|Table of Contents|
Table of Contents
List of Tables
List of Figures
Chapter 1. Introduction
Chapter 2. Materials and procedures
Chapter 3. Synthesis of cyclometallated imine cations
Chapter 4. Syntheses of cyclometallated ruthenium amide complexes
Chapter 5. Kinetics and reactivitiy studies on the cyclometallated ruthenium amide complexes
Chapter 6. Summary
SYNTHESIS OF RUTHENIUM AMIDE COMPLEXES BY NUCLEOPHILIC
ATTACK ON CYCLOMETALLATED IMINE LIGANDS
GAINES CHARLES MARTIN
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 1991
Over the past several years, there has been a growing list of people to whom the author owes a great deal of thanks. Professor James M. Boncella in his role as research director, friend and confidant. His influence has led to the author's greater appreciation of chemistry and science. It has been good fortune to have had his guidance during this time.
Dr. George Ryschkewitsch, Dr. David Richardson, Dr. William Jones, and Dr. David Clark have been very helpful in creating a learning environment which has been both stimulating and fruitful. The assistance of certain support faculty, especially Dr. Roy W. King, has been one of the immeasurable benefits of being a student in this department. The crystallographic data and structures presented in this work were obtained and solved by Dr. E.J. Wucherer of the University of Louisville. His efforts deserve special thanks, and the author is deeply indebted.
The author would like to acknowledge several of his peers in graduate
school who deserve mention due to their positive input on the author's progress through graduate school; they are Thomas Cundari, Alan Goldstein, and Greg Harris. Don Swieter must also be acknowledged for his very special role in
introducing the author to chemistry and aiding in the authors development throughout graduate school. The assistance of Julia Alvarez in assembling this manuscript was extremely important and essential for its timely completion, and the author extends heartfelt thanks for her contribution.
The author gratefully acknowledges the financial support of this research by the Department of Chemistry, University of Florida, and by the Petroleum Research Fund, administered by the American Chemical Society, and the National Science Foundation.
Finally, the author expresses his gratitude to his mother for providing the support that only a mother can provide, which can never be repaid, and to his father who was not here to see the completion of this work.
TABLE OF CONTENTS
ACKNOW LEDGEMENTS .................................... ii
LIST O F TABLES ......................................... vi
LIST O F FIG URES ........................................ vii
A BSTRACT ............................................. x
1 INTRODUCTION ................................ 1
2 MATERIALS AND PROCEDURES ................... 8
M aterials ................................. 8
Procedures ............................... 9
3 SYNTHESIS OF CYCLOMETALLATED
IM INE CATIO NS ............................... 11
Experim ental ............................. 11
Physical Properties ........................ 28
Cyclometallation Reactions ................... 36
4 SYNTHESES OF CYCLOMETALLATED
RUTHENIUM AMIDE COMPLEXES ................. 43
Experim ental ............................. 43
Physical properties ........................ 49
Stereochemistry of Lithium
Alkyl and Hydride Addition .................. 52
Varible Temperature NMR Studies on
(n -C6Me6)Ru(Me2PhNC(H)(Me)Ph)(PMe3), 6 ... 54
5 KINETICS AND REACTIVITY STUDIES ON THE
CYCLOMETALLATED RUTHENIUM AMIDE
COMPLEXES ................................. 71
Introduction .............................. 71
Experim ental ............................. 74
Discussion .............................. 92
(n -C6H6)Ru(PhNC(H)(Me)Ph)(PMe3) .........102
Reactions with Electrophilic
Reagents .............................. 105
6 SUM MARY ................................... 114
REFERENCES ..................................... 119
BIOGRAPHICAL SKETCH ............................. 123
LIST OF TABLES
1. Summary of the Imine Cations Listed in the
Experim ental Section .................................. 14
2. Selected Bond Lengths and Angles from the
X-Ray Structural Analysis of 1a .......................... 38
3. Summary of the Amide Complexes Listed in the
Experimental Section .................................. 55
4. Selected Bond Lengths and Angles from the
X-Ray Structural Analysis of 2a .......................... 63
5. Ln 3a vs. t Data for Isomerization at 301C .................. 76
6. Ln 3a1 vs. t Data for Isomerization at 400C ................... 78
7. Ln [Laj vs. t Data for Isomerization at 500C .................. 80
8. Ln 3[a vs. t Data for Isomerization at 600C .................. 82
9. Ln Qal vs. t Data for Isomerization at 70C ................... 84
10. Ln r3al vs. t Data for Isomerization at 700C
with a 40:1 Excess of PMe3 ............................ 86
11. Ln r3a] vs. t Data for Isomerization at 700C
with added P(CD3)3 .................................. 88
12. Eyring Plot to Determine Thermodynamic
Parameters for the Isomerization of 3a to 2a ................. 90
LIST OF FIGURES
1. Amination of Norbornene Using An Amide Catalyst ............. 2
2. The Transition Series, Illustrating the Separation
of the ETMs and the LTMs .............................. 3
3. Planar and Pyramidal Amide Linkages ...................... 4
4. Potential Back Donation from Amide Nitrogen Lone Pair ......... 5
5. Formation of a Transition Metal Amide by Nucleophilic Attack on
A Coordinated Imine ................................... 6
6. Proton NMR Spectrum of la ............................ 31
7. Two-Dimensional COSY NMR Spectrum of a ............... 32
8. Illustration of the Chemical Shift Inequivalent Protons in 1a ...... 33
9. Illustration of the Number of Potentially Chemical Shift Inequivalent
Protons in a Monodentate Imine Complex ................... 34
10. Possible Hindered Rotation About the C-N Bond of la due to Steric
Encumberance ...................................... 35
11. ORTEP Drawing of 1 a from X-Ray Analysis ................. 37
12. Proposed Mechanism for the Formation of la ................ 40
13. Hydrolysis of the Intermediate Imine Cation
Yielding Aniline Complex and Benzaldehyde ................. 42
14. Proton NMR Spectrum of 2a with Expanded View of
Benzylic Hydrogen Coupling............................. 51
15. Proton NMR Spectrum of 2c with Expanded View of
Benzylic Hydrogen Coupling ............................ 53
16. Diastereoselectivity Exhibited by Addition
of MeLi to 1a Producing 2a ............................. 54
17. Diastereoselectivity Exhibited by Addition of Hydride
Across the C-N Double Bond of the Coordinated Imine in 1 b
Leading to Compound 2b .............................. 56
18. Summary of the Observed NOE Enhancement in 2a ........... 57
19. NOE Experiment Showing Irradiation of the i6-C6Me6 Peak of 2a 58 20. NOE Experiment Showing Irradiation of the PMe3 Peak of 2a .... 59 21. ORTEP Drawing of 2a from X-Ray Analysis ................. 62
22. Structural Representation of Compound 6 ................... 65
23. Proton NMR Spectrum of Compound 6 ..................... 66
24. Variable Temperature Proton NMR Spectra of the
Ortho Protons of 6. .................................. 67
25. Variable Temperature Proton NMR Spectra of the
Methyl Protons of 6 ................................... 69
26. Illustration of the Possible Modes of Addition of an Incoming
Nucleophile to the Imine C-N Bond ....................... 72
27. Isomerization of 3a to 2a, Showing Nomenclature
and the Relative Geometries ............................ 73
28. Plot of In 3al vs. t for Isomerization at 300C ................. 77
29. Plot of In [3a] vs. t for Isomerization at 400C ................. 79
30. Plot of In [3a] vs. t for Isomerization at 501C ................. 81
31. Plot of In  vs. t for Isomerization at 600C ................. 83
32. Plot of In [3al vs. t for Isomerization at 700C .................. 85
33. Plot of In [3a] vs. t for Isomerization at 700C
with an 40:1 Excess of PMe3 ........................... 87
34. Plot of In [3al vs. t for Isomerization at 700C
with added P(CD3)3 .................................. 89
35. Eyring Plot to Determine AH I and AS'
for the Isomerization of 2a to 3a .......................... 91
36. Two possible Intermediates in the Mechanism
for the Isomerization of 3a to 2a .......................... 94
37. Mechanistic Steps for the Isomerization of 3a to 2a and the
Rate Equation for the Observed Isomerization Process ......... 97 38. Incorporation of P(CD3)3 into 3a ........................ 100
39. Routes to the Incorporation of P(CD3)3
into 2a during the Isomerization of 3a o 2a ................ 101
40. Proposed Planar Intermediate During the
Isomerization of 3a to 2a .............................. 103
41. Addition of Hydride Across the Imine C-N Bond and the Addition of
Hydride to the Arene Ring in i ......................... 104
42. Proton NMR Spectrum of Product of Reaction
of li with Li(t-OBu)3AIH in C6D6 ........................ 106
43. Proton NMR Spectrum of Product of Reaction
of 1i with Li(t-OBu)3AIH in C6D6 After 2 Weeks ............. 107
44. Reaction of 2a with HBF4 to Form 7 ..................... 108
45. Proton NMR Spectrum of 7 in CDC13 .................... 109
46. Possible Product of Reaction of 2a with DMA ............... 110
47. Proton NMR Spectrum of Reaction of 2a with DMA ........... 111
48. gosphorus NMR Spectrum of 15N enriched 2a Showing
P- 'N Coupling .................................. 112
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
SYNTHESIS OF RUTHENIUM AMIDE COMPLEXES BY NUCLEOPHILIC
ATTACK ON CYCLOMETALLATED IMINE LIGANDS
Gaines Charles Martin
Chairman: Professor J.M. Boncella Major Department: Chemistry
Compounds of the type (n6-C6R6)Ru(PMe3)X2 (where R=H or alkyl and
X=CI or I) react with two equivalents of a variety of benzylidene imines and two equivalents of AgBF4 to give cationic orthometallated ring complexes of the type [(n6-C6R6)Ru((R')N=C(R")C6H4)(L)]+BF4- (where R'=phenyl or alkyl, R"=H, alkyl).
Strong nucleophiles ( R, H) add to the imine carbon to give the amide complexes (rI6-C6R6)Ru((R')NC(R")(R'")C6H4)(PMe3), (where R"'=H or alkyl). These are formed with ca. 100% diastereoselectivity in a kinetically controlled addition reaction.
Physical, chemical and spectral properties of the imine and amide
complexes are discussed in detail. Crystal structures of both a cyclometallated imine cation and an amide of ruthenium are reported. Investigations into the reactivity of these amido complexes with electrophiles are conducted. Studies
of the dynamics of the amide complexes using NMR techniques include determination of the activation barriers for rotation about slowly rotating bonds.
Discussion of the synthetic methods includes addressing factors affecting the diastereoselectivity of nucleophilic attack, which appears to be the result of extreme crowding in the molecules. The mechanism by which the kinetic product isomerizes to the thermodynamic product is addressed. A kinetic study provided the enthalpy and entropy of activation for the isomerization process. The isomerization follows first order kinetics and may occur via phosphine dissociation or arene ring slippage.
The use of transition metals in catalysis has led to more economical and efficient means to produce important industrial and consumer materials.1 Amongst these materials are aminated compounds. These are organic compounds which have been functionalized by incorporation of an amine group into their structures, in this case using an organometallic catalyst. The reaction shown in Figure 1 is an example of the reaction of a transition metal amide complex with an organic molecule leading to the replacement of a double bond with an amine group.2
Although there are numerous methods by which these aminated
compounds may be prepared, industrial demands on quality, purity of product, and economy of processes inspire a never ending search for better routes to products.3 As a result, interest in the synthesis of late-transition metal amide complexes has been heightened in the past several years, primarily due to their possible use as catalysts in C-N bond forming reactions.4
Late transition metal amide (LTM) complexes are a relatively new class of compounds. LTMs are those metals occurring in the transition series
following and including the Fe, Ru, Os triad of the periodic table of the elements, as shown in Figure 2.
Et3 P" Ir % H + NH2 Ph PhHN
C1 I NHPh -[Ir]
Figure 1. Amination of Norbomene Using an Amide Catalyst.
