.5 mL of solvent. Before startin g the catalytic reactions, the charged reactor was purged three times with 10 20 bar of syngas (CO/H2 = 1/1) and then pressurized to 100 bar. The reaction mixture was stirred at 800 rpm at 50 C for the appropriate reaction time (typically 24h). Once com plete the reactor was cooled to room temperature, the pressure was reduced to 1.0 bar in a well -ventilated hood and the reaction mixture was collected in a vial. The reaction mixtures were analyzed directly without further purification. The % conversio n and regioselectivity were determined by 1H NMR spectroscopy and gas chromatography. T he enantiomeric purity was determined by GC using Supelcos Beta Dex 225 column. Temperature program: 100 C for 5 min, then 4 C/min to 160 C. Retention times: 4.8 min for vinyl acetate, 11 ( S ) and 12.8 ( R ) min for the enantiomers of methyl 2 -methyl 3 oxopropanoate (branched regioisomer), 16 min for methyl 4 oxobutanoate (linear regioisomer), 9 min for styrene, 18 ( S ) and 18.2 ( R ) min for the enantiomers of 2 phenylp ropanal (branched regioisomer), and 22 min for 3 -phenylpropanal (linear regioisomer).

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47 2.2.8 X -ray Crystallography Data were collected by Dr. Khalil A. Abboud at 173 K using a Siemens SMART PLATFORM equipped with a CCD area detector and a graphite monochromator utilizing MoK radiation ( = 0.71073 ). Cell parameters were refined using up to 8192 reflections. A full sphere of data (1850 frames) was collected using the -scan method (0.3 frame width). The first 50 frames were re -measured at the end of data collection to monitor instrument and crystal stability (maximum correction on I was < 1 %). Absorption corrections by integration were applied based on measured indexed crystal faces. The structures were solved by direct methods in SHELXTL6119, and refined using full matrix least squares. The nonH atoms were treated anisotropical ly, whereas the hydrogen atoms were calculated in ideal positions and were riding on their respective carbon atoms. Crystallographic data and structure refinement details for all compounds are listed in appendix B. 2.3 Results and Discussion 2.3 .1 Prepar ation and Solution State Analysis of [DEAM -BI](OTf)2 (2 -1 ) Figure 2 2 illustrates the synthesis of compound 2 -1 The ditriflate is synthesized according to a literature procedure reported by Zsolnai et al .1 18 A straightforward substitution reaction is used to replace t he t rifl uo romethane sulfonyl (OTf) with 1 benzylimidazole, a commercially available substrate Unlike other derivatives of 2 -1 such as the methylimidazolium salt [DEAM -MBI](OTf)2,120 2 -1 does not precipitate from the reaction medium A fter solv ent removal, the isolated white solid is used without further purification. If desired, sonication in ethyl acetate or crystallization via diffusion of pentane into ethanol solution followed by filtration provides analytically pure compound. A 1H NMR s pectrum of 2 -1 reveals a signature downfield imidazolium proton resonance (N CH N ) at 9.27 ppm. Coupling between the imidazolium proton and th e imidazole olefinic

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48 protons (N CH CH N) should form a doublet of doublets; however, relatively weak coupling causes the peak to appear as an unresolved multiplet. Two additional unresolved multiplets appear at 7.83 and 7.78 ppm corresponding to the olefinic protons Upfi eld, the backbone br idgehead (C CH CH) and bridge (CH CH CH2) protons appear as a singlet at 4.08 ppm and a multiplet at 2.10 ppm, respectively. The diastereotopic methylene protons on the ligand arms resonate as a pair of doublet of doublets at 3.92 ( J= 13.9, 4.2 Hz ) and 3.62 ( J = 13.7, 8.9 Hz ) In the 13C{1H} NMR spectrum the imidazolium carbon (N CH N) resonates at 136. 7 ppm F ull assignment of the 13C{1H} NMR spectrum is in section 2.2.1; however, for comparison with subsequent compounds it is worth noting that the most downfield signal appears at 142.5 ppm corresponding to an aromatic carbon 2.3 .2 Preparation and Solution State Analysis of [DEAM -BY] ( 2 -2 ) Generation of free di carbene 2 -2 was accomplished at 35 C under an N2 atmosp here (Figure 2 3 ). Deprotonation of 2 -1 occurs immediately upon addition of the base potassium bis(trimethylsilyl)amide KN(TMS)2, forming a brilliant yellow solution. 2 2 is isolated from the yellow solution in 71% yield as a n air sensitive pale yellow solid. The absence of an imidazolium resonance at 9.27 ppm in the 1H NMR spectrum of the yellow solid confirms complete deprotonation. Increased electron density within the heterocycle s of 2 -2 shifts the olefinic resonances upfield, from 7.83 and 7.78 ppm in 2 -1 to 6.47 and 6.51 ppm. The 1H NMR spectrum is consistent with the formation of a free di -carbene but cannot be used as conclusive evidence. Instead of forming the free di -carbene it is possible that deprotonation of 2 -1 could form an enetetramine echoing Wanzlicks findings.42 In fact, r e lated benzimidazole derivatives prefer form ation of enetetraamines resulting in simila r 1H NMR spectra, provided the N-alkyl group is not too large.103, 120 Conversely f ormation of an enetetraamine from 2 -1 is unlikely, as the electronic nature of unsaturated imidazoles increases

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49 the barrier to double bond formation.121 A diagnostic carbene carbon reson ance at 216.2 ppm in the 13C{1H} spectrum verifies the identity of 2 -2 as a free di carbene species. F ree N -heterocyclic carbene carbons resonate between 205 and 245 ppm,122 whereas enetetra a mine carbons are shifted well upfield to approximately 145 ppm.96 2 .3 .3 Preparation and Solution State Analysis of [(DEAM -BY)Rh(COD)]OTf (2 -3 ) A mononuclear, cationic Rh(I) complex, 2 -3 is readily formed from the free di carbene 2 -2 (section 2. 2.3 a ); however, in situ deprotonation of 2 -1 followed by reaction with [Rh(COD)Cl]2 is a more convenient and higher yielding route ( Figure 2 4 ). Complex 2 -3 forms as a yellow orange precipitate and is isolated via filt ration. Chelation of 2 -1 to a single r hodium center creates a C1 symmetric compound. The lowered symmetry causes each proton and carbon to become chemically and magnetically unique resulting in complex 1H and 13C{1H} NMR spectra Although the 1H NMR spectrum was completely assigned using gDQCOSY, gHMBC and NOESY two -dimensional NMR techniques individual resonances throughout the 1D spectra can be difficult to distinguish. Between 5 and 6 ppm a sparse region of the spectra, are four distinct double ts attributed to the diastereotopic methylene protons of the Nbenzyl substituent ( 5.97; d, J= 15.9 Hz, 5.36; d, J= 15.6 Hz, 5.17; d, J= 16.1 Hz, and 5.09 ppm; d, J= 16.1 Hz ). The o ther diastereotopic protons (CH CH2N) appear as four doublet s of doublets at 4.69 ( J= 13.3, 3.1 Hz ), 4.19 4.30 ( overlapping dd) 3.97 ( J= 14.0, 7.8 Hz) and 3.12 ( J= 14.2, 2.0 Hz) ppm. The bridge protons, that resonate as singlets in compounds 2 -1 and 2 -2 now appear as doublets at 4.62 (d, J= 1.1 Hz) and 4.43 (d, J= 0.8 Hz) ppm. Th e most striking feature of the 1H NMR spectrum is the large separation between the two bridgehead protons, appearing at 4.40 ppm and 1.87 ppm. The rigid arrangement of the complex forces the Rh center directly above one of the bridgehead protons deshield ing it Two distinct doublet resonances associated with the two Rh CNHC carbons in the 13C{1H} NMR spectrum of

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50 2 -3 at 181.8 (JRhC = 54.1 Hz) and 179.4 (JRhC = 52.7 Hz ) provide further evidence of the chelated ligand forming a C1 symmetric compound 2.3 .4 Preparation and Solution State Analysis of [-DEAM -BY][Rh(COD)Cl]2 (2 -4 ) The dimeric starting material [Rh(COD)Cl]2 used in the synthesis of 2 -3 is also utilized to create the bimetallic [ DEAM BY][Rh(COD)Cl]2 (2 -4 ) (Figure 2 5 ). D eproton ation of 2 -1 followed by dropwise addition of the resulting solution into cold THF containing [Rh(COD)Cl]2 forms 2 -4 in 94% yield. Compound 2 -4 is significantly more soluble than its monometallic counterpart 2 -3 Pure 2 -4 is procured as a yellow -brown powder by remov al of all volatiles from the reaction mixture followed by washing with cold ether and extraction into THF. The two Rh(I) centers of 2 -4 are bridged by the ethanoanthracene ligand through coordination of one NHC moiety to each metal center. Unlike monome tallic chelate 2 -3 C2 symmetry is retained in 2 -4 The 1H and 13C{1H} NMR spectra of 2 -4 clearly reveal higher symmetry. The benzyl methylene protons, corresponding to four doublet resonances in 2 -3 appear as two doublets at 5.88 (J= 13.6 Hz ) and 4.56 (J= 13.7 Hz ) ppm in the 1H NMR spectrum of 2 -4 T h e olefinic imidazole protons (N CH CH N) appear as two doublets at 6.90 (J= 1.9 Hz ) and 4.57 (J= 1.9 Hz ) ppm and the bridge and bridgehead protons as a doublet at 4.23 ( J= 2.8 Hz) and doublet of doublets at 3.57 ( J= 13.3, 2.6 Hz) ppm respectively. Two equivalent RhCNHC bonds are evident by a single distinct doublet at 179.5 (d, JRhC = 51.2 Hz) ppm in the 13C{1H} NMR spectrum. 2.3 .5 Preparation and Solution State Analysis of [(DEAM -BY)Ir (COD)]OTf (2 -5 ) and [DEAM -BY][Ir (COD)Cl]2 (2 -6 ) M onoand dinuclear Ir(I) complexes, 2 -5 and 2 -6 were constructed by the same synthetic method as the Rh(I) counterparts replacing [Rh(COD)Cl]2 with the Ir(I) equivalent (Figures 2 6 and 2 7 ). NMR spectra of mononuclear Ir compound 2 -5 are expectedly similar to

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51 the spectra of 2 -3 excluding a few key features. Although 2 -3 and 2 -5 are structurally similar, altering the metal center results in a slight variation in geometry, thus altering the exact location of corresponding resonances The major alteration in NMR spectra is seen in the13C{1H} NMR. Instead of the doublets in the 13C{1H} NMR spectrum of 2 -3 the iridium bound carbons resonate as singlets at 179.4 and 176.5 ppm Unlike 103Rh, t he predominant iridium isotopes, 191Ir and 193Ir, have quadrapolar nuclei with spin of 3/2 thereby negating M C sp in -spin coupling in the spectra of both 2 -5 and 2 -6 2.4 X -ray Structural Analysis and Comparisons To obtain a more complete understanding of molecules 2 -1 through 2 -6 a structural study was performed by single crystal X ray diffraction. Solid -state investigations of these molecules allow comparison of structural variations between analogs 2.4 .1 Compari son of Organic Precursors 2 -1 and 2 -2 Suitable crystals for X ray diffraction studies of both 2 -1 and 2 -2 were obtain ed by diffusion crystallization Compound 2 -1 crystallize s by diffusion of pentane into an ethanol solution containing the salt, and cry stals of the free di carbene are similar ly grown by diffusion of pentane into a saturated benzene solution of 2 -2 Figure 2 8 displays the solid -state structure of the dicationic imidazolium salt 2 -1 and the neutral free di -carbene 2 -2 The asymmetric unit of 2 -1 contains one ligand molecule and two triflate anions in a monoclinic space group. Investigation of the packing structure suggests an intermolecular attraction between the olefin of the cationic imidazole and the electron rich ar yl ring of its neighboring molecule The shortest distance between the carbons of the olefin and aryl ring is 3.72 and the distance between the olefin and the plane of the aromatic ring is 3.42 Unlike 2 -1 the neutral free di -carbene 2 -2 crystallize s in an orthorhombic crystal system with no discernible intermolecular attractions.

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52 The metric parameters for both molecules correspond to those expected for imidazolium salts and their corresponding free carbenes.122, 123 Deprotonation increases the electron density at the carbene center, causing the N -C N angles to contract from 108.8(2) and 107.9(2) in 2 -1 to 102.0(3) and 101.8(3) in 2 -2 The N Ccarbene bond lengths in 2 -2 (1.370(4) N1 C20 1.352(5) N2 C20, 1.378(5) N3 C31, and 1.360(4) N4 C31 ) are notably longer than the N (CH) distances in 2 -1 (1.322(3) N1 C20, 1.334(3) N2 -C20, 1.328(3) N3 C31, and 1.330(3) N4 C31) Contracting of the N C N angle and lengthening N -Ccarben e bond are both expected due to increased -bond character upon formation of the free carbene.124 The increased electron density does not affect the imidazole backbone No appreciable bond length alteration of the N Calkene or C=C bonds is apparent between compounds 2 -1 and 2 -2 (Table 2 1 and 2 2) T he only chemical alteration between 2 -1 and 2 -2 occurs on the heterocycle, but the largest difference in their s olid state structure s is the conformation of the ligand arms. The torsion angle between the pendant arms ( C28 C15 -C16 C17 ) in 2 -2 is 109.0(3) but the same torsion angle in 2 -1 is 119.1(2) The 10 variation displays the flexibility of these ligands and is due in part to the electrostatic repulsion between the two positively charged heterocycles of 2 -1 Formation of a neutral heterocycle reduces this repulsion in 2 -2 2.4 .2 Monometallic [(DEAM -BY)M (COD)]OTf 2 -3 and 2 -5 X ray diffraction studies confirm the structure and orientation of the C1 symmetric chelating complexes 2 -3 and 2 -5 (Figure 2 9 ). As expected the two mononuclear complexes form similar crystals structures. The crystal lattice of both complexes form m onoclinic cell s with P2(1)/n space group s. Each asymmetric unit contains a cationic molecule, its triflate counter ion, and a solvent molecule.

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53 Both M(I) ions sit in a slightly distorted square -planar coordination sphere. The NHCs occupy cis coordination sites opposite a chelated 1,5 -cyclooctadiene (COD). E xamination of the molecular structure suggests chelation forces the ligand to adopt a strain ed geometry. The dihedral angles C28 C15 C16 C17 of 95.8(2) for 2 -3 and 96.2(8) for 2 -5 are significantly smaller than those for the organic precursor molecules 2 -1 and 2 -2 Although ligand bite angles correspond to values expected for square planar c omplexes ( C20 Rh C31 of 89.93(8) and C20 Ir -C31 of 91.2(3) ), conformational strain is evident by unsymmetrical NHC M bonds. This feature is significant in the solid state structure of Rh(I) compound 2 -3 One NHC -M bond length, C31 Rh, is 2.037(2) corresponding closely to the average M NHC bond length found in the Cambridge Structural Database by Baba et. al.124 The second Rh -NHC bond is longer at 2.068(2) for C20 continue in 2 -5 the difference lies within the error of the data ( 2.031(9) for Ir C20 and 2.059(8) for Ir C31 ). As previously discussed, b inding of NHCs to metal centers is believed to be highly electrostatic in nature, allowing the NHC to retain much of its free carbene character. Supporting this assertion the N -C N bond lengths and angles of 2 -3 and 2 -5 correspond closely to those noted for free carbene 2 -2 Figure 2 1 0 displays average metric parameters for NHC M species and their free carbene precursors.124 The N -C N of 2 -2 is slightly smaller than in the metal complexes wh ereas the N -C N of the imidazolium salt ( 2 -1 ) is approximately 5 broader than in 2 -3 or 2 -5 The N -Ccarbene bond lengths of each chelate complex resemble the slightly longer bonds of compound 2 -2 rather than those of 2 -1 (Tables 2 1, 2 2, 2 3, and 2 5 ).

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54 2 4 3 Bimetallic Complexes [-DEAM -BY][M(COD)Cl]2 2 -4 and 2-6 Figures 2 5 and 2 7 display the X ray crystal structures of bimetallic complexes 2 -4 and 2 6 Similar to the monometallic compounds, the bimetallic compounds form crystal lattices with sim ilar structures. Both molecules crystallize in the P space group and form triclinic crystal systems. The solution state assignment of C2 symmetry for the dinuclear complexes is retained in the solid -state structures. The C2 axis bisects the C15 C16 bond, passing through the center of the DEA backbone The t wo neutral M(I) centers are bridged by the chiral ligand, each NHC acting as a monodentate ligand in a distorted square planar coordination sphere that includes a chlorid e and a chelating COD. The NHC moieties are parallel to each other but face opposite directions, situating the metal centers directly above opposing backbone aryl rings The absen ce of strain from chelation permits M CNHC bond lengths ( 2.021(5) Rh 1 C20, 2.024(5) Rh 2 C31, and 2.033(3) for both Ir1 C20 and Ir 2 C31 ) that correspond to reported literature values .124 The similarities also extend to the N -CNHC distances and N -C N angles. (Table 2 4 and 26 ) The large torsion angles of C28 C15 C16 C17 of 125.2(5) and 125.5(3) for 2 -4 and 2 -6 respectively, again signify the flexibility of the ligand 2.5 Initial Catalytic Testing The monometallic Rh complex ( )2 -3125 was investigated toward the hydroformylation of styrene, vinyl acetate, and allyl cyanide ( Table 2 7 ) by Dr. Mu hammad T. Jan.126 It was noted that the catalysis gave relatively high yields but lacked any significant enantiocontrol In our laboratory, r elated cat alysts were being investigated toward the hydrogenation of trans methylstilbene and methyl 2 acetamidoacrylate, the h ydroformylation of styrene and the hydrogen transfer from 2 -propanol to methyl ketones.127 These studies yielded t wo important

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55 observations. The first observation found that a complex closely related to 2 -3 showed fluxional behavior even at room temperature resulting in an ill defined chiral pocket. The second ob servation was the formation of Rh or RhH(CO)4 species as the active catalyst. Mercury poisoning experiment s and an induction period in kinetic studies suggested that the ligand was reductively eliminating from the metal center under the conditions required for catalysis. 2.6 Conclusions Solid -state analysis of NHC containing compounds 2 -1 through 2 -6 displays the structural variation available using this ligand. The bimetallic complexes retain the intended C2 symmetry but chelation of the ligand induce s a C1 symmetric structure. Although the C2 sym metry is a privileged orientation, there is no fundamental reason C1 symmetric compounds cannot be successful in asymmetric catalysis, and in fact, some C1 symmetric compounds have been quite successful in chiral induction catalysis.128 However, i nitial catalytic trials involving ( )2 -3 and related catalyst species suggests this initial ligand architecture does not induce a rigid chiral pocket even at ambient temperature Optimization of the initial ligand design should be possible by increasing the rigidity of the ligand and further defining the chiral pocket.

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56 Figure 2 1. Examples of chelating NHCs. 104 113, 115, 120, 127, 129147

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57 Figure 2 2 S ynthesis of [DEAM BI](OTf)2 (2 -1 ) Figure 2 3 Synthesis of DEAM BIY (2 -2 ) Figure 2 4 Synthesis of [(DEA M BY)Rh(COD)]OTf ( 2 -3 )

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58 Figure 2 5 Synthesis of [ DEAM -BY][Rh(COD)Cl]2 (2 -4 ) Figure 2 6 Synthesis of [(DEAM BY)Ir(COD)]OTf (2 -5 ) Figure 2 7 Synthesis of [ DEAM -BY][Ir(COD)Cl]2 (2 -6 )

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59 Figure 2 8. X -ray Crystal Structure of 2 -1 (left) and 2 -2 (right) with ellipsoids drawn at 50% probability and hydrogens removed* for clarity [*Theoretical position of imidazolium proton (pink) is included]. Figure 2 9. Molecular Structure of 2 -3 (left) and 2 -5 (right) with ellipsoids drawn at 50% probability Triflate counterion and hydrogens (excluding H16 and H15) removed for clarity.

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60 Figure 2 10. Average bond angles and length of free NHCs (top) and M NHCs( bottom ) reprinted with permission from E.Baba et al. Inorganica Chimica Acta 2005, 358, 2870. Figure 2 11. Molecular Structure of 2 -4 (left) and 2 -6 (right) with ellipsoids drawn at 50% probability and hydrogens removed for clarity. Table 2 1. Selected bond lengths () and angles ( ) for complex 2 -1 2 1 Bond lengths C18 C19 1.343(4) C29 C30 1.344(3) N3 C31 1.328(3) N3 C29 1.374(3) N3 C28 1.473(3) N4 C31 1.330(3) N4 C30 1.369(3) Angles N1 C20 N2 108.8(2) N3 C31 N4 107.9(2) Torsion Angles C28 C15 -C16 C17 119.1(2)

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61 Table 2 2 Selected bond lengths () and angles ( ) for complex 2 -2 2 2 Bond lengths C18 C19 1.337(5) C29 C30 1.346(5) N1 C18 1.369(5) N1 C20 1.370(4) N1 C17 1.458(5) N2 C20 1.352(5) N2 C19 1.382(5) Angles N1 C20 N2 101.8(3) N3 C31 N4 102.0(3) Torsion Angle C17 C16 C15 C28 109.0(3) Table 2 3 Selected bond length () and angles ( ) for complex 2 -3 2 -3 Bond lengths Rh C20 2.068(2) Rh C31 2.037(2) N1 C18 1.384(3) N1 C20 1.367(3) N1 C17 1.468(3) N2 C20 1.359(3) N2 C19 1.387(3) Angles C20 Rh C31 89.93(8) N1 C20 N2 103.82(18) N3 C31 N4 104.13(18) Torsion Angle C17 C16 C15 C28 95.8(2) Distance Rh1 C16 3.375(2)

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62 Table 2 4 Selected bond length () and angles ( ) for complex 2 -4 2 4 Bond lengths Rh1 C20 2.021(5) Rh2 C31 2.024(5) N1 C20 1.364(6) N1 C18 1.368(6) N1 C17 1.463(6) N2 C20 1.362(6) N2 C19 1.376(6) N2 C21 1.460(6) C18 C19 1.354(7) C29 C30 1.340(7) Rh2 Cl2 2.3741(15) Rh1 Cl1 2.3622(15) Angles N1 C20 N2 104.5(4) N3 C31 N4 103.1(4) Torsion Angle C17 C16 -C15 C28 125.2(5) Table 2 5 Selected bond lengths () and angles ( ) for complex 2 -5 2 5 Bond lengths Ir C20 2.031(9) Ir C31 2.059(8) N1 C18 1.382(10) N1 C20 1.351(10) N1 C17 1.467(10) N2 C20 1.361(10) N2 C19 1.375(11) N2 C21 1.469(10) Angles C20 Ir C31 91.2(3) N1 C20 N2 103.7(7) N3 C31 -N4 104.1(7) Torsion Angle C17 C16 C15 C28 96.2(8) Distance Ir1 C15 3.345(8)

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63 Table 2 6 Selected bond length () and angles ( ) for complex 2 -6 2 6 Bond lengths Ir1 C20 2.033(3) Ir2 C31 2.033(3) N1 C20 1.355(4) N1 C18 1.382(4) N1 C17 1.475(4) N2 C20 1.365(4) N2 C19 1.384(4) N2 C21 1.457(4) C18 C19 1.349(5) C29 C30 1.353(5) Ir1 Cl1 2.3673(9) Ir2 Cl2 2.3530(10) Angles N1 C20 N2 103.9(3) N3 C31 N4 104.2(3) Torsion Angle C17 C15 -C16 C28 125.5(3) T able 2 7 Initial catalytic h ydroformylation results utilizing complex 2 -3 Substrate Catalyst Solvent Conversion % b:l % ee Styrene 2 3 Chloroform 80 94:6 NA Styrene 2 3 Toluene 100 93:7 NA Styrene 2 3 Toluene 100 93:7 0 Vinyl Acetate 2 3 Chloroform 21 96:4 NA Vinyl Acetate 2 3 Toluene 45 95:5 0 Allyl cyanide 2 3 Toluene 15 10:2 Allyl cyanide 2 3 Toluene 50 10:5

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64 CHAPTER 3 SECOND GENERATION DI NHC CATALYSTS148 3.1 Introduction The intricate relationship between ligand structure and catalytic selectivity often requires optimization of a catalyst via modification of the ligand design. Chapter 2 introduced the first generation of di NHC liga nds produced in our laboratory. Initial catalytic testing120, 127 indic ated that the first generation chelating bis NHC complexes possessed a n overly flexible chiral pocket under catalytic conditions Two modifications could be made to the ligand design to increase the definition of the chiral pocket; either the nitrogen substituent could be altered to increase the steric bulk around the metal center or the ligand backbone could be altered to increase the overall rigidity. Although both avenues have been investigated, i nitial effort s were focused on altering the rigidity of the backbone itself. In stead of overhauling the entire backbone design, we cho se to reduce the ligand flexibility by eliminating the methylene linker between the ethanoanthracene backbone and the NHC coordinating moiety, leaving only two linking carb ons between the imidazole units To investigate the effect of electronic variation two different N -heterocycles were investigated (Figure 3 1 ). During ligand preparation, several reports were published a lerting of po tential problem s with this new archit ecture As was observed with the initial ligand design chelating bis NHCs are capable of two different coordination modes, chelation to a single metal center or coordination to two independent metal centers producing bridged bimetallic species. Because NHC ligands do not tend to reversibly dissociate from a metal center, the kinetic product is formed unless transmetallation reagents are utilized.149 Several studies have attempted to describe the architectural features that promote chelation o ver bridging complex e s and vice

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65 versa .58, 150153 The commonly accepted reactivity p atterns for chelating bis -NHC s are as follows: 1 When small alkyl Nsubstituents are used, the linker length has a strong effect on the mode of coordination.150 2 Small linkers (1 or 2 units) favor a bridging mode due to negative steric interactions of the Nsubstituents with co -ligands. Chelating species can be formed when the co -ligands on the metal are small or the complex is capable of forming an octahedral geometry .58 3 Longer linkers ( 3 units) favor chelation unless the steric bulk of the nitrogen substituents is sufficiently large ( ex. t -butyl).58 4 Systems that do not involve halogenated compounds ( from the metal or imidazole salt) typically favor formation of chelating cationic complexes. Halogen abstraction (by use of a silver salt) can also promote chelate formation.151 These results suggest that a di NHC ligand with a linker of 2 units and small Nmethyl substituent should favor a bridged 2:1 complex. Ligand architectures containing short linkers typically force both bulky azole rings into the crowded x y -plane of the metal complex. In these cases, bulky co ligands ( e.g. COD or NBD) promote the formation of bridging complexes to circumvent overcrowding in the x y plane. Longer linkers allow orientation of the bulky azole plane along the z axis thereby allowing chelation without steric crowding As will be discussed later, the second -generation ligand backbone although only two carbon units link the azole rings, fortuitously allows the azole ring to orient along the z axis. Th is chapter will describe the synthesis of monometallic and bimetallic complexes supported by the constrained second-generation ligands 1,1' (9,10-dihydro -9,10ethanoanthracene 11,12-diyl)di(3 -methyl 1H imidazol 3 ium) diiodide [DEA -MI](I)2 (3 -3 ) and 1,1' (9,10-dihydro 9,10-ethanoanthracene 11,12diyl)di(3 methyl 1H -benz imidazol 3 ium) diiodide [DEA -M BI](I)2 (3 -4 ).

