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Radical reactivity of seventeen electron cationic carbyne complexes

HIDE
 Title Page
 Acknowledgement
 Table of Contents
 List of Tables
 List of Figures
 List of schemes
 Abstract
 1. Introduction and background
 2. Photophysics and photoredox...
 3. Formation of a,w-dienes upon...
 4. Oxidation of metal carbynes...
 5. Effect of ligand variation on...
 6. Experimental procedures
 Appendix. Tables of crystallographic...
 References
 Biographical sketch
 
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Title:
Radical reactivity of seventeen electron cationic carbyne complexes
Physical Description:
xii, 129 leaves : ; 29 cm.
Language:
English
Creator:
Torraca, Karen E., 1971-
Publication Date:

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Subjects / Keywords:
Complex compounds   ( lcsh )
Carbynes   ( lcsh )
Chemistry thesis, Ph.D   ( lcsh )
Dissertations, Academic -- Chemistry -- UF   ( lcsh )
Genre:
bibliography   ( marcgt )
non-fiction   ( marcgt )

Notes

Thesis:
Thesis (Ph.D.)--University of Florida, 1999.
Bibliography:
Includes bibliographical references (leaves 121-128).
Statement of Responsibility:
by Karen E. Torraca.
General Note:
Typescript.
General Note:
Vita.

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
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oclc - 43460947
System ID:
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MISSING IMAGE

Material Information

Title:
Radical reactivity of seventeen electron cationic carbyne complexes
Physical Description:
xii, 129 leaves : ; 29 cm.
Language:
English
Creator:
Torraca, Karen E., 1971-
Publication Date:

Subjects

Subjects / Keywords:
Complex compounds   ( lcsh )
Carbynes   ( lcsh )
Chemistry thesis, Ph.D   ( lcsh )
Dissertations, Academic -- Chemistry -- UF   ( lcsh )
Genre:
bibliography   ( marcgt )
non-fiction   ( marcgt )

Notes

Thesis:
Thesis (Ph.D.)--University of Florida, 1999.
Bibliography:
Includes bibliographical references (leaves 121-128).
Statement of Responsibility:
by Karen E. Torraca.
General Note:
Typescript.
General Note:
Vita.

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 030481396
oclc - 43460947
System ID:
AA00017688:00001

Table of Contents
    Title Page
        Page i
        Page ii
    Acknowledgement
        Page iii
        Page iv
    Table of Contents
        Page v
        Page vi
        Page vii
    List of Tables
        Page viii
    List of Figures
        Page ix
    List of schemes
        Page x
    Abstract
        Page xi
        Page xii
    1. Introduction and background
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
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        Page 23
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        Page 25
        Page 26
    2. Photophysics and photoredox properties of low valent carbynes
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
        Page 39
    3. Formation of a,w-dienes upon photooxidation of alkenyl carbyne complexes
        Page 40
        Page 41
        Page 42
        Page 43
        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
    4. Oxidation of metal carbynes in the presence of alkynes. Alkyne addition vs. H-shift in the carbene intermediate
        Page 50
        Page 51
        Page 52
        Page 53
        Page 54
        Page 55
        Page 56
        Page 57
        Page 58
        Page 59
    5. Effect of ligand variation on the site of protonation in the metal carbynes CpL2Mo=CBu and TpL2Mo=CBu [L = CO, P(OR)3]
        Page 60
        Page 61
        Page 62
        Page 63
        Page 64
        Page 65
        Page 66
        Page 67
        Page 68
    6. Experimental procedures
        Page 69
        Page 70
        Page 71
        Page 72
        Page 73
        Page 74
        Page 75
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        Page 88
        Page 89
        Page 90
        Page 91
        Page 92
        Page 93
    Appendix. Tables of crystallographic data
        Page 94
        Page 95
        Page 96
        Page 97
        Page 98
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        Page 117
        Page 118
        Page 119
        Page 120
    References
        Page 121
        Page 122
        Page 123
        Page 124
        Page 125
        Page 126
        Page 127
        Page 128
    Biographical sketch
        Page 129
        Page 130
        Page 131
Full Text












RADICAL REACTIVITY OF SEVENTEEN ELECTRON
CATIONIC CARBYNE COMPLEXES











By

KAREN E. TORRACA


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


1999




























"In the struggle for existence, it is only on those who hang on for ten minutes after all is

hopeless, that hope begins to dawn."