The amide linkage is characterized by a metal-nitrogen a-bond, a three coordinate nitrogen atom, and a lone electron pair on the nitrogen atom, as shown in Figure 35. This is in contrast to the amine linkage, which may be described as a dative bond to the metal through the nitrogen lone pair electrons and a four coordinate nitrogen atom. In the figure, the R groups can be H, alkyl, aryl, or heteroatom groups such as SiMe3. The amide group has been shown crystallographically to adopt either a planar or tetrahedral geometry.6
Late transition metal complexes differ from their early transition metal (ETM) counterparts in a number of ways.7 Early transition metals are more electropositive than LTMs, and their compounds tend to exhibit more ionic character. Early transition metals are often considered to be hard acids. They
Sc Ti V Cr Mn Fe Co Ni Cu Zn
Y Zr Nb Mo Tc Ru Rh Pd Ag Cd
La Hf Ta W Re Os lr Pt Au Hg
Early Transition Metals Late Transition Metals
Figure 2. The Transition Series, Illustrating the Separation of the ETMs and the LTMs.
tend to interact favorably with hard bases and form stable compounds with them. Late transition metals are considered to be soft acids and usually do not form stable compounds with hard bases.8 Since the NR2" group is considered to be an exempliary hard base, the inherent stability of the LTM amide is questionable. In terms of bonding capabilities, the trend with the ETMs is that they often possess vacant d-orbitals of proper symmetry and energy to favorably interact with 7-donor orbitals of ligands. With the LTMs, these same orbitals are usually the HOMO of the metal and are not able to interact favorably with 7c-donor ligands.9 Thus, the ETM amides are usually planar about the nitrogen, while the LTM amides are pyramidal.
In general, the metal-nitrogen bond in LTM amides has more covalent character than that of ETM amides, as would be expected depending on oxidation state.10 Since LTMs have d-orbitals which are incapable of
Ln M- N R LnM N
Figure 3. Planar and Pyramidal Amide Unkages
interacting favorably with i-donors, the amide lone pair must be localized on the nitrogen or be delocalized onto other N-bonded substituents such as a phenyl group or some other electron withdrawing group, Figure 4.11 Thus, resonance and inductive effects may also be important in LTM amides, stabilizing the amide functionality in a fashion similar to the ETM amide's 7C bonding capability.
In the absence of n-donation, the lone electron pair of the LTM amide is forced to remain localized on the nitrogen atom and subsequently behaves as a potent nucleophile. In addition, due to the greater covalent character of the LTM amide M-N bond in contrast to that of the ETM amide, the LTM amide exhibits chemical reactivity reminiscent of the isoelectronic metal alkyl complexes of the LTMs, for example the observation of migration of the amide group and possession of similar homolytic bond dissociation energies.12
Transition metal amide compounds have most frequently been
synthesized by metathetical exchange of a halide or other leaving group with an alkali-metal amide.1 3 This method, although useful for the syntheses of some compounds, can suffer from undesirable side reactions such as reduction of the metal or deprotonation of the ancillary ligands. It is possible that amide complexes of metals such as ruthenium are uncommon due to a lack of viable synthetic procedures rather than because of thermodynamic instability of the MNR2 bond. Recent studies indicate that when such compounds can be made, they are at least moderately stable.1 4
M N R
Figure 4. Potential, Back Donation from Amide Nitrogen Lone
Thus, this work has examined an alternative route to such compounds in order to facilitate the development of their chemistry. The objectives of this research were first to prepare any precursor compounds neccessary to make amides, second to prepare the amides, third to study their properties and behavior, and fourth to study their reaction chemistry.
The synthetic procedure used here exploits the enhanced electrophilicity of the carbon atom of an imine that is coordinated to a transition-metal cation. Attack of a nucleophile at the coordinated imine as shown in Figqure 5, will lead to the formation of the desired amide complex.
/R + R
Ln M-N + Nu Ln M-N
R + NNu
Figure 5. Formation of a Transition Metal Amide
by Nucleophilic Attack on a Coordinated Imine.
Although monodentate N-bound imine complexes are rare as a result of the weak Lewis basicity of the imine nitrogen,15 orthometallated benzylideneaniline complexes can be readily prepared from LTM halides. Orthometallated complexes of Schiff bases and other N-donor ligands that are related to the metallated cations prepared in this work are well-known, and their chemistry has been reviewed in separate work by Bennett.16 Since the orthometallated benzylideneaniline complexes contain an imine coordinated to a metal cation, the imine carbon should be susceptible to nucleophilic attack, giving an orthometallated benzylphenylamide as the product.
Ruthenium is a late transition metal whose complexes in the 2 oxidation state are well known.17 Compounds of the formula (T16_Arene)Ru(L)(X)2, prepared originally by Bennett, were the starting materials for the study.1 8 These compounds may be prepared using a variety of different arene groups, two electron donor ligands (L), or halogens (X). Their syntheses are straightforward and the compounds are air-stable. The cyclometallated imine cations were prepared by reactions of these compounds with imines and silver salts. 19
Chapter Two provides a quick glance at the reagents and methods used in this study. Chapter Three introduces the general reaction used to prepare the cation precursors to the amides. These cations were themselves studied in detail in terms of properties and reactivity, and this work is also discussed in Chapter Three. Chapter Four introduces the general reaction used to prepare the LTM amides, and some of the properties of the amides. In Chapter Five, the behavior and reactivity of the amides are discussed.
CHAPTER 2 MATERIALS AND PROCEDURES
Ruthenium (ll) Chloride
Ruthenium trichloride was purchased from the Johnson-Mathey Chemical Company and was used without further purification.
Amines were distilled from Na and stored in resealable ampules.
Imines were prepared by literature methods20, sublimed prior to use and stored in a drybox.
Methyl lithium, phenyl lithium, and Li(t-OBu)3AIH were obtained from Aldrich Chemical Company and used without further purification.
The silver tetrafluoroborate was obtained from Aldrich Chemical
Company. It was dried by heating at 1100 under vacuum for eight hours, and was stored in a drybox.
Diethyl ether, pentane, hexanes, toluene, and benzene were dried using sodium benzphenone ketyl and distilled before use. Tetrahydrofuran was dried using sodium-potassium alloy followed by distillation. Dichloromethane was dried using phosphorus pentoxide followed by distillation. All were stored over 4A molecular sieves.
All deuterated solvents were purchased from MSD Isotopes, Johnson Mathey, or Aldrich Chemical Company. They were dried using 4A molecular sieves and stored over 4A molecular sieves.
Protection from Atmosphere
All manipulations were carried out under an atmosphere of either
dinitrogen or argon, using standard glovebox or Schlenk line techniques, except for workup of the cations, which are stable in air.
Infrared spectra were obtained using either a Nicolet 5DXB FT-IR or Perkin-Elmer 1600 FT-IR spectrophotometer.
Nuclear Maqnetic Spectra
Carbon and proton NMR spectra were recorded on either a JEOL FX100, Varian FX-200, Varian 300-VXR, or General Electric QE-300 NMR spectrometer. Phosphorus NMR spectra were recorded on a Varian 300-VXR NMR spectrometer.
All melting points were determined using a Thomas-Hoover Melting Point Apparatus.
Linear regression and error calculations were performed using the Quattro software package.
Elemental analyses were obtained from Atlantic Microlabs or the analytical services at the University of Florida.
SYNTHESIS OF CYCLOMETALLATED RUTHENIUM IMINE CATIONS
The synthesis of imine cations was accomplished in an attempt to
incorporate a nitrogen containing imine functionality into a cationic ruthenium complex. Doing so would perhaps enable nucleophilic addition to the imine C-N double bond to occur in subsequent reactions, thereby producing the amide functionality.
Most of the variations attempted during the development of the
cyclometallation reactions are summarized here for the sake of brevity. A noncoordinating solvent is required for these reactions. The reactions have been attempted in tetrahydrofuran, with an intractable mixture of products being formed. The reactions have been successfully carried out in mixed dichloromethane-benzene solutions. As per methods used by other workers to prepare related cyclometallated compounds, the synthesis of the cations has also been attempted by using various solvents such as methanol, acetone, and acetic acid.21 Attempted reactions in all of these solvents led to mixtures of unidentifiable products.
Leaving groups which have successfully led to the cyclometallated
products include only chloride and iodide ions. Attempts to prepare the acetate, triflate, or nitrate salts (instead of using the fluoroborate salts) by heating have proven unsuccessful. For example, heating (1j6-C6Me6)Ru(OAc)2PMe3 in the presence of imines has resulted in mixtures of products, and no evidence of the cyclometallated cations.22
Sometimes dark green solutions, instead of the normal yellow solutions, result from the cyclometallation attempts. After the methylene chloride is removed, the green-colored residue is more soluble in tetrahydrofuran than the normal yellow product, and requires workup using an alumina column, which removes the impurity which produces the green color from the mixture. The green coloration may be due to the reduction of Ag+ and resulting formation of dark metallic silver in otherwise yellow solutions.
Bulky imines such as Ph2C=NPh, s-(-)-PhC(H)=NC(H)(CH3)Ph and
PhC(H)=NtBu did not produce cyclometallated products. This is due either to the steric crowding of the product, or to electronic factors such as the weak Lewis basicity of Ph2C=NPh. The phenyl ring in Ph2C=NPh is electron withdrawing enough so that the ligand may not coordinate to the metal, since the nitrogen electron pair is weakly basic.23 The cations have been prepared using benzene, cymene, and hexamethylbenzene rings as arene ligands. The ligands trimethylphosphine, triethylphosphine, and carbon monoxide have all been used to prepare the cations by this method. There
appears to be a steric restriction on-the choices of ligands and ligand combinations available in the synthesis of the cations, since cations of large imines and phosphines could not be made.
The list of syntheses below demonstrates that the method of
cyclometallation is an effective and versatile route to a new class of transition metal imine cations. The general reaction used to form the imine cations is summarized in equation 3-1. Table 1 is a list of the cations whose synthesis is described in this study. All of the cyclometallated cations may be isolated after their synthesis by use of chromatographic separation. Some of the cations could not be isolated by techniques other than through the use of chromatography.
R < R
R R + 2AgBF4 + 2 R'N=-OR'Ph
L Ru. CI
R R +
CI R R + BF4
R -7-- R Equation 3-1
R I R
QH-CNR ...... "I R'
2 AgCI L
Table 1. [mine Cations Prepared in this Study.
R R + BFRl Rl 4
Compound R R'RfL
I a CH 3 H C61-5 PMe3
l b OH 3 CH3 C 6H 5 PMe 3
1c OH3 H C6H4CH3 PMe3
1d H H 6 H 5 'Me 3
1e H H C61-5 PEt3
1f H H CH 2 H3 PMe 3
i g p-Cymene H C61-15 PMe3
1h OH 3 H C61-15 00
ii H OH3 06HA PMe3
lj OH 3 H (3,5-Me2)O6H 3 PMe3
1 k OH 3 H CH2CH3 PMe3
iip-Oymene CH 3 C 6H 5 PEt3
Preparation of [(16-C Me6)Ru((Ph)N=C(H)C6H)(PMe3)]BF4,la.
To a stirring solution of (1n6-C6Me6)RuPMe3CI2 (0.277g, 0.675mmol)
was added 0.262g ( 1.35mmol) of benzylidene aniline and 0.263g (1.35mmol) AgBF4 as a mixture in 50mL dichloromethane. An immediate color change from red to yellow was accompanied by the appearance of a white ppt. The reaction was stirred for six hours and allowed to settle for one hour. Filtration of the yellow solution followed by solvent removal under reduced pressure gave a yellow foamy material which was washed with pentane (3xl0mL) and Et20 (3xlOmL). The material was scraped from the sides of the flask and washed with THF (3xlOmL). The resultant bright yellow solid was isolated as the crude product ( 0.287g, 0.473mmol), 70% yield. Crystals suitable for elemental analysis may be obtained from a CH2C12/pentane layer. Anal. Calcd for C28H37BF4NPRu: C 55.4; H 6.15; N 2.31. Found: C, 55.2; H, 6.25; N, 2.29. Mp 280-2820 C (dec). IR(Nujol, cm-1): 1535, 1585. 1H NMR (300 MHz, CDCI3, 220 C): 8.33 (d, JP-H= 2.9 Hz, 1 H, imine H); 7.66 (d, JH-H=8.4 Hz, 1 H, phenyl H.); 7.52 (d, JH-H=8.1 Hz, 1 H, phenyl H); 7.46 (t, JH-H=8.4 Hz, 2 H, aniline H); 7.33 (t, JH-H=7.2 Hz, 1 H, aniline H); 7.25 (d, JH-H=8.1 Hz, 2 H, aniline H); 7.19 (t, JH-H=8.1 Hz, 1 H, phenyl H); 7.04 (t, JH-H=7.8 Hz, 1 H, phenyl Hj); 1.80 (s, 18 H, C6Me6), 1.07 (d, JP-H=9.1 Hz, 9 H, PMe3). 13C[1H] NMR (74.4 MHz, CDCI3, 220 C): 187.0 (d, JP-c=21.7 Hz, imine ); 175.3, 151.3, 146.5, 137.7, 131.2, 130.5, 129.9, 128.6, 123.2, 121.9 (aniline and
phenyl C_); 102.8 (d, JP-c= 2.4 Hz, C6Me6); 15.72 (C6Me6); 14.80, (d, Jp C=32.9 Hz, PMe3). 31p [1H] NMR (121 MHz, CDCI3, 220 C): 7.60. Preparation of [(R6 -C.Me)Ru((Ph)N=C(Me)C6H41(M3)BF4,1b.