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66 3.2 Experimental Section 3.2 .1 GC A nalysis of C hiral 9,1 0 -Dihydro -9,10-Ethanoanthracene -11,12-D i amine (3 -1) Synthesis of racemic and enantioenriched diamine 3 -1 was ac hieved via literature methods.154, 155 Resolved diamine 3 -1 was then dissolved in CH2Cl2 and a few drops of trifluoroacet ic anyhydride were added. The solution was concentrated and dissolved in acetone. Enantiopurity of ( R ) 3 -1 and ( S ) 3 -1 was measured by gas chromatography Column: Chirasil Val; oven temperature: start 100 C for 2 min, increase by 10 C/min until 180 C, hold for 20 min. tR: (S,S ): 22.4 min; ( R,R ) : 25.1 min. All sample s were found to be greater than or equal to 95% enantiomerically pure. 3.2.2 Synthesis of Trans -1,1' -(9,10-Dihydro -9,10-Ethanoanthracene -11,12-Diyl)di(1H I midazole) (3 -2) Glyoxal (6 mL of 40% aqueous solution, 2 equiv., 51.6 mmol) was added t o a methanol solution (40 mL) containing diamine 3 -1 (6.1 g, 25.8 mmol). The solution immediately turned bright yellow and became warm forming a light yellow precipitate. The mixture was stirred for 16 h. Additional MeOH ( 40 mL) was added, followed by solid NH4Cl (5.52 g, 4 equiv., 103.4 mmol) and formaldehyde ( 7.7 mL of 37% solution in water, 4 equiv., 103.4 mmol). The resulting mixture turned dark orange and was heated at reflux for 4 h. Phosphoric acid (7.1 mL of 85% solution in water, 4 equiv., 103.4 m mol ) was added slowly and the resulting mixture was heated at reflux for 16 h. The mixture was cooled to room temperature and volatiles were removed. Dichloromethane was added and the mix ture was basified to pH 14 with 2.5 M NaOH solution. The organic extract was dried over sodium carbonate, filtered, and concentrated to a sticky red oil consisting of roughly a 1:1 mixture of the desired diimidazole 3 -2 and a partially reacted monoimidazo le/amine compound.103 Diimidazole 3 -2 was isolated by flash column chromatography using 5% MeOH in CHCl3 as the eluent. Chromatography produced pure 3 -2 as

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67 a beige colored solid ( 1.03 g, 12%) 1H NMR ( 300 MHz, CDCl3) ppm : 7.43 7.50 (m, 2 H, Ar ), 7.22 7.35 (m, 6 H, Ar ), 7.08 (t, J= 1.1 Hz, 2 H, NC H CHN), 6.92 (t, J= 1.1 Hz, 2 H, NCHC H N), 6.17 (t, J= 1.4 Hz, 2 H, NC H N), 4.49 (2 overlapping s, 4 H, bridge and bridgehead H) 13C NMR (75.3 MHz, CDCl3) (ppm): 140.39 (N C H=N), 138.16 and 136.16 ( C= C), 129.79 (C aro matic), 127.67 ( C aromatic, overlapping signals), 126.63 ( C aromatic), 124.32 (N CH =NC H = CH) 117.10 (N CH =N CH = CH) 64.67 (N -CH CH C=), 50.78 (N CH -CH C=). HRMS (CIP CI) calcd (found) for C22H19N4 (M+H)+ 339.1610 (339.1649). 3.2.3 Synthesis of Trans -1,1' (9,10-Dihydro -9,10-Ethan oanthracene -11,12-Diyl)di(3 Methyl -1H -Imidazol -3 -Ium) D iiodide [DEA -MI](I)2 (3 -3 ) Diimidazole 3 -2 (1.0 g, 2. 96 mmol) was dissolved in anhydrous MeCN ( 2 5 mL) in a glass ampoule fitted with a sealable Teflon stopcock. MeI ( 0 .7 4 mL, 4 equiv., 11.8 mmol) was added and the flask was evacuated then sealed under vacuum. The flask was shielded from light and was heated in a sand bath at 105 C for 48 h. The mixture was cooled to room temperature and the precipitate was filt ered and washed with cold MeCN to produce 3 -3 as a n off -white solid; yield (1. 41 g, 77%). 1H NMR (300 MHz, (CD3)2SO ) ppm : 8.93 (br. s, 2 H, NC H N), 7.68 (t, J= 1.7 Hz, 2 H, NC H CHN), 7.62 (d, J= 7.1 Hz, 2 H, Ar ), 7.33 7.43 (m, 4 H, Ar ), 7.23 7.31 (m, 2 H, Ar ), 6.60 (t, J= 1.5 Hz, 2 H, NCHC H N), 5.48 (br. s, 2 H, bridge H), 5.05 (br. s, 2 H, bridgehead H), 3.82 (s, 6 H, C H3) 13C NMR (75.3 MHz, (CD3)2SO ) (ppm): 139.1 and 137.3 (C= C), 136.7 (N CH=N), 127.6 (C aromatic), 127.5 (C aromatic), 126.3 (C aromatic), 125.5 (C aromatic), 123.6 (N CH =NC H = CH ), 119.7 (N CH =N CH = CH ), 63.0 (N CH CH -C=), 48.3 (N CH -CH C=), 36.1 (N CH3). HRMS (FIA -ESI) calcd (found) for C24H24IN4 (M I)+ 495.1040 (495.1040).

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68 3.2.4 Synthesis of Trans -1,1 -(9,10-Dihydro -9,10-Ethanoanthracene -11,12-Diyl)di(3 -Methyl 1H -Benzimidazol -3 -Ium) D iiodide [DEA -MBI](I)2 (3 -4 ) Dibenzimidazole103 (970 mg, 2.2 mmol) was dissolved in anhydrous MeCN ( 10 mL) in a glass ampoule fitted with a sealable Teflon stopcock. MeI ( 0.55 mL, 4 equiv, 8.8 mmol) was added, and the vessel was evacuated and sealed. The flask was shielded from light and heated in a sand bath at 105 C for 48 h. The mixture was cooled to room temperature and the solid was filtered and washed with cold MeCN to afford 3 -4 as a light beige powder ; yield 1.05 g (66%). 1H NMR ( 300 MHz, (CD3)2SO ) ppm : 8.85 (s, 2 H NC H N ), 7.99 8.07 (m, 2 H Ar ), 7.82 7.92 (m, 4 H Ar ), 7.66 7.77 (m, 4 H Ar ), 7.47 (td, J= 7.5 1.13 Hz, 2 H Ar ), 7.27 (td, J= 7.4 0.99 Hz, 2 H Ar ), 7.15 7.22 (m, 2 H Ar ), 5.99 (s, 2 H bridge H ), 5.16 (s, 2 H bridgehead H ), 3.92 4.01 (m, 6 H C H3) 13C NMR (75.3 MHz, (CD3)2SO ) (ppm): 140.5 (N= CH N), 138.5 and 137.5 ( C=C ), 131.3 and 130.6 (N C= C-N), 127.8 ( C aromatic), 127.7 ( C aromatic ), 126.8 ( C aro matic), 126.8 ( C aromatic ), 126.6 ( C aromatic), 126.2 ( C aromatic), 114.2 and 113.7 (N CCH CH CH CHC N), 61.3 (N CH CH -C=), 48.0 (N CH -CH C=), 33.8 (N C H3). HRMS (ESI FTICR) calcd (found) for C32H28IN4 (M I)+ 595.1353 (595.1272). 3.2.5 Synthesis of Trans 9,10 Dihydro 9,10 Ethanoanthracene 9,10 (1 M ethyl) Bibenzimidazole), DEA MbBY (3 -5 ) KN(TMS)2 (116 mg 0.58 mmols) in 5 mL of dry THF was added drop wise to a 10 mL THF solution of 3 -4 (200 mg 0.27 mmol ). The reaction was allowed to stir at room temperature for 3 h and then filtered. Solvent was removed from the filtrate in vacuo to produce a yellow powder. Excess base was extracted by washing the yellow precipitate with Et2O (10 mL) to afford 3 -5 as a yellow solid ; yield 53 mg (40% ). 1H NMR (300 MHz, C6D6) ppm: 6.95 (m, 12 H, Ar ), 6.77 (dt, J = 7.5, 1.1 Hz, 2 H, Ar ), 6.39 (dd, J = 7.5, 1.0 Hz, 2 H, Ar ), 4.95 (s, 2 H, bridgehead C H ), 3.40 (s, 2 H, bridgehead C H ) 2.63 (s, 6 H, NC H3). 13C NMR (75.3 M Hz, C6D6)

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69 ppm: 145.5 and 138.28 (NC CH CHCH CHCN ), 144.0 and 139.2 (N -C= C -N), 127.4 (C, Ar ), 126.9 (C, Ar ), 126.4 (C, Ar ), 123.9 (C, Ar ), 122.8 (C= C), 121.5 (C, Ar ), 119.8 (C, Ar ), 109.1 and 106.9 (NCCH CH CHCHCN), 65.9 (NCH CH C), 46.6 (N C HCH C), 36.2 (N C H3). MS(DIP -CI): Calc. for [C32H26N4]: m/z 466.5564 [M+], found m/z 466.2157. The molecular structure of 3 -5 as determined by X ray crystallography is displayed in Figure 3 7 crystals were grown by a diffusion of ether into a THF solution containing the compound. 3.2.6 Synthesis of [ DEA MY][Rh(NBD)I]2 (3 -6 ) as a M ixture with 3 -9 At 35 C, KN(TMS)2 (46 mg, 0.23 mmol) in 3 mL dry THF was added drop wise to a suspension of 3 -3 (76 mg, 0.12 mmol) in THF (3 mL) The reaction mixture was then stirred for 45 min while warming to room temperature. After cooling the mixture to 35 C, it was added dropwise to a cold solution of [Rh(NBD)2]BF4 (100 mg, 0.27 mmol) in THF (3 mL) This mixture was allowed to stir at room temperature for 2.5 h before the solvent was removed in vacuo The resulting residue was triturated with Et2O (2x3 mL) and pentanes (2x3 mL). After drying o vernight, the residue was taken up in pentanes, filter ed and then washed with Et2O and extracted into benzene. The solvent was removed, producing a yellow/orange solid (53 mg). A 1H NMR spectrum of the solid revealed 25 mol% of 3 -9 was present as an impurity that could not be removed. 1H NMR ( 300 MHz, C6D6) ppm : 7.85 (d, JHH = 7.1 Hz, 2ArH ) 6.86 7.11 (m, 6ArH ), 6.41 (s, 2bridge H ), 5.91 (d, JHH = 1.7 Hz, NC H CHN ) 5.77 (d, JHH = 1.7 Hz, NCHC H N ), 5.48 (s, 2bridgehead H ), 5.19 (br s, 2 NBD -CH ), 5.05 (br s, 2 NBDCH ), 3.38 ( br s, 2 NBD CH ), 3.28 (s, 6C H3), 3.12 (d, JHH = 2.3 Hz, 2 NBD -CHCH CH) 2.89 (br. s., 2 NBD -CH) 1.64 (d, JHH = 2 .5 Hz, 2NBD CHCH CH) 0.96 (m 4 NBD CH2). The molecular structure 3 -6 as determined by X ray crystallography is displayed in Figure 3 8 crystals were grown by diffusion of ether into a THF solution containing the compound

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70 3.2.7 Synthesis of [ DEA MBY][Rh(diene)Cl]2 (3 -7 ) as a M ixture with 3 -8 Dibenzimidazolium salt 3 -4 (54 mg 0.07 mmol), KN(TMS)2 (28 mg 0.14 mmol), and [Rh(COD)Cl]2 (44 mg 0.09 mmol) were weighed into separate 20 mL vials and suspended in 3 mL of dry THF. After the reagents were cooled to 35 C, the KN(TMS)2 solution was added drop wise to the salt suspension. The reaction mixture was allowed to warm to room temperature for 45 min before being co oled again to 35C. The react ion mixture was then added dropwise to the cold [Rh(COD)Cl]2 suspension which was then allowed to warm to room temperature for 1 h while stirring The solvent was removed in vacuo and the residue was triturated with Et2O (2 x3 mL) and pentane (2x3 mL). The residue was taken up in pentanes and filtered, washed with Et2O, and extracted into benzene. A yellow/orange solid was obtained upon solvent removal. The solid material consists of ~33% 3 -7 -COD and 67% 3 -8 The mixture obtained prevented meaningful assignment of NMR spectral signals. To remedy this problem the analogous 3 -7 NBD was synthesized in hopes of generating a larger percentage of the dinuclear species. Synthesis of 3 -7 -NBD : Dibenzimidazolium salt 3 -4 (53 mg 0.07 mmol ), KN(TMS)2 (28 mg 0.14 mmol ), and [Rh(NBD)2]BF4 (60 mg 0.16 mmol ) were weighed into separate 20 mL vials and suspended in 3 mL dry THF. The reagents were cooled to 35 C and KN(TMS)2 was added drop wise to the salt suspension, stirred at room temperature for 45 min, and cooled again to 35 C. The reaction mixture was then added drop wise to the cold [Rh(NBD)2]BF4 suspension and allowed to warm while stir ring at room temperature for 1 h. The solvent was removed in vacuo and the residue was tri turated with Et2O (2x3 mL) and pentane (2x3 mL). The residue was then taken up in pentanes and filtered, washed with Et2O, and extracted with benzene. A yellow/orange precipitate (41 mg) was produced upon solvent removal which consisted of 48% 3 -7 -COD an d 52% 3 -8 -NBD 1H NMR ( 300 MHz, C6D6) ppm: 8.09 ( d, JHH = 7.4 Hz, 2ArH ),

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71 7.80 (2 H, s) 7.04 7.10 ( m, 2 ArH) 6.63 6.83 ( m, 10ArH) 6.49 6.56 ( m, 2 ArH) 5.98 (s, 2 bridge H ), 5.70 (s, bridgehead H ) 5.25 ( t, JHH = 4.0 Hz, 2 NBD -H C=CH), 4.81 (t, JHH = 4.0 Hz, 2 NBD H C=CH), 4.41(m, 2 NBD HC=CH ), 3.62 (m, 2 NBD HC=CH ), 3.56 (br s 6 CH3) 3.04 (m, 2 NBD CHCH CH), 1.52 (m, 2 NBD CHC H CH), 0.74 (d, JHH = 8.5 Hz, 2 NBD -H CH), 0.60 (d, JHH = 8.2 Hz, NBD HC H ) The molecular structure of 3 -7 -COD as determined by X -ray crystallography is displayed in Figure 3 9 crystals were grown by diffusion of pentane into a methylene chloride solution containing the compound and THF 3.2.8 Synthesis of the R hodium (I) Trans 9,10 Dihydro 9,10 Ethanoanthracene 9,10 bis(1 Methylbenzimidazolidine 2 Y lidene ) Cyclooctadiene I odide, [(DEA MBY)Rh(COD)]I (3 -8 ) Dibenzimidazolium salt 3 -4 (100 mg 0.14 mmol) was suspended in 5 mL THF and stirred overnight. At 35 C, KN(TMS)2 (53 mg 0.2 6 mmol ) in 3 mL THF was added dropwise to the salt suspension and allowed to warm to room temperature and stir for 1 h. After cooling the solution to 35 C, [Rh(COD)Cl]2 (34 mg 0.07 mmol ) in 3 mL THF was then added dropwise to the reaction and allowed to stir for 1 h at room temperature. The reaction mixture was allowed to stir at room temperature overnight and the resulting solid was filtered, washed wit h Et2O and extracted with CHCl3 to provide [(DEA MBY)Rh(COD)]I 3 8 as a yellow powder ; yield 59 mg (53%). 1H NMR ( 500 MHz, CDCl3) ppm: 9.26 (d, J= 10.0 Hz, 16), 7.81 (d, J = 7.0 Hz, 11), 7.72 (d, J = 7.1 Hz, 8 ), 7.63 (d, J = 7.3 Hz, 5 ), 7.50 7.52 (m, 10, 18, 21), 7.44 (m, 9 ), 7.38 (m, 18 & 19), 7.32 (m, 2, 4, 29), 7. 20 (m, 3 & 28), 7.04 (m, 27), 6.95 (d, J= 8.2 Hz, 26), 5.19 (s, 14), 5.16 (s, 13), 5.13 (m, 39), 4.55 (m, 38), 4.45 (s, 24 CH3), 4.36 (dd, J = 9.9, J = 0.7 Hz, 15), 4.29 (m, 34), 3.95 (s, 32 CH3), 3.83 (m, 35), 2.72 (m, 33 & 40), 2.30 (m, 33), 2. 23 (m, 37 CH 2), 2. 16 (m, 40), 1.74 (m, 36), 1.31 (m, 36). 13C NMR (75.3 MHz, CD3Cl) ppm: 193.6 (d, JRhC = 54.1 Hz, 31),191.4 (d, JRhC = 52.4 Hz, 23), 146.6 ( s, 6 ), 144.1 (s, 7 ), 138.4 ( s,

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72 12), 136.6 ( s, 30), 136.0 ( s, 22), 135.7 ( s, 1 ), 131. 6 (s, 25), 128.3 (s, 10), 128.1 (s, 9 ), 127. 7 ( s, 4 ), 127. 6 (s, 2 ), 127. 4 ( s, 3 ), 127.0 (s, 11), 124.6 (s, 19), 12 4.4 ( s, 20), 12 4.1 ( s, 8 ), 123. 9 (s, 27), 123.6 (s, 28), 122.2 ( s, 5 ), 111.6 (s, 21), 111.5 (s, 29), 111.4 (s, 26), 110.5 (s, 18), 94.2 ( d, JRhC = 8.3 Hz, 35), 91.7 ( d, JRhC = 7.7 Hz, 39), 90.9 ( d, JRhC = 7.2 Hz, 34), 90.1 ( d, JRhC = 7.7 Hz, 38), 65.9 (s, 16), 62. 3 (s, 15), 49.2 (s, 13), 48.1 (s, 14 ), 39.6 (s, 24), 35. 7 (s, 32), 30. 9 (s, 37), 30.7 (s, 33), 30.6 (s, 40), 29.8 (s, 36). Numbering correlates to X ray Crystal structure (Figure 3 10) Anal. Calc. for C40H38N4IRh plus one molecule CH2Cl2: C, 55.36%; H, 4.53%; N, 6.30%. Found: C, 55.06%; H, 4.56%; N, 6.17%. The molecular structure of 3 -8 as determined by X ray crystallography is displayed in Figure 3 10, crystals were gro wn by diffusion of ether into a methylene chloride solution containing the compound The equilibrium geometry of 3 -8 as calculated by ground -state geometry optimization calculations using the hybrid density functional B3LYP156 with the LANL2DZ157160 basis set utilizing effective core potentials (ECP) for the core rhodium elect rons is displayed in Figure 3 11. All calculations reported in this manuscript wer e done using the Gaussian161 p rogram. 3 .2.9 Synthesis of R hodium(I) Trans 9,10 Dihydro 9,10 Ethanoanthracene 9,10 bis(1 Methylimidazolidine 2 Ylidene C yclooctadie ne I odide, [(DEA MY)Rh( COD)]I (3 -9 ) Diimidazolium salt 3 -3 (100 mg 0.16 mmol ) was suspended in 3 mL dry THF and stirred overnight. At 35C, KN(TMS)2 (61 mg 0.31 mmol) in 3 mL of dry THF was added dropwise to the salt suspension and allowed to stir at room temperature for 1.5 h. At -35 C a solution [Rh(COD)Cl]2 (40 mg 0.08 mmol) in 3 mL of dry THF was added dropwise to the salt suspension and allow ed to stir for 1.5 h. A precipitate formed that was filtered and washed with Et2O to afford 3 -9 as a yellow powder ; yield 99 mg (87%). 1H NMR ( 300 MHz, CDCl3) ppm: 8.23 (dd, J = 7.5, 1.0 Hz, H16 ), 7.84 (d, J = 1.7 Hz, NC H =CHN), 7.74 ( dd, J = 6.4 1.8 Hz CCHCH CHCHC ), 7.58 (dd, J = 6.4, 2.1 Hz, CCHCHC H CHC), 7.52 ( dd, J = 7.1 1.1 Hz,