G. K. Chesterton














ACKNOWLEDGMENTS


My first and greatest acknowledgment goes to God for giving me the ability and

patience to make it through graduate school and still love chemistry.

I want to thank my husband for his support and love that kept me sane during this

time as well as his much needed company during long nights in the NMR room.

Thanks go to my advisor, Dr. Lisa McElwee-White, for allowing me to work in her

research group and helping me to understand organometallic chemistry from an organic

viewpoint. Thanks also go to her for all the help and guidance in my career.

I'd like to thank my committee members for all their help and encouragement.

Great appreciation goes to professor William Dolbier for his time and thoughts on my

chemistry. In addition, thanks go to professor Kirk Schanze for his collaboration with the

photophysics part of this project.

Thanks go to Jennifer McCusker and Denise Main for making sure my graduate

career was not boring while in the McElwee-White research group. Thanks also go to

previous post docs Margaret Kerr and Yingxia He for their help with my chemistry.

Thanks go to Joanne Bedlek for helping me to keep going, especially when everything

wasn't working. Thanks also go to the many others in other groups for their input as well

as chemicals and the use of instruments when needed.

Special thanks go to Donna Balcom, who can fix anything! Thanks also go to all

the people in the business office for making purchasing one of the easiest group jobs I had

at UF. Thanks also go for all their support and understanding in the stressful times.

Thanks go to the electronics shop for helping me with computer problems even

if they were Macintoshes.








Finally, I'd like to thank my parents, Lois and Clyde Reese, for all their help and

encouragement and standing by me in all my decisions. Although my father passed away

before I could finish, his example in life to do everything to the best of his ability, whether

in school, teaching, or as a father, will never be forgotten.















TABLE OF CONTENTS


Vage
ACKNOW LEDGM ENTS ..........................................................................iii

LIST OF TABLES....................................... ............... ...... ........... .. viii

LIST O F FIG U RES.............................................................................. .. ix

LIST OF SCHEM ES.............................................................................. ....x

A B STR A CT ...................................................................................... ... xi

CHAPTERS

1 INTRODUCTION AND BACKGROUND....................... ......... ...............1

Organometallic Radicals....... ...........................................................
Metal-Centered Reactivity............ ..................................................2
Ligand-Centered Reactivity............... ............... ............. .................... 3
Free-Radical Addition to Organometallics .....................................3
Radical Generation at the Ligand.................................. .......... .5
Ligand Coupling ...................................................................
H-Atom Abstraction ................................... ..................... .... 15
Intermolecular Coupling Reactions with Unsaturated Substrates .......... 17
Metal and Ligand Reactivity Hapticity Changes............................ 18
Miscellaneous Ligand-Centered Reactions........................................... 19
Seventeen-Electron Cationic Carbynes..................................... 20
Sum m ary..... .......................... ............................................... 25

2 PHOTOPHYSICS AND PHOTOREDOX PROPERTIES OF
LOW VALENT CARBYNES ............................................................... 27

Introduction .............. .. .... .......................................................... 27
Photochemistry of Organometallic Complexes..................................... 28
Photophysics of Cp{P(OPh)3}(CO)W-CPh......................................... 29
Electron Transfer Quenching ............................. .... ..... ............... 31
Thermodynamics and Kinetics of Photoinduced Electron Transfer............... 35
Photoinduced Electron Transfer and Photochemical Reactivity
in Carbyne Complexes............................................................... 38
Sum m ary ......................................................... .......... ..... .... 39

3 FORMATION OF a,to-DIENES UPON PHOTOOXIDATION OF
ALKENYL CARBYNE COMPLEXES............................................. ..... 40








Introduction............ ........... ....... ..................... .......... ..... ...... .. 40
Synthesis of (rl-C5H,)(CO) {P(OMe) }Mo=CCH2(CH2),CH=CH2
[n = 2 (71b), 3 (71c), and 4 (71d)] ...............................................44
Photooxidation of (rl-C5Hs)(CO) P(OMe)3 }Mo-CCH2(CH2),CH=CH2
[n = 2 (71b), 3 (71c), and 4 (71d)] .................. ......................... 45
M echanistic Considerations.............................................................. 47
Sum m ary ......................................... .......... ................. .............. 49