To a stirring solution of (r6-C6Me6)RuPMe3CI2 (0.505g, 0.814mmol) in dichloromethane (50mL) was added AgBF4 (0.317g, 1.63mmol) and methylbenzylidene aniline (0.318g, 1.63mmol). The mixture was stirred for four hours and then allowed to settle. The solution was filtered and the solvent removed under reduced pressure. The remaining yellow foamy solid was washed with pentane (3xlOmL) and diethyl ether (3xl0mL). Addition of CH2C12 to dissolve the solid followed by layering with pentane gave crystalline product (0.267g, 0.430mmol), 53% yield. Anal. Calcd for C29H39BF4PRu: C, 56.1, H,
6.34, N, 2.26. Found: C, 55.9; H, 6.40; N, 2.22. Mp 271-2730 C (dec). IR (Nujol, cm-1): 1520, 1567. 1H NMR (300MHz, CDCI3, 220 C): 7.58-7.50 (m, 4 H, phenyl and aniline H); 7.32 (t, JH-H=6.5 Hz, 1 H, phenyl or aniline H); 7.25 (t, JH-H=7.8 Hz, 2 H, aniline H.); 7.12 (t, JH-H=7.4 Hz, 1 H, phenyl or aniline H);
7.01 (d, JH-H=7.9 Hz, 2 H, aniline H_); 2.39 (d, JP-H=1.5 Hz, 3 H, imine Me);
1.81 (s, 18 H, C6Me6); 1.11 (d, JPH=9.23 Hz, 9 H, PMe3). 13C[1H] NMR (75 MHz, CDCI3, 220 C): 184.7 (d, JP-C=22 Hz, imine C); 180.4, 150.3, 147.8, 137.8, 130.5, 129.5, 129.1, 127.7, 123.6, 122.9 (phenyl or aniline C.__); 103.0 (6Me6); 18.2 (imine Me); 15.7 (C6Me6); 14.9 (d, JP c=32.7 Hz, PMe3). 31p[1H] NMR (121 MHz, CDCI3, 220 C): 2.70.
Prep of [(n6-C6Me6)Ru((p-MePh)N=C(H)CgH Me ,
A flask was charged with (116-C6Me6)RuPMe3CI2 (0.192g, 0.468 mmol), AgBF4 (0.182g, 0.936 mmol), and (p-MePh)N=CHPh (0.183g, 0.936 mmol) and CH2C12 (50mL). This reaction mixture was stirred for 12 hours, and the white precipitate was allowed to settle. The supernatent was filtered away and the precipitate was extracted with CH2C12 (3x5mL). The extract was combined with the supernatent and concentrated under reduced pressure. An alumina column ( 1/2" diameter x 1" length, adsorption ) was used to filter the solution. The CH2C12 solution was loaded onto the column and was eluted with CH2C12. The eluent was collected and the solvent removed under reduced pressure. The solid was then washed with H20 (3xlOmL) and dissolved in CH2C12 (5mL). The product was precipitated from the stirring methylene chloride solution by dropwise addition of Et20 (40mL). The red-yellow powder was crystallized by layering CH2CI2/pentane to give brown needles (0.219g, 0.360mmol), 77% yield. Anal. Calcd for C35H39BF4NPRu: C, 56.13; H, 6.33; N, 2.21. Found: C, 55.89; H, 6.23; N, 2.21. Mp. 264-2660 C. IR (Nujol, cm-1): 1531, 1581. 1H NMR (300MHz, CDCI3, 220 C): 8.33 (d, JP-H=2.89 Hz, 1 H, imine H.); 7.67 (d of d, JP-H=1.47 Hz, JH-H= 7.4 Hz, 1 H, phenyl H); 7.57 (d, JH-H=7.63 Hz, 1 H, phenyl H.); 7.30 (d, JH-H=8.00 Hz, 2 H, phenyl H); 7.19 (m, 3 H, phenyl H_); 7.08 (t, JH-H=7.4 Hz, 1 H, phenyl H_); 2.40 (s, 3 H, N-Ph Me); 1.85 (s, 18 H, Cy6); 1.11 (d, JP-H=9.33 Hz, 9 H, PMe3). 31P[1H] NMR (121 MHz, CDCI3, 220 C): 0.44.
Preparation of [(16-C6H )Ru((Ph)N=C(H)C6H4 )(PMe3)]+BF4, Id.
A 150mL. round bottom Schlenk type flask was charged with (.6C6H6)RuPMe3CI2 (0.239g, 0.734 mmol), AgBF4 (0.286g, 1.47 mmol) and PhN=CHPh (0.266g, 1.47 mmol) and CH2CI2 (40mL). The mixture was stirred for 12 hours. The resultant bright yellow solution and white precipitate was allowed to settle. The solution was filtered and tha solvent was removed under reduced pressure leaving a yellow foamy residue. This solid was washed with Et20 (3x20mL) and THF (3xlOmL) leaving the product as a bright yellow powdery solid, (0.295g, 0.570 mmol), 77 % yield. Anal. Calcd for C22H25BF4NPRu: C, 50.50; H, 5.01; N, 2.68. Found: C, 50.38; H, 4.93; N,
2.60. Mp 202-2040 C (dec). IR (Nujol, cm-1): 1532, 1581. 1H NMR (300 MHz, CDCI3, 220 C): 8.73 (d, JP-H=2.98 Hz, 1 H, imine H_); 8.02 (m, 1 H, phenyl H); 7.90 (m, 1 H, phenyl H); 7.60 (m, 4 H, phenyl H_.); 7.45 (m, 1 H, phenyl h); 7.22 (m, 2 H, phenyl g; 5.94 (s, 6 H, C6H6 ); 1.40 (d, JP-H=10.42 Hz, 9 H, PMe3). 13C[1H] NMR (75 MHz, CDC13, 220 C): 180.9 (imine C); 160.6, 147.4, 137.8, 136.9, 136.6, 136.0, 134.7, 131.1, 129.9, 128.9 (phenyl or aniline g; 98.9 (.6H6); 22.2 (d, JP-C=34.8 Hz, PMe3). 31p [1H] NMR (121 MHz, CDCI3, 220 C): 4.33.
Preparation of [(,n6-C6H6)Ru((Ph)N=C(H)C6H )(PEt3) BF le.
A flask was charged with (rj6-C6H6)Ru(PEt3)Cl2 (0.135g, 0.218 mmol), AgBF4 (0.079g, 0.436 mmol), PhN=CHPh (0.085g, 0.436 mmol), and CH2CI2
(30mL). The deep red slurry became yellow after several hours of stirring. The reaction was allowed to stir for a total of 12 hours. After settling, the supernatent was filtered away from the white precipitate which was then extracted with CH2CI2 (3x5mL). This extract was combined with the supernatent. The solution was then concentrated under reduced pressure. An alumina column ( 1/2" diameter x 1 1/2" length, adsorption ) was used to filter the solution. The CH2C12 solution was loaded onto the column and eluted using a 90/10 CH2C12/acetone mixture. The eluent was then evaporated to dryness. The solid was redissolved in CH2CI2 (30mL) and this solution was extracted with H20 (3x10mL). The CH2Cl2 solution was evaporated to dryness and the oily solid was then triturated with Et20 (70mL) giving 0.075g ( 0.13 mmol, 61 % yield), of yellow powder. Anal. Calcd for C25H31BF4NPRu-1/4 CH2CI2: C, 51.8; H, 5.42; N, 2.39. Found: C, 52.2; H, 5.44; N, 2.31. Mp. 2002020 C. IR (Nujol, cm-1): 1525, 1572. 1H NMR (300MHz, CDCI3, 220 C):
8.34 (d, JP-H=2.67 Hz, 1 H, imine H_1); 7.83 (d, JH-H=1.76 Hz, 1 H, phenyl g; 7.71 (d, JH-H=1.76 Hz, 1 H, phenyl H_1); 7.47 (m, 2 H, phenyl J-; 7.38 (m, 3 H, phenyl Hf); 7.18 (m, 2 H, phenyl H.); 5.70 (s, 6 H, C6L6); 1.59 (m, 6 H, PEt3 CH2); 1.01 (m, 9 H, PEt3 CH3). 13C[1H] NMR (75 MHz, CDCI3, 220 C): 141.0, 131.5, 131.0, 130.8, 129.7, 128.8, 123.3, 122.4, 123.0, 122.4, 123.0,
122.4 (phenyl C_); 92.1 (C6H6); 17.5 (d, Jp.-C=29.7 Hz, PEt3 CH2); 8.02 (PEt3 CH3). 31p[1 H] NMR (121 MHz, CDCI3, 220 C): 25.3.
Preparation of [(6-C6H6)Ru((Et)N=C(H)6H)(PMe3)BF, if.
A flask was charged with (1q6-C6H6)RuPMe3CI2 (0.164g, 0.503 mmol), AgBF4 (0.196g, 1.06 mmol) and CH2C12 (30mL) without stirring. To the suspension was added EtN=CHPh (0.145mL, 1.06 mmol). The mixture was stirred for eight hours during which time a white precipitate formed. The mixture was allowed to settle and the supernatent.filtered, giving a yellow solution. The CH2CI2 was removed under reduced pressure leaving a yellow foamy solid. The solid was washed with Et20 (3xlOmL) and THF (3x5mL). The resulting yellow powder was crystallized from acetone/pentane producing yellow crystals, (0.194g, 0.407 mmol), 81 % yield. Anal. Calcd for C18H25BF4NPRu: C, 45.49; H, 5.51; N, 8.95. Found: C, 45.29; H, 5.38; N,
8.94. Mp. 233-2350 C. IR (Nujol, cm-1): 1543, 1599. 1H NMR (300MHz, CDCI3, 22 C)): 8.20 (d, JP-H=3.03 Hz, 1 H, imine H_); 7.69 (d, JH-H=7.94 Hz, 1 H, phenyl -.); 7.56 (d, JH-H=6.84 Hz, 1 H, phenyl j; 7.10 (m, 2 H, phenyl H);
5.85 (s, 5 H, C6H6); 4.03 (m, 2 H, Et CH2); 1.42 (d, JH-H=7.21 Hz, Et CH3); 1.12 (d, JP-H=10.2 Hz, 9 H, PMe3). 13C[1H] NMR (75 MHz, CDCI3, 220 C): 179.9 (d, JP-C=27.4 Hz, imine C_.); 172.2, 146.2, 140.2, 129.6, 123.3 (phenyl C_); 91.6 (C6H6); 61.3 (Et CH2); 16.5 (d, JP-C=35.9 Hz, PMe3); 15.9 (Et CH3). 31P[1H] NMR (121 MHz, CDCI3, 220 C): 4.23.