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73 CCHCHCH CHC ), 7.46 (dd, J = 6.9, 1.0 Hz, CCHC H CHCHC), 7.11 7.39 (overlapping signals, 5 H, Ar and NCH=C H N), 6.96 (d, J = 2.0 Hz, NC H =CHN), 6.69 (d, J = 1.7 Hz, NC H =CHN), 5.17 (d, J = 1.1 Hz, NCHC H C), 4.87 (overlapping d and m, J = 0.6 Hz, NCHC H C and COD CH ), 4.15 (m, COD CH ), 4.03 (s, CH3), 3.73 (m, 2 COD CH ), 3.64 (s, CH3), 3.62 (dd, J = 1.4 Hz, 15), 2.44 2.66 (m, 1 COD CH2), 2.18 2.41 (m, 2 COD CH2), 1.98 2.17 (m, 1 CO D -CH2), 1.69 1.98 (m, 3COD -CH2), 1 .47 1.68 (m, 1COD -CH2). 13C NMR (75.3 MHz, CDCl3) ppm: 180.1 (1 C, d, JRhC = 54.7 Hz, N CN), 179.3 (1 C, d, JRhC = 52.7 Hz, N CN), 143.7 (C, Ar ), 142.6 (C, Ar ), 136.9 (C, Ar ), 136.1 (C, Ar ), 128.6 (C, Ar ), 127.8 (C, Ar ), 127.7 (C, Ar ), 127.4 (C, Ar ), 127.2 (C, Ar ), 126.9 (C, Ar ), 125.1 (C, Ar ), 125.0 (N CHCHN), 124.7 (NCH CHN), 123.7 (N CHCHN), 122.4 (C, Ar ), 115.9 (NCH CHN), 92.6 (d, JRhC = 8.6 Hz, COD CH), 88.3 (d, JRhC = 7.4 Hz, COD CH), 87.9 (d, JRhC = 8.3 Hz, COD CH), 85.8 (d, JRhC = 7.4 Hz, COD CH), 66.5 (s, CH CHN), 63.7 (s, CH CHN), 48.5 (s, C CHC), 47.7 (s, C CHC), 40.8 (s, N C H3), 37.5 (s, N CH3), 32.5 (s, COD CH2), 31.8 (s, COD CH2), 29.0 (s, COD CH2), 28.0 (s, COD -CH2). Anal. Calc. for C32H34N4IRh: C, 54.56%; H, 4.86%; N, 7.95%. Found: C, 54.47%; H, 4.72%; N, 8.25%. The molecular structure of 3 -9 as calculated by ground -state geometry optimization calculations using the hybrid density functional B3LYP156 with the LANL2DZ157 160 basis set utilizing effective core potentials (ECP) for the core rhodium electrons is displayed in Figure 3 12. 3.3 Results and Discussion 3.3.1 Constrained P recursors [DEA -MI](I)2 (3 -3 ) and [D EA -MBI](I)2 (3 -4 ) Synthesis of the constrained 9,10 dihydro9,10 -ethanoanthracene (DEA) ligands requires assembly of each azole onto the diamine 3 -1 S ynthesis of 3 -1 was achieved using three different procedures. Initially 3 -1 was synthesized from a di -carboxylic acid via a literature preparation reported by Trost et al.154 A similar procedure reported by Lennon et al.155 enabled the formation of 3 -1 via a multi -step one -pot synthesis beginning from anthracene. The initial

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74 step in this procedure is the formation of a diacid chloride T o avoid formation of a dicarboxilic acid by hydrolysis, the reaction procedure was slightly modified .162 Both ( R,R ) and ( S, S ) 3 -1 are available through resolution of diastereotopic salts formed from (S ) and ( R ) -mandelic acid, respectively.155 The enantiopurity of c hiral 3 -1 was tested by g as c hromatography ( Section 3.2.1 ) and found to be no less than 95% enantio p ure. T he synthesis of diimidazolium salt [DEA MI](I)2 (3 -3 ) was accomplished by adaptation of a known procedure for generating monoimidazoles (Figure 3 2) .163, 164 The procedure was found to form an equimolar mixture of the desired diimidazole 3 -2 and an imidazole amine. The products are separated and purified by repeated column chromatography. Subsequent formation of 3 -3 required alkylation of 3 -2 by heating with methyli odide in dry acetonitrile over two days. A 1H NMR spectrum of [DEA -MI](I)2 (3 -3 ) revealed a singlet at 3.82 ppm and is assigned to the methyl protons. The imidazolium proton (N CH N) is located downfield at 8.93 ppm and the olefinic protons of the heterocycle appear as a multiplet at 7.6 7 ppm and as a doublet of doublets at 6.60 ppm ( J = 1.5 Hz). Noteworthy in the 13C{1H} spectrum of 3 -3 is the imidazolium carbon (N CH N), which appears downfield at 136.8 ppm. Figure 3 3 illustrates the procedure used to synthesize the related dibenzimid azolium derivative The benzimidazole was constructed using a modified procedure for the conversion of a primary amine into the corresponding benzimidazole.143 Reaction of d iamine 3 -1 with two equivalents of 2 -fluoronitrobenzene in DMF followed by precipitation via water addition results in the formation of the brilliant orange dinitroamine Initially the dinitroamine was reduced with H2 (1 atm over Pd/C) to yield the tetraamine af ter seven d ays However, upon further investigation i t was determined that the reaction could be accomplished overnight at 40 bar H2 pressure.165 The reaction endpoint is signa led by dissipation of the brilliant yellow orange color

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75 of dinitroamine compound Cyclization to form the neutral dibenzyl imidazole was achieved by reaction of tetraamine with t riethylorthoformate T he dibenzimidazolium salt [DEA -MBI](I)2 (3 -4 ) was formed via reaction of the dibenzylimidazole103 with MeI in dry acetonitrile carried out in a sealed flask over two days The 1H NMR spectrum of 3 -4 revealed two singlets at 3.96 ppm and 8.85 ppm, which are assigned to the methyl and imida zolium (NC H N) protons, respectively. Consistent with Karplus theory,166 singlets manifest from adjacent p rotons on the bridge and bridgehead carbons (bridge = 5.16 ppm, bridgehead = 5.99 ppm) rather than doublets, due to a torsion angle of approximately 90. 3.3.2 Synthesis and Characterization of DEA -MbBY ( 3 -5 ) The first step in the formation of most NHC complexes is deprotonation of the imidazole precursor. Deprotonation of 3 -4 was accomplished by treatment with 2.1 equiv of KN( TMS )2 in THF ( Figure 3 4 ). U pon isolation, the deprotonated product was found to be enetetramine 3 -5 which was isolated in 40 % yield as a canary yellow solid. F ormation of these electron -rich olefins from benzimidazole or saturated im i dazole moieties is relatively common along with their subsequent utiliz ation as precursor s to bis NHC TM complexes .96, 120, 167 Both steric and electronic factors influence the relative stability of these dimers.168, 169 As discussed in C hapter 2, unsaturated imidazoles do not tend to dimerize although a rare example has been reported.170 The ability of saturated imidazoles and benzimidazoles to form dimers is correlated with a smaller HOMO -LUMO gap in these species relative to the unsaturated imidazoles.171, 172 The steric bulk of the exocyclic N -substituents plays a key role in d etermining the stability of saturated imidazol e and benzimidazole free carbene species.168 Small subst ituents result almost exclusively in enetetraamine formations for saturated imidazoles; however, unbridged benzimidazoles with small nitrogen substituents can display an observable equilibrium between the enetetraami ne and free carbene species.173 Resonances

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76 associated with a free carbene species are not observed i n either the 1H or 13C NMR spectra of 3 5 In the case of unbridged azoles entropy considerations are expected to favor the free carbene by as much as 10 kcal/mol.174 The much sma ller loss in entropy associated with intramolecular dimerization may be the reason an equilibrium between the two species is not observed. The mechanism by which carbenes dimerize has been investigated using both experimental and computational methods .174176 These reports suggest two mechanism s for intermolecular dimer formation. D irect carbene + carbene dimerization through a non least motion attack of the nucleophilic -orbital on the empty p-orbital of a neighboring carbene is possible when all proton sources are rigorous ly excluded from the system Proton -catalyzed dimerization is suggested for reactions in which any proton source is available. Nucleophilic attack of a free carbene on a neighboring imidazole followed by deproton ation typically by another carbene, has been found to be a lower -energy process in many cases. Since the free carbene species is never isolated for 3 -5 the proton -catalyzed mechanism is most likely responsible its formation The absence of an imidazolium proton resonance at 8.85 ppm in the 1H NMR spectrum of 3 -5 indicated that deprotonation was complete Conclusive evidence of the enetetramine formation was provide d by 13C{1H} NMR spectroscopy. Free NHC carbons resonate within the range of 205 to 245 ppm, whereas enetetramine carbons are shifted well upfield.96 The 13C{1H} NMR spectrum of 3 -5 revealed a distinct resonance at 122.8 ppm, and is assigned to the newly formed double bond (N2C=C N2). Further evidence for the formatio n of an enetetramine was gathered by single -crystal X ray diffrac tion that will be discussed in S ection 3.3.5 3.3.3 Synthesis and Characterization of [ -DEA-MY][Rh(NBD)I]2 (3 -6 ) and [ DEA MBY][Rh(COD)Cl]2 (3 -7 -COD) The bimetallic complexes [ DEA -MY][Rh(NBD)I]2 (3 -6 ) and [ DEAM Y][Rh(COD)Cl]2 (3 -7 -COD) were synthesized in THF by first treating 3 3 and 3 -4 with

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77 KN(TMS)2 to generate the corresponding enetetramine and free di NHC, respectively, followed by addition of metal substrate. The complexes were obtained a s mixtures with the corresponding mononuclear species which complicated analysis (Figure 3 5) The molecular structures of 3 -6 and 3 -7 -COD were confirmed by single -crystal X -ray crystallography and are presented in Figure s 3 8 and 39 3.3.4 Synthesis and Characterization of [(DEA -MBY)Rh(COD)]I (3 -8 ) and [(DEA MY)Rh(COD)]I ( 3 -9 ) Treatment of the dibenzimidazolium salt 3 -4 at 35 C, with 2.1 equiv. of KN(TMS)2 followed by 0.5 equiv. of [Rh(COD)Cl]2 in THF, resulted in precipitation of crystalline yellow 3 8 in 53% yield (Figure 3 6). The absolute assignment of each proton and carbon is accomplished by gDQCOSY gHMBC and NOESY two -dimensional NMR techniques. Similar to compound 2 -3 in solution th e chelated complex 3 -8 displays C1 symmetry. The low symmetry is demonstrated by nonequivalent methyl resonances observed at 4.46 ppm and 3.95 ppm. A distinct but unexpected doublet is observed downfield at 9.26 ppm ( J= 10 Hz). Using two dimensional NMR analysis this proton was assign ed to one of the aliphatic proton s on the bridge It is coupled to the other bridge proton that resonates upfield, at 4.36 ppm ( J= 10.2 Hz). In the 1H NMR spectrum of monometallic complex 2 -3 t he aliphatic bridge protons are also separated (by 3 ppm ) but the most downfield proton appears at 4.40 ppm The unusual position of the resonance at 9.26 ppm suggested that the bridge proton is in very close proximity to the rhodium center. The formati on of chelate species 3 -8 rather than a bridging 2:1 complex, does not conflict with the stud ies presented earlier that suggested a ligand with a two carbon linker should form a bridging species As stated previously, deprotonation of 3 -4 results in form ation of enetetramine 3 -5 thereby positioning the two heterocycle moieties in close proximity, akin to a

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78 transmetallation reagent. Lappert commonly utilized these electron rich olefins as NHC precursors.96 In Lapperts systems, i nsertion of a metal into the C=C bond required temperatures well above 100 C. The formation of complex 3 -8 at room temperature is due to the strain induced by the dihydroethanoanthracene backbone. It is also plausible that the conformation of the backbone promotes chelating species because it allows the azole rings to orient al ong the z axis of the metal. Synthesis of chelate 3 -9 from imidazolium salt 3 -3 is accomplished using the same procedure as described for 3 -8 Complex 3 -9 is obtained as a yellow powder in 87% yield. T he compound was characterized by 1H and 13C{1H} NMR spectroscopy. C1-symmetry is again evidenced clearly by nonequivalent methyl resonances at 4.03 ppm and 3.64 ppm. The downfield aliphatic proton in the bridge position resonates at 8.23 ppm, which is upfield relative to compound 3 -8 Presumably the rhodium ion rests farther away from the bridge proton in 3 -9 resulting in the upfield shift. This may be due to a more relaxed configuration created by the smaller imidazole heterocycles. Presumably, deprotonation of 3 -3 forms a free di NHC intermediate, un restrained except by the rigid ethanoanthracene backbone. Although the rigid backbone may play a significant role in chelate formation, a significant amount of bridging 2:1 compound should be formed. However, these results should not be interpreted as a contradiction to the investigations reported in the introduction but rather as supporting the need for thorough investigation of each new ligand system instead of attempting to generalize the findings of a specific investigation. 3. 3 5 X -ray A nalysis of DEA -MbBY ( 3 -5 ) The structure of racemic 3 -5 was confirmed by single -crystal X ray cryst allography and is presented in Figure 3 7 Two independent molecules possessing the same stereochemistry are

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79 found in the asymmetric unit and are related to the opposit e enantiomer via an inversion center. Only one molecule is presented in Figure 3 7, but the metric parameters are similar for all like species. For example, the C=C double bond for each independent molecule is 1.3426(19) and 1.3416(19) similar to th at observed previously for a derivative featuring a two -carbon expanded ring.120 All four nitrogen atoms are pyramidalized (C N Cavg = 116.07(13)), indicating significant loss of aromaticity, and representative of an sp3hybridized nitrogen. In viewing the molecule from the top ( Figure 3 7 -B) it is clear the methyl groups are bent out of the plane created by the four nitrogen atoms. The benzimidazole groups are nearly coplanar, separated by only 15 resulting in an incredibly small torsion angle N1 C16 C15 N3 of 76.6(1) 3. 3.6 X -ray Analysis of Bimetallic C omplexes [ -DEA -MY][Rh(NBD)I]2 (3 -6) and [ -DEA MBY][Rh(COD)Cl]2 (3 -7 -COD) Each bimetallic complex features a ligand that bridges two separate distorted square -planar rhodium centers via a Rh -carbene bond. The coordination spheres are completed by a halid e (Cl, 3 -7 ; or I, 3 -6 ) and a chelating diene (NBD, 3 -6 ; and COD, 3 -7 ). As expected, in 3 -6 the average bond distance between the Rh and alkene carbons opposite the Rh-NHC (d(Rh CtransNHC) = 2.2125(6) ) are elongated by 0.116(6) compared to those opposite the I (d(Rh CtransI) = 2.097(6) ). T he relatively small -donor strength of benzimida zolidynes versus imidazolidynes imparts a similar difference (0.109(6) ) in the Rh alkene bond in complex 3 -7 In fact, the average Rh NHC bond l engths between 3 -6 (d(Rh NHCavg = 2.018(4) ) and 3 -7 (d(Rh NHCavg = 2.007(3) ) differ only by 0.011(5) Unfortunately, the variations in trans influences of Cl versus I and NBD versus COD precludes a meaningful comparison. Within 3 -6 the rhodium iodide bonds are divergent and preserve the ligand C2-symmetry, whereas in 3 -7 the solid -state symmetry is broken by rotation of one RhCl bond inward. The

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80 inward rotation results in a 3.332 separation between Cl1 and the centroid of the he terocycle. Though packing forces cannot be ruled out, a beneficial interaction between the chloride lone Interestingly, the torsion angle N2 C15 C16 N4 for 3 -6 is 106.0(4) but the addition of s teric bulk on the azole backbone reduces the angle by 8 in 3 -7 (N1 -C16 C15 N3 = 98.3(2) ). 3.3.7 Structural Analysis of Monometallic Complexes [(DEA -MBY)Rh(COD)]I ( 3 -8 ) and [(DEA -MY)Rh(COD)]I (3 -9 ) Confirmation of the identity and orientation of 3 -8 is obtained with a single crystal X ray diffraction experiment. Figure 3 10 displays the solid-state structure of 3 -8 and selected bond leng ths and angles can be found in T able 3 4 The C1-symmetric complex is comprised of a slightly distorted square -p lanar Rh(I) ion chelated by COD and the di NHC. The asymmetric coordination is clear from the M carbene bond lengths of 2.033(4) and 2.051(5) for C23Rh1 and C31Rh, respectively. The constrained ligand forces a small bite angle between the NHC group s and the Rh (I) ion ( C23 Rh1 C31 = 84.14(17)). The most remarkable feature of the structure is that upon chelation, the benzimidazole rings force the torsion angle between N1 C15 C16 N3 to contract to a miniscule 68.8(5) In accordance with the 1H NMR resonance at 9.26 ppm for H16, a close Rh-C16 interaction is evident (d(Rh1 C16) = 3.033(4) ), though crystallographic data does not warrant the assignment of an agostic interaction. Instead, the rhodium center is fortuitously placed above H16 due to th e natural twist of the molecule. Unfortunately, a single crystal of X ray quality could not be obtained for 3 -9 To compare the two structures the aid of Jason Swails was enlisted to perform ground state geometry optimization calculations using the hyb rid density functional B3LYP156 with the LANL2DZ157160 basis set utilizing effective core potentials (ECP) for the core rhodium electrons. The crystal structure of 3 -8 was used as a sta rting point. Geometry optimization of this structure produced

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81 an almost identical structure (3 -8 -calc ) to that obtained by X ray c rys tallography. The root mean square deviation ( RMSD ) for the two structures was 0.168 meaning that the average difference between locations of the same atom is less than 0.2 Table 3 6 lists selected bond lengths and angles for the calculated 3 -8 -calc and X ray crystal structure 3 -8 The C31RhC23 is approximately a degree larger in the gas phase calculation and the torsion angle is extended by a little more than a degree. The aryl rings of the benzimidazole, C18 through C21 and C26 through C 29 were subsequently replaced by two imidazole protons to form structure 3 -9 The gas phase equilibrium geometry structure of 3 -9 is shown in Figure 3 11. Visual inspection (Figure 3 11) reveals little alteration relative to the structure calculated for 3 -8 ; howe ver, comparison of selected metric parameters shows di stinct architectural variations (Table 3 7 ). The two N C N angles of 3 -9 calc are two degrees smaller than in 3 -8 -calc which is also seen in comparison of the X ray structures for the bimetallic speci es. The reduced steric bulk on the back of the imidazole allows the chiral pocket to expand significantly. The distance from the Rh ion to the bridge proton H16 is approximately the same i n the two calculated structures. H owever, when the two structures are overlaid, a distinct increase in the tilt angle of the imidazoles can be seen relative to the tilt angle for the benzimidazole structure (Figure 3 12). The ethanoanthracene backbones (C1 C14) are aligned resulting in an RMSD of 0.0485 between the backbone atoms. The RMSD of the remaining atoms in common between the two molecules is 0.7870 Reducing the bulk on the back of the azole permits the rhodium center to shift up and away from the aryl backbone. The aryl ri ng of the backbone aids in the definition of the chiral pocket; therefore, the shift of the rhodium center away from the backbone increases the flexibility of the ligand and reduces the definition of the chiral pocket. Comparison of the distance from the bottom of the

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82 cyclooctadiene ring to the aryl ring below shows a more than 0.5 increase in the size of the chiral pocket for 3 -9 -calc relative to 3 -8 -calc The largest difference between the two structures is the 10 expansion of the torsion angle N1 -C1 5 C16 N3 for 3 -9 3.4 Conclusions This chapter presented the structural analysis of the mono and bimetallic Rh(I) complexes supported by the two secondgeneration C2 symmetric chelating di N heterocyclic carbene ligands based upon a trans ethanoanthracene backbone. The direct attachment of the NHC units to the DEA backbone reduced the size of the chiral pocket and increased the definition. A mixture of X ray diffrac tion data and computational ground state configurations allowed comparison of the two structures of the monometallic Rh(I) compounds, suggesting that the bulk of the benzimidazole actually serves to increase the definition of the chiral pocket. Figure 3 1. First and second generation ligand architectures.

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83 Figure 3 2. Synthesis of [DEA MI](I)2 (3 -3 ) F igure 3 3. Synthesis of [DEA MBI](I)2 (3 -4 ) Figure 3 4 Synthesis of DEA -MBY (3 -5 )

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84 Figure 3 5. Synthesis of binuclear compounds [ DEA-MY][Rh(NBD)I]2 ( 3 -6 ) and [ DEAMBY][Rh(COD)Cl]2 (3 -7 ) as mixtures with 3 -8 and 3 -9 Figure 3 6. Synthesis of r hodium monomer complexes [(DEA -MBY)Rh(COD)]I (3 -8 ) and [(DEA MY)Rh(COD)]I (3 -9 ).

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85 Figure 3 7 Molecular structure of 3 -5 from the sid e (left) and top (right) view. Ellipsoids are drawn at the 50% probability level. Figure 3 8 Molecular structure of compound 3 -6 Ellipsoids are drawn at the 50% probability level.

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86 Figure 3 9 Molecular structure of 3 -7 from side (left) and top (right) view. Ellipsoids are drawn at the 50% level Figure 3 10. Molecular Structure of 3 -8 from a Side on (Left) and Top View (right) Ellipsoids are drawn at the 50% probability level.

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87 Figure 3 11. Calculated equilibrium geometries of 3 -8 -calc and 3 -9 -calc Figure 3 12. Overlay of calculated structures 3 -8 -calc and 3 -9 -calc Comparison of the calculated structures 3 -8 -calc (orange) and 3 -9 -calc (blue) from the side (left) and top (right). The backbone has been deleted for clarity in the top view

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88 Table 3 1 Selected bond length () and angles ( ) for complex 3 -5 3 5 Bond lengths C25 C17 1.3426(19) N3 C25 1.4484(17) N4 C25 1.4264(17) N3 C26 1.4063(17) N1 C17 1.4211(17) N2 C17 1.4062(17) N1 C18 1.3903(17) C26 C31 1.4004(18) C23 C18 1.4112(18) Angles N1 C17 N2 106.56(11) N3 C31 N4 108.87(11) Torsion Angles N1 C16 -C15 N3 76.6(1) Table 3 2 Selected b ond length () and angles ( ) for complex 3 -6 3 6 Bond lengths Rh1 C23 2.016(4) Rh2 C19 2.020(4) N1 C19 1.347(5) N2 C19 1.356(5) N3 C23 1.350(5) N4 C23 1.362(5) C17 C18 1.332(6) C21 C22 1.332(6) Rh1 I1 2.6489(5) Rh2 I2 2.6562(5) Angles N1 C19 N2 104.3(3) N3 C23 N4 104.3(3) Torsion Angles N2 C15 C16 N4 106.0(4)

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89 Table 3 3 Selected bond lengt hs () and angles ( ) for complex 3 -7 3 7 Bond lengths Rh1 C17 2.012(2) Rh2 C25 2.002(2) N1 C17 1.374(3) N2 C17 1.353(3) N3 C25 1.365(3) N4 C25 1.358(3) C18 C23 1.398(3) C26 31 1.400(3) Rh1 Cl1 2.3828(6) Rh2 Cl2 2.3626(7) Angles N1 C17 N2 106.0(2) N3 C25 N4 106.2(2) Torsion Angles N1 C16 C15 N3 98.3(2) Table 3 4 Selected bond lengt hs () and angles ( ) for complex 3 -8 3 -8 Bond lengths Rh C23 2.033(4) Rh C31 2.051(5) N1 C23 1.365(5) N2 C23 1.375(5) N3 C31 1.370(5) N4 C31 1.347(5) C25 C30 1.376(6) C17 C22 1.397(6) Angles C23 Rh C31 84.14(17) N1 C23 N2 104.7(4) N3 C31 N4 105.9(4) Torsion Angles N1 C15 C16 N3 68.8(5) D istance Rh1 C16 3.033(4)

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90 Table 3 5 Comparison of measured and calculated bond lengths () and angles ( ) for 3 -8 3 -8 3 -8 -calc Distances Rh C31 2.051(5) Rh C31 2.052 Rh C23 2.033(4) Rh C23 2.068 N2 C24 1.461(5) N2 C24 1.468 N4 C32 1.467(5) N4 C32 1.466 N2 C23 1.375(5) N2 C23 1.384 N1 C23 1.365(5) N1 C23 1.395 N4 C31 1.347(5) N4 C31 1.372 N3 C31 1.370(5) N3 C31 1.391 C16 H16 1.001 C16 H16 1.097 H16 Rh 3.033(4) H16 Rh 2.298 C4 C36 3.831 C4 C36 4.238 Angles C31RhC23 84.14(17) C31RhC23 85.3 N1C23N2 104.7(4) N1C23N2 105.2 N3C31N4 105.9(4) N3C31N4 106 .0 Torsion Angle N1 C15 -C16 N 3 68.8(5) N1 C15 -C16 N 3 70.36 Distances Rh H16 3.033(4) Rh H16 2.298 Table 3 6 Comparison of bond lengths () and angles ( ) for calculated s tructures 3 -8 -calc and 3 -9 -calc Calculation 3 -8 -calc 3 -9 -calc Distances Rh C31 2.052 Rh C31 2.053 Rh C23 2.068 Rh C23 2.078 N2 C24 1.468 N2 C24 1.472 N4 C32 1.466 N4 C32 1.47 N2 C23 1.384 N2 C23 1.385 N1 C23 1.395 N1 C23 1.396 N4 C31 1.372 N4 C31 1.375 N3 C31 1.391 N3 C31 1.386 C16 H16 1.097 C16 H16 1.095 Angles C31RhC23 85.3 C31RhC23 87.1 N1C23N2 105.2 N1C23N2 103.6 N3C31N4 106 .0 N3C31N4 104.2 Torsion Angle N1 C15 C16 N 3 70.36 N1 C15 C16 N 3 80.64 Distances Rh H16 2.298 Rh H16 2.394 C36 C4 4.238 C36 C4 4.946