4 OXIDATION OF METAL CARBYNES IN THE PRESENCE
OF ALKYNES. ALKYNE ADDITION VS. H-SHIFT IN
THE CARBENE INTERMEDIATE .................................................. ...... 50

Introduction... ....... ................ .................. ........ .... ........... ..... 50
Chem ical O xidation..................................................................... .. 50
Oxidation in the Presence of Alkynes ................................................... 52
X-ray Structure of (r'-C5H,)(CO) {P(OPh)3 } Mo[l': 2-CH {P(OPh)3 -
C(Ph)=CH(CH2CH2CH2CH3) }..................................... ......... 53
Reaction with Other Alkynes............................ ........................ ...... 55
Mechanistic Considerations................................................. ......... 55
Sum m ary ......................... ....................... ........ ........................ 59

5 EFFECT OF LIGAND VARIATION ON THE SITE OF
PROTONATION IN THE METAL CARBYNES CpL2Mo-CBu
AND TpL2Mo-CBu [L = CO, P(OR)3] ............................................................. 60

Introduction.. ......................... ...... ......................... ......... 60
Protonation of Cp{P(OPh)3}(CO)Mo-CBu (81a) .................. .............. 63
Protonation of Cp{P(OMe)3} Mo-CBu (103) ........................................ 64
Protonation of Cp(CO)2Mo=CBu (105)........................................ ....... 66
Protonation of Tp(CO),Mo-CBu (107).............................................. 67
Protonation of Tp{P(OMe)3 }(CO)Mo-CBu (109)................................... 67
Sum mary..... .... ..... ........ ........ .............. ... ........... ........ ... 68

6 EXPERIMENTAL PROCEDURES .......................................................... 69

G eneral........ ............................................................................ .. 69
Equipment and Instrumental Methods................................................. 70
General Instrumentation ........................................................ 70
Photophysical M ethods ........... .............. .................... ....... 70
2D NM R M ethods............................................. .. ................... 71
Sytheses....... ..................................... .......................... 72
Cl{P(OPh)3)2(CO)2W=CPh (111)...........................................72
Cp{ P(OPh)3 (CO)W -CPh (70)............................................. 72
(rl -C5H,)(CO) P(OMe)3 )Mo-CCH2(CH2)2CH=CH2 (71b).............. 73
(rl -C5H5)(CO) {P(OMe)3 Mo-CCH2(CH2)3CCH H2 (71c)...............74
(115-C5H5)(CO) {P(OMe)3 } Mo-CCH2(CH2)4CH=CH2 (71d) .............. 74
(rl -C5H5)C2{ P(OMe)3 }Mo=CCH2(CH2)2CH=CH2 (78b) ............... 75
(1 -C5H,)C12{ P(OMe)3 } Mo-CCH2(CH),3CH=CH2 (78c) ............... 75
(nr -CH,)C2 { P(OMe)3 }Mo-CCH,(CH2)4CH=CH2 (78d)................. 76
Cl{P(OPh)3 2(CO)2Mo-CBu (113).................................... 76
Cp P(OPh)3}(CO)Mo=CBu (81a)..................................... 77
[(r -C5H,)(CO) {P(OPh)3 } Mo[rl:T2-CH { P(OPh)3) C(Ph)=CH-
(CH2CH2CH2CH3)}](BF4) (82a) ............. ........................78