Prep of [(16-p-Cymene)Ru((Ph)N=C(H)C,6H04E)(PMe3)1BF 1g
A flask was charged with (116-Cymene)RuPMe3CI2 (0.578g, 0.151
mmol), AgBF4 (0.587g, 3.02 mmol), and PhN=CHPh (0.548g, 3.02 mmol), and CH2C12 (75mL). The deep red slurry eventually became yellow over a period of about 10 hours. At this time, the stirring was stopped and the mixture was allowed to settle. The supernatent was filtered and the solid residue was extracted with CH2CI2 (3x1 OmL). This solution was then concentrated under reduced pressure. An alumina column ( 1/2" diameter x 1 1/2" length, adsorption ) was used to filter the solution. The CH2C12 solution was loaded onto the column and eluted using a 90/10 CH2CI2/acetone mixture. The eluent was then evaporated to dryness. The solid was redissolved into CH2C12 (50mL) and the solution was extracted with H20 (3x15mL). The CH2CI2 solution was dried over CaSO4, filtered, and evaporated to dryness. The oily solid was triturated with Et20 (100mL) giving 0.640g ( 1.13 mmol, 75 % yield), of yellow powder. Anal. Calcd for C26H33BF4NPRu: C, 53.02; H, 5.87; N, 2.47. Found: C, 53.10; H, 5.89; N, 2.43. Mp. 230-2320 C. IR (Nujol, cm-1): 1539, 1583. 1H NMR (300MHz, CDCI3, 220 C): 8.35 (d, JP-H=3.00 Hz, 1 H, imine H); 7.80 (d, JH-H=7.50 Hz, 1 H, phenyl H); 7.68 (d, JH-H=6.60 Hz, 1 H, phenyl H_.); 7.51 (t, JH-H=7.50 Hz, 3 H, phenyl h!); 7.40 (t, JH-H=7.50 Hz, 1 H, phenyl H_); 7.31 (d, JH-H=7.20 Hz, 2 H, phenyl H); 7.24 (t, JH-H=7.50 Hz, 1 H, phenyl J); 7.14 (t, JH-H=7.20 Hz, 1 H, phenyl H); 5.71 (m, broad, 2 H, 16-cym H);
5.32 (m, 2 H, 16-cym ;H) 5.21, (d, JH H=6.00 Hz, 1 H, I6-cym HI); 2.44 (m, 1
H, isopr H_); 2.28 (s, 3 H, Me); 1.25 (d, JP-H=9.90 Hz, 9 H, PMe3); 1.00 (d, JHH=6.90 Hz, 3 H, isopr Me); 0.62 (d, JH H=6.60 Hz, 3 H, isopr Me). 13C[1H] NMR (75 MHz, CDC13, 220 C): 183.8 (d, JP-C=12.4 Hz, imine C); 172.9, 153.6, 146.5, 140.5, 130.8, 129.6, 128.4, 123.5, 121.6, 119.7 (phenyl g); 119.6, 106.5, 97.1, 88.2, 87.7, 85.8 (1i6-cym Q; 30.7 ( 16-cym Me); 23.0 (isopr Me); 20.8 (isopr .Q); 18.8 (isopr Me); 15.8 (d, JP-C=34.9 Hz, PMe3). 31p [1H] NMR (121 MHz, CDCl3, 220 C): 2.04.
Preparation of [(TI6-C6Me6)Ru((Ph)N=C(H)CHA)(CO)]+BF4, 1 h.
A flask was charged with (T6-C6Me6)RuCl2CO ( 0.200g, 0.552mmol),
AgBF4 ( 0.215g, 1.10Ommol), and PhN=CHPh ( 0.200g, 1.10Ommol) and CH2Cl2 (30mL). The slurry was stirred for 12 hours and then allowed to settle. The yellow solution was filtered leaving a white precipitate. Acetone (10mL) was added to the solution, followed by filtration through Celite. The solvent was removed under reduced pressure. The residue was redissolved in CH2C12 (25mL) and extracted with H20 (3x5mL). The solvent was again removed under reduced pressure to give a dark yellow oily residue. This was triturated with Et20 (100mL) to produce a yellow powder ( 0.242g, 0.411 mmol), 75% yield. Anal. Calcd for C26H28BF4NORu-1/4 CH2C12: C, 54.4; H, 4.95; N,
2.42. Found: C, 54.8; H, 4.99; N, 2.30. Mp. >3000 C. IR (Nujol, cm-1): 1986, 1579, 1542. 1H NMR (300 MHz, CDC13, 220 C): 8.45 (s, 1H, imine H); 7.86 ( d of d, JP-H=1.5 and JHH=7.2 Hz, 1H, phenyl H.); 7.54 (m, 3H, phenyl H); 7.34
(t of d, JP-H=1.5 and JH-H=7.8 Hz, 1 H, phenyl ); 7.21 (t, JH H=7.20 Hz, 1 H, phenyl H); 2.00 (s, 18H, g6-_C6Me6). 13C[1H] NMR (75 MHz, CDCI3, 220 C): 194.0 (CO); 176.9 (imine C_); 174.1, 149.7, 146.6, 137.2, 132.4, 132.3, 129.9, 129.0, 125.2, 122.2 (phenyl C); 111.5 (phenyl C); 16.1 (i16-CC6 ).
Preparation of [(n6-CH6)Ru((Ph)N=C(Me)C6H41)(PMe3),41BF1 li.
A flask was charged with 0.173g( 0.422mmol) (T16-C6H6)Ru(PMe3)Cl2, 0.164g( 0.844mmol) AgBF4, 0.165g (0.844mmol) PhN=C(Me)Ph, and CH2CI2 (30mL). After stirring for six hours, the mixture was allowed to settle and was poured directly onto an alumina column ( 1 1/2" length, 1" diameter, adsorption). The yellow band was eluted first with CH2C12 and then with a 90/10 CH2C12/acetone mixture. The resulting solution was evaporated to dryness. The yellow residue was redissolved in CH2Cl2 (10mL) and extracted with H20 (3x15mL). Fine yellow crystals were isolated by precipitation from CH2Cl2 by dropwise addition of hexanes. The material was recrystallized from CH2C12/ hexanes, (0.112g,0.209mmol), 50% yield. Anal. Calcd for C23H27BF4NPRu-1/8 CH2C12: C, 50.73; H, 4.78; N, 2.56 Found: C, 50.73; H, 4.93; N, 2.43. Mp. 238-2400 C. IR (Nujol, cm-1): 1603, 1542. 1H NMR (300 MHz, C6D6, 220C): 7.95 (d, JH-H=7.80 Hz, 1H, phenyl h); 7.76 (d, JHH=6.00 Hz, 1H, phenyl H); 7.56 (t, JH-H=7.80 Hz, 2H, phenyl H_); 7.38 (t, JHH=7.20 Hz, 1H, phenyl H.); 7.22 (m, 4H, phenyl H.I.); 5.76 (s, 6H, C6_H); 2.34 (d,
JH-H=1.80 Hz, 3H, Me); 1.33 (d, JP-H=9.90 Hz, 9H, PMe3). 13C[1H] NMR (74.4 MHz, C6D6, 220C): 31 P[1H] NMR (121 MHz, C6D6, 220C):
Prep of r(n6-C6Me6)Ru(((3,5Me2)Ph)N=C(H)C6H)EE(PMe3)BF,,1lI .
A flask was charged with 0.173g( 0.855mmol) (j6-C6Me6)Ru(PMe3)Cl2,
0.358g( 1.710 Ommol) AgBF4, 0.333g ( 1.710Ommol) (3,5-diMe)PhN=CHPh, and CH2C12 (40mL). After stirring for eighteen hours, the mixture was allowed to settle and then poured directly onto an alumina column ( 1 1/2" length, 1" diameter, adsorption). The yellow band was eluted with a 75/35 CH2Cl2/ acetone mixture. The resulting solution was evaporated to dryness. The yellow residue was redissolved in CH2C12 (15mL) and extracted with H20 (3xlOmL). The CH2CI2 solution was evaporated to dryness and the yellow residue washed with diethyl ether and scraped down the sides of the flask. The material was recrystallized from CH2CI2/ hexanes, (0.340g,0.533mmol), 63% yield. Anal. Calcd for C30H44BF4NPRu: C, 56.53; H, 6.96; N, 2.20 Found: C, 56.44; H, 6.49; N, 2.07. IR (Nujol, cm-1): 1578, 1531. 1H NMR (300 MHz, C6D6, 220C): 8.41 (d, JP-H=3.00 Hz, 1H, imine j); 7.71 (d, JH-H=7.35 Hz, 1H, phenyl o-CH);
7.60 (d, JH-H=7.50 Hz, 1H, phenyl o-CH_.); 7.24 (t, JH-H=7.50 Hz, 1H, phenyl m-CH); 7.12 (t, JH-H=6.60 Hz, 1H, phenyl m-CH); 7.05 (s, 1H, Me2 aniline pHi.); 6.96 (s, 2H, Me2 aniline o-); 2.41 (s, 6H, Me2 aniline M); 1.90 (s, 18H, CS6); 1.16 (d, JP-H=9.30 Hz, 9H, PMe3). 13C[1H] NMR (74.4 MHz, C6D6, 220C): 172.5 (imine C); 151.1, 146.5, 139.6, 137.8, 130.7 (d, Jpoc=27.7 Hz,
phenyl .); 130.1, 128.1, 127.5 (d, JP-C=24.6 Hz, phenyl C.); 123.3, 119.7 (phenyl .); 102.9 (C6Me6); 21.3 ( aniline Me); 16.0 (C6Me6); 14.8 (d, Jp C=32.8 Hz, PMe3). 31P[1H] NMR (121 MHz, C6D6, 220C): -0.72.
Prep of [(n6-CMe)Ru((Et)N=C(H)CH1)(PMe3,,)]+BF1-, 1k.
A flask was charged with 0.108g( 0.263mmol) (16-C6Me6)Ru(PMe3)Cl2, 0.102g( 0.526mmol) AgBF4, 0.076mL ( 0.526mmol) (3,5-diMe)PhN=CHPh, and CH2C12 (40mL). After stirring for eighteen hours, the mixture was allowed to settle and then poured directly onto an alumina column ( 1 1/2" length, 1" diameter, adsorption). The yellow band was eluted with a 75/35 CH2Cl2/ acetone mixture. The resulting solution was evaporated to dryness. The brown residue was redissolved in CH2C02 (15mL) and extracted with H20 (3xlOmL). The CH2CI2 solution was evaporated to dryness and the yellow residue washed with diethyl ether and scraped down the sides of the flask. The material was then recrystallized from CH2Cl2/ hexanes to yield 0.060g(0.108mmol) of crystalline product, 40% yield. Anal. Calcd for C24H37BF4NPRu: C, 51.8; H, 6.70; N, 2.52 Found: C, 56.44; H, 6.49; N, 2.07. IR (Nujol, cm-1): 1588. 1H NMR (300 MHz, C6D6, 220C): 8.26 (s, 1 H, imine H_.); 7.55 (d of d, JH-H=8.6 Hz, JP-H=1.0 Hz, 1H, phenyl H)i; 7.47 (d, JH-H=8.6 Hz, 1H, phenyl H_; 7.14 (t of d, JH-H=8.1 Hz, JP-H=1.3 Hz, 1 H, phenyl n; 7.04 (t, JH-H=8.1 Hz, 1 H, phenyl H)i; 3.82 (d of d, JH. H=9.2 Hz, JP-H=2.1 Hz, 1H, CH2CH3); 3.67 (d of d,
JH-H=9.2 Hz, JP-H=1.1 Hz, 1H, CH2CH3); 2.03 (s, 18H, C e); 1.16 (d, JpH=9.8 Hz, 9H, PMe3). 31P[1H] NMR (121 MHz, C6D6, 220C):
Prep of [(6-p-Cymene)Ru((Ph)N=C(CH36HPEt]BF 11.
A flask was charged with 0.215g( 0.510mmol) (16_p
Cymene)Ru(PEt3)Cl2, 0.199g( 1.02mmol) AgBF4, 0.199g (1.02mmol) PhN=C(Me)Ph, and CH2C12 (40mL). After stirring for eighteen hours, the mixture was allowed to settle and then poured directly onto an alumina column ( 1 1/2" length, 1" diameter, adsorption). The yellow band was eluted with a 75/35 CH2CI2/ acetone mixture. The resulting solution was evaporated to dryness. The purplish residue was redissolved in CH2Cl2 (15mL) and extracted with H20 (3xlOmL). The CH2CI2 solution was evaporated to dryness and the yellow residue washed with diethyl ether and scraped down the sides of the flask. The material was recrystallized from CH2CI2/ hexanes, (0.142g,0.224mmol), 44% yield. Anal. Calcd for C30H41BF4NPRu: C, 56.78; H, 6.51; N, 2.21 Found: C, 56.43; H, 6.53; N, 1.93. IR (Nujol, cm-1): 1566, 1532. 1H NMR (300 MHz, C6D6, 220C): 7.68 (d, JH-H=7.80 Hz, 1H, phenyl Hj.); 7.52 (m, 3H, phenyl -); 7.33 (t, JHH=7.20 Hz, 1H, phenyl H.; 7.24 (t, JHH=7.50 Hz, 1H, phenyl h); 7.12 (t, JH-H=7.50 Hz, 1H, phenyl h); 6.98 (d, JHH=9.0 Hz, 2H, phenyl H; 6.96 (s, 2H, Me2 aniline 0-i; 2.41 (s, 6H, Me2 aniline Me); 1.90 (s, 18H, C6Me6); 5.50 (d, JH-H=6.0 Hz, 1H, p-Cymene H);
5.22 (d, JHH=6.0 Hz, 1H, p-Cymene H); 5.95 (d, J.H=6.00 Hz, 1 H, p-Cymene
H_); 4.76 (d, JH-H=6.00 Hz, 1H, p-Cymene H.); 2.61 (p, JH-H=6.60 Hz, 1H, isopropyl CH.); 2.29 (d, JH-H=1.5 Hz, 3H, isopropyl CH3), 2.06 (s, 3H, isopropyl CH3); 1.59 (m, 6H, P(CH2CH3)), 0.98 (m, 9H, P(CH2CH3)); 0.65 (d, JPH=6.0 Hz, 3H, imine Hj). 31P[1H] NMR (121 MHz, C6D6, 220C): 25.2.