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91 CHAPTER 4 THIRD GENERATION CATALYSTS 4.1 Introduction Coupling experimental observation with computational analysis has become a vital tool in the application and optimization of catalytic species. Chapter 3 described the design and structural analysis of the constrained second -generation ligands. Using gas -p ha se ground state optimized geometry calculations it was determined that the steric bulk of the azole backbone plays a significant role in determining the chiral structure To further improve the catalyst design, the ligands reported in chapter 3 were subjected to architectural modifications (Figure 4 1) Through the slight variation of specific structural components a more thorough understanding of the relationship between ligand and catalyst structure is obtained. Independent alteration of the alkyl N -substituents and azole ring size is accomplished. Formation and structural analysis of C1 symmetric mononuclear rhodium species from the altered ligands is described. 4.2 Experimental Section 4.2.1 Synthesis of Trans -1,1 (9,10-Dihydro -9,10-Ethanoanthracene -11,12-D iyl) di (3 I sopropyl -1 H -Imidazol -3 -I um) D iiodide [DEA -iPrI](I)2 (4 -1 ) Diimidazole 3 -3 (2.34 g, 6.9 mmol) was dissolve d in dry MeCN (5 mL) in a sealable glass flask 2 iodopropane ( 2.8 mL, 4 equiv., 27 mmol) was added under argon and the flask was evacuated then sealed under vacuum. The flask was shielded from light and was heated in a sand bath at 105 C for 48 h. The mixture was cooled to room temperature and the precipitate was filtered and washed with cold MeCN to produce 4 -1 as a white solid; yield 1.99 g ( 43%). 1H NMR ( 300 MHz, (CD3)2SO ) ppm : 8.82 (s, 2 H, NC H N), 7.86 (t, J= 1.8 Hz, 2 H, NCHC H N), 7.64 (d, J= 7. 1 Hz, 2 H, Ar ), 7.19 7.42 (m, 6 H, Ar ), 6.78 (t, J= 1.8 Hz, 2 H, NC H CHN), 5.61 (s, 2 H, bridgehead H), 5.06 (s, 2 H, bridge H), 4.57 (spt, J= 6.5 Hz, 2 H, NC H CH3), 1.40 and 1.39

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92 (overlapping d, J= 6. 8 Hz, 6 H, NCHC H3). 13C NMR (75 MHz, ( CD3)2SO ) ppm : 139.3 (2 C, N CHCHN), 138.3 (s, 2 C, NCH CHN), 135.2 (s, 2 C, N CHN), 128.4 (s, 2 C, Ar ), 128.3 (s, 2 C, Ar ), 126.9 (s, 2 C, Ar ), 126.6 (s, 2 C, Ar ), 121.4 (s, 2 C, Ar ), 121.1 (s, 3 C, Ar ), 63.5 (s, 2 C, bridge C), 53.3 (s, 2 C, N CHCH3), 49.5 (s, 2 C, bridgehead C ), 22.9 (s, 2 C, NCH CH3), 22.7 (s, 2 C, NCH C H3). 4.2.2 Synthesis of Trans -1,1 -(9,10-Dihydro -9,10-Ethanoanthracene -11,12-Diyl)di(3 I so propyl -1H -Benzimidazol -3 -Ium) D iiodide [DEA -iPrBI](I)2 (4 -2) Dibenzimidazole103 (900 mg, 2 mmol) was dissolved in anhydrous MeC N (10.0 mL) in a sealable glass bomb flask. 2-iodopropane (0.82 mL, 4 equiv, 8 mmol) was added, and the vessel was evacuated and sealed. The flask was shielded from light and heated in a sand bath at 105 C for 48 h. The mixture was cooled to room tempe rature and the solid was filtered and washed with cold MeCN to afford 4 -2 as a light beige powder ; yield 430 mg ( 28% ). 1H NMR (300 MHz, (CD3)2SO ) ppm 8.50 (d, J= 8. 2 Hz, 2 H Ar ), 8.43 (s, 2 H NC H N ), 8.16 (d, J= 8.0 Hz, 2 H Ar ), 7.87 7.96 (m, 2 H Ar ), 7.68 7.86 (m, 4 H Ar ), 7.46 (t, J= 7. 5 Hz, 2 H Ar ), 7.24 (t, J= 7. 4 Hz, 2 H Ar ), 7.04 (d, J= 7. 5 Hz, 2 H Ar ), 6.21 (br. s., 2 H bridge H ), 5.13 (br. s., 2 H bridgehead H ), 5.02 (spt, J= 6. 6 Hz, 2 H NC H (CH3)2), 1.44 (d, J= 6. 6 Hz, 6 H NCHC H3), 1.37 (d, J= 6. 6 Hz, 6 H NCHC H3). 13C NMR (75 MHz, (CD3)2SO ) ppm : 138.7 (s, Ar ), 138.7 (s, N CHN), 138.2 (s, Ar ), 138.1 (s, Ar ), 131.7 (s, Ar ), 130.5 (s, Ar ), 128.7 (s Ar ), 128.4 (s, Ar ), 127.8 (s, Ar ), 127.6 (s, Ar ), 126.6 (s, Ar ), 115.6 (s, Ar ), 114.6 (s, Ar ), 61.8 (s, bridge C ), 51.3 (s, N CH(CH3)2), 48.7 (s, bridgehead C ), 22.5 (s, CH3), 22.0 (s, CH3). 4.2.3 Synthesis of N,N' -bis(4 -N itrotolyl) -9,10-Dihydro -9,10-Ethanoanthracene -11,12D iamine ( 4 3 ) To a solution of diamine 3 -1 (1.05 g, 4.5 mmol) in anhydrous DMF (10 mL) was added anhydrous K2CO3 (1.36 g, 2.2 equiv., 10 mmol) and 3-fluoro 4 nitrotoluene (1.45 g 2.1 equiv., 9

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93 mmol). The resulting bright orange mixture was heated at 65 C for 18 h. The mixture was cooled to roo m temperature and 50 mL of water was added. The resulting bright orange precipitate was isolated by filtration and washed with water producing 2.09 g of crude product (92% yield). Dinitro 4 -3 was purified by stirring in boiling EtOH (10 mL/g) for 30 min. After cooling to 0 C the orange solid was filtered and finally washed with cold EtOH ; yield 1.03g (45%). 1H NMR ( 300 MHz, CDCl3) ppm : 8.05 (d, J = 8.8 Hz, 2H, Ar ), 7.94 (d, J = 8.8 Hz, 2 H, N H ), 7.42 7.49 (m, 4H, Ar ), 7.28 7.34 (m, 4 H, Ar ), 6.50 (s, 2 H, Ar ), 6.42 6.49 (m, 2H, Ar ), 4.49 (d, J = 2.9 Hz, 2 H, bridge CH ), 3.7 5 3.84 (br m, 2H, bridge head CH ), 2.05 (s, 6C H3). 13C NMR (75 MHz, CDCl3) ppm : 147.9 (C, Ar ), 143.5 (C, Ar ), 139.7 (C, Ar ), 138.4 (C, Ar ), 127.4 (C, 2Ar), 126.9 (C, 2Ar), 1 26.1 (C, Ar ), 124.7 (C, Ar ), 117.7 (C, Ar ), 114.4 (C, Ar ), 61.3 (bridge CH ), 49.4 (bridge head CH ), 21.8 (CH3). HRMS (APCI TOF) calculated (found) for C30H26N4O4 (M+H)+ 507.2021 (507.2062). 4.2.4 Synthesis of N,N' -bis(4 Aminotolyl) -9,10-Dihydro -9,10-Ethanoanthracene -11,12D iamine ( 4 -4 ) Pd/C (10 wt%, 50% wet; 310 mg ) was added to a solution of dinitro 4 -3 (1.027 g, 27.2 mmol) in CH2Cl2 (25 mL) and MeOH (10 mL). The resulting mixture was stirred under H2 (40 atm) for 12 hr and then filtered through Celite to remove the Pd/C T he filtrate was concentrated to afford 4 -3 as a brown solid ; yield 900 mg (99%). 1H NMR (300 MHz, CDCl3) ppm : 7.30 7.42 (m, 4 H, Ar ), 7.15 7.26 (m, 4 H, Ar ), 6.62 6.75 (m, 4 H, Ar ), 6.52 6.62 (m, 2 H, Ar ), 4.44 (s, 2 H bridgehead C H ), 3.56 3.90 (br s, 6 H N H2/N H ), 3.53 (s, 2H, bridge C H ), 3.46 (s, MeOH), 2.26 (s, 6 H, C H3). 13C NMR (75 MHz, CDCl3) ppm : 141.6 (s, Ar ), 139.52 (s, Ar ), 135.7 (s, Ar ), 126.6 (s, Ar ), 126.3 (s, Ar ), 126.2 (s, Ar ), 124.4 (s, Ar ), 120.4 (s, Ar ), 117.5 (s, Ar ), 116.9 (m, Ar ), 116.9 (s, Ar ), 113.4 (s, Ar ) 62.1 (s, bridge C), 48.7 (s, bridgehead C), 21.0 (s, CH3). HRMS ( APCI TOF ) calculated (found) for C28H27N4 (M+H)+ 447.2543 (447.2557).

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94 4.2.5 Synthesis of Trans -1,1 (9,10-Dihydro -9,10-Ethanoanthracene -11,12-D iyl) di (1 H Tolyl imidazole) ( 4 -5 ) To a solution of tetraamine 4 -4 (900 mg, 2.02 mmol) in anhydrous HC(OEt)3 (30 mL) was added paratoluenesulfonic acid monohydrate (70 mg, 0.2 equiv., 0.40 mmol). The resulting mixture was stirred at room temperature for 48 h and then filtered. Hexane was added to the filtrate, resulting in precipitation of a pale yellow solid. The solid was filter ed and washed with hexanes to produce d i tolylimidazole 4 -5 ; yield 830 mg ( 79% ). 1H NMR (300 MHz, CDCl3) ppm : 7.59 (dd, J= 7. 6 4.40 Hz, 4H, Ar ), 7.33 7.42 (m, 2H, Ar ), 7.23 7.31 (m, 4H, Ar ), 7.18 (s, 2H, Ar ), 7.03 (dd, J= 8. 2 0.88 Hz, 2H, Ar ), 6.53 ( s, 2 H, NCN), 5.04 (s, 2 H, bridge H ), 4.66 (s, 2 H, bridgehead H ), 2.27 (s, 6 H, C H3). 13C NMR (75 MHz, CDCl3) ppm : 140.6 (s, Ar ), 138.6 (s, Ar ), 133.9 (s, Ar ), 128.9 (s, Ar ), 128.3 (s, Ar ), 128.3 (s, Ar ), 127.1 (s, Ar ), 126.2 (s, Ar ), 124.9 (s, Ar ), 124.7 (s, Ar ), 120.0 (s, Ar ), 109.4 (s, Ar ), 62.2 (s, bridge C), 50.2 50.9 (m, bridgehead C), 21.8 (s, CH3). HRMS (APCI TOF) calculated (found) for C30H23N4 (M+H)+ 467.2230 (467.2233). 4.2.6 Synthesis of Trans -1,1 -(9,10-Dihydro -9,10-Ethanoanthracene -11,12-D iyl) di (3 -M ethyl 1 H -Tolyli midazol -3 -Ium) D iiodide [DEA -MTI](I)2 (4 -6 ) Ditolylimidazole 4 -5 (530 mg, 1.14 mmol) was dissolved in anhydrous MeCN (5.0 mL) in a glass ampoule fitted with a seal able Teflon stopcock. MeI (0.290 m L, 4 equiv, 4.54 mmol) was added, and the vessel was evacuated and sealed. The flask was shielded from light and heated in a sand bath at 105 C for 48 h. The mixture was cooled to room temperature and the solid was filtered and washed with cold MeCN to afford 4 -6 as a light beige powder ; yield 500 mg (58%). 1H NMR (300 MHz, (CD3)2SO ) ppm : 8.80 (s, 2 H, N CH N), 7.86 (t, J= 8. 8 Hz, 4 H, Ar ), 7.42 7.55 (m, 4 H, Ar ), 7.13 7.34 (m, 6 H, Ar ), 5.86 (s, 2 H, bridgehead H), 5.12 (s, 2 H, bridge H), 3.91 (s, 6 H, N CH3), 2.45 (s, 6 H, Ar -CH3),. 13C NMR (75 MHz, (CD3)2SO ) ppm : 141.4 (s,

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95 N CHN), 139.74 (s, Ar ), 138.5 (s, Ar ), 137.59 (s, Ar ), 131.42 (s, Ar ), 130.47 (s, Ar ), 128.95 (s, Ar ), 128.60 (s, Ar ), 128.53 (s, Ar ), 127.30 (s, Ar ), 127.14 (s, Ar ), 114.19 (s, Ar ), 113.94 (s, Ar ), 62.06 (s, bridge C), 48.96 (s, bridgehead C), 34.19 (s, Ar CH3), 21.96 (s, CH3). 4.2.7 Synthesis of Trans -1,1 -(9,10-Dihydro -9,10-Ethanoanthracene -11,12-D iyl)di(3 I sopropyl -1H -Tolylimidazol -3 -Ium) D iiodide [DEA -iPrTI](I)2 (4 -7) Dito lylimidazole 4 -5 (420 mg, 0.9 mmol) was dissolved in anhydrous MeCN (5.0 mL) in a sealable glass flask 2 iodopropane (0. 360 mL, 4 equiv, 3.6 mmol) was added, and the vessel was evacuated and sealed. The flask was shielded from light and heated in a sand bath at 105 C for 48 h. The mixture was cooled to room temperature and the solvent was removed in vacuo. The crude solid was purified by f lash chromatography using 5% MeOH in CHCl3; yield 3 00 mg (40% ). 1H NMR (300 MHz, CDCl3) ppm : 9.64 (br. s, 2 H, NC H N), 9.16 (br. s., 2 H, Ar ), 8.21 (d, J= 7. 5 Hz, 2 H, Ar ), 7.32 7.58 (m, 8 H, Ar ), 7.17 (t, J= 7. 5 Hz, 2 H, Ar ), 6.81 (d, J= 7. 2 Hz, 2 H, Ar ), 6.75 (d, J= 1. 9 Hz, 2 H, bridge H), 4.96 (d, J= 2. 1 Hz, 2 H, bridgehead H), 4.90 (overlapping spt, J= 6. 7 Hz, 2 H, NC H (CH3)2), 1.65 (2 overlapping d, J= 6. 7 Hz, 12 H, NC H (CH3)2). 4.2.8 Synthesis of R hodium(I) T rans 9,10 Dihydro 9,10 Ethanoanthracene 9,10 bis(1 Isopropylimidazolidine 2 Y lidene ) C yclooctadien e I odide, [ (DEA iPrY )Rh( COD)]I (4 8 ) Diimidazolium salt 4 -1 (500 mg, 0.73 mmol ) was suspended in 5 mL dry THF and stirred overnight. At 105C, KN(TMS)2 (309 mg 1.5 mmol) in 3 mL of dry THF was added dropwise to the salt suspension and allowed to stir at room temperature for 1 h. At 105 C a solution of [Rh(COD)Cl]2 (182 mg 0.36 mmol) in 5 mL of dry THF was added dropwise to the salt suspension and allowed to stir overnight A precipitate formed that was filtered and washed with diethyl ether and extracted into CHCl3 to afford 4 -8 as a bright yellow powder ; yield 312 mg (56% ). 1H NMR (300 MHz, CDCl3) ppm : 8.30 (dd, J= 7. 8 1.32 Hz, 1 H bridge H ), 8.18 (t,

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96 J= 1. 0 Hz, 1 H Ar NC H CHN ), 7.82 7.89 (m, 1 H Ar ), 7.54 7.60 (m, 1 H Ar ), 7.50 (ddd, J= 6. 5 4.5 1.9 Hz, 2 H Ar ), 7.17 7.31 (m, 5 H NCHC H N overlapping Ar ), 6.97 (d, J= 2. 1 Hz, 1 H NCHC H N ), 6.79 (d, J= 2. 1 Hz, 1 H NC H CHN), 5.33 (d, J= 1. 5 Hz, 1 H bridg ehead H ), 5.31 (spt, J= 6. 8 Hz, 1 H, NC H (CH3)2), 4.86 (d, J= 1. 2 Hz, 1 H bridgehead H ), 4.70 (br. s., 1 H COD -CH ), 4.37 (spt, J= 6. 8 Hz, 1 H NC H (CH3)2), 4.19 (m, 1 H COD CH ), 3.69 (d, J= 6. 8 Hz, 1 H, bridge H), 3.60 (br. s., 2 H COD -CH ), 2.40 2.57 (m, 2 H COD CH2), 2.06 2.38 (m, 3 H COD -CH2), 1.88 2.06 (m, 2 H COD CH2), 1.72 ( m 1 H COD CH2), 1.49 (d, J= 6. 8 Hz, 3 H NCHC H3), 1.36 (d, J= 6. 8 Hz, 3 H NCHC H3), 1.26 (d, J= 6. 5 Hz, 3 H NCHC H3), 1.25 ( d J =6. 4 3 H NCHC H3). 13C NMR (75 MHz, CDCl3) ppm : 178.0 (d, JRhC =53.00 Hz, N CN), 177.8 (d, JRhC =53.00 Hz, N CN), 143.8 (s, CH CCH), 142.8 (s, CH CCH), 136.7 (s, CH CCH), 136.2 (s, CH CCH), 128.6 (s, C Ar ), 127.6 (s, C Ar ) 127.5 (s, C Ar ), 127.2 (s, C Ar ), 127.0 (s, C Ar ), 125.2 (s, C Ar ), 125.2 (s, C Ar ) 124.9 (s, C Ar omatic), 122.2 (s, N CHCHN), 119.0 (s, N CHCHN), 118.9 (s, N CHCHN), 116.7 (s, NCHCHN), 92.3 (d, JRhC =9.21 Hz, COD CH), 88.6 (d, JRhC =8.06 Hz, COD -CH), 87.5 (d, JRhC =8.06 Hz, COD CH), 85.3 (d, JRhC =7.20 Hz, COD CH), 66.3 (s, C H CHN), 63.3 (s, CH CHN), 54.9 (s, N CHCH3), 52.0 (s, N CHCH3), 48.2 (s, CCHC), 47.7 (s, C CHC), 31.8 (s, COD -CH2), 30.9 (s, COD -CH2), 29.5 (s, CODCH2), 29.1 (s, grease) 27.9 (s, COD CH2), 25.3 (s, CH3CH CH3), 23.9 (s, CH3CH C H3), 23.6 (s, CH3CH CH3), 22.4 (s, CH3CH CH3). 4.2.9 Synthesis of R hodium(I) T rans 9,10 Dihydro 9,10 Ethanoanthracene 9,10 bis(1 Isopropylbenzylimidazolidine 2 Y lidene ) C yclooctadien e I odide, [ (DEA iPrBY )Rh(COD)]I (4 -9) Diimidazolium salt 4 -2 (100 mg, 0.13 mmol ) was suspended in 3 mL dry THF and cooled to 100 C. KN(TMS)2 (54 mg, 0.27 mmol) in 3 mL of cold dry THF was then added dropwise to the salt suspension and allowed to warm to room temperature while stir ring The suspension

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97 turns bright yellow upon deprotonation. After 1 h the suspension is then cooled again to 100 C. A cold solution of [Rh(COD)Cl]2 (32 mg, 0.06 mmol) in 3 mL of dry THF was added dropwise to the salt suspension and allowed to stir overnight. A yellow precipitate formed that was filtered and washed with THF and diethyl ether to afford 4 -9 as a yellow powder ; yield 10 mg (10%). 1H NMR (300 MHz, CDCl3) ppm : 9.45 (d, J= 10. 3 Hz, 1 H bridge H ), 7.81 (d, J= 7. 0 Hz, 1 H Ar ), 7.75 (d, J= 7. 0 Hz, 1 H Ar ), 7.54 7.65 (m, 3 H Ar ), 7.13 7.54 (m, 9 H Ar ), 7.01 7.12 (m, 2 H Ar ), 6.22 (spt, J= 6. 7 Hz, 1 H overlapping NC H (CH3)2 with COD -CH ), 5.21 (s, 1 H bridgehead H ), 5.17 (s, 1 H bridgehead H ), 5.02 (spt, J= 6. 7 Hz, 2 H overlapping NC H (CH3)2 with COD CH ), 4.55 ( m, 1 H COD CH ), 4.43 (dd, J= 10. 1 1.0 Hz, 1 H b ridge H ), 4.13 (t, J= 6. 7 Hz, 1 H COD CH ), 3.64 3.78 (m, 1 H COD CH ), 2.69 2.90 (m, 1 H COD CH2), 2.51 2.66 (m, 1 H COD CH2), 2.26 2.51 (m, 3 H COD CH2), 1.92 (d, J= 6. 7 Hz, 3 H), 1.88 2.04 (overlapping m, 1 H), 1.61 (d, J= 7. 0 Hz, 3 H NCH(CH3)2), 1.55 1.65 (overlapping m, 2H, COD -CH2) 1.58 (d, J= 6. 7 Hz, 3 H NCH(C H3)2), 1.52 (d, J= 7. 0 Hz, 3 H NCH(CH3)2), 1.22 1.37 (m, 1 H NCH(CH3)2) 13C NMR (75 MHz, CDCl3) ppm : 191.7 (d, J= 54. 5 Hz, N CN), 190.8 (d, J= 51. 5 Hz, N CN), 146.9 (s, Ar ), 144.4 (s, Ar ), 138.7 (s, Ar ), 137.2 (s, Ar ), 135.9 (s, Ar ), 133.6 (s, Ar ), 133.19 (s, Ar ), 132.9 (s, Ar ), 128.3 (s, Ar ), 128.1 (s, Ar ), 127.8 (s, Ar ), 127.6 (s, Ar ), 127.4 (s, Ar ), 127.1 (s, Ar ), 124.2 (s, Ar ), 124.1 (s, Ar ), 124.0 (s, Ar ), 123.7 (s, Ar ), 123.1 (s, Ar ), 122.1 (s, Ar ), 113.2 (s, Ar ), 113.0 (s, Ar ), 112.1 (s, Ar ), 111.2 (s, Ar ), 94.2 (d, J= 8. 6 Hz, COD -CH), 91.9 (d, J= 8. 1 Hz, COD CH), 89.9 (d, J= 7. 2 Hz, COD -CH), 89.5 (d, J= 6. 6 Hz, COD -CH), 65.3 (s, CH C HN), 62.3 (s, CH CHN), 57.8 (s, N CHCH3), 53.9 (s, N CHCH3), 49.1 (s CCHC ), 47.9 (s C CHC ), 32.0 (s COD -CH2), 31.79(s COD CH2), 29.4 (s COD -CH2), 28.7 (s COD -CH2), 22.6 (s, NCH CH3), 22.5 (s, NCH CH3), 21.8 (s, NCHC H3), 21.5 (s, NCH CH3).