[(01-C5H5)(CO) { P(OPh)3 Mo[l' :rl2-CH { P(OPh)3 }C(CH5)=CH-
(CH,)](BF4) (82b)........................................................ 79
[(rl-C5sH)(CO) { P(OPh)3)Mo[r' :1'-CH { P(OPh)3 }C-
(CH2CH2CHCH3)=CH(CH2CH2CH2CH3)](BF4) (82c) .............. 80
[(05-C5H,)(CO) {P(OPh)3} HMo=CBu](BF4) (84).......................... 81
[(Tr1-C5Hs)(CO) { P(OPh)3} Mo[T' :T2-CH {PPh} C(C6H,)=CH-
(CH2CHCH2CH3)](BF4) (86) .............. ............................. 81
[(Tr5-CHs)(CO) { P(OPh)3 } Mo[' :12-CH { P(OMe) } C(C6H,)=CH-
(CH2CH2CH2CH3)](BF4) (87) ....................................... 82
[(T5-CsH5)(CO) { P(OPh)3 } Mo[r'l:T12-CH { P(OPh)3 C(SiMe3)=CH-
(CH2CH2CH2CH3)](BF4) (89) ......................................... 83
[(r5-C5Hs)(CO) {P(OMe)3 Mo ['l :r2-CH {P(OMe) } C(C6H,)=CH-
(CH2CH2CH2CH3)](BF4) (90).......................................... 84
Cl{P(OMe)3}4Mo=CBu (115).............................. ............... 85
Cp {P(OM e)3 } 2M o CBu (103)................................................ 86
[Cp { P(OMe)3 }2HMo=CBu] [BF4] (104)..................................... 86
CI(C5sHN)2(CO)2Mo-CBu (117)........................................... 87
Cp(CO)2M o=CBu (105) ................................................ ....... 87
[Mo2(p-H) {pL-C2(nBu)2 (CO)4Cp2][BF4] (106).............................. 88
Tp(CO)2M o=CBu (107)............... .............. ....................... 88
[Tp(CO)2Mo=C(H)Bu][BF4] (108)..................................... ...... 89
Tp {P(OMe)3}(CO)Mo=CBu (109) ........................................... 89
[Tp(CO) { P(OMe)3 }HMo=CBu][BF4] (110)................................ 90
Photooxidation of alkenyl carbynes ................................................ 91
(r5-C5H5)(CO) { P(OMe)3 }Mo=CCH2(CH2)2CH=CH, (71b) .............. 91
(T5-C5H5)(CO) {P(OMe)3 } MosCCH2(CH2)3CH=CH, (71c)............... 91
(TI-CsH,)(CO) {P(OMe)3 }Mo=CCH2(CH2)4CH=CH2 (71d) ............. 91
GC analysis of reaction products from 71b......................................... 92
X-ray Data Collection and Structure Refinement for (TI5-CHs)(CO) {P(OPh)3}-
Mo[rl :r2-CH {P(OPh) } C(Ph)=CH(CH2CH2CH2CH3)] (82a)................ 92
APPENDIX: TABLES OF CRYSTALLOGRAPHIC DATA ............................... 94
REFERENCES ............................................................................... 121
BIOGRAPHICAL SKETCH................................................................ 129














LIST OF TABLES


Table pge

2.1 Rate constants for electron transfer quenching of tungsten carbyne
com plex 70 ........................................................ ................ 33

A. 1 Crystallographic data and structure refinement.............................. ...95

A.2 Atomic coordinates ( x 104) and equivalent isotropic displacement
parameters (A2 x 103) for 82a ...................................................... 96

A.3 Bond lengths [A] and angles [o] for 82a ............................................99

A.4 Anisotropic displacement parameters (A2 x 103) for 82a..........................115

A.5 Hydrogen coordinates (x 104) and isotropic displacement
parameters (A2 x 10 ) for 82a............................... ................. ......118














LIST OF FIGURES


Figure page

1.1 Orbital Mixing Diagram for Cp(CO){P(OMe)3 }W-C-Ph............................. 21

2.1 (- ) Absorption spectrum of 70 in CH3CN solution.
(------) Luminescence spectrum of 70 in CH3CN solution...................... 30

2.2 Transient absorption difference spectra following 355 nm laser
excitation (10 mJ/pulse, 10 ns fwhm) ..............................................31

2.3 Plots of log kq vs. E/m(A/A"') for electron acceptors listed in Table 2.1 .......... 34

4.1 Thermal ellipsoids diagram of 82a showing the crystallographic
numbering scheme ................................................................. 54














LIST OF SCHEMES


Scheme page

1.A Various reaction modes of iron sandwich complexes..................................2