Prep of [(116-C6Me6)Ru((Ph)N(H)C(H)(Me)C6H4)(PMe3)BF, 7.
To a stirring solution of 2a (0.150g, 0.285 mmol) in THF (20mL) was
added 1.5mL of 0.19 M HBF4 solution. The red color of the solution instantly disappeared and an off-white precipitate began to form. The mixture was stirred for 1 hour and allowed to settle. The supernatent was filtered away and the solid was washed with Et20 (3x15mL). The off-white powder was crystallized from CH2C12 / pentane to give colorless crystals, 0.146g ( 0.235 mmol), 82 % yield. Anal. Calcd for C29H41BF4NPRu.1/4CH2CI2: C, 54.6; H, 6.49; N, 2.17. Found: C, 54.5; H, 6.52; N, 2.05. Mp. 249-2500 C. 1H NMR (300MHz, CDCI3, 220 C): 7.49 (t, JH-H=6.99 Hz, 2 H, phenyl H); 7.43 (t, JHH=6.97 Hz, 1 H, phenyl H); 7.25 (m, 3 H, phenyl H_); 7.12 (t, JH-H=6.25 Hz, 1 H, phenyl H); 7.02 (t, JH-H=7.36 Hz, 1 H, phenyl H); 6.79 ( d, JH-H=7.36 Hz, 1 H, phenyl H); 4.58 (d, JH-H=9.92 Hz, 1 H, N-Hf.); 3.83 (q, JH-H=6.25 Hz, 1 H, phenyl iH); 1.91 (s, 18 H, C6Me6); 1.46 (d, JH-H=6.25 Hz, 3 H, phenyl Me);
1.29 (d, JP-H=8.45 Hz, 9 H, PMe3). 13C[1H] NMR ( 75 MHz, CDCI3, 220 C): 145.8, 137.9, 129.5, 127.9, 127.5, 124.2, 123.8, 122.8 (phenyl C.); 101.2
CMe6); 69.8 (phenyl C); 19.6 (phenyl Me); 17.5 (d, JH-H=30.7 Hz, PMe3); 16.2 (C6 ). 31p[1H] NMR (121 MHz, CDCI3, 220 C): 1.36.
The cyclometallated cations are air stable solids. They melt at
temperatures in the range of 200-3000C. The hexamethylbenzene compounds (ie.[(T6-C6Me6)Ru((R)N=C(R')C6H4)(L)]+BF4") are readily soluble in dichloromethane, chloroform, and acetone. They are insoluble in pentane and diethyl ether, and they are moderately soluble in tetrahydrofuran. The benzene compounds [(n16-C6H6)Ru((R)N=C(R')C6H4)(L)]+BF4" are less soluble in dichloromethane and chloroform than their hexamethylbenzene counterparts.
Nuclear Magnetic Resonance Spectroscopy
Proton and carbon NMR spectra of the imine cations and amide
complexes were collected using the instruments listed in Chapter Two. All of the samples were referenced against residual protons in the deuterated solvent, and are reported relative to tetramethylsilane. The chemical shifts, 8, in parts per million and coupling constants, J, in Hertz, of the 1H, 13C and 31 p resonances are reported in the experimental section. Proton, 13C, and 31P NMR spectra were extremely useful in characterizing the compounds and in studying various reactions.
In the case of [(r6-C6Me6)Ru((Ph)N=C(H)C6H4)(PMe3)]+BF4 ', 1H NMR spectra were obtained using both one and two-dimensional NMR techniques. The spectra are shown in Figqures 6 and 7. Inspection of the spectra led to nearly complete identification of 1 a. The interpretation of these spectra follows, along with general comments. The chemical shift and coupling patterns of the ligands warrant some discussion as each peak in Figqure 6 is mentioned, beginning with the resonance farthest upfield, the phosphine resonance. Eventually, the discussion will turn to those peaks in the phenyl region. At that time, references will be made to the two dimensional spectrum in Figure 7, since it contains the most information and will be most useful for discussion.
In the upfield region of the 1-D spectrum, Figqure 6, the doublet at 1.07 ppm corresponds to the methyl protons of the trimethylphosphine ligand. They exhibit a coupling constant of 9.1 Hz. The magnitude of this coupling constant is typical for the entire series of cyclometallated cations which contain phosphine ligands. The methyl protons of noncoordinated trimethylphosphine appear at ca. 0.77 ppm (JP-H=3 Hz) in the proton NMR.24 The chemical shift of the PMe3 protons is sensitive to variations in the ligand environment of the metal. In comparison to the chemical shift of the protons of (116C6Me6)Ru(PMe3)Cl2 at 1.46 ppm (JP-H=10.5 Hz), the phosphine protons of la are shifted upfield. This is unusual since the cyclometallated complex is a cation and the dichloride complex is neutral. Generally, complexes which have
been converted from neutral to cationic exhibit overall deshielding of protons, and subsequent downfield chemical shifts.25
The chemical shift of the phosphine ligand of the r6-C6H6 analogue is affected in the same fashion as its 16-C6Me6 counterpart. The phosphine protons appear at 1.40 ppm in the cation [(i6-C6H6)Ru((Ph)N=C(H)C6H4) (PMe3)]+BF4"), 1d, while they are shifted downfield to 1.73 ppm in the (i6. C6H6)Ru(PMe3)Cl2 complex. The ri6-C6Me6 1H NMR chemical shift positions exhibit similar trends between l.1a and (7q6-C6Me6)Ru(PMe3)Cl2. In the former complex the Ti6-C6Me6 protons appear at 1.80 ppm while in the latter, at 2.03 ppm.
It is convenient now to turn to the 1H 450 COSY 2D NMR spectrum of the phenyl region of 1a shown in Fiqure 7, in order to interpret the phenyl resonances of the complex. Inspection of the region reveals seven different resonances. These are associated with the three different protons on the phenyl ring bound to the nitrogen atom, and to the four different protons contained on the cyclometallated phenyl ring, shown in Fiqure 8.
Some uncertainty existed concerning whether the cation was metallated or not. With seven different protons, a simple monodentate imine monochloride complex, as shown below in Figqure 9, was not possible. The initial product of the cyclometallation reaction was thought to be the imine chloride cation shown in Figure 9. A non-cyclometallated imine monochloride complex would feature four triplets and two doublets in the phenyl region, corresponding to the ortho,
CL C', CD
CD ca 3:
(D 19 CX.
co + M
Figure 8. Illustration of the Chemical Shift Inequivalent Protons in 1 a
meta, and para protons of the two different phenyl rings. It could display as many as eight or ten chemically inequivalent protons if one or both of the ligand's phenyl rings experience hindered rotation about their respective C-N or C-C bonds (this point is mentioned due to results presented in the next chapter).
The cyclometallated imine complex can display only two possible
numbers of chemical shift inequivalent protons as well. It may feature seven chemical shift inequivalent protons if there is free rotation about the C-N bond of the ligand, or nine different protons if there is hindered rotation about the C-N bond, as shown in Figure 10 below. The monodentate imine complex is
~~ + BF#0" H
H, "3' H I H.H H 9
H 1 H
Figure 9. Illustration of the Number of Potentially Chemical Shift Inequivalent Protons in a Monodentate Imine Complex.
therefore impossible, since there are seven chemical shift inequivalent protons in the phenyl region of la.
Coupling patterns in the 2D COSY spectrum of 1 a shown in Fiqure 7
show that the two peaks of area two are coupled to one another. One of those peaks, the triplet, is coupled to another triplet of area one. This is consistent with the presence of a mono-substituted phenyl ring. The remaining four peaks, a doublet of doublets, a doublet, a triplet of doublets, and a triplet, coupled with each other but not with the other three resonances, indicating the presence of an ortho-disubstituted phenyl ring. This supports the proposed structure of the cyclometallated complex.
~~ + BF4
Figure 10. Possible Hindered Rotation about the C-N Bond of la due to Steric Encumberance.
Finally, the peak furthest downfield remains. Referring back to Figure 6, the imine proton of 1a appears at 8.33 ppm as a doublet (JP-H=2.9 Hz) due to four bond coupling to the PMe3 phosphorus atom. The imine protons of the various cyclometallated cation derivatives appear consisitently in the region between eight and nine ppm, and nearly all show long range P-H coupling.
The crystal structure of 1 a reveals discrete anion and cation entities.
The anion exhibits a noncrystallographic threefold disorder of F2, F3, F4 while B and F1 are not disordered and roughly define a pseudo-threefold axis for the
ranges expected for such a structure. An ORTEP drawing of 1a is found in Figure 11 while selected bond lengths and angles are found in Table 2. The five-membered metallocyclic group is nearly planar (0.05A) with a short N-C7 bond distance (1.294A) indicative of a C=N double bond. The hexamethylbenzene ring is planar (0.03A) but the ruthenium atom is not centered directly below the ring. The phenyl carbon atom exerts a strong trans influence causing C15 and C16 to be ca. 0.08A further from the metal atom than are the other ring carbon atoms. Such a trans influence has been identified in the crystal structures of a variety of arene complexes.26 The details of the structure determinations may be found in reference 38.
Cyclometallation reactions, such as those observed in this work, have been known for thirty years. Investigations into the mechanism of these reactions have been carried out since that time.27 The most acceptable mechanism for the process is presented here. The discussion that follows is a step by step description of the mechanistic route leading to product formation.
Shown in Figure 12 is a proposed mechanism for the formation of
1 a.28 The mechanism involves formation of AgCI upon reaction of the di-
Table 2. Selected Bond Lengths and Angles from the X-Ray
Structural Analysis of la.
Ru-P 2.316(1) Ru-C17 2.260(2)
Ru-N 2.093(3) Ru-C1 8 2.267(2)
Ru-Cl 2.058(2) Ru-C1 9 2.241(2)
Ru-C14 2.247(2) N-C7 1.294(3)
Ru-C15 2.340(2) N-C8 1.430(3)
P-Ru-N 89.03(6) N-C7-C6 116.6(2)
P-Ru-CI 83.62(8) C1-C6-C7 114.8(2)
N-Ru-C1 77.46(9) Ru-C1-C6 114.2(2)
chloride complex with the first equivalent of AgBF4, step 1. This is accompanied by ligation of the imine ligand through nitrogen coordination in a monodentate fashion, step 2. This is then followed by loss of a second chloride through abstraction with the second equivalent of AgBF4, step 3.
When loss of the second chloride does occur, the phenyl ring of the
ligand can coordinate to the metal in an 9 2 fashion by forming a coordinated ndonor interaction, yielding a bidentate imine ligand. The exact mode of coordination is not known. The most likely coordination modes are through either side on or end on coordination through the C-H bond of the phenyl ring.29 The ortho proton on the T12 coordinated phenyl ring of the ligand has greatly enhanced acidity due to Lewis acid coordination.30 It may then be removed by abstraction with base, leading to the cyclometallated product, steps
4 and 5.
Attack by Water
The N-bound monodentate intermediate formed prior to loss of the
second chloride (step three in Figure 12) is a cationic imine complex, and the imine carbon atom is extremely electrophilic.31 At this point in the cyclometallation mechanism, traces of moisture may react with the ligand causing it to undergo hydrolysis leading to its aldehyde and amine components.32 It is therefore crucial that water be excluded from the reaction.
I I Z
The reaction of the proposed monochloride intermediate with water is the major side reaction in the synthesis of the cations. For example, in the synthesis of La, the imine PhN=CHPh is used and the complex [(p6C6Me6)Ru(CI)(NH2Ph)(PMe3)]+BF4" and free benzaldehyde are produced. These are the products expected on hydrolysis of imines. The synthesis of this monoaniline cation has been carried out separately by addition of one equivalent of aniline and one equivalent of AgBF4 to (16-C6Me6)RuCl2PMe3 in methylene chloride.33 The proposed reaction of the monoimine intermediate with water to yield the observed products is presented in Fiqure 13.