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98 4.2.10 Synthesis of R hodium(I) T rans 9,10 Dihydro 9,10 Ethanoanthracene 9,10 bis(1 M e thyltolylimidazolidine 2 Y lidene ) C yclooctadien e I odide, [ (DEA MTY )Rh( COD)]I (4 -10) Di imidazolium salt 4 -6 (500 mg 0.66 mmol) was suspended in 5 ml THF and stirred overnight. At 35C, KN(TMS)2 (279 mg 1.4 mmol) in 5 mL THF was added dropwise to the salt suspension and allowed to warm to room temperature and stir for 1 h. After cooling the solution to 35 C, [Rh(COD)Cl]2 (164 mg 0.33 mmol ) in 3 mL THF was then added dropwise to the reaction and allow ed to stir for 1 h at room temperature. The reaction mixture was allowed to stir at room temperature overnight and the resulting solid was filtered, washed with Et2O and extracted with CHCl3 to provide [(DEA MTY)Rh(COD)]I 4 -10 as a dark yellow powder (113 mg, 20%) 1H NMR (300 MHz, CDCl3) ppm : 9.06 (d, J= 9.9 Hz, 1 H CHC H N), 7.74 (dd, J= 7. 0 1.2 Hz, 1 H, Ar ), 7.64 (dd, J= 7.0 1.2 Hz, 1 H, Ar ), 7.56 (d, J= 7. 0 Hz, 1 H, Ar ), 7.33 7.47 (m, 3 H Ar ), 7.03 7.32 (m, 7 H Ar ), 6.89 (d, J= 8. 5 Hz, 1 H Ar ), 6.68 (s, 1 H), 5. 1 (s, 1H, CC H C) 5. 0 8 ( s 1 H CC H C), 4.90 5.04 (m, 1 H COD -CH ), 4.39 4.50 (m, 1 H COD CH ), 4.29 (s, 3 H NC H3), 4.22 (dd, J= 10., 0.80 Hz, 1 H CHCH N ), 4.10 4.19 (m, 1 H COD CH ), 3.76 (s, 3 H NC H3), 3.73 ( m 1 H COD CH ), 2.46 (s, 3 H tolyl -CH3), 2.53 ( m, 2 H COD CH2), 2.14 (s, 4 H COD CH2), 2.14 (s, 3 H, tolyl C H3), 1.55 1.72 (m, 1 H COD CH2), 1.14 1.33 (m, 1 H COD -CH2). 13C NMR (75 MHz, CDCl3) ppm : 192.9 (d, JRhC =52.00 Hz, NCN), 190.8 (d, JRhC =52.00 Hz, NCN), 146.7 (Ar), 144.46 (Ar), 138.8 (Ar), 136.2 (Ar), 135.8 (Ar), 134.9 (Ar), 134.4 (Ar), 134.3 (Ar), 134.1 (Ar), 131.7 (Ar), 128.8 (Ar), 128.1 (Ar), 128.0 (Ar), 127.7 (Ar), 127 .4 (Ar), 127.2 (Ar), 125.7 (Ar), 124.5 (Ar), 124.1 (Ar), 122.2 (Ar), 111.8 (N CCH), 111.1 (N CCH), 110.8 (N CCH), 110.7 (N CCH), 94.1 (d, JRhC =8.06 Hz COD CH), 91.0 (d, JRhC =8.06 Hz COD CH), 90.5 (d, JRhC =6.91 Hz, COD CH), 89.9 (d, JRhC =7.49 Hz, COD -CH), 65.8 (s, CH C HN), 62.2 (s, CH CHN), 49.1 (s, C CHC), 48.0 (s, C CHC), 39.3 (s,

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99 N CH3), 35.3 (s, N CH3), 30.9 (s, COD CH2), 30.7 (s, COD CH2), 29.8 (s, COD C H2), 28.2 (s, COD -CH2), 22.1 (s, tolyl C H3), 21.5 (s, tolyl CH3) 4 3 Results and Discussion 4.3.1 Synthesis and Characterization of [DEA -iPrI] (I )2 (4 -1) and [(DEA iPrY)Rh( COD)]I (4 -8 ) The synthesis of [DEA-iPrI] (I)2 (4 -1) and [(DEA iPrY)Rh(COD )]I (4 -8 ) mirror that reported for the methyl imidazole derivatives 3 -3 and 3 -9 (Figure 4 2) as does their solution state analysis 1H NMR spectra for imidazolium salts 4 -1 and 3 -3 are nearly identical, a slight downfield shift of the imidazole protons (from 7.68 and 6.60 ppm for 3 -3 to 7.86 and 6.78 ppm for 4 -1 ) and an upfield shift of the imidazole (NC H N) proton from 8.93 for 3 -3 to 8.82 in 4 -1 di splays the slight variation between the two co mpounds R eplacement of the methyl substituents with an isopropyl group introduces a septet at 4.57 ppm (spt, J= 6. 5 Hz) and overlapping doublets at 1.40 and 1.39 ppm (d, J=J=6. 8 Hz). Metallation of 4 -1 utilizing a single equivalent of rhodium produces the expected mononuclear C1 symmetric complex 4 -8 Increas ing the steric bulk of the N -subs tituents is not expected to alter the twist of the molecule but could affect the position of the rhodium center relative to the ligand backbone. T herefore it is not surprising that the 1H NMR spectra for 4 -8 displays a doublet of doublet s resonance corresponding to the H16 bridge proton at 8.30 ppm (J= 7. 8 1.3 Hz) shifted slightly downfield relative to the H16 resonance in 3 -9 [8.23 ppm (dd, J = 7.5, 1.0 Hz)] but with a similar coupling pattern. The C1 symmetry of the molecule is displayed clearly by the multiple isopropyl resona nces, two septets at 5.31 ( J= 6.8 Hz ) and 4.37 ppm (J= 6.8 Hz ) as well as four sets of doublets at 1.49 ( J= 6.7 Hz), 1. 36 ( J= 6.7 Hz), 1.26 ( J= 6. 5 Hz), and 1.25 ppm ( J =6. 4 Hz)

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100 The yields associated with the bulkier compounds (4 -1 and 4 -8 ) are noticeably lower than for their methyl analogs (3 -3 and 3 -9 ). T he decreased production of monomeric complex 4 -8 could be the result of the nitrogen substituents increased steric bulk As discussed in chapter 3, chelation to a single metal center is facilitated by the ability of the bulky imidazole plane to orient along the less crowded z -axis of the complex. This orientation, although favorable for chelation, places the nitrogen substituent s in close proximity to one another The distance between the alkyls is irrelevant for small substituents like methyl ; however, the significant increase in steric bulk associat ed with replacing the methyl of 3 -8 or 3 -9 with an isopropyl substituent may increase the barrier to product formation 4.3.2 Synthesis and Characterization of [DEA -iPrBY] (I )2 (4 -2), [ DEA MTY](I )2 (4 -6), [DEA -iPrTY ](I )2 (4 -7) and the Corresponding Monome tallic Rhodium Complexes [(DEA iPrBY )Rh( COD)]I (4 -9) and [ (DEA MTY )Rh( COD)]I (4 -10) A lterations to the N -substituents and azole rings of the original benzimidazole structure ( 3 4 ) were accomplished based on convention and combined computational and experimental results. Convention, regarding N -heterocyclic carbenes, holds that the steric bulk around the metal center is modulated almost exclusively by altering the size of the Nsu bstituents. Experimental and computational data reported in chapter 3 suggests that for this ligand family, the size of the imidazole also plays a significant role in defining the chiral pocket. Taking this into account three modified ligand structures were prepared Substitution of the methyl Nsubstituent of 3 -4 for the bulkier isopropyl substituents results in the formation of l igand 4 -2 (Figure 4 3) Addition of steric bulk to the benzimidazole by placing a methyl group in the meta -position forms 4 -6 (Figure 4 4) and ligand 4 -7 contains both architectural variations (Figure 4 5) The 1H NMR spectrum of salt 4 -2 reveals a modification to the typical imidazolium salt spectra. All of the previously reported salts contain imidazolium proton s (NCH N) th at resonate

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101 well downfield of the aryl region (9.7 0 ppm for 2 -1 8.93ppm for 3 -3 8.85 for 3 -4 and 8.30 ppm for 4 -1 ) whereas the singlet imidazolium resonance of 4 -2 appears at 8.43 ppm, upfield of an aryl resonance (8.50 ppm (d, J= 8. 2 Hz) ). Comparison of all the imidazolium proton resonances suggest s increasing the size of the N -substituent or azole ring shifts the corresponding resonance upfield. The opposite affect is seen for the bridge proton H16 in the monometallic benzimidazole struct ure s Investigation of the resulting monometallic complex 4 -9 (Figure 4 6) again displays the diagnostic downfield resonance at 9.45 ppm (d, J= 7. 0 ) which is shifted downfield by 0.2 ppm compared to 3 -8 This suggests the rhodium center may be forced clo ser to the proton by the addition of the isopropyl substituents. Furthermore, the monometallic complex 4 -9 was formed in only 10% yield, supporting the claim that increased bulk on the nitrogen substituents hinders chelation. Crude spectra of the reactio n mixture subsequent to product isolation displayed peaks corresponding to a C2 symmetric bimetallic complex implying that the increase in steric bulk may shift the kinetically favored product toward the bimetallic complex The bimetallic complex was not pursued further though its isolation is plausible L igand 4 -6 w as synthesized using a similar protocol as for 3 -4 (Figure 4 4) Diamine 3 -1 was treated with 2.1 equivalents of 3 -fluoro 4 -nitrotoluene in DMF over 18 h at 65 C to form the sticky orange dinitro -diamine compound 4 -3 After purification of 4 -3 the compound was hydrogenated overnight using 40 bar H2 pressure and Pd/C to afford the tetraamine 4 -4 Cyclization was achieved by treating 4 -4 with triethylorthoformat e over a two day period. Ditolylimidazole 4 -5 was then combined with MeI at 105 C in a seal flask to produce the methylated ditolylimidazole salt 4 -6 A 1H NMR spectrum of 4 -6 reveals a broad singlet for the imidazol ium proton at 8.80 ppm which suggests very little alteration in the ligand relative to 3 -4 (imidazolium proton appears at 8.85 ppm) In fact, the only substantial variation in the 1H NMR

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102 spectrum of [DEA -MTI](I)2 (4 -6 ) relative to [DEA -MBI](I)2 (3 -4) is an addition al methyl resonance at 2.45 ppm corresponding to the methyl substituents on the ary l ring of the benzimidazole Solution state analysis of the corresponding monometallic rhodium compound 4 10 (Figure 4 7) again nearly matches that shown for 3 -8 except for t wo addition al m ethyl resonances due to C1 symmetry. During the preparation of ligand 4 -6 and the resulting monometallic complex 4 -10, a ground state geometry optimization calculation was performed by adding the methyl substituent to the benzimidazole of the crystal structure of 3 -8 as a starting point Figure 4 8 displays the calculated structure of 4 -10. Table 4 1 compares selected metric parameters for complexes 3 -8 calc and 4 -10-calc and Figure 4 9 displays an overlay of the two structures, showing that the complexes are nearly identical excluding the addition of the methyl group. The choice to position the methyl group at the meta -position was influenced by the structure of 3 -8 In the constrained monometallic complex, o ne of the benzylimidazoles sit s directly above the ethanoanthracene backbone at a distance of approximately 3.5 Addition of a substituent at the orthoposition would likely come in very close proximity to the backbone thereby hindering the formation of monometallic complexes and promoting the formation of the les s desirable bimetallic complex Ligand 4 -7 combines both architectural alterations to include isopropyl Nsubstituent s and methyl group s on the back of the benzimidazole Only the chiral version of the salt (R,R) 4 -7 was synthesized producing a meager 300 mg The chiral salt is sparingly soluble in CDCl3. T herefore to retain the valuable imidazolium salt CDCl3 was utilized as the NMR solvent to facilitate reisolation of ( R,R ) 4 -7 which is difficult from (CD3)2SO This precludes direct comparison w ith the other imidazolium salt 1H NMR spectra which were all obtained in

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103 (CD3)2SO. However, the imidazolium salt resonances are clearly present in the 1H NMR spectrum. The diagnostic broad imidazolium resonance is dis played at 9.64 ppm and t he aryl protons span a relatively large range from 7.17 to 9.16 ppm. The bridge and bridgehead protons both resonate as doublets at 6.75 ( J= 1. 9 Hz) and 4.96 ppm ( J= 2. 1 Hz) respectively. The isopropyl methine septet overlaps sligh tly with the bridgehead proton at 4.90 ppm ( J= 6. 7 Hz) and is coupled to the isopropyl groups which appear at 1.6 ppm (J= J= 6. 7 Hz). Attempts to form the rhodium monomeric compound were unsuccessful. [Rh(COD)Cl]2 was initially utilized as the rhodium source to maintain similar structures throughout the family of Rh complexes. W hen initial synthesis of the monomer failed, substitution of the dimeric rhodium starting material with the monomeric cationic rhodium source, Rh(NBD)2BF4, was attempted Howe ver, isolation of monomeric compound was unsucce ssful and investigation of the crude reaction mixture by solution state analysis revealed no sign of a monomeric species. Formation of a monomeric complex from ligand 4 -7 should be thermodynamically feasible c onsidering the similarity of the equilibrium geometries for 3 -8 and 4 -10 and the formation of the isopropyl substituted complex 4 -9 4.4 Conclusions The four new ligand s described in this chapter present alterations to the architectures of 3 -3 and 3 -4 to increase the definition of the chiral pocket Ligands 4 -1 and 4 -2 represent an increase in the Nsubstituents size The reduced yields associated with synthesizing the corresponding monometallic complexes 4 -8 and 4 -9 are likely the result of negative steric interaction s between the isopropyl Nsubstituents. Increasing the size of the substituents on the imidazole by placing a methyl group in the meta -position does not appear to alter the calculated equilibrium geometry of the resulting metal complex but combining the two alterations precludes the formation of a monometallic rhodium complex.

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104 Figure 4 1. Generations of ligands to date. Figure 4 2. Synthesis of ligand [DEA -iPrI](I)2 4 -1 (top) and [(DEA -iPr Y)Rh(COD)]I 4 -8 (bottom).

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105 Figure 4 3. Synthesis of ligand [DEA -iPrBI](I)2 4 -2 Figure 4 4. Synthesis of ligand [DEA -MTI](I)2 4 -6 Figure 4 5. Synthesis of ligand [DEA -iPrTI](I)2 4 -7

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106 Figure 4 6 Synthesis of [(DEA iPr BY)Rh(COD)]I 4 -9 Figure 4 7 Synthesis of [(DEA M T Y)Rh(COD)]I 4 -10. Figure 4 8. Calculated structure for [(DEA -M T Y)Rh(COD)]I 4 -10.

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107 Figure 4 9. Overlay of the calculated structure [(DEA M BY)Rh(COD)]I 3 -8 -calc and [(DEA M T Y)Rh(COD)]I 4 -10-calc The side view (left) displays the similarity of the two structures as does the top -view (right) with the backbone removed for clarity. Table 4 1. Selected bond lengths () and angle ( ) for calculated structures 3 -8 -calc and 4 -10calc 3 -8 -calc 4 -10-calc Distances Rh C31 2.052 Rh C31 2.054 Rh C23 2.068 Rh C23 2.07 N2 C24 1.468 N2 C24 1.468 N4 C32 1.466 N4 C32 1.466 N2 C23 1.384 N2 C23 1.383 N1 C23 1.395 N1 C23 1.394 N4 C31 1.372 N4 C31 1.371 N3 C31 1.391 N3 C31 1.392 C16 H16 1.097 C16 H16 1.096 Angles C31RhC23 85.3 C31RhC23 85.3 N1C23N2 105.2 N1C23N2 105.2 N3C31N4 106.0 N3C31N4 105.9 Torsion Angle N1 C15 C16 N3 70.36 N1 C15 C16 N3 70.34 Distances Rh H16 2.298 Rh H16 2.295 C36 C4 4.238 C36 C4 4.226

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108 CHAPTER 5 ASYMMETRIC CONJUGATE ADDITION 5.1 Introduction Solution and solid state structural analysis are important method s in characterizing and optimizing catalyst architectures. However, in the design and optimization of a catalyst species, the most valuable information is gained from catalytic application. As discussed in chapter 2, initial catalytic trials revealed that first generation complexes were susceptible to degradation under certain catalytic conditions. These results suggest that our catalysts degrade via C -H reductive elimination involving a Rh H species. Therefore, a catalytic application that does not invo lve Rh H formation should prohibit degradation and allow the enantioselectivity of the catalysts to be investigated. To test the capabilities of the constrained Rh(I) mononuclear complexes they were applied to the well -established asymmetric conjugate ad dition of boronic acids to cyclic enones Asymmetric conjugate addition of organometallic reagents to electron deficient olefins is an important method for enantioselective carbon -carbon bond formation.177 Although a variety of transition metals have been applied to conjugate addition,178181 c opper and rhodium based catalysts have been the most thoroughly investigated. The first a symmetric copper based addition was reported in 1988 by Lippard.182 Chiral a minotroponeimine ligands were used in the copper catalyzed reaction between 2 -cyclohexe n 1 one and alkyllithium reagents producing a maximum e.e. of 14%. Subsequent to this report many research groups endeavored to improve the enantioselectivity and catalytic activity of this reaction, typically using dialkyl zinc reagents and cyclic enones.28 A breakthrough in the late 1990s revealed p hosphoramidites as highly enantioselective ligands when applied to the copper catalyzed addition of alkylzinc to 2 -

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109 cyclohexen1 one.183 Since this report, a variety of different ligand architectures have been found to be highly enantioselective toward this reaction .28, 184 187 Copper based catalysts are typically utilized at low temperatures ( often well below 0 C)28 to introduce alkyl group s via an organozinc reagent R hodium catalysts on the other hand, can be used at ambient to high (above 100 C) temperature s with a wide variety of organometallic reagents ,188195 to introduce alkenyl or aryl substituents. A ryl stannanes ,188191, 112 arylsilicon,192 113 aryltitanium,193, 194, 114 and alkenylzirconium195, 115 reagents h ave been used as transmetallating reagents in 1,4addition reactions However, the commercial availability and stability of boronic acids have made them the most popular choice .196, 197 The first rhodium catalyzed 1,4-conjugate addition of aryl and alkenylboronic acids to enones was reported by Miyaura in 1997.198 In this communication, the authors focused on acyclic enones with no reported e.e. measurements. Rh(acac)(CO)2/dppb (dppb = d iphenylphos phino butane ) was used as the precatalyst and the reaction proceeded at 50 C in aqueous solvents with modest yields. A year later, the same authors reported a chiral application using the bis -phosphine ligand ( S ) BINAP as the chiral auxiliary.199 Although two acyclic enones were investigated, the focus of the paper was addition to 2 -cyclohexen1 -one. To achieve high yields and chiral induction it was necessary for the authors to increase the rea ction temperature to 100 C. Mechanistic investigation200 of this system revealed transmetallation of the aryl group from boronic acid to rhodium as the initial catalytic step Transmetallation occurs via a four centered transition states shown in Figure 5 1 .201 Addition of base is important when utilizing a rhodium catalyst containing a halogen ligand T he boronic acid is quaternized by the base increasing the nucleophilicity of the aryl group and facilitating transmetallation. Non -halogenated catalyst s are

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110 typically activated by reaction with protonated solvent s forming a Rh OH or Rh OMe complex depending on the solvent mixture Under these conditions, base is not strictly required but does have a strong accelerating effect.201 Kinetic studies by Hayashi et al.202 on the Rh BINAP sy stem revealed transmetallation a s the rate limiting step (rls) These studies also uncovered the formation of a homochiral dimer that is inactive towards catalysis, but it s position prior to the rl s means that th e equilibrium constant between monomer and dimer can influence the overall rate of the reaction. The reaction was found to be first order overall and half -order in catalyst. Interestingly, Hayashi also discovered a negative nonlinear effect between the enantiop urity of the ligand and the e.e. of the product. Subs equent to transmetallation, transient coordination of the enone to the metal center is followed by insertion of the enone into the rhodium aryl bond In asymmetric reactions, the products stereochemistry is determined by this diastereo meric transition state .28 When ( S ) BINAP is used as the chiral control the ( S )-product is formed suggesting approach of the enone from its 2 si face. Insertion of the enone forms a n oxa allylrhodium species which is then hydrolyzed yielding the product and the catalytically active L*Rh OH species In the initial mechanistic studies, NMR experiments revealed that all of the individual step s could be accomplished at 25 C.200 H owever, catalytic reactions starting from Rh(acac)(binap) required temperatures well above 60 The tightly bound acetylacetonato (acac) ligand was found responsible for the high temperature requirement T emperature and time requirements were drastically reduced w hen the acac ligand was replaced with a hydroxyl (OH) group.

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111 Rhodium 1,4 addition of boronic acids to cyclic enones has become a benchmark reaction for a variety of ligands to test their capability towards asymmetric induction.203210 Utilization of NHC ligands is fairly rare in rhodium catalyzed conjugate additions Monode ntate paracyclophane -substituted NHCs reported by Andrus et al.211, 212 were found to provide high yields and asymmetric induction utilizing 2 mol% [Rh(acac )(C2H4)2] at 60 C in THF/wa ter. The best e.e. was produced by the paracyclophane with a bulky ortho -methoxyphenyl substituent. Moderate to high enantioselectivities have also been achieved using a bidentate diphenylphosphinoNHC rhodium complex synthesized by Helmchen and coworkers.213 Recently, Douthwaite et al. reported the synthesis of a rhodium catalyst supported by a chiral NHC -phenoxyimine ligand.214 The complex was found to be active towards conjugate addition but with no enantioselectivity. NHCs have found more extensive application in copper215217 based 1,4 addition to enones. T he first asymmetric copper conjugate additions utilizing NHCs were reported by Alexakis215 and Roland216 in 2001. Eac h reported similar C2 symmetric saturated imidazole ligands in the addition of diethylzinc to 2 -cyclohexen 1 one mediated by Cu(OTf)2 with a maximum e.e. of 50% reported by Alexakis. S everal groups have reported fair e.e.s ranging from the 27% initially reported by Roland to 93% reported by Alexakis218 and Mauduit .219 The Hoveyda group -substituted cyclic enones catalyzed in situ using a chiral silver NHC and Cu(OTf)2.220, 221 The addition produced quaternary stereogenic centers with yields ranging from 67 98% and e.e. s as high as 97%. In comparison to the prolific success of rhodium and copper catalyzed conjugat e additions, p alladium catalyzed 1,4 additions are uncommon .222226 Recently, Min Shi reported the first palladium(II) cata lyzed 1,4 addition using a chelating bis NHC ligand.113 The bis NHC ligand is

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112 based on the privileged binaphthalene backbone introduced in chapter 2 Using 3 mol% catalyst at room temperature over 36 h, the reaction provided yields as high as 99% and e.e. s ran ging from 32% for the addition of phenylboronic acid to cyclopentenone to 97% for the addition of 2 naphthylboronic acid to 2 cyclohexen1 -one. Taking into account the benchmark success of rhodium catalyzed asymmetric 1,4 addition of aryl boronic acids and Min Shis report of successful application of a chelating bis NHC complex this reaction appeared to be an ideal test fo r our ligand system. The importance of this application does not reside in its novelty but rather in its utilization as a tool to measure the chiral induction ability of this novel ligand design. 5.2 Experimental Section 5 .2.1 General Catalytic Procedure Under inert atmosphere, [L*Rh (COD)]X (16 mol 1.5mol%), a ryl boronic acid (1 .5 mmol ), and KOH (0.5 mmol ) were combined with 2 mL of dry 1,4 -dioxane in a sealable flask Under positive argon flow, enone (1 mmol ) and degassed methanol (0.5 mL) were added to the flask. The flask was sealed and heated with stirrin g until the reaction was complete. The substrate was purified by column chromat ography on silica gel with 9:1 h exanes:Et2O as the mobile phase. The e.e. of the resulting cyclic ketone was determined using HPLC analysis. 5.2.2 3-P henylcyclohexanone (5 -1 ) Colorless oi l; p urified by column chromatography, eluent h exanes / Et2O 9:1. Chiral HPLC: Chiralcel IA column (hexanes/2 propanol, 98:2, 0.4 mL/min); tR: 20.38 min ( S )227, 23.28 min (R ). 1H NMR (300 MHz, CDCl3) ppm : 7.28 7.38 (m, 2 H), 7.18 7.27 (m, 3 H), 2.94 3.08 (m, 1 H), 2.30 2.65 (m, 4 H), 2.03 2.20 (m, 2 H), 1.72 1.94 (m, 2 H). 13C NMR (75 MHz,