1 .B Radical addition of cyclohexene oxide to a chromium carbene........................4

1 .C Formation of methyl arene via a radical decomposition pathway ....................5

1 .D Intermolecular radical addition of a completed samarium ketyl to an alkene........6

1.E Reactivity of 17-electron vs. 19-electron species.......................................9

1.F Formation of alkylidene dimers from radical reactivity at carbon.................. 12

1.G Hapticity changes and radical reactivity............................................... 19

1 .H Various modes of reaction from a 17-electron cationic carbyne.................... 19

1.1 Metal-centered reactivity of 17-electron cationic carbynes........................... 23

1.J Products from the photooxidation of carbynes.................................. ..... 23

1.K Proposed mechanism for the formation of olefins from primary
alkyl susbstituents.................................................................... 24

1 .L Hydrogen atom abstraction at the carbyne ligand.................................. 25

2.A Mechanism of electron transfer ................................... .............. .. 36

3.A Formation of cyclohexanone and 1,4-pentadiene from
the photooxidation of butenyl carbyne (71a).................................... 41

3.B Formation of cycloalkenones from alkenyl carbynes................................ 43

3.C Synthesis of alkenyl carbynes........................................................ 45

3.D Formation of dichloromolybdenum carbynes and dienes
from the photooxidation of alkenyl cabynes..................................... 46

4.A Formation of 1-pentene from the oxidation of butyl carbyne........................ 52

4.B Oxidation of carbynes in the presence of alkynes.................................... 53














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


RADICAL REACTIVITY OF SEVENTEEN ELECTRON
CATIONIC CARBYNE COMPLEXES

By

Karen E. Torraca

August 1999

Chairman: Lisa McElwee-White
Major Department: Chemistry


This dissertation describes the preparation, reactivity, and photochemistry of a

series of low-valent carbyne complexes, Cp(CO){P(OR)3 }M=C-R' (M = Mo, W; R = Me,

Ph; R' = aryl, alkyl). Photolysis of these types of complexes in chlorinated solvents leads

to the generation of highly reactive seventeen-electron cationic carbynes via electron

transfer from the excited state of the carbyne to the solvent. This electron transfer was

examined by Ster-Volmer kinetics on a quenching study with various pyridinium salts and

nitroaromatics.

Photooxidation of complexes Cp(CO){P(OMe)3)Mo=C-CH2(CH2),CH=CH2 [n =

2, 3, and 4] resulted in the formation of both dienes CH2=CH(CH2),CH=CH2 and

dicholoromolybdenum carbynes Cp{P(OMe)3} Cl2Mo=C-CH2(CH2),CH=CH2. Both of

these products are derived from the same reactive seventeen-electron cationic carbyne

species. The product ratios allow evaluation of the relative reactivity of the carbyne radical

cation at the carbyne carbon (leading to olefins) versus its reactivity at the metal center

(leading to dichloromolybdenum carbynes). The preference for radical reactivity in the








carbyne ligand is in the range of 3:1 to 4:1, which is unusual for organometallic radical

systems generally dominated by metal-centered reactivity.

One-electron oxidation of the carbyne complex (nl-C5H,)(CO){ P(OPh)3 } Mo=C-

CH2CH2CH2CH3 in the presence of phenylacetylene results in H-abstraction and addition

of the alkyne to the resulting metal carbene. The final product of the addition is the rn'i2-

allyl complex (rl 5-CsH5)(CO) {P(OPh)3 } Mo[l' :i2-CH {P(OPh)3} C(Ph)=CH-

(CH2CH2CH2CH3)]. These examples are the first where the carbene could be intercepted

in a bimolecular reaction.

In order to determine whether the above reaction occurred by radical addition of the

seventeen-electron cationic carbyne to the alkyne or reaction of the alkyne with the cationic

carbene, a study was undertaken to generate the cationic carbene species independently.

Although unable to generate these species via protonation studies, an interesting trend in

protonation was discovered in a series of carbynes. The site of thermodynamic protonation

of the Fischer carbynes CpL2Mo-CBu and TpL2Mo-CBu [L = CO, P(OR)3] with HBF4

depends on the number of Ti-acid CO ligands. As the number of carbonyls increases from

zero to two and the electron density at the metal center is decreased by backbonding, the

protonation site shifts from the metal to the carbyne carbon.