The aniline complex is formed when water is added to the
cyclometallation reactions. Trace quantities of water react to give small amounts of side products in the reactions. However, if large enough quantities of water are present, then only the aniline complex is formed. Similar observations in cyclometallation reactions have been made by other workers and concur with this observation. Attack by water on monodentate coordinated imines leads to amine complexes due to Lewis acid catalyzed hydrolysis of the C-N bond of the imine.34
Reaction of CO complex with (CH3)3N+-O" in CH3CN
The addition of trimethylamine N-oxide to a solution of CO complex 1 h In acetonitrile leads to the acetonitrile complex with the loss of CO as CO2 and the formation of free trimethylamine. The reaction is carried out at room
+ F + SF4
P Ru + H20 Ru +
N N H'C
Figure 13. Hydrolysis of the Intermediate Imine Cation Yielding Aniline Complex and Benzaidehyde
temperature for twelve hours. There is no appreciable change in the appearance of the solution, which is tan colored, after the reaction is complete. The materials are mixed in a 1:1 molar ratio of CO complex and N-oxide, without extreme care to exclude air from the system. The 1HNMR spectrum of the product is only slightly different from that of the starting material. The most obvious difference is the presence of a three proton singlet attributable to the coordinated acetonitrile ligand. Elemental analysis failed to provide a consistent composition, due possibly to the lability of the acetonitrile ligand.
The material will react with Lewis bases such as trimethylphosphine to yield products whose identities are as yet undetermined. Apparently, the products do not include the tI'imethylphosphine analog, 1 a, which is the expected product of the reaction of this acetonitrile complex with trim methyl phosphi ne.
SYNTHESES OF CYCLOMETALLATED AMIDE COMPLEXES OF RUTHENIUM
This Chapter introduces the synthesis and properties of the amide
complexes. The reaction chemistry of the imine cations is summarized below. Discussion of the reactivity of the amide complexes introduced here will be in Chapter Five. The cyclometallated cation l.a is an example of an hexamethylbenzene trimethylphosphine complex. It reacts with strong nucleophiles such as alkyl lithium reagents and hydride reagents. It does not react with weaker nucleophiles. Attack by these reagents occurs only at the imine carbon. In contrast, addition of these strong nucleophiles to [(1T6C6H6)Ru((Ph)N=C(H)C6H4)(PMe3)]+BF4, ld, occurs at the imine carbon and to the coordinated i6-C6H6 ligand, leading to mixtures of products. Nucleophilic attack on [(ri6C6H6)Ru((Et)N=C(H)C6H4)(PMe3)]+BF4- -1_f, gives an intractable mixture of products. The N-alkyl substituted imine cations failed to produce amides upon reaction with lithium reagents. This may be the result of deprotonation of the acidic protons on the a(-carbon atom of the ligand.
Preparation of f(16-C6Me6)Ru((Ph)NC(H)(Me)C6H )(PMe3) 2a
To a stirring suspension of la (0.103g, 0.171 mmol) in tetrahydrofuran (20mL) was added 1.4 M methyllithium (0.18 mL, 0.257 mmol) at room temperature. Reaction of the yellow mixture occurred in five minutes to produce an orange solution. The solvent was then removed under reduced pressure and the product was extracted with toluene (3xl0mL), evaporated to dryness and extracted again using hexanes (3xlOmL). The orange hexane solution was then filtered and the hexane evaporated to yield the product, an orange solid ( 0.081g, 0.162 mmol), 94% yield. Anal. Calcd for C29H40NPRu: C, 65.1; H, 7.54; N, 2.62. Found: C, 64.8; H, 7.51; N, 2.59. Mp 203-2050 C. (dec). 1H NMR (300 MHz, C6D6, 220 C): 7.64 (t, JH-H=8.4 Hz, 1 H, phenyl ji; 7.52 (t, JH-H=7.2 Hz, 1 H, phenyl H.); 7.41-7.30 (m, 5 H, phenyl and aniline jj); 7.14 (d, JH-H= 8.1 Hz, 1 H, phenyl H.): 6.82 (t, JH-H=7.5 Hz, 2 H, aniline .); 5.01 (d of d, JH-H= 5.87 Hz, JP-H= 2.47 Hz, 1 H, benzylic H); 1.78 (d, JHH= 5.7 Hz, 3 H, benzylic Me); 1.94 (s, 18 H, CMe); 0.93 (d, JP-H=9.0 Hz, 9 H, PMe3). 13C[1H] NMR (74.4 MHz, C6D6, 220 C): 158.4, 138.4, 130.8, 129.5, 124.1, 122.3, 121.1, 121.0, 112.0, 106.3, 99.5 (phenyl and aniline C); 68.0 (benzylic C); 24.3 (benzylic Me); 16.5 (C6e6); 16.0 (d, JP-C=30.0 Hz, PMe3). 31P[1 H] NMR ( 121 MHz, C6D6, 220 C): 8.977.
Preparation of [(n 6-CMe6)Ru((Ph)NC(H)(Ph)C6H1)(PMe3)_2b
A suspension of la (0.360g, 0.599 mmol) in THF (25mL) was cooled to 200C. and phenyllithium (0.24mL, 0.599 mmol) was added. The resulting orange solution was allowed to warm to room temperature and the solvent was removed under reduced pressure. The orange solid was extracted using toluene (3xlOmL), filtered, and evaporated to dryness. It was extracted again using hexanes (3xlOmL), filtered, and the solvent removed under reduced pressure. The orange product was isolated crude, (0.276g, 0.527 mmol), 88 % yield. Anal. Calcd for C34H42NPRu: C, 68.4; H, 7.09; N, 2.35. Found C, 68.1; H, 7.13; N, 2.31. Mp 145-1480 C dec. 1H NMR (300 MHz, C6D6, 220 C):
7.78-7.75 (m, 2 H, phenyl H); 7.28-7.21 (m, 4 H, phenyl H_); 7.17-7.07 (m, 6 H, phenyl j); 6.53 (t, J=8.1 Hz, 1 H, phenyl or aniline -.), 5.97 (s, 1 H, benzylic H);
4.59 (s, 18 H, C6Me6); 0.64 (d, JHH=90 Hz, 9 H, PMe3). 31P[1H] NMR (121 MHz, C6D6, 220 C): 7.92.
Preparation of [(n6-COMeG)Ru((Ph)NC(Me)(H)CH 3)(PMe3a
To a stirring suspension of lb (0.437g, 0.710 mmol) in tetrahydrofuran
(20mL) was added LiAI(OtBu)3H (0.271g, 0.710mmol) at -20 C. The orange solution was allowed to stir for five minutes. The solvent was removed under reduced pressure. The resulting orange residue was extracted with toluene (3x10mL), filtered and evaporated. It was extracted again with hexanes (3xlOmL). The orange hexane solution was then filtered and evaporated to
dryness giving a bright orange solid (0.318g, 0.639 mmol), 90 % yield. Mp. 132-1360 C.(dec). 1H NMR (300 MHz, C6D6, 220 C): 7.31-7.19 (m, 2 H, phenyl or aniline _); 7.16-7.12 (m, 2 H, phenyl or aniline .j); 7.08-7.02 (m, 2 H, phenyl or aniline HI); 6.83 (d, JH-H=6.9 Hz, 1 H, phenyl or aniline H); 6.67 (d, JH-H=5.4 Hz, 1 H, phenyl or aniline H); 6.53 (t, JH-H=6.9 Hz, 1 H, phenyl or aniline H); 5.15 (q, JH-H=5.7 Hz, 1 H, benzylic ); 1.56 (d, JH-H=5.7 Hz, 3 H, benzylic Me; 1.51 (s, 18 H, C6Me6), 0.93 (d, JP-H=8.7 Hz, 9 H, PMe3). 31p [1H] NMR (121 MHz, C6D6, 220 C): 4.16.
Preparation of r(T6-C6Me,)Ru((Ph)NC(H)(H)C06H 4)(PMe3),
To a stirring slurry of la (0.100g, 0.182 mmol) in tetrahydrofuran (20mL) at 00 C. was added a tetrahydrofuran (10mL) suspension of LiAI(OtBu)3H (0.046g, 0.182 mmol). The solution chenged color from yellow to red within several minutes. The solution was allowed to warm to room temperature and stir for 30 min. The solvent was then removed under reduced pressure. The resulting red solid was extracted with toluene (3x10 mL) and the toluene was removed in vacuo. Extraction into Et20, followed by concentrating and cooling the Et20 solution, produced red crystals, (0.084g, 0.172 mmol), 94 % yield. Anal. Calcd for C28H38NPRu: C, 64.6: H, 7.35; N, 2.69. Found: C, 64.5; H,
7.38, N, 2.74. Mp 132-1360 C. (dec). 1H NMR (300 MHz, C6D6, 220 C): 7.42 (t, JH-H=6.6 Hz, 1 H, phenyl Hj), 7.28 (t, JH-H=8.4 Hz, 1 H, phenyl Hj); 7.21 (t, JH-H=5.1 Hz, 1 H, phenyl .H); 7.18-7.08 (m, 8 H, phenyl H); 6.76 (t, JH-H=8.7
Hz, 1 H, phenyl h!); 6.57 (t, JH-H=6.9 Hz, 1 H, phenyl h); 6.47 (d, JH-H= 8.1 Hz, 1 H, phenyl Hj); 4.75 (d, JN-H=16.5 Hz, 1 H, benzylic h); 4.47 (d of d, JHH=16.5 Hz, JH-H=3.3 Hz, 1 H, benzylic H); 1.62 (s, 18 H, C66); 0.78 (d, JpH=8.7 Hz, 9 H, PMe3). 13C[ H] NMR (75 MHz, C6D6, 220 C): 159.0, 153.3, 129.6, 127.5, 124.2, 122.0, 121.3, 120.3, 119.6, 112.3, 108.3 (phenyl C); 99.6 (6Me6); 82.8 (benzylic C); 16.4 (d, JpC=29.4 Hz, PMe3); 16.2 (C6Me6). 31P[1H] NMR ( 121 MHz, C6D6, 220 C): 7.54.
Preparation of (n6-C6Me6)Ru((p-MePh)NC(H)(Me)Ph)(PMe3 L 2d.
A 1.4M MeLi solution (0.17mL, 0.24 mmol) was added dropwise to a
stirring tetrahydrofuran slurry (30mL) of 1c (0.147g, 0.237 mmol) at -20 C. The mixture was allowed to stir for 30 minutes. The tetrahydrofuran was removed under reduced pressure. The residue was extracted into toluene (3x20mL) and filtered. The toluene was removed under reduced pressure and the resulting red solid was extracted using diethyl ether, (3x20mL), filtered, concentrated and cooled to give red crystals, 0.120g ( 0.218 mmol), 91 % yield. C30H42NPRu-1/8 CH2CI2: C, 56.1; H, 6.33; N, 2.25. Found: C, 55.9; H, 6.23; N, 2.21. 1H NMR (300MHz, CDCI3, 220 C): 7.01 (m, 1 H, phenyl H; 4.72 (m, 1 H, benzylic H_); 2.40 (s, 3 H, aniline Me); 1.69 (s, 18 H, C6M); 1.50 (d, JHH=6.16 Hz, benzylic Me); 0.65 (d, JP-H=9.09 Hz, PMe3). 13C[1H] NMR (75 MHz, CDCl3, 220 C): 159.6, 156.4, 138.5, 138.4, 128.5, 124.0, 122.2, 121.1, 121.0, 115.7 (phenyl C); 99.5 (CQ6Me6); 68.1 (phenyl C); 24.5 (aniline Me); 20.7
(benzylic Me); 16.5 (C6Me6); 16.1 (d, Jp-C=29.6, PMe3). 31P[1H] NMR (121 MHz, CDC13, 220 C): 9.32.
Preparation of [( 16-C6H6)Ru((Ph)NC(H)(Me)C6H )(PMe3), 5
At -20 C, ld (0.160g, 0.310 mmol) was slurried in THF (35mL) and 1.4 M methyllithium (0.22 mL, 0.310 mmol) was added. Within five minutes, a red solution formed. The solution was allowed to stir for 30 minutes and solvent was then removed under reduced pressure. The red solid was extracted with toluene, (3x15mL) and filtered. The toluene was removed under reduced pressure and the resulting red solid was then extracted with diethyl ether, (3x15mL). The ether solution was filtered, concentrated and cooled to give red crystals, (0.128g, 0.284 mmol), 91 % yield. 1H NMR (300MHz, CDCl3, 220 C):
7.34 (t, JH-H=7.14 Hz, 2 H, phenyl H); 7.09 (d, JH-H=3.89 Hz, 2H, phenyl H_);
7.00 (m, 2 H, phenyl H); 6.80 (d, JH-H=8.10 Hz, 2 H, phenyl H); 6.56 (t, JHH=6.83 Hz, 1 H, ring H); 4.90 (m, broad, 1 H, benzylic H); 4.70 (s, 6 H, C6H6); 1.43 (d, JH-H=5.97 Hz, 3 H, benzylic Me); 0.67 (d, JP-H=9.82 Hz, 9 H, PMe3) 13C[1H] NMR (75 MHz, C6D6, 220 C): 172.0, 161.0, 159.0, 158.2, 138.8, 128.9, 124.5, 122.8, 121.3, 108.0 (phenyl Q; 89.5 (C6H6); 66.8 (phenyl C_); 21.6 (benzylic Me); 17.2 (d, JP-c=31.5 Hz, PMe3). 31 P[1H] NMR (121 MHz, C6D6, 220 C): 10.82.