PAGE 113

113 CDCl3) ppm : 210.8 (s), 144.2 (s), 128.5 (s), 126.5 (s), 126.4 (s), 48.8 (s), 44.6 (s), 41. 1 (s), 32.6 (s), 25 .4 (s). 5.2.3 3-(2 -Methylphenyl) -C yclohexanone (5 -2 ) Colorless oil; p urified by column chromatography, eluent hexanes/ Et2O 9:1. Chiral HPLC: Chiralpak IA column (hexanes/2 -propanol, 98:2, 0.4 mL/min); tR: 16.708 min ( R )227, 19.708 min (S ). 1H NMR (300 MHz, CDCl3) ppm : 7.21 7.28 (m, 2 H), 7.11 7.20 (m, 2 H), 3.15 3.29 (m, 1 H), 2.39 2.57 (m, 4 H), 2.33 (s, 3 H), 2.18 (s, 1 H), 1.99 (br. s., 1 H), 1.75 1.93 (m, 2 H) 13C NMR (75 MHz, CDCl3) ppm : 211.4 (s), 142.5 (s), 135.3 (s, 3 C), 130.9 (s), 126. 7 (s), 126.6 (s), 125.2 (s), 48.6 (s), 41.5 (s), 40.5 (s), 32.2 (s), 26.0 (s), 19.5 (s). 5.2.4 3 -(1 -Naphthalenyl) -C yclohexanone (5 -3 ) White solid ; purified by column chromatography, eluent hexanes/ Et2O 9:1. Chiral HPLC method capable of complete resolution has not been determined to date. 1H NMR (300 MHz, CDCl3) ppm : 8.04 (d, J= 8. 2 Hz, 1 H), 7.83 7.92 (dd, J= 7.8,1.2 Hz, 1 H), 7.76 (d, J= 7.9 Hz, 1 H), 7.35 7.58 (m, 4 H), 3.78 3.93 (m, 1 H), 2.37 2.8 3 (m, 4 H), 2.11 2.30 (m, 2 H), 1.81 2.08 (m, 2 H). 13C NMR (75 MHz, CDCl3) ppm : 211.4 (s), 140.3 (s), 134.2 (s), 131.1 (s), 129.3 (s), 127.5 (s), 126.4 (s), 125.9 (s), 125.7 (s), 122.9 (s), 122.6 (s ), 48.8 (s), 41.7 (s), 39.6 (s), 32.5 (s ), 25.8 (s ). 5.2.5 3 -(4 -Methoxyphenyl) -C yclohexanone (5 -4 ) Colorless oil; purified by column chromatography, eluent hexanes/ Et2O 9:1. Chiral HPLC method capable of complete resolution has not been determined to date. 1H NMR (300 MHz, CDCl3) ppm : 7.12 (d, J= 8.5 H z, 2 H), 6.85 (d, J= 8.5 Hz, 2 H), 3.77 (s, 3 H), 2.87 3.01 (m, 1 H), 2.28 2.60 (m, 4 H), 1.99 2.17 (m, 2 H), 1.78 (s, 2 H). 13C NMR (75 MHz, CDCl3) ppm :

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114 211.3 (s), 158.5 (s ), 136.8 (s), 127.7 (s), 114.2 (s), 55.4 (s), 49.4 (s), 44.2 (s), 41.4 (s), 33.2 (s), 25.7 (s). 5.2.6 3 -(4 -Fluorophenyl) -C yclohexanone (5 -5 ) Colorless oil; purified by column chromatography, eluent hexanes/Et2O 9:1. Chiral HPLC column: Chiralpack IA column (hexanes/2 -propanol, 98:2, 1.0 mL/min); tR: 14.0 min (+), 15.1 min ( ).227 1H NMR (300 MHz, CDCl3) ppm : 7.10 7.21 (m, 2 H), 6.93 7.03 (m, 2 H), 2.90 3.05 (m, 1 H), 2.27 2.60 (m, 4 H), 1.99 2.18 (m, 2 H), 1.69 1.88 (m, 2 H). 13C NMR (75 MHz, CDCl3) ppm : 210.8 (s), 163.4 (s), 160.1 (s), 140.3 (s), 128.3 (s), 128.1 (s), 115.7 (s), 1 15.5 (s), 49.3 (s), 44.2 (s), 41.3 (s), 33.1 (s), 25.6 (s). 5.2.7 3 -P henylcyclopentanone (5 -6 ) Colorless oil; purified by column chromatography eluent hexanes/Et2O 9:1. Chiral HPLC method capable of complete resolution has not been determined to date. 1H NMR (300 MHz, CDCl3) ppm : 7.30 7.39 (m, 2 H), 7.22 7.29 (m, 3 H), 3.35 3.51 (m, 1 H), 2.61 2.74 (m, 1 H), 2.22 2.54 (m, 4 H), 1.90 2.09 (m, 1 H). 13C NMR (75 MHz, CDCl3) ppm : 218.6 (s), 143.3 (s), 128.9 (s), 126.9 (s), 126.9 (s), 46.0 (s), 42.4 (s), 39. 1 (s), 31.4 (s). 5.3 Results and Discussion Catalytic investigation was accomplished using the chiral versions of compounds 2 -3 3 8 3 -9 and 4 -8 These studies quickly revealed that 2 -3 was not capable of transferring its chirality at temperatures required for catalytic turnover. As previously conjectured, the flexibility of this ligand produces an undefined chiral pocket particularly at high te mperatures. Catalyst 3 -8 however, produced much larger enantiomeric excesses than has been previously reported utilizing closely related ligands in asymmetric catalysis .120 As expected, the more flexible analog 3 -9 produced much lower e.e.s than 3 -8 Increasing the steric bulk of the N-

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115 substituents (4 -8 ) does not appear to have a significant effect on the chiral induction ability of the unsaturated imidazole complex A catalytic cycle (Figure 5 2) is proposed based on mechanistic and kinetic studies accomplished by Hayashi et al.202 and Mi y a ura.189 The precatalyst I is activated by loss of COD forming a solvated species II. As reported for the BINAP system by Hayashi, our catalyst system may be capable of formi ng a dimeric complex III. From the active catalyst species II transmetallation of the aryl boronic acid via the transition state IV produces the phenyl compound V Subsequent insertion of the olefin is accomplished through a diastereo meric transition sta te VI This transition state is responsible for determining the enantiotopic identity of the product and forming the oxa allyl -Rh species VII that is then hydrolyzed to form the product. The most enantioselective catalyst, 3 -8 was utilized to optimiz e the conditions for asymmetric conjugate addition ( Table 5 1 ). M any unrelated catalysts have been reported to achieve high yields and enantioselectivities at room temperature,28 but our system requires temperatures well above 70 C. As was discovered with the original Rh(acac)binap system, dissociation of COD is believed to necessitate these high temperatures as well as the long reaction times. Attempts to replace the COD li gand by utilization of alternative rhodium precursors or by ligand substitution were unsuccessful or led to catalyst degradation. The reaction conditions found to produce the highest yield and enantiomeric excesses utilized 10/1 dioxane:methanol at 80 C with 0.5 equivalents of base and 3 mol% catalyst over 24 hrs for addition of phenyl boronic acid to 2 -cyclohexe n 1 one The addition of o tolylboronic acid to 2 -cyclohexe n 1 -one was found to achieve the same level of enantiopurity utilizing 4/1 dioxane:methanol and 1.5% of ( R,R) 3 -8 For the addition of pheny lboronic acid, the ( S,S )

PAGE 116

116 enantiomer of the ligand produces ( S ) 5 -1 and the ( R,R ) enantiomer forms ( R ) 5 -1 suggesting a similar pattern of chiral induction to that reported for the privileged ( S,S ) BINAP ligand.28 Omission of base or utilization of pyridine led to no product formation and substituting potassium hydroxide with potassium carbonate led to reduced yields and e.e.. Altering the solvent mixt ure to THF/Methanol had little effect but did lead to a small decrease in e.e. and attempting the reaction in pure methanol drastically increased the yield but produces no e.e. suggesting catalyst degradation. Typical solvent mixtures for rhodium catalyz e d conjugate addition reactions include water to facilitate hydrolysis and formation of the final product. However, substitution of methanol with deionize d degassed water reduced e.e. measurements from 82% to 5 % under the same reaction conditions. Loss o f enantioselectivity may be due to water facilitated dissociation of the chiral backbone or formation of dimer III. To completely remove water from the system, anhydrous methanol was utilized, le a d ing to a slight decrease in both yield and enantiocontrol suggesting a fine balance between catalyst activation and degradation by protonated solvents Investigation of chiral catalysis utilizing a variety of other boronic acids (Tables 5 2 through 5 7 ) leads to several conclusions. Comparison of the catalytic runs involving 4 methoxyboronic acid and 4 -fluoroboronic acid suggest transmetallation is facilitated by electron donating substituents 4 -methoxyboronic acids produced significant yields after only 14 hours, as the fluoro analog required 24 hrs and produced lower yields for 3 -8 and 3 -9 Utilization of o tolyl boronic acid allowed for increased steric bulk about the chiral pocket during the olefin insertion step. This was expected to increase th e enantiomeric excess produced particularly for the more flexible catalysts 3 -9 and 4 -8 by affecting the structure of diastereotopic transition state VI The close proximity of the methyl group to the metal center could serve to further define the

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117 chiral pocket, affecting the approach and insertion of the olefin. The e.e. s produced by these reactions are higher than those obtained utilizing phenylboronic acid, but this affect is not drastic. For 4 -8 the increase in e.e. is small but the yield is drastica lly reduced, inferring that the isopropyl group may hinder the overlap be tween hindered aryl substituents and the enone in the transition state VI Comparison of reactions forming 3 phenylcyclopentanone (5 -6 ) with those form ing the much bulkier 3 (1 -naphthalenyl) -cyclohexanone (5 -3 ) (Tables 5 4 and 57 ) show that the more flexible catalysts 3 -9 and 4 -8 produce higher yields when the size of the boronic acids is increased. However, t he more constrained catalyst 3 -8 produces small amounts of bulky 5 -3 but large amount s of the relatively small 5 -6 5.4 Conclusions Catalytic trials involving catalyst 2 -3 3 -8 3 -9 and 4 -8 display the large variation in catalytic behavior that can emanate from relatively small alterations in ligand structure. The significan t increase in the enantio selectivity of catalyst 3 -8 is assigned to an increase in the size of the imidazole, an area that is not typically associated with catalytic behavior. These findings further support the assertion that the purely rational design of catalyst should not be attempted before empirical investigation can be accomplished. Figure 5 1. Transmetallation of aryl substituents to rhodium catalysts.

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118 Figure 5 2. Catalytic cycle for the 1,4 addition of boronic acids to cyclic enones.

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119 Table 5 1 Optimization of catalytic conjugate addition involving compound 3 -8 Product Catalyst Solvent Temp C % e .e. Yield a Hours 5 1 (+/ ) 2 5 Dioxane/Water 85 NA 0 20 5 1 (+/ ) 2 3 Dioxane/Water 85 NA 99 20 5 1 () 2 3 Dioxane/MeOH 82 0 98 18 5 1 (+/ ) 3 8 Dioxane/MeOH 78 NA 60 22 5 1 (S,S ) 3 8 Dioxane/MeOH 50 NA 0 17 5 1 (+/ ) 3 8 f Dioxane/MeOH 80 NA 0 17 5 1 (S,S ) 3 8 Dioxane/MeOH 75 70 25 22 5 1 (S,S ) 3 8 b Dioxane/ MeOH 80 NA 0 17 5 1 (S,S ) 3 8 c Dioxane/ MeOH 80 46 30 17 5 1 ( S,S ) 3 8 Dioxane/MeOH 75 70 33 24 5 1 (S,S ) 3 8 Dioxane/MeOH 80 69 55 24 5 1 (S,S ) 3 8 d Dioxane/MeOH 80 73 72 24 5 1 (1eq ) (S,S ) 3 8 Dioxane/MeOH 80 72 59 24 5 1 (2eq ) ( S,S ) 3 8 Dioxane/MeOH 80 57 68 24 5 1 (R,R ) 3 8 THF/MeOH 80 77 e 73 24 5 1 (R,R ) 3 8 Dioxane/H2O 80 5 e 82 24 5 1 (R,R ) 3 8 Dioxane/MeOH (10:1) 80 82 e 86 24 5 1 ( R,R ) 3 8 Dioxane/MeOH (2:1) 80 61 e 70 24 5 1 (S,S ) 3 8 Dioxane/H2O (4:1) 80 5 83 24 5 1 (R,R ) 3 8 Dioxane/MeOH(4:1) 80 78 e 56 24 5 1 (S,S ) 3 8 d Dioxane/MeOH (10:1) 80 54 98 24 5 1 ( S,S ) 3 8 d Dioxane/anh MeOH (10:1) 80 43 74 24 aIsolated Yield after column chromatography bPyradine instead of KOH cK2CO3 instead of KOH d 3 mol% catalyst I solated after column eR -enantiomer fNo Base Table 5 2. Formation of 5 -1 catalyzed by 3 -8 3 -9 and 4 -8 Product Catalyst Solvent Temp C % e.e. Yield a Hours 5 1 (S,S ) 3 8 Dioxan e /MeOH 75 71 33 24 5 1 ( R,R ) 3 8 Dioxane/MeOH 80 78 b 56 24 5 1 (S,S ) 3 9 Dioxane/MeOH 75 6 17 24 5 1 (S,S ) 3 9 Dioxane/MeOH 82 4 20 23 5 1 (R,R ) 3 9 Dioxane/MeOH 82 5 b 19 23 5 1 ( S,S ) 3 9 MeOH 81 0 50 17 5 1 (R,R ) 4 8 Dioxane/MeOH 75 5 b 13 24 5 1 (R,R ) 4 8 Dioxane/MeOH 80 7 b 26 24 aIsolated yield after column chromatography bR -enantiomer

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120 Table 5 3 Formation of 5 -2 catalyzed by 3 -8 3 -9 and 4 -8 Product Catalyst Solvent Temp C % e.e. Yield a Hours 5 2 ( S,S ) 3 8 Dioxane/MeOH d 80 c 65 18 24 5 2 ( S, S ) 3 8 Dioxane/MeOH 76 b 82 40 24 5 2 ( S,S ) 3 9 Dioxane/MeOH 80 c 20 70 24 5 2 ( S,S ) 3 9 Dioxane/MeOH 76 b 10 22 24 5 2 ( R,R ) 4 8 Dioxane/MeOH 80 c 15 d 41 24 5 2 ( R,R ) 4 8 Dioxane/MeOH 76 b 8 d 25 24 aIsolated yield after column chromatography b 1.5 mol % catalyst c 3 mol % catalyst dR enantiomer Table 5 4 Formation of 5 -3 catalyzed by 3 -8 3 -9 and 4 -8 Product Catalyst Solvent Temp C % e.e. Y ie ld a Hours 5 3 (S,S ) 3 8 Dioxane/MeOH 80 NA b 45 24 5 3 ( S,S ) 3 9 Dioxane/MeOH 80 NA b 83 24 5 3 ( R,R ) 4 8 Dioxane/MeOH 80 NA b 69 24 a Isolated yield subsequent to column b HPLC/GC method was not found to fully resolve the enantiomers Table 5 5 Formation of 5 -4 catalyzed by 3 -8 3 -9 and 4 -8 Boronic Acid Catalyst Solvent Temp C % e.e. Yield a Hours 5 4 ( S,S ) 3 8 Dioxane/MeOH 80 NA b 57 14 5 4 (S,S ) 3 9 Dioxane/MeOH 80 NA b 98 14 5 4 ( R,R ) 4 8 Dioxane/MeOH 80 NA b 29 14 aIsolated yield subsequent to column b HPLC/GC method was not found to fully resolve the enantiomers Table 5 6 Formation of 5 -5 catalyzed by 3 -8 3 -9 and 4 -8 Product Catalyst Solvent Temp C % e.e. Y i e ld a Hours 5 5 ( S,S ) 3 8 Dioxane/MeOH 80 47 45 24 5 5 ( S,S ) 3 9 Dioxane/MeOH 80 11 65 24 5 5 (R,R ) 4 8 Dioxane/MeOH 80 0 71 24 aIsolated yield subsequent to column Table 5 7 Formation of 5 -6 catalyzed by 3 -8 3 -9 and 4 -8 Product Catalyst Solvent Temp C % e.e. Yie ld a Hours 5 6 ( S,S ) 3 8 Dioxane/MeOH 80 NA b 71 15 5 6 ( S,S ) 3 9 Dioxane/MeOH 80 NA b 50 15 5 6 ( R,R ) 4 8 Dioxane/MeOH 80 NA b 22 15 aIsolated yield subsequent to column b HPLC/GC method was not found to fully resolve the enantiomers

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121 CHAPTER SIX CONCLUSIONS AND FUTU RE DIRECTION Structural investigation of catalysts 2 -3 3 -8 3 -9 4 -8 4 -9 4 -10 and the unsuccessful formation of a mononuclear catalyst from ligand 4 -7 has shown that there is a fine balance between u ndefined and overly hindered ligand structures The overly flexible ligand 2 -1 was modified by reducing the length of the ligand arms. The two constrained ligands 3 -3 and 3 -4 although very similar in structure, formed monometallic chiral catalysts ( 3 -8 and 3 -9 ) that induced drastically different cat alytic selectivities (Chapter 5). Gas-phase ground state geometry optimization calculations were used to show that the variation in the chiral pocket between 3 -8 and 3 -9 was due largely to the difference in choice of azole a lthough some of the catalytic variation may be due to electronic differences between the imidazole and benzimidazole Increasing the size of the Nsubstituents ( 4 -1 ) does little to improve the poor enantioselectivity of the unsaturated imidazole catalyst 3 -9 The fair enantioselecti vity of 3 -8 at high temperatures could be improved if catalytic turnover could be achieved at reduced temperatures. Substitution of the cyclooctadiene coligand is the most straightforward pathway to achieving an optimized catalytic structure. Although p revious attempt s have not led to the desired product, further investigation of this avenue is needed. According to the calculated structure of tolylimidazole complex 4 -10, its configuration is nearly identical to 3 -8 The similar minimum energy structures should present comparable chiral inductions, although small variations could lead to large alteration in the structure of the diastereotopic transition state that determines the products enantiotopic identity. Increasing the size of the Nsub stituent of 3 -8 resulted in the extremely low yielding formation of monometallic complex 4 -9 In order to isolate amount s of 4 -9 required for catalytic investigation it may be

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122 useful to substitute the dimeric [Rh(COD)Cl]2 with the monometallic cationic Rh(NBD)2BF4 precursor F ormation of a silver salt from ligand 4 -2 that could be used for transmetallation could also increase the yield of monometallic complex 4 -9 A lternative ligand structures (Figure 6 1) could be used to increase the definition of the chiral pocket. However, caution must be taken to avoid the design of overly hindered ligands that favor the formation of bimetallic complexes. The addition of a methyl substituent in the ortho position ( 6 -1 ) should lead to a very rigid monometallic complex if it can be formed. Ortho substitution of a fluoro substituent should induce less steric inhibition to monometallic complex formation; however, synthetic procedures required to form this ligand are more complex than for 6 -1 and the electronic interaction between the fluoro substituent and the aryl backbone may also preclude monometallic catalyst synthesis. Although the meta methyl substituent did not alter the structure of the monometallic catalyst ( 4 -6 ), introduction of a significantly bulky substituent in this position ( 6 -3 R = t Bu or biphenyl ) should alter the structure. The unsaturated imidazole complexes 3 -9 and 4 -1 do not appear to be promising in high temperature catalysis. However, they should present much higher enantioselectivities if utilized at room temperature. An alternative structure 6 -4 is proposed whereby the bulk of the backbone is increased Substitution of glyoxal with an alkyl substituted dione, such as butane 2,3 -dione, would introduce alkyl groups on the back of the im idazole. The stability of the rhodium and iridium complexes reported herein has allowed the structural investigation of a series of di NHC ligands. Although structural knowledge is vastly important in catalytic investigation, the stability of these comp lexes is likely the source of the observed sluggish reactivity. Formation of metal complexes containing labile co ligands should allow the formation of electron rich metal centers capable of a high degree of enantioselectivity.

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123 Figure 6 1. Proposed lig and structures for enhanced chiral induction.

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124 APPENDIX A NUCLEAR MAGNETIC RESONANCE

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125 Figure A 1 : 1H NMR spectrum of (+/ ) [DEAM BI][OTf]2 (2 -1 ) in (CD3)2SO 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 Chemical Shift (ppm)

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126 Figure A 2 : 13C NMR spectrum of (+/ ) [DEAM BI][OTf]2 (2 -1 ) in (CD3)2SO 145 140 135 130 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45 40 35 Chemical Shift (ppm)

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127 Figure A 3 : 1H NMR spectrum of (+/ ) DEAM BIY (2 -2 ) in C6D6. 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 Chemical Shift (ppm)

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128 216 208 200 192 184 176 168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 Chemical Shift (ppm) Figure A 4 : 13C NMR spectrum of (+/ ) DEAM BIY (2 -2 ) in C6D6.

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129 Figure A 5. 1H NMR spectrum of (+/ ) [(DEAM BIY) Rh (COD)] OTf (2 3 ) in CDCl3. 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 Chemical Shift (ppm)

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130 Figure A 6 : 13C NMR spectrum of (+/ ) [(DEAM BIY) Rh (COD)] OTf (2 -3 ) in CDCl3. 184 176 168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 16 Chemical Shift (ppm)

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131 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 Chemical Shift (ppm) Figure A 7 : 1H NMR spectrum of (+/ ) (DEAM BIY)Rh2(COD)2Cl2 (2 -4 ) in CDCl3.

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132 184 176 168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 16 Chemical Shift (ppm) Figure A 8 : 13C NMR spectrum of (+/ )(DEAM BIY)Rh2(COD)2Cl2 (2 -4 ) in CDCl3.

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133 Figure A 9: 1H NMR spectrum of ( +/ ) [(DEAM BIY)Ir(COD)]OTf (2 -5 ) in CDCl3. 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 Chemical Shift (ppm)

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134 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 Chemical Shift (ppm) Figure A 10: 1H NMR spectrum of (+/ ) [(DEAM BIY)Ir(COD)]OTf (2 -5 ) in CD2Cl2.

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135 176 168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 Chemical Shift (ppm) Figure A 11: 13C NMR spectrum of (+/ ) [(DEAM BIY)Ir(COD)]OTf (2 -5 ) in CD2Cl2

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136 Figure A 12: 1H NMR spectrum of (+/ ) (DEAM BIY)Ir2(COD)2Cl2 (2 -6 ) in CDCl3. 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 Chemical Shift (ppm)

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137 176 168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 Chemical Shift (ppm) Figure A 13: 13C NMR spectrum of (+/ ) (DEAM BIY)Ir2(COD)2Cl2 (2 -6 ) in CDCl3.

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1 38 Figure A 14: 1H NMR spectrum of 1,1 (9,10-dihydro 9,10-ethanoanthracene11,12-diyl)di(3 -methyl 1H -benzimidazol 3 ium) diiodide ( 3 -4 ) in (CD3)2SO 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 Chemical Shift (ppm)

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139 Figure A 15: 1H NMR spectrum of (+/ ) trans 9,10 dihydro 9,10 ethanoanthracene 9,10 (1 methyl)bibenzimidazole), [(DEA MbBY] (3 -5 ) in C6D6. 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 Chemical Shift (ppm)

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140 Figure A 16: 13C{1H} NMR spectrum of (+/ ) trans 9,10 dihydro 9,10 ethanoanthracene 9,10 (1 methyl)bibenzimidazole), [(DEA MbBY] (3 -5 ) in C6D6. 150 145 140 135 130 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45 40 35 Chemical Shift (ppm)

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141 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 Chemical Shift (ppm) Figure A 17: 1H NMR spectrum of [ DEA MY][Rh(NBD)I]2 (3 -6 ) as a mixture with 3 -9 in C6D6.

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142 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 Chemical Shift (ppm) Figure A 18: 1H NMR spectrum of [ 2 DEA MBY][Rh(NBD)I]2 (3 -7 -NBD ) as a mixture with 3 -8 -NBD in C6D6.

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143 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 Chemical Shift (ppm) Figure A 1 9 : 1H NMR spectrum of (+/ ) Rhodium(I) trans 9,10 dihydro 9,10 ethanoanthracene 9,10 bis(1 methylbenzimidazolidine 2 ylidene cyclooctadiene iodide, [(DEA MBY)Rh(COD)]I (3 -8 ) in CDCl3.

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144 Figure A 20: 13C{1H} NMR spectrum of (+/ ) Rho dium(I) trans 9,10 dihydro 9,10 ethanoanthracene 9,10 bis(1 methylbenzimidazolidine 2 ylidene cyclooctadiene iodide, [(DEA MBY)Rh(COD)]I (3 -8 ) in CDCl3. 192 184 176 168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 Chemical Shift (ppm)

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145 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 Chemical Shift (ppm) Figure A 21: 1H NMR spectrum of (+/ ) Rhodium(I) trans 9,10 dihydro 9,1 0 ethanoanthracene 9,10 bis(1 methylimidazolidine 2 ylidene cyclooctadiene iodide, [(DEA MY)Rh(COD)]I (3 -9 ) in CD3Cl.

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146 176 168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 Chemical Shift (ppm) Figure A 22: 13C{1H} NMR spectrum of (+/ ) Rhodium(I) trans 9,10 dihydro 9,10 ethanoanthracene 9,10 bis(1 methylimidazolidine 2 ylidene cyclooctadiene iodide, [(DEA MY)Rh(COD)]I (3 -9 ) in CD3Cl

PAGE 147

147 Figure A 23: 1H NMR spectrum of (+/ ) [DEA iPrI][I]2 (4 -1 ) in (CD3)2SO 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 Chemical Shift (ppm)

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148 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 16 8 Chemical Shift (ppm) Figure A 24: 13C NMR spectrum of (+/ ) [DEA iPrI][I]2 (4 -1 ) in (CD3)2SO

PAGE 149

149 Figure A 25. 1H NMR spectrum of (+/ ) [DEA iPr BI][I]2 (4 -2 ) in (CD3)2SO 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 Chemical Shift (ppm)

PAGE 150

150 Figure A 26. 13C NMR spectrum of (+/ ) [DEA iPr BI][I]2 (4 -2 ) in (CD3)2SO 145 140 135 130 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 Chemical Shift (ppm)

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151 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 Chemical Shift (ppm) Figure A 27. 1H NMR of N,N' -bis(4 -nitrotolyl) 9,10 dihydro9,10 -ethanoanthracene 11,12diamine ( 4 -3 ).