CHAPTER 1
INTRODUCTION AND BACKGROUND



Organometallic Radicals



Organometallic radicals have been a topic of interest due to their reactivity and

proposed involvement in catalysis.1-5 Organometallic radicals can be generated from

closed shell (18-electron) transition metal complexes in the following ways: homolysis of

metal-metal bonds or metal-ligand bonds, electron transfer, atom abstraction, or addition of

organic radicals to closed shell complexes. The resulting species are described as 17-

electron, 19-electron, or (18 + 8)-electron, depending on the location of the unpaired

electron with respect to the valence shell of the metal. In the simplest view, 17-electron and

19-electron complexes are produced by one-electron oxidation and reduction, respectively,

of an 18-electron complex at the metal. An (18 + 8)-electron complex bears spin density in

the ligand orbitals.6

From this simple view, it would be expected that the reactive site of the

organometallic radical would lie on the metal for 17-electron and 19-electron complexes and

within the ligand for (18 + 8)-electron complexes. However, for complexes whose ligands

provide variable bonding modes, changes in ligand geometry can alter the electron count at

the metal so that several different radical species can be in equilibrium at any time.

Examples such as the iron sandwich complexes CpFe(C6,R) where R = H, Me1,7 undergo

reactions characteristic of different radical types. Although the spectroscopic and structural

data are consistent with formulation as Fe(I) 19-electron complexes, various reaction

modes suggest 17-electron, 18-electron, or 19-electron species (Scheme 1.A).7 Both








metal-centered and ligand-centered radical reactivity can occur in these "chameleon-like"

radicals. In addition, their reactive sites may not correlate to the location of the spin density

in the most stable form of the complex as determined spectroscopically.



Scheme 1.A. Various reaction modes of iron sandwich complexes.


Fen Fe- Fe1


18 e- 19 e- 17 e-

ligand-ligand electron transfer associative
coupling ligand substitution

Fen" n p

t Fell (MeO)3P'. Fell
H (MeO)I P(O)(OMe)2
H H J (MeO)3P

2




Metal-Centered Reactivity



The processes illustrated in Scheme 1.A are a subset of the known reactions of

organometallic radicals. These include radical coupling, atom transfer, associative

substitution, electron transfer, metal-alkyl homolysis and migratory insertion. Although

the literature contains extensive examples of metal-centered radical reactivity, there are

relatively few examples of reactivity of the radicals within the ligands. There are even

fewer cases in which both metal-centered and ligand-centered radical reactivity are observed

from the same molecule. The more common metal-centered reactions involve dimerization

by formation of metal-metal bonds, halogen atom abstraction and hydrogen abstraction.

These topics have been reviewed extensively and will not be discussed further.3 Organic








free radical reactions that are mediated by organometallic complexes have also been recently

reviewed8-11 and will not be covered within this discussion. Another recent emphasis in

the area of odd-electron organometallics has been the design of electron reservoirs. Little

consideration will be given to these systems here because they involve reversible electron

transfer and do not result in permanent chemical reactions.12,13 In addition, there are

several examples of 18+8 complexes which have significant spin density on the ligands as

determined spectroscopically.6 Inclusion of these complexes will be limited to cases which

have demonstrated radical reactivity at the ligands. In order to place ligand-centered radical

reactivity into perspective, this review will cover systems which display ligand-centered

radical reactivity with emphasis on literature since the last major review of organometallic

radicals in 1995.1



Ligand-Centered Reactivity



First, systems involving the addition of organic radicals to organometallic

complexes will be considered. Next, reactions involving selective generation of ligand-

centered radical species will be discussed. A survey of radical ligand-ligand coupling will

be followed by an overview of organometallic radicals that show both ligand-centered and

metal-centered reactivity due to changing hapticity of the coordinated ligands. After short

consideration of a few other ligand-centered radical reactions, a final discussion will be

given to chemistry involving 17-electron cationic carbynes.


Free Radical Addition to Organometallics


Recently, Elschenbroich and Agbaria have described a system in which an organic

radical (R-) is added