Preparation of ( M-CMe)Ru((3,5-Me2)NC(H)(Me)Ph)(PMe~g
To a slurry of 1_ (0.123g, 0.193 mmol) in tetrahydrofuran (25mL) was added 0.14M MeLi (1.38mL, 0.193 mmol) at 00 C. The resulting orange solution was warmed to room temperature and stirred for thirty minutes. The THF was removed under reduced pressure and the orange residue was extracted into toluene. The toluene solution was filtered and the solution evaporated to dryness. The residue was then dissolved in hexanes, filtered, concentrated, and cooled to yield orange microcrystals (0.098g, 0.174 mmol), 90% yield. Anal. Calcd for C30H42NPRu: C, 56.1; H, 6.33; N, 2.25. Found: C, 55.9; H, 6.23; N, 2.21. 1H NMR (300MHz, CDCI3, 220 C); 7.07 (m, 4H, ring H; 6.97 (br, 1H, aniline p-H); 6.18 (br, 2H, aniline o-); 4.80 (br, 1H, benzylic H); 2.42 (br, 6H, aniline Me); 1.68 (s, 18H, C 6Me6); 1.58 (d, JH-H= 7.50 Hz, benzylic Me); 0.65 (d, JP-H=6.62 Hz, 9H, PMe3). 13C[1H] NMR (75 MHz, CDCI3, 220 C): 159.5, 158.8, 138.4, 137.9, 135.0, 124.0, 122.3, 121.0, 118.5, 110.9, 110.4 (phenyl C); 99.5 (6Me6); 68.1 (benzylic C); 24.7 (benzylic Me); 16.6 (C6Me6); 16.3 (d, JP-H=29.8 Hz, PMe3). 31P[1H] NMR (121 MHz, CDC3, 220 C): 9.24.
The amide complexes are red-orange solids which may be stored in air for an indefinite period of time. They are slightly air sensitive in solution. They
are soluble in nearly all polar organic solvents, and their solubility decreases with decreasing polarity of the organic solvent. The amides are insoluble in water.
Nuclear Magnetic Resonance Spectroscopy
The compounds were characterized using 1H NMR, 31 NMR and 13C NMR spectroscopy. It is useful to describe the details of the spectra of two of the complexes as representative of the general features of the 1 H NMR spectra of all the amides. A 1H NMR spectrum of (I6C6Me6)Ru((Ph)NC(H)(Me)C6H4) (PMe3), 2a, is shown in Figure 14. Starting in the upfield region of the spectrum, the PMe3 resonance appears as a doublet (JP-H=9.0 Hz) at 0.93 ppm. The methyl protons derived from the addition of MeLi appear as a doublet (JH-H=5.7 Hz) at 1.78 ppm, due to coupling to the benzylic proton. The I6-C6Me6 methyl protons appear as a singlet at 1.94 ppm. The benzylic proton appears as a quartet of doublets (JH.H=5.8 Hz and JPH=2.5 Hz) at
5.01 ppm. The phenyl region of this compound contains resonances which are not completely resolved. Overlap of phenyl peaks is common in the 1H NMR spectra of the amide complexes, thus the information contained in this region is of limited use.
A proton NMR spectrum of 2c is shown in Figure 15. The expanded portion of the spectrum is of the CH2 protons at the benzylic position. The pattern that is observed is an AB quartet. Additional long range P-H coupling is
2 '0 3:
CD co CL
observed in only one of the protons, due to the geometric orientation of that proton to the phosphorus atom in the molecule.
Assignment of the carbon spectra were complicated by the presence of a large number of inequivalent carbon atoms in the amide complexes, a result of the asymmetry of the molecule.
Stereochemistry of Lithium Alkyl and
Hydride Addition to form Amides.
Interesting stereochemical phenomena have been exhibited in some of the reactions of the cations with nucleophiles. An example is the reaction of 1 b with hydride, and 1a with methyl lithium. The details of these reactions will be discussed here. First, the reaction of hydride with la will be presented.
When la is stirred with one equivalent of Li(t-BuO)3AIH in
tetrahydrofuran at -20 C, an immediate reaction occurs, producing the orange pentane soluble product (,q6-C6Me6)Ru((Ph)NC(H)(H)C6H4)(PMe3) 2c, in ca. 95 % yield. The 1 H NMR spectrum of 2c (Figure 15) features a pair of doublets at 5.5 and 4.5 ppm (one which is coupled with the phosphine ligand, and another that is not) that are assigned to the diastereotopic benzylic protons. Other strong nucleophiles such as lithium alkyls will also add to the imine carbon to give the compounds in Table 3. If the attacking nucleophile is different from the substituent already bonded to the imine carbon, then the formation
0 C) cm
0 z L
of two sets of diastereomers is possible since both the ruthenium atom and the benzylic carbon atom are chiral centers.
When methyllithium is added to a solution of 1_a in tetrahydrofuran, only one product, complex 2, is observed by 1H NMR spectroscopy, shown in Figure 16. The structure of this compound was elucidated using difference NOE spectroscopy and x-ray crystallography. Thus, 2a is formed with ca. 100 % diastereoselectivity. The other diastereomer, (n6C6Me6)Ru((Ph)NC(Me)
(H)C6H4(PMe3)), can be synthesized by addition of Li(t-BuO)3AIH to [(16 C6Me6)Ru((Ph)N=C(Me) C6H4(PMe3))]+BF4", 1, followed by rapid workup of the reaction mixture, Figure 17. Under these conditions, 3a is the only detectable product of the reaction. These experiments demonstrate that both methyl addition to l a and hydride addition to lb occur endo to the T16-C6Me6 ring rather than between the "legs" of the piano stool.
+ BF4I !
Figure 16. Diastereoselectivity Exhibited by Addition of MeLi to la Producing 2a .
Table 3. Ust of Derivatives of the Cyclometaflated Amides
Me 3 P Ru
Compound R R' Rol R.
2a CH3 H CH3 C6H5
2b CH-3 H C6H5 C61-5
3a CH3 CH3 H C6H5
2c CH3 H H C6H5
2d CH3 H CH:3 p-MeC6H4
5 H H CH3 CAH
6 CH3 H OH3 (3,5-0H3)2C6H5
P Ru THF \ Ru
Z\-Z/ + U(t-O13U) AH
Figure 17. Diastereoselectivity Exhibited by Addition of Hydride
Across the C-N Double Bond of the Coordinated Imine
1 b Leading to Compound 2b.
Difference NOE Spectroscopy
The use of difference NOE spectroscopy in the determination of the structure of molecules has been discussed elsewhere.35 The utility of difference NOE spectroscopy is that it allows determination of solution molecular structure through spatial magnetic interactions, and is a powerful tool in the elucidation of stereochemical details. Figure 18 shows the results of the difference NOE experiment used to determine the stereochemistry of addition of MeU to the metallated cation la. In these experiments, the NOE enhancement of a signal indicates that the protons responsible for that signal are in relatively close proximity to the irradiated protons.
The difference NOE experiment is shown in Figqures 19 and 20. Figure 19 shows the effects of irradiation of the T16-C6Me6 protons of 2a. The
faa~alon oe K%
InOe Enhancement of the Benzytic Methyl Peak 5%
Enhancement of the Cis Proton nation of the
Figure 18. Summary of the Observed NOE Enhancement in 2a
spectrum at the top is the difference spectrum, which contains enhanced peaks. The spectrum at the bottom is a normal proton NMR spectrum of the complex. The benzylic methyl group shows a 1% NOE enhancement upon irradiation of the Ti6-C6Me6 protons. The signal for the benzylic proton shows no observable enhancement in the difference spectrum. This indicates that the methyl group is in close physical proximity to the irradiated 116-C6Me6 protons.
In Figure 20, the irradiation of the PMe3 proton resonance at 0.65 ppm results in a 5% NOE enhancement of the benzylic proton resonance at 4.75 ppm. This is shown in the upper spectrum. The lower spectrum is again a
CD X co
0 -6. CL
LLJ z 0
c CL "I0 CL
0 CD N
0 CD cl)
CL coo x
A= e w
0 Lu z
c CL IRS jej
normal proton NMR spectrum. These experiments are useful because they allow elucidation of stereochemistry in the absence of an x-ray structure. As discussed below, an x-ray crystallographic study provided the final proof that the addition of MeLi to 1a yields a product wherein the methyl group is trans to the phosphine ligand.
X-Ray Crystalloqraphic Study
Crystals of (16-C6 Me6)Ru((Ph)N-C(H)(Me)C6H4)(PMe3), 2a, were grown by slow evaporation of toluene solution. The crystallographic study of 2a was complicated by a disorder of the metallocycle fragment. The first determination revealed that the metallocycle, with its two phenyl rings, formed a nearly planar base. This extended planar structure appeared to lie one way about 75% of the time and the other way 25%. In other words, the independent unit was ca. 75% R and ca. 25% S conformation at the Ru atom. Both configurations showed the methyl group on the metallocycle to be in the endo position pointing toward the T 6-C6Me6 ring. The determination reported herein was carried out after careful optical inspection of crystals after recrystallization. Despite careful crystal selection, several large peaks in the final difference map and large thermal parameters for the metallocycle and phenyl atoms indicate that some small amount of disorder (perhaps 10%) exists. The disorder appears to concern only the relative orientation of the Ru-Cl and Ru-N linkages. In both
structure determinations, the methyl group C8 lies in the endo position toward the coordinated arene.
An ORTEP drawing of 2a is found in Figure 21 while selected bond
lengths and angles are found in Table 4. The bond distances and angles for 2a fall within the expected ranges. The N-C7 distance is considerably longer than in the cation, 1as would be expected for a nitrogen-carbon single bond. The T16-C6Me6 ligand is planar (0.02A). Coordination of the metal atom to the arene ring is not perfectly symmetric, the Ru-C(15), Ru-C(16), and Ru-C(17) bond distances are longer than the other metal ring distances. C(15) and C(16) are again approximately trans to the Ru-C(1) bond. The atoms of the metallocycle and the two phenyl rings lie within 0.5A of their calculated leastsquares plane. The exact conformation of the five-membered metallocyclic ring is difficult to discern but the N atom does lie 0.27A out of the plane of the other four atoms (Ru, C1, C6, C7) away from the coordinated r6i-C6Me6. Unfortunately, the disorder in the structure does not allow definitive conclusions to be made about whether or not the N atom is pyrimidal or planar, however, a pyramidal geometry would be expected since the Ru atom is already electronically saturated without 7c donation from the amide N atom.
Table 4. Selected Bond Lengths and Angles from the X-Ray
Structural Analysis of 2a.
Ru-P 2.290(2) Ru-C1 8 2.25(2)
Ru-N 2.08(2) Ru-C19 2.24(2)
Ru-C1 2.20(1) Ru-C20 2.22(1)
Ru-C15 2.322(9) N-C7 1.40(1)
Ru-C16 2.30(1) N-C9 1.32(2)
P-Ru-N 87.2(2) N-C7-C6 105.5(9)
P-Ru-C1 81.4(3) C1-C6-C7 117.(2)
N-Ru-C1 76.4(5) Ru-C1 -C6 116.(2)
Ru-N-C7 121.3(9) C6-C7-C8 110.3(9)
Variable Temperature NMR Studies on
() -C6Me6)Ru(((3,5)-Me2Ph)NC(H)(Me )CH PMe)The extent of steric crowding in the amide complexes has been apparent in some of their 1 H NMR spectra. The phenyl region of the room temperature 1H NMR spectrum of complex 2a exhibits resonances which indicate that the N-phenyl ring of the compound rotates slowly on the NMR timescale at room temperature.36 The features that are observed in the phenyl region of 2a include temperature dependant broadening of line shapes and incorrect numbers of resonances for a freely rotating phenyl ring. Attempts at using high temperature NMR to observe rapid rotation in this compound were unsuccessful. To obtain information concerning the energy barrier for rotation about the C-N bond of these amides, the analogous complex (T16C6Me6)Ru((3,5-Me2Ph)NC(H)(Me)C6H4)(PMe3), 6, Fiqure 22, was prepared. The phenyl region of 6 is simple and allows the rotation about the N-C(phenyl) bond to be readily observed by 1 H NMR, Figure 23.