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152 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 16 8 Chemical Shift (ppm) Figure A 28. 13C NMR of N,N' -bis(4 -nitrotolyl) 9,10 -dihydro 9,10-ethanoanthracene 11,12diamine ( 4 -3 ).

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153 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 Chemical Shift (ppm) Figure A 29. 1H NMR of N,N' -bis(4 aminotolyl) 9,10-dihydro 9,10-ethanoanthracene 11,12-diamine ( 4 -4 ).

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154 145 140 135 130 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 Chemical Shift (ppm) Figure A 30. 13C NMR of N,N' -bis(4 aminotolyl) 9,10-dihydro 9,10 ethano anthracene 11,12-diamine ( 4 -4 ).

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155 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 Chemical Shift (ppm) Figure A 31. 1H NMR 1,1' (9,10 -dihydro 9,10-ethanoanthracene 11,12-diyl)di(1 H tolylimidazole) ( 4 -5 ).

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156 145 140 135 130 125 120 115 110 105 100 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 Chemical Shift (ppm) Figure A 32. 13C NMR 1,1' (9,10-dihydro 9,10-ethanoanthracene 11,12diyl)di(1 H tolylimidazole) ( 4 -5 ).

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157 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 Chemical Shift (ppm) Figure A 33. 1H NMR spectrum of (+/ ) [DEA MT I][I]2 (4 -6 ) in (CD3)2SO

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158 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 16 Chemical Shift (ppm) Figure A 34. 13C NMR spectrum of (+/ ) [DEA MT I][I]2 (4 -6 ) in (CD3)2SO

PAGE 159

159 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 Chemical Shift (ppm) Figure A 35: 1H NMR spectrum of R,R [DEA iPr T I][I]2 (4 -7 ) in CDCl3.

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160 Figure A 36. 1H NMR spectrum of (+/ ) Rhodium(I) trans 9,10 dihydro 9,10 ethanoanthracene 9,10 bis(1 isopropyl imidazolidine 2 ylidene cyclooctadiene iodide, [(DEA iPr Y)Rh(COD)]I (4 -8 ) in CDCl3. 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 Chemical Shift (ppm)

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161 Figure A 37. 1H NMR spectrum of (+/ ) Rhodium(I) trans 9,10 dihydro 9,10 ethanoanthracene 9,10 bis(1 isopropyl imidazolidine 2 ylidene cyclooctadiene iodide, [(DEA iPr Y)Rh(COD)]I (4 -8 ) in CDCl3 176 168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 16 Chemical Shift (ppm)

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162 Figure A 38. 1H NMR spectrum of (+/ ) Rhodium(I) trans 9,10 dihydro 9,10 ethanoanthracene 9,10 bis(1 isopropylbenz imidazolidine 2 ylidene cyclooctadiene iodide, [(DEA iPrB Y)Rh(COD)]I (4 -9 ) in CDCl3. 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 Chemical Shift (ppm)

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163 192 184 176 168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 Chemical Shift (ppm) Figure A 39. 13C NMR spectrum of (+/ ) Rhodium(I) trans 9,10 dihydro 9,10 ethanoanthracene 9,10 bis(1 isopropylbenz imidazolidine 2 ylidene cyclooctadiene iodide, [(DEA iPrB Y)Rh(COD)]I (4 -9 ) in CDCl3.

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164 Figure A 40. 1H NMR spectrum of (+/ ) Rhodium(I) trans 9,10 dihydro 9,10 ethanoanthracene 9,10 bis(1 methylt olylimidazolidine 2 ylidene cyclooctadiene iodide, [(DEA MTY)Rh(COD)]I (4 -10) in CDCl3. 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 Chemical Shift (ppm)

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165 Figure A 41. 13C NMR spectrum of (+/ ) Rhodium(I) trans 9,10 dihydro 9,10 ethanoanthracene 9,10 bis(1 methyltolylimidazolidine 2 ylidene cyclooctadiene iodide, [(DEA MTY)Rh(COD)]I (4 -10) in CDCl3. 192 184 176 168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 16 Chemical Shift (ppm)

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166 APPENDIX B REFINEMENT DATA Table B 1 Crystal data, structure solution and refinement for 2 -1 identification code rx14 empirical formula C40 H36 F6 N4 O6 S2 formula weight 846.85 T (K) 173(2) () 0.71073 crystal system Monoclinic space group P2(1)/c a () 12.5937(8) b () 24.6077(16) c () 12.9797(9) (deg) 90 (deg) 97.815(1) (deg) 90 V ( 3 ) 3985.1(5) Z 4 calcd (Mg mm 3 ) 1.411 crystal size (mm3) 0.29 x 0.26 x 0.22 abs coeff (mm 1 ) 0.214 F (000) 1752 range for data collection 1.63 to 24.99 limiting indices 8 h 14, 29 k 15, 15 l 15 no. of reflns collcd 12702 no. of ind reflns ( Rint) 6516 (0.0349) completeness to = 27.49 0.93 absorption corr Integration refinement method Full -matrix least -squares on F 2 data / restraints / parameters 6516 / 0 / 509 R 1,a wR 2b [I > 2 ] 0.0467, 0.1194 [5128] R 1, a wR 2 b (all data) 0.0602, 0.1279 GOFc on F2 1.035 largest diff. peak and hole 0.411 and 0.361 e. 3 a R 1 = || Fo | Fc||/ | Fo|. b w R 2 = ( ( w ( Fo 2 Fc 2)2)/ ( w ( Fo 2)2))1/2. c GOF = ( w ( Fo 2 Fc 2)2/( n p ))1/2 where n is the number of data and p is the number of parameters refined.

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167 Table B 2 Crystal data, structure solution and refinement for 2 -2 identification code rx12 empirical formula C38 H34 N4 formula weight 546.69 T (K) 173(2) ) 0.71073 crystal system Orthorhombic space group Pna2(1) a () 10.3902(9) b () 21.6719(19) c () 13.1662(11) (deg) 90 (deg) 90 (deg) 90 V (3) 2964.7(4) Z 4 calcd (Mg mm3) 1.225 crystal size (mm3) 0.18 x 0.10 x 0.05 abs coeff (mm1) 0.072 F (000) 1160 range for data collection 1.81 to 25.00 limiting indices 11 h 25 k 25, 15 l 14 no. of reflns collcd 15241 no. of ind reflns ( Rint) 5055 ( 0.0624) completeness to = 27.49 100.00% absorption corr Emprirical, Psi scan refinement method Full -matrix least -squares on F2 data / restraints / parameters 5055 / 1 / 379 R 1,a wR 2b [I > 2 ] 0.0570, 0.1523 [4229] R 1,a wR 2b (all data) 0.0700, 0.1775 GOF c on F 2 1.075 largest diff. peak and hole 0.161 and 0.268 e.3 a R 1 = || Fo | Fc||/ | Fo|. b w R 2 = ( ( w ( Fo 2 Fc 2)2)/ ( w ( Fo 2)2))1/2. c GOF = ( w ( Fo 2 Fc 2)2/( n p ))1/2 where n is the number of data and p is the number of parameters refined.

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168 Table B 3 Crystal data, structure solution and refinement for 2 -3 CH2Cl2. identification code rx11 empirical formula C48 H48 Cl2 F3 N4 O3 Rh S formula weight 991.77 T (K) 173(2) ) 0.71073 crystal system Monoclinic space group P2(1)/n a () 9.8237(13) b () 18.047(3) c () 24.957(3) (deg) 90 (deg) 92.909(2) (deg) 90 V (3) 4418.9(10) Z 4 calcd (Mg mm3) 1.491 crystal size (mm3) 0.16 x 0.16 x 0.10 abs coeff (mm1) 0.615 F (000) 2040 range for data collection 1.39 to 27.50 limiting indices 12 h 12, 22 k 23, 25 l 32 no. of reflns collcd 29619 no. of ind reflns ( Rint) 10128 (0.0483) completeness to = 27.49 0.997 absorption corr Integration refinement method Full -matrix least -squares on F2 data / restraints / parameters 10128 / 1 / 570 R 1,a wR 2b [I > 2 ] 0.0359, 0.0988 [8286] R 1,a wR 2b (all data) 0.0459, 0.1024 GOFc on F2 1.077 largest diff. peak and hole 0.801 and 1.078 e.3 a R 1 = || Fo | Fc||/ | Fo|. b w R 2 = ( ( w ( Fo 2 Fc 2)2)/ ( w ( Fo 2)2))1/2. c GOF = ( w ( Fo 2 Fc 2)2/( n p ))1/2 where n is the number of data and p is the number of parameters refined.

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169 Table B 4 Crystal data, structure solution and refinement for 2 -4 C6H6. identification code rx10 empirical formula C60 H64 Cl2 N4 Rh2 formula weight 1117.87 T (K) 173(2) ) 0.71073 crystal system Triclinic space group P a () 13.839(2) b () 13.995(2) c () 14.479(2) (deg) 80.356(3) (deg) 70.239(3) (deg) 75.220(3) V (3) 2541.5(7) Z 2 calcd (Mg mm3) 1.461 crystal size (mm3) 0.13 x 0.05 x 0.02 abs coeff (mm1) 0.798 F (000) 1152 range for data collection 1.50 to 27.50 limiting indices 17 h 17, 18 k 12, 18 l 18 no. of reflns collcd 17430 no. of ind reflns ( Rint) 11405 (0.0811) completeness to = 27.49 97.80% absorption corr Integration refinement method Full -matrix least -squares on F2 data / restraints / parameters 11405 / 0 / 613 R 1,a wR 2b [I > 2 ] 0.0538, 0.1185 [6208] R 1,a wR 2b (all data) 0.1125, 0.1376 GOFc on F2 0.881 largest diff. peak and hole 0.554 and 0.672 e.3 a R 1 = || Fo | Fc||/ | Fo|. b w R 2 = ( ( w ( Fo 2 Fc 2)2)/ ( w ( Fo 2)2))1/2. c GOF = ( w ( Fo 2 Fc 2)2/( n p ))1/2 where n is the number of data and p is the number of parameters refined.

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170 Table B 5 Crystal data, structure solution and refinement for 2 -5 C6H6. identification code rx18 empirical formula C53 H52 F3 Ir N4 O3 S formula weight 1074.25 T (K) 173(2) ) 0.71073 crystal system Monoclinic space group P2(1)/n a () 10.1135(17) b () 17.996(3) c () 24.932(4) (deg) 90 (deg) 92.221(4) (deg) 90 V (3) 4534.3(13) Z 4 calcd (Mg mm3) 1.574 crystal size (mm3) 0.09 x 0.02 x 0.02 abs coeff (mm1) 3.053 F (000) 2168 range for data collection 1.40 to 27.50 limiting indices 13 h 13, 22 k 23, 19 l 32 no. of reflns collcd 29378 no. of ind reflns ( Rint) 10343 (0.1461) completeness to = 27.49 99.30% absorption corr Integration refinement method Full -matrix least -squares on F2 data / restraints / parameters 10343 / 1 / 571 R 1,a wR 2b [I > 2 ] 0.0872, 0.0965 [5988] R 1,a wR 2b (all data) 0.1676, 0.1127 GOFc on F2 1.034 largest diff. peak and hole 1.085 and 1.791 e.3 a R 1 = || Fo | Fc||/ | Fo|. b w R 2 = ( ( w ( Fo 2 Fc 2)2)/ ( w ( Fo 2)2))1/2. c GOF = ( w ( Fo 2 Fc 2)2/( n p ))1/2 where n is the number of data and p is the number of parameters refined.

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171 Table B 6 Crystal data, structure solution and refinement for 2 -6 C6H6. identification code rx17 empirical formula C60 H64 Cl2 Ir2 N4 formula weight 1296.45 T (K) 173(2) ) 0.71073 crystal system Triclinic space group P a () 13.8318(17) b () 13.9515(17) c () 14.5432(18) (deg) 80.640(2) (deg) 70.355(2) (deg) 75.494(2) V (3) 2549.4(5) Z 2 calcd (Mg mm3) 1.689 crystal size (mm3) 0.15 x 0.12 x 0.04 abs coeff (mm1) 5.363 F (000) 1280 range for data collection 1.49 to 27.50 limiting indices 17 h 17, 18 k 16, 18 l 18 no. of reflns collcd 17315 no. of ind reflns ( Rint) 11384 (0.0589) completeness to = 27.49 97.50% absorption corr Integration refinement method Full -matrix least -squares on F2 data / restraints / parameters 11384 / 0 / 613 R 1,a wR 2b [I > 2 ] 0.0293, 0.0760 [9922] R 1,a wR 2b (all data) 0.0348, 0.0791 GOFc on F2 1.007 largest diff. peak and hole 1.769 and 1.397 e.3 a R 1 = || Fo | Fc||/ | Fo|. b w R 2 = ( ( w ( Fo 2 Fc 2)2)/ ( w ( Fo 2)2))1/2. c GOF = ( w ( Fo 2 Fc 2)2/( n p ))1/2 where n is the number of data and p is the number of parameters refined.

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172 Table B 7 Crystal data, structure solution and refinement for 2( 3 -5 ). identification code rx08 empirical formula C64 H52 N8 formula weight 933.14 T (K) 173(2) ) 0.71073 crystal system Monoclinic space group P21/n a () 10.5224(7) b () 38.633(3) c () 11.9173(7) (deg) 90 (deg) 102.497(1) (deg) 90 V (3) 4729.7(5) Z 4 calcd (Mg mm3) 1.310 crystal size (mm3) 0 .19 x 0.19 x 0.08 abs coeff (mm1) 0.078 F (000) 1968 range for data collection 1.83 to 27.50 limiting indices 13 h 12, 50 k 48, 14 l 15 no. of reflns collcd 32190 no. of ind reflns ( Rint) 10772 (0.0356) completeness to = 27.49 99.00% absorption corr Integration refinement method Full -matrix least -squares on F2 data / restraints / parameters 10772 / 0 / 651 R 1,a wR 2b [I > 2 ] 0.0416, 0.0943 [7390] R 1,a wR 2b (all data) 0.0695, 0.1028 GOFc on F2 1 largest diff. peak and hole 0.200 and 0.212 e.3 a R 1 = || Fo | Fc||/ | Fo|. b w R 2 = ( ( w ( Fo 2 Fc 2)2)/ ( w ( Fo 2)2))1/2. c GOF = ( w ( Fo 2 Fc 2)2/( n p ))1/2 where n is the number of data and p is the number of parameters refined.

PAGE 173

173 Table B 8 Crystal data, structure solution and refinement for 3 -6 THF identification code rx09 empirical formula C42 H46 I2 N4 O Rh2 formula weight 1082.45 T (K) 173(2) ) 0.71073 crystal system Monoclinic space group P2(1)/c a () 12.8891(12) b () 14.6531(14) c () 22.462(2) (deg) 90 (deg) 104.806(2) (deg) 90 V (3) 4101.5(7) Z 4 calcd (Mg mm3) 1.753 crystal size (mm3) 0.09 x 0.07 x 0.05 abs coeff (mm1) 2.347 F (000) 2120 range for data collection 1.63 to 27.50 limiting indices 15 h 14, 15 k 19, 27 l 20 no. of reflns collcd 15923 no. of ind reflns ( Rint) 8001 ( 0.0353) completeness to = 27.49 85.00% absorption corr Integration refinement method Full -matrix least -squares on F2 data / restraints / parameters 8001 / 0 / 460 R 1,a wR 2b [I > 2 ] 0.0380, 0.0684 [5927] R 1,a wR 2b (all data) 0.0622, 0.0746 GOF c on F 2 0.977 largest diff. peak and hole 0.581 and 0.477 e.3 a R 1 = || Fo | Fc||/ | Fo|. b w R 2 = ( ( w ( Fo 2 Fc 2)2)/ ( w ( Fo 2)2))1/2. c GOF = ( w ( Fo 2 Fc 2)2/( n p ))1/2 where n is the number of data and p is the number of parameters refined.

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174 Table B 9 Crystal data, structure solution and refinement for 3 -7 CH2Cl2. identification code rx13 empirical formula C50 H54 Cl6 N4 Rh2 formula weight 1129.49 T (K) 173(2) ) 0.71073 crystal system Monoclinic space group P2(1)/n a () 12.4529(12) b () 22.822(2) c () 17.3074(16) (deg) 90 (deg) 101.420(2) (deg) 90 V (3) 4821.3(8) Z 4 calcd (Mg mm3) 1.556 crystal size (mm3) 0.20 x 0.18 x 0.17 abs coeff (mm1) 1.057 F (000) 2296 range for data collection 1.50 to 27.50 limiting indices 13 h 16, 27 k 29, 22 l 20 no. of reflns collcd 32115 no. of ind reflns ( Rint) 11074 (0.0691) completeness to = 27.49 99.90% absorption corr Integration refinement method Full -matrix least -squares on F2 data / restraints / parameters 11074 / 0 / 569 R 1,a wR 2b [I > 2 ] 0.0354, 0.0936 [9845] R 1,a wR 2b (all data) 0.0402, 0.0969 GOFc on F2 1.025 largest diff. peak and hole 0.837 and 1.392 e.3 a R 1 = || Fo | Fc||/ | Fo|. b w R 2 = ( ( w ( Fo 2 Fc 2)2)/ ( w ( Fo 2)2))1/2. c GOF = ( w ( Fo 2 Fc 2)2/( n p ))1/2 where n is the number of data and p is the number of parameters refined.

PAGE 175

175 Table B 10. Crystal data, structure solution and refinement for 3 -8 CH2Cl2. identification code rx20 empirical formula C 41 H 40 Cl 2 I N 4 Rh formula weight 889.48 T (K) 173(2) ) 0.71073 crystal system Monoclinic space group P2(1)/c a () 10.7075(11) b () 30.420(3) c () 12.1504(12) 90 112.696(2) 90 V ( 3 ) 3651.2(6) Z 4 3 ) 1.618 crystal size (mm 3 ) 0.16 x 0.08 x 0.02 abs coeff (mm 1 ) 1.495 F(000) 1784 1.34 to 27.50. limiting indices 9 h 13, 36 k 39, 15 l 15 no. of reflns collcd 23756 no. of ind reflns (R int ) 8317 ( 0.1039 ) 99.10% absorption corr Integration refinement method Full -matrix least -squares on F2 data / restraints / parameters 8317 / 0 / 442 R1,a wR2b [I > 2s] 0.0496, 0.0705 [4514] R1,a wR2b (all data) 0.1158, 0.0824 GOFc on F2 0.853 largest diff. peak and hole 0.834 and 0.608 e. 3 a R 1 = || Fo | Fc||/ | Fo|. b w R 2 = ( ( w( Fo 2 Fc 2)2)/ ( w ( Fo 2)2))1/2. c GOF = ( w ( Fo 2 Fc 2)2/( n p ))1/2 where n is the number of data and p is the number of parameters refined.

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176 LIST OF REFERENCES 1. T. H. Maugh II, Science, 1983, 219, 474. 2. M. J. Krische, Tetrahedron, 2005, 61, 6169. 3. K. Kolasinski, Surface Science: Foundations of Catalysis and Nanoscience John Wiley & Sons, Chichester, 2002. 4. A. P. Kieboom, J. Moulijn, P. W. N. M. V. Leeuwen and R. A. V. Santen, in Catalysis: An Integrated Approach, eds. R. A. Van Santen, P. W. N. M. Van Leeuwen, J. A. Moulijn and B. A. Averill, Elsevier Science, Amsterdam, Editon edn., 2000. 5. J. Tyndall, Catalysis Letters 2000, 67, 5. 6. S. K. Ritter, Chemical & Engineering News 2008, http://pubs.acs.org/cen/coverstory/86/8633cover3box2.html Accessed 6/18/2009. 7. B. Cornils and W. A. Herrmann, Journal of Catalysis 2003, 216, 23. 8. E. Morales, The North American Catalysis Society http://www.nacatsoc.org/default.asp, Accessed 5/1/2009. 9. B. Bosnich, ed., Asymmetric Catalysis Martinus Nij hoff Publishers, Dordrecht / Boston / Lancaster, 1986. 10. G. K. Boreskov, Heterogeneous Nova Publishers, 2003. 11. F. D. Gunstone, Guidebook to stereochemistry Longman Group Limited, New York, 1975. 12. J. B. Biot, Bull. Soc. Philomath. 1815, Paris, 190. 13. J. B. Biot, Bull. Soc. Philomath. 1816, Paris, 125. 14. P. Cintas, Angew. Chem. Inter. Ed. 2007, 46, 4016. 15. G. B. Kauffman and R. D. Myers, Chem. Educator 1998, http://chemeducator.org/bibs/0003006/00030257.htm, Accessed 6/21/2009. 16. R. Co rradini, S. Sforza, T. Tedeschi and R. Marchelli, Chirality 2007, 19, 269. 17. R. Crossley, Tetrahedron, 1992, 48, 8155. 18. J. L. Bada, Nature 1995, 374, 594. 19. D. L. Nelson and M. M. Cox, Principles of Biochemistry 4th edn., W. H. Freeman and Compan y, New York, 2005.

PAGE 177

177 20. J. C. Leffingwell, in Leffingwell Reports Chirality & Bioactivity I.: Pharmacology Editon edn., 2003, vol. 3. 21. S. C. Stinson, Chem. Eng. News 2000, 78, 55. 22. E. J. Ariens, Soudigen, W., Timmermans, P. B. M. W. M., ed., Stereochemistry and Biological Activity of Drugs Blackwell Scientific Publications, Oxford, 1983. 23. S. C. Stinson, Chem. Eng. News 2001, 79, 45. 24. S. C. Stinson, Chem. Eng. News 2001, 79, 45. 25. B. M. Trost, PNAS 2004, 101, 5348. 26. E. Fogassy, M Ngrdi, D. Kozma, G. Egri, E. Plovics and V. Kiss, Org. Biomol. Chem. 2006, 4 3011. 27. R. N. Patel, Current Organic Chemistry 2006, 10, 1289. 28. K. Mikami and M. Lautens, eds., New Fronteirs in Asymmetric Catalysis John Wiley & Sons, New Jersey, 2007. 29. M. Lemaire, Pure Appl. Chem. 2004, 76, 679. 30. W. A. Nugent, T. V. RajanBabu and M. J. Burk, Science 1993, 259 479. 31. G. W. Parshall, Homogeneous Catalysis: the applications and chemistry of catalysis by soluble transition metal complexes John Wiley & Sons, New York, 1980. 32. T. P. Yoon, E. N. Jacobsen, Science 2003, 299 1691. 33. T. P. Dang and H. B. Kagan, J. Chem. Soc. Chem. Commun. 1971, 481. 34. H. B. Kagan and T. P. Dang, J. Am. Chem. Soc., 1972, 94, 6429. 35. J. K. Whitesell, Che m. Rev. 1989, 89, 1581. 36. F. Jo, Aqueous Organometallic Catalysis Kluwer Academic Publishers, Dordrecht / Boston / London, 2001. 37. F. Glorius, ed., N-Heterocyclic Carbenes in Transition Metal Catalysis Springer -Verlag, Berlin Heidelberg, 2007. 38. R. H. Crabtree, J. Organomet. Chem. 2005, 690, 5451. 39. H. W. Wanzlick, E. Fjedor and K. H. Jerg, Chem. Ber. 1963, 96, 1208. 40. H. W. Wanzlick and E. Schikora, Angew. Chem. 1960, 72, 494.

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178 41. H. W. Wanzlick and H. J. KLEINER, Angew. Chem. 1961, 73, 493. 42. H. W. Wanzlick, Angew. Chem. Int. Ed. 1962, 1 75 80. 43. H. W. Wanzlick, H. J. Schnherr, Angew. Chem. Int. Ed. Engl. 1968, 7 148. 44. K. J. fele, Organomet. Chem. 1968, 12, 42. 45. -M uir, Chem. Commun. 1971, 400. 46. M. F. Lappert, J. Organomet. Chem. 2005, 690. 47. A. Arduengo, M. Kline, J. C. Calabrese, F. Davidson, J. Am. Chem. Soc., 1991, 113, 9704. 48. A. J. Arduengo, R. L. Harlow and M. Kline, J. Am. Chem. Soc. 1992, 113, 361. 49. D. Enders, O. Niemeier and A. Henseler, Chem. Rev. 2007, 107, 5606. 50. V. Cesar, S. Bellemin Laponnaz and L. H. Gade, Chem. Soc. Rev. 2004, 33, 619. 51. F. E. Hahn and M. C. Jahnke, Angew. Chem. Int. Ed. 2008, 47, 3122. 52. W. A. Herrmann, Angew. Chem. Int. Ed. 2002, 41, 1290. 53. H. Clavier and S. P. Nolan, Annu. Rep. Prog. Chem., Sect. B 2007, 103, 193. 54. R. E. Douthwaite, Coord. Chem. Rev. 2007, 251, 702. 55. S. Diez Gonzlez and S. P. Nolan, Coord. Chem. Rev. 2007, 251, 874. 56. J. M. Pra etorius and C. M. Crudden, Dalton Trans. 2008, 4079. 57. J. A. Mata, M. Poyatos and E. Peris, Coord. Chem. Rev. 2007, 251, 841. 58. M. Poyatos, J. A. Mata and E. Peris, Chem. Rev. 2009. 59. O. Schuster, L. Yang, H. G. Raubenheimer and M. Albrecht, Chem. Rev. 2009, ASAP 60. P. L. Arnold and I. J. Casely, Chem. Rev. 2009, ASAP 61. C. Samojlowicz, M. Bieniek and K. Grela, Chem. Rev. 2009, ASAP 62. P. De Frmont, N. Marion and S. P. Nolan, Coord. Chem. Rev. 2008, 253, 862. 63. S. P. Nolan, ed., N-hete rocyclic Carbenes in Synthesis Wiley -VCH, Weinheim, Germany, 2006. 64. P. De Frmont, N. Marion and S. P. Nolan, Coord. Chem. Rev. 2009, 253, 862.

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179 65. J. Lennard Jones and J. A. Pople, Discus. Faraday Soc. 1951, 10, 9. 66. A. D. Walsh, J. Chem. Soc. 1953, 2260. 67. R. Hoffmann, J. Am. Chem. Soc., 1968, 90, 1475. 68. C. Heinemann, T. Mller, y. Apeloig, H. Schwarz, J. Am. Chem. Soc. 1996, 118, 2023. 69. C. Boehme, G. Frenking, J. Am. Chem. Soc. 1996, 118, 2039. 70. J. F. Lehmann, S. G. Urquhart, L. E. Ennis, A. P. Hitchcock, K. Hatano, S. Gupta, M. K. Denk, Organometallics 1999, 18, 1862. 71. S. Dez Gonzlez and S. P. Nolan, Coord. Chem. Rev. 2007, 251, 874. 72. A. J. Arduengo, III, J. R. Goerlich and W. J. Marsha ll, J. Am. Chem. Soc. 1995, 117, 11027. 73. E. Despagnet -Ayoub and R. H. Grubbs, J. Am. Chem. Soc. 2004, 126, 10198. 74. R. W. Alder, M. E. Blake, C. Bortolotti, S. Bufali, C. P. Butts, E. Linehan, J. M. Oliva, A. G. Orpen and M. J. Quayle, Chem. Commun. 1999, 241. 75. R. Jazzar, H. Liang, B. Donnadieu and G. Bertrand, J. Organomet. Chem. 2006, 691, 3201. 76. C. C. Scarborough, I. A. Guzei and S. S. Stahl, Dalton Trans. 2009, 2284. 77. A. J. Arduengo, III, H. V. R. Dias, R. L. Harlow and M. Kline, J. A m. Chem. Soc. 1992, 114, 5530. 78. C. A. Tolman, Chem. Rev. 1977, 77, 313. 79. A. C. Hillier, W. J. Sommer, B. S. Yong, J. L. Petersen, L. Cavallo and S. P. Nolan, Organometallics 2003, 22, 4322. 80. R. Dorta, E. D. Stevens, N. M. Scott, C. Costabile, L Cavallo, C. D. Hoff and S. P. Nolan, J. Am. Chem. Soc. 2005, 127, 2485. 81. M. Lattman and R. A. Kemp, eds., Modern Aspects of Main Group Chemistry American Chemical Society, Washington DC, 2006. 82. G. Frenking, M. Sol and S. F. Vyboishchikov, J. Organomet. Chem. 2005, 690, 6178. 83. T. Scherg, S. K. Schneider, G. D. Frey, J. Schwarz, E. Herdtweck and W. A. Herrmann, Synlett, 2007, 18, 2894. 84. A. T. Termaten, M. Schakel, A. W. Ehlers, M. Lutz, A. L. Spek and K. Lammertsma, Chem. Eur. J. 2003, 9 3577.

PAGE 180

180 85. M. T. Lee and C. H. Hu, Organometallics 2004, 23, 976. 86. X. L. Hu, I. Castro Rodriguez and K. Meyer, J. Am. Chem. Soc. 2004, 126, 13464. 87. W. A. Herrmann and C. Kcher, Angew. Chem. Int. Ed. 1997, 36, 2163. 88. M. Nichues, G. Erker, G. K ehr, P. Schwab, R. Frhlich, O. Blacque and H. Berke, Organometallics 2002, 21, 2905. 89. X. Hu, I. Castro Rodriguez, K. Olson and K. Meyer, Organometallics 2004, 23, 755. 90. X. Hu, Y. Tang, P. Gantzel and K. Meyer, Organometallics 2003, 22, 612. 91. M Srebro and A. Michalak, Inorg. Chem. 2009, 48, 5361. 92. N. M. Scott, R. Dorta, E. D. Stevens, A. Correa, L. Cavallo and S. P. Nolan, J. Am. Chem. Soc. 2005, 127 3516. 93. R. Dorta, E. D. Stevens and S. P. Nolan, J. Am. Chem. Soc. 2004, 126, 5054. 94. K. Getty, M. U. Delgado Jaime and P. Kennepohl, J. Am. Chem. Soc. 2007, 129, 15774. 95. E. N. Jacobsen, A. Pfaltz and H. Yamamoto, eds., Comprehensive Asymmetric Catalysis I Springer -Verlag, Berlin Heidelberg, 1999. 96. M. F. Lappert, J. Organomet. Chem. 1988, 358, 185. 97. P. L. Arnold and S. Pearson, Coord. Chem. Rev. 2007, 251, 596. 98. D. Pugh and A. A. Danopoulos, Coord. Chem. Rev. 2007, 251, 610. 99. V. P. W. Bhm, T. Weskamp, C. W. K. Gstttmayr and W. A. Herrmann, Angew. Chem. Int. Ed. 2000, 39, 1602. 100. J. Huang, H. J. Schanz, E. D. Stevens and S. P. Nolan, Organometallics 1999, 18, 2370. 101. L. H. Gade and S. Bellemin -Laponnaz, Coord. Chem. Rev. 2007, 251, 718. 102. O. Khl, Chem. Soc. Rev. 2007, 36, 392. 103. R. J. Lowry, M. K Veige, O. Clment, K. A. Abboud, I. Ghiviriga and A. S. Veige, Organometallics 2008, 27, 5184. 104. C. M. Zhang and M. L. Trudell, Tetrahedron Lett. 2000, 41, 595. 105. D. S. Clyne, J. Jin, E. Genest, J. C. Gallucci and T. V. RajanBabu, Org. Lett. 2000, 2 1125. 106. L. G. Bonnet, R. E. Douthwaite and R. Hodgson, Organometallics 2003, 22 4384.

PAGE 181

181 107. W. L. Duan, M. Shi and G. B. Rong, Chem. Commun. 2003, 2916. 108. M. Shi and W. -L. Duan, Appl. Organometal. Chem. 2005, 19, 40. 109. Q. Xu, W. L. Duan, Z. Y. Lei, Z. -B. Zhu and M. Shi, Tetrahedron, 2005, 61 11225. 110. T. Chen, J. J. Jiang, Q. Xu and M. Shi, Org. Lett. 2007, 9 865. 111. T. Zhang, M. Shi and M. Zhao, Tetrahedron, 2008, 64, 2412. 112. W. Wang, T. Zhang and M. Shi, Organometallics 2009, 28, 2640. 113. T. Zhang and M. Shi, Chem. Eur. J., 2008, 14, 3759. 114. G. Ma, T. Zhang and M. Shi, Org. Lett. 2009, 11, 875. 115. Q. Xu, X. Gu, S. J. Liu, Q. Y. Dou and M. Shi, J. Org. Chem. 2007, 72, 2240. 116. Either the Pd(II) iodide, Pd(II) acetate, or Pd(II)trifluoroacetate 117. Several ligands were reported with similar BINAM -bis(benzimidazole) or H8 BINAM bis(benzimidazole) backbones, ligand variation was through alteration of N -substituents. 118. K. -L. Gibis, G. Helmchen, G. Huttner, L. Zsolnai a nd J. O. C. 181, J. Organomet. Chem. 1993, 445 181. 119. SHELXTL6; Bruker -AXS, Madison, WI, (2000). 120. M. S. Jeletic, I. Ghiviriga, K. A. Abboud and A. S. Veige, Organometallics 2007, 26, 5267. 121. Z. Shi and R. P. Thummel, J. Org. Chem. 1995, 60, 5935. 122. D. Bourissou, O. Guerret, F. P. Gabbai and G. Bertrand, Chem. Rev. 2000, 100, 39. 123. H. M. Tuononene, R. Roesler, J. L. Dutton and R. J. Ragogna, Inorg. Chem. 2007, 46, 10693. 124. E. Baba, T. R. Cundari and I. Firkin, Inorg. Chem. Acta, 20 05, 358, 2867. 125. All chiral versions are prepared in the same manner as the racemic excluding resolution procedures of the reported ligand. 126. R. J. Lowry M. T. Jan, K. A. Abboud, I. Ghiviriga, and A. S. Veige, Polyhedron in press, 2009. 127. M. S. Jeletic, M. T. Jan, I. Ghiviriga, K. A. Abboud and A. S. Veige, Dalton Trans. 2009, 2764.

PAGE 182

182 128. A. Pfaltz and I. William J. Drury, PNAS 2004, 101, 5723. 129. S. K. Schneider, J. Schwarz, G. D. Frey, E. Herdtweck and W. A. Herrmann, J. Organomet. Che m. 2007, 692, 4560. 130. H. Clavier, J. C. Guillemin and M. Mauduit, Chirality 2007, 19, 471. 131. W. A. Herrmann, L. J. Goossen and M. Spiegler, Organometallics 1998, 17 2162. 132. L. G. Bonnet, R. E. Douthwaite and B. M. Kariuki, Organometallics 2003, 22, 4187. 133. E. Bappert and G. Helmchen, Synlett, 2004, 1789. 134. J. J. Van Veldhuizen, J. E. Campbell, R. E. Guidici and A. H. Hoveyda, J. Am. Chem. Soc., 2005, 127 6877. 135. C. Bolm, T. Focken and G. Raabe, Tetrahedron: Asymmetry 2003, 14, 1733. 136. S. Gischig and A. Togni, Organometallics 2004, 23, 2479. 137. T. Frocken, G. Raabe and C. Bolm, Tetrahedron: Asymmetry 2004, 15, 1693. 138. T. Frocken, J. Rudolph and C. Bolm, Synthesis 2005, 3 429. 139. A. A. D. Tulloch, A. A. Danopoulos, G. J. Tizzard, S. J. Coles, M. B. Hursthouse, R. S. Hay Motherwell and W. B. Motherwell, Chem. Commun. 2001, 1270. 140. A. A. Danopoulos, A. A. D. Tulloch, S. Winston, G. Eastham and M. B. Hursthouse, J. Chem. Soc. Dalton Trans. 2003, 1009. 141. M. C. Perry, X. H. Cui and K. Burgess, Tetrahedron: Asymmetry 2002, 13, 1969. 142. M. Y. Machado and R. Dorta, Synthesis 2005, 15, 2473. 143. M. Shi and H. X. Qian, Tetrahedron, 2005, 61, 4949. 144. C. Marshall, M. F. Ward and W. T. A. Harrison, Tetrahed ron Lett. 2004, 45, 5703. 145. C. Marshall, M. F. Ward and W. T. A. Harrison, J. Organomet. Chem. 2005, 690, 3970. 146. A. R. Chianese and R. H. Crabtree, Organometallics 2005, 24, 4432. 147. T. Makino, H. Masu, K. Katagiri, R. Yamasaki, I. Azumaya and S. Saito, Eur. J. Inorg. Chem. 2008, 4861. 148. Adapted with permission from R. J. Lowry, M. K. Veige, O. Clment, K. A. Abboud, I. Ghiviriga and A. S. Veige, Organometallics, 2008, 27, 5184. Copyright 2008 American Chemical Society.

PAGE 183

183 149. R. H. Crabtree, J. Organomet. Chem. 2006, 691, 3146. 150. J. A. Mata, A. R. Chianese, J. R. Miecznikowski, M. Poyatos, E. Peris, J. W. Faller and R. H. Crabtree, Organometallics 2004, 23, 1253. 151. C. H. Leung, C. D. Incarvito and R. H. Crabtree, Organometallics 2006, 25, 6099. 152. Y. A. Wanniarachchi, M. A. Khan and L. M. Slaughter, Organometallics 2004, 23, 5881. 153. S. Burling, L. D. Field, H. Li, B. A. Messerle and R. Turner, Eur. J. Inorg. Chem. 2003, 3179. 154. B. M. Trost, D. L. Van Vranken and C. Bingel, J. Am. Chem. Soc. 1992, 114, 9327. 155. E. Fox, A. Gerlach, I. C. Lennon, G. Meek and C. Praquin, Synthesis 2005, 19, 3196. 156. C. L. Lee, W. Yang and R. G. Parr, Phys. Rev. B. 1988, 37, 785. 157. T. H. Dunning Jr. and P. J. Hay, in Methods of Electronic Structure Theory ed. H. F. Schaefer III, Plenum Press, New York, Editon edn., 1977, vol. 2. 158. P. J. Hay and W. R. Wadt, J. Chem. Phys. 1985, 82, 270. 159. P. J. Hay and W. R. Wadt, J. Chem. Phys. 1985, 82, 284. 160. P. J. Hay and W. R. Wadt, J. Chem Phys. 1985, 82, 299. 161. Gaussian 03, Revision E.01,M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgomery, T. Vreven Jr., K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al -Laham, C. Y. Peng, A. Nan ayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonzalez and J. A. Pople, Gaussian, Inc., Wallingford CT, 2004. 162. In order to avoid formation of the diacid, the water used in Lennon et al.s reaction of the diacid chloride w as replaced with N,N dimethyl formamide. 163. A. A. Gridnev and I. M. Mihaltseva, Synth. Commun. 1994, 24, 1547. 164. J. P. Liu, J. B. Chen, J. F. Zhao, Y. H. Zhao, L. Li and H. B. Zhang, Synthesis 2003, 2661. 165. Hydrogenation was accomplished in a ste el Parr Instruments autoclave.

PAGE 184

184 166. M. Karplus, J. Am. Chem. Soc., 1963, 85, 2870. 167. F. E. Hahn, T. von Fehren and T. Lugger, Inorg. Chem. Acta, 2005, 358, 4137. 168. A. Poatter, F. Ragone, S. Giudice, C. Costabile, R. Dorta, S. P. Nolan and L. Cavallo, Organometallics 2008, 27, 2679. 169. M. K. Denk, A. Hezarkhani and F. Zheng, Eur. J. Inorg. Chem. 2007, 3527. 170. T. A. Taton and P. Chen, Angew. Chem. Int. Ed. 1996, 35, 1011. 171. C. Heinemann and W. Thiel, Chem. Phys. Lett. 1994, 217, 11. 172. E. A. Carter and W. A. Goddard III, J. Phys. Chem. 1986, 90, 998. 173. Y. Liu, P. E. Lindner and D. M. Lemal, J. Am. Chem. Soc. 1999, 121, 10626. 174. D. C. Graham, K. Cavell and B. F. Yates, J. Phys. Org. Chem. 2005, 18, 298. 175. R. W. Alder and M. E. Blake, J. Phys. Chem. A 1999, 103, 11200. 176. G. C. Lloyd Jones, R. W. Alder and G. J. J. Owen -Smith, Chem. Eur. J., 2006, 12, 5361. 177. K. Tomioka, Y. Nagaoka, V. In Comprehensive Asymmetric Catalysis, E. N. and A. P. Jacobsen, H. Yamamoto (Eds.), Springer: Berlin, 1999, 31.1, in Comprehensive Asymmetric Catalysis eds. E. N. Jacobsen, A. Pfaltz and H. Yamamoto, Springer, Berlin, Editon edn., 1999, vol. 3, pp. 11051120. 178. K. Kobayashi, T. Nishikata, Y. Yamamoto and N. Miyaura, Bull. Chem. Soc. Jpn. 2008, 81, 1019. 179. T. Hayashi and K. Sasaki, Chemistry Lett. 2008, 37, 842. 180. R. Shintani and T. Hayashi, Chemistry Lett. 2008, 37, 724. 181. Y. J. Xu, L. -Z. Gong, A. -Q. Mi and Y. -Z. Jiang, Synthesis 2004, 7 1057. 182. G. M. Villacorta, C. P. Rao and S. J. Lippard, J. Am. Chem. Soc., 1988, 110, 3175. 183. B. L. Feringa, M. Pineschi, L. A. Arnold, R. Imbos and A. H. M. De Vries, Angew. Chem. Int. Ed. 1997, 36, 2620. 184. S. J. Degrado, H. Mizutani and A. H. Hoveyda, J. Am. Ch em. Soc. 2001, 123 755. 185. B. Breit and A. C. Laungani, Tetrahedron Asym. 2003, 14, 3823. 186. M. T. Reetz, A. Gosberg and D. Moulin, Tetrahedron Lett. 2002, 43, 1189. 187. I. J. Krauss and J. L. Leighton, Org. Lett. 2003, 5 3201.

PAGE 185

185 188. S. Oi, M. Moro, S. Ono and Y. Inoue, Chem. Lett. 1998, 27, 83. 189. T. Hayashi and M. Ishigedani, J. Am. Chem. Soc., 2000, 122, 976. 190. S. Oi, M. Moro, H. Ito, Y. Honma, S. Miyano and Y. Inoue, Tetrahedron, 2002, 58, 91. 191. M. Dziedzic, M. Malecka and B. Furman, Org. Lett. 2005, 7 1725. 192. S. Oi, Y. Honma and Y. Inoue, Org. Lett. 2002, 4 667. 193. T. Hayashi, N. Tokunaga, K. Yoshida and J. W. Han, J. Am. Chem. Soc. 2002, 124, 12102. 194. N. Tokunaga, K. Yoshida and T. Hayashi, Proc. Natl. Acad. Sci. USA 2004, 101, 5445. 195. K. C. Nicolaou, W. Tang, P. Dagneau and R. Faraoni, Angew. Chem. Int. Ed. 2005, 44, 3874. 196. N. Miyaura and Z. Suzuki, Chem. Rev. 1995, 95, 2457. 197. D. G. Hall, ed., Boronic Acids: Preparation and Applications in Organic Synthesis and Medicine Wiley -VCH, Weinheim, 2005. 198. M. Sakai, H. Hayashi and N. Miyaura, Organometallics 1997, 16, 4229. 199. Y. Takaya, M. Ogasawara, T. Hayashi, M. Sakai and N. Miyaura, J. Am. Chem. Soc., 1998, 120 5579. 200. T. Hayashi, M. Taka hashi, Y. Takaya and M. Ogasawara, J. Am. Chem. Soc. 2002, 124, 5053. 201. N. Miyaura, Bull. Chem. Soc. Jpn. 2008, 81, 1543. 202. A. Kina, H. Iwamura and T. Hayashi, J. Am. Chem. Soc. 2006, 128, 3904. 203. B. P. Morgan and R. C. Smith, J. Organomet. Chem. 2008, 693, 11. 204. T. Gendrineau, O. Chuzel, H. Eijsberg, J. P. Genet and S. Darses, Angew. Chem. Int. Ed. 2008, 47, 7669. 205. W. C. Yuan, L.-F. Cun, A. Q. Mi, Y. Z. Jiang, L. Z. Gong and W. C. Yuan, Tetrahedron, 2009, 65, 4130. 206. R. Mariz, X. Luan, M. Gatti, A. Linden and R. Dorta, J. Am. Chem. Soc. 2008, 130, 2172. 207. R. Shintani, Y. Ichikawa, K. Takatsu, F. -X. Chen and T. Hayashi, J. Org. Chem. 2009, 74, 869. 208. R. Jana and J. A. Tunge, Org. Lett. 2009, 11, 971.

PAGE 186

186 209. R. Mariz, A. Bric eno, R. Dorta and R. Dorta, Organometallics 2008, 27, 6605. 210. S. Helbi, S. Sauer, N. Cramer, S. Laschat, A. Baro and W. Freya, Adv. Synth. Catal. 2007, 349, 2331. 211. Y. Ma, C. Song, C. Ma, Z. Sun, Q. Chai and M. B. Andrus, Angew. Chem. Int. Ed. 2003, 42, 5871. 212. C. Song, C. Ma, Y. Ma, W. Feng, S. Ma, Q. Chai and M. B. Andrus, Tetrahedron Lett. 2005, 46, 3241. 213. J. -M. Becht, E. Bappert and G. Helmchen, Adv. Synth. Catal. 2005, 347, 1495. 214. G. Dyson, J. C. Frison, S. Simonovic, A. C. Whitwood and R. E. Douthwaite, Organometallics 2008, 27, 281. 215. F. Guillen, C. L. Winn and A. Alexakis, Tetrahedron: Asymmetry 2001, 12, 2083. 216. J. Pytkowicz, S. Roland and P. Mangeney, Tetrahedron: Asymmetry 2001, 12, 2087. 217. A. Alexakis, C. L. Winn, F. Guillen, J. Pytkowicz, S. Roland and P. Mangeney, Adv. Synth. Catal. 2003, 345. 218. C. L. Winn, F. Guillen, J. Pytkowicz, S. Roland, P. Mangeney and A. Alexakis, J. Organomet. Chem. 2005, 690, 5672. 219. H. Clavier, L. Coutable, L. Toupet, J. C. Guillemin and M. Mauduit, J. Organomet. Chem. 2005, 690 5237. 220. K. -s. Lee, M. K. Brown, A. W. Hird and A. H. Hoveyda, J. Am. Chem. Soc. 2006, 128, 7182. 221. M. K. Brown, T. L. May, C. A. Baxter an d A. H. Hoveyda, Angew. Chem. Int. Ed. 2007, 46, 1097. 222. F. Gini, B. Hessen and A. J. Minnaard, Org. Lett. 2005, 7 5309. 223. T. Nishikata, Y. Yamamoto and N. Miyaura, Adv. Synth. Catal. 2007, 349, 1759. 224. T. Nishikata, Y. Yamamoto and N. Miyaura Tetrahedron Lett. 2007, 48, 4007. 225. C. S. Cho, S. Motofusa, K. Ohe and S. Uemura, J. Org. Chem. 1995, 60, 883. 226. X. Lu and S. Lin, J. Org. Chem. 2005, 70, 9651. 227. P. Kask, V. B. Arion and M. Widhalm, Tetrahedron: Asymmetry 2006, 17, 3084.

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187 BIOGRAPHICAL SKETCH Roxy Joanne Lowry was born in the town of Melba Idaho in the summer of 1982. Her love of science and teaching manifest ed early in her education leading to her unofficial status of math and science tutor throughout high school After graduatin g as v aledictorian of Greenleaf Friends Academy in 2000, she attended George Fox University to further investigate her interest in c hemistry She enjoyed a variety of research experiences throughout her undergraduate career; spending two ye ars investigating binary precursors for self assembled monolayers with Dr. Carlisle Chambers and a summer researching endocrine disruptors in the environment with Dr. Eugene Billiot in Corpus Christi, TX Roxy graduated from GFU magna cum laude with a Bac helor of Science in chemistry in May 2004. Combining her desire to further her education and to experience new places she left the Northwest to begin her graduate career at the University of Florida. There she discovered her interest in organometallic chemistry under the advisement of Dr. Adam Veige. Subsequent to completing her Ph.D. at University of Florida she has accepted a position with Dr. Brookhart and Dr. Meyer at University of North Carolina Chapel Hill developing solar cells as part of a Energ y Frontier Research Center.