This experiment was designed to provide some information concerning the extent of steric inhibition towards N-C bond rotation. The NMR study of compound 6 led to the observation of fluxional behavior which allowed for the determination of the energy barrier for rotation about the N-C bond. Proton NMR spectra at several different temperatures provide a profile of the fluxionality of the system, as discussed below.
a Ha Me
Figure 22. Structural Representation of Compound 6.
At room temperature, there are five peaks in the 1H NMR spectrum of 6 that provide information concerning the fluxionality of the complex. In Fiqure 24 it can be seen that the aniline ring portion of the cyclometallated ligand features two ortho protons, two meta-substituent methyl groups, and one para proton. When the ring is freely rotating about the C-N bond, the two ortho protons are equivalent and the two methyl groups are equivalent. However, when the ring is experiencing hindered rotation about the C-N bond, the methyl protons and the ortho protons on the ring will experience chemical shift inequivalence.
In Figure 25, the two singlets centered at 2.25 ppm are attributable to the two sets of methyl group protons on the aniline ring. The one para proton and two ortho protons of the ring can be observed as a singlet of area one at 6.20
\ Ru ,
H Me Ham
SCH H "a C0 3 1050 C
L_ A A600
l., p j i b4 ,. i, i 1 I ii,, '
7 6 5
Figure 24. Variable Temperature Proton NMR Spectra of the
Ortho Protons of 6 .
ppm (para) and two singlets each of area one at 6.17 and 6.50 ppm (ortho). The ortho proton peaks broaden into the baseline at 610C and coalesce into a singlet at 1050C. The coalescence temperature is 690C.
The fluxional NMR spectra of the downfield region of the spectrum
shown in Figure 23 are displayed in stacked plots over the temperature range of 220 to 1050C, Figure 24. Using the two site exchange approximation, AG for rotation about the N-C bond can be calculated and is approximately +14.2(3) kcal/mol.37
The same type of analysis may be used to examine the methyl groups, whose behavior is similar to but independent of the fluxionality exhibited by the phenyl protons. Their fluxional NMR spectra are shown in Figure 25. The coalescence of the methyl peaks over a temperature range of 10 to 600C produced a similar value (+14(1) kcal/mol) for the energy barrier for rotation about the C-N bond of the aniline ring.
The hindered rotation of the aniline ring in 6 is a consequence of some
type of steric or electronic barrier. It is possible that this hindered rotation is the result of a n-bonding interaction between the aniline ring sp2-hybridized carbons and the nitrogen lone pair. Based on the crystallographic evidence presented for compound 2a, the nearly coplanar five-membered metallocycle and the aniline phenyl ring are suggestive of a possible n interaction between trhe nitrogen lone pair and the phenyl group. It is possible that this amount of tbonding is sufficient to slow C-N bond rotation and that the phenyl groups in
H *a 600 C
c3 \/ Hb
3 H b
Figure 25. Variable Temperature Proton NMR Spectra of the Methyl
Protons of 6.
these LTM amide complexes are acting as n acceptors to a degree that would inhibit C-N bond rotation. The cause of the inhibited rotation probably lies in steric factors as well, and is supported by the crystal structure (Figqure 21), which demonstrates the congested environment of the molecule.38
KINETIC AND REACTIVITY STUDIES ON THE CYCLOMETALLATED AMIDE COMPLEXES
The reactivity of the amide complexes is discussed here. The product of the reaction of lb with Li(OtBu)3AIH is the amide complex 3a. The five membered ring formed by the chelated imine ligand in the cation is planar.39 It is possible that attack by incoming nucleophiles may occur on either side of the ring, although there may be a preferred face for addition to occur. If there is a preference, then the reaction is diastereoselective, as shown in Fiure 26.40 In the case of aluminohydride addition to 2b, the product formed suggests that there may be a preference, and therefore diastereoselectivity. The reaction yields only the isomer in which the hydride has added across the C-N double bond of the chelated imine ring where the hydrogen atom is trans to the phosphine ligand. There is no evidence of formation of the product where the hydride has added cis to the phosphine.
\+ B.Fbj Trns Addion
Figure 26. Ilustration of.the Possible Modes of Addi ion of an Incoming
Nucleophile to the [mine C-N Bond.
It was observed that an isomerization was occurring that converted the initial product of aluminohydride addition, 3a to a single new compound identified as the amide complex, 2a. This isomerization begins immediately following the conversion of cation 1 b to the amide complex 3a.
Apparently, the initial product of the reaction of 1 b with Li(OtBu)3AIH is the kinetically preferred product 3a which is thermodynamically unstable. The addition of hydride is thus a kinetically controlled addition reaction. This kinetic product then isomerizes to the thermodynamically more stable product, 2a.41
In initial experiments, a portion of 3a was observed in C6D6 by 1 H NMR over a period of several hours at room temperature. In this time period, a
Figure 27. Isomerzation of 3a to 2a Showing Nomenclature and the Relative Geometies
significant increase in the areas of the proton resonances attributable to 2a occurred, accompanied by a decrease in the areas of the resonances attributable to 3 indicating that there was a process leading to the isomerization of 3a to 2a as shown in Figure 27. This process occurs in THF and benzene solution, but not in the solid phase.
Kinetics Experiments Used to Measure Rate Constants and Thermodynamic Parameters for Isomerization of 3a to 2a
A kinetics study was undertaken to investigate the isomerization process. Proton NMR was used to obtain data to determine rate constants for the conversion of 3a to 2a. Several NMR tube solutions of the isomer 3a were prepared in C6D6 and kept frozen until the experiment was ready to begin.
The samples were prepared in a concentration range of 0.0150 M to 0.0450 M. The samples were placed in a constant temperature bath. They were monitored periodically using 1 H NMVR to measure the degree of isomerization which had occurred. The ratio of 3a to 2a was measured by integration of the C6Me6 and PMe3 resonances during the course of the reaction. The isomerization process is first order with respect to the concentration of 3a since a plot of ln[3a1 vs. t gave a straight line.4
Data was acquired on three samples at each of the various temperatures to provide a basis for error measurement when calculating the rate constants at each temperature. Data was acquired at five temperatures in order to construct an Eyring plot to obtain A Ht and A S*values.
The samples were prepared in an inert atmosphere and placed into
sealed NMVR tubes. In order to slow the reaction to a negligible rate between measurements, the samples were removed from the constant temperature bath and cooled in an ice bath between each sampling. This allowed the sample concentration percentages to be determined accurately via precise start and stop times while the samples were observed by 1 H NMR.
Calculation of the Rate Constant.
After the integral values were obtained, the percent starting material was calculated by multiplication of the ratio of reactant integral by the reciprocal of the sum of the product and reactant integrals. The reactant concentration was then calculated at various times throughout the experiment by determination of the product of initial concentration of reactant multiplied by the reactant percentage at a given time t. In each experiment, five to seven data points were collected, with points spread through at least two half-lives. The experiment at 300C was measured through four half lives. Experiments at other temperatures were consequently performed for fewer half-lives. After the data were collected, they were used to construct a plot of In [reactant] vs. time, where reactant is complex 3a. This was done using a linear least-squares fit line, the slope of which was the rate constant k for each sample.
Calculation of Thermodynamic Parameters.
Experiments were carried out at 300, 400, 500, 600, and 700 C in order to construct an Eyring plot to determine the thermodynamic quantities A H and A S* associated with the isomerization.43 The data are listed here in tables along with their coincident graphs. These represent the kinetics runs accumulated to determine A H* and A S values as well as phosphine effects.
Table 5. Ln [3a] vs. t Data for Isomerization at 300 C.
Sample A Sample B Sample C
Time (s) In [3a] In [3a] In [3a]
12600 -3.48 -3.36 -3.29
22800 -3.55 -3.36 -3.36
61200 -3.94 -3.75 -3.75
78900 -4.24 -4.17 -4.01
92400 -4.35 -4.17 -4.10
112500 -4.49 -4.24 -4.40
152100 -4.97 -4.74 -4.70
164400 -5.02 -4.72 -4.88
182100 -5.11 -5.25 -5.07
k (s-1) 4.4(1)x10-5 4.4(2)x10-5 4.60(8)x10-5
Initial [3a]A = 0.0361 M
Initial r[3aB = 0.0440 M
Initial 13alc = 0.0431 M
Table 6. Ln [3a] vs. t Data for Isomerization at 400 C.
Sample A Sample B Sample C
Time (s) In [3a] In [3a] In [3La]
0 -2.74 -3.06 -2.60
1800 -2.81 -3.13 -2.67
6300 -3.02 -3.34 -2.88
11550 -3.27 -3.38 -2.90
18600 -3.57 -3.89 -3.43
30300 -3.98 -4.28 -3.80
33750 -4.12 -4.42 -3.94
k (s-1) 1.80(4)x10-5 1.8(1)x10-5 1.7(1)x10-5
Initial [3a]A = 0.0650 M
Initial [3a]B = 0.0465 M
Initial [3al- = 0.0743 M
ca I C',C13
ug 0 0)
7 7 7
Table 7. Ln [3a] vs. t Data for Isomerization at 5000.
Sample A Sample B Sample C
Time (s) In [3a] In [3a] In r3a]
0 -3.13 -3.13 -3.06
3600 -3.73 -3.73 -3.64
5400 -4.03 -4.03 -3.96
8100 -4.47 -4.49 -3.65
10800 -4.86 -4.88 -4.77
19800 -5.99 -6.17 -6.15
k (s-1) 6.5(2)x10-5 6.6(1)x1 0-5 6.8(1)x 10-5
Initial f3alA = 0.0433 M
Initial [3a] = 0.0433 M
Initial [3a] = 0.0469 M
c,4 c,4 c,
Table 8. Ln [3al vs. t Data for Isomerization at 600 C.
Sample A Sample B Sample C
Time (s) In [3a] In [U3a In [3a]
0 -3.01 -4.05 -3.67
320 -3.21 -3.88
520 -3.39 -4.44 -3.96
770 -3.52 -4.59 -4.18
1145 -3.80 -4.77 -4.50
1445 -3.98 -5.05 -4.63
2060 -4.51 -5.54 -5.21
2670 -4.92 -5.88 -5.65
k (s-1) 7.3(1)x10-4 7.0(3)x10-4 7.7(2)x10-4
Initial [3a]A = 0.0492 M
Initial [3a]B = 0.0174 M
Initial 13alC = 0.0254 M
S 8 a !i! 8 2
lei Ld 0 0 0 to
Table 9. Ln [f3a] vs. t Data for Isomerization at 700 C.
Sample A Sample B Sample C
Time (s) In [3a] In [3a] In r3a]
0 -3.61 -4.15 -3.67
60 -3.68 -4.22 -3.75
120 -3.77 -4.30 -3.82
240 -3.94 -4.46 -3.97
420 -4.23 -5.93 -4.27
660 -4.66 -5.22 -4.71
960 -5.17 -5.70 -5.28
k (s-1) 1.67(3)x10-3 1.72(6)x10-3 1.70(2)x10-3
Initial [3ajA = 0.0270 M
Initial [3a]B = 0.0159 M
Initial [3a1C = 0.0254 M
LL C14 (04
Table 10. Ln [3a] vs. t Data for Isomerization
at 700C with a 40:1 excess of PMe3.
Sample A Sample B
Time (s) In r3a] In [3a
0 -4.16 -3.78
60 -4.28 -3.92
180 -4.45 -4.18
360 -4.99 -4.60
540 -5.42 -5.00
720 -5.74 -5.39
900 -6.15 -5.76
k (s-1) 2.27(9)x10-3 2.20(2)x10-3
Initial [3ajA = 0.0156 M Initial [3alB = 0.0228 M
CV) (D CD
0 CL co
co Ca C6 C.) > X
o 15 E
L6 wi u j U-i
Table 11. Ln [3al vs. t Data for Isomerization
at 700C with added P(CD3)3.
Time (s) In [Reactant]
k(s-1) 0.9(1) x 10-3
Initial 13al = 0.0050 M
____~0 o__ CO_ _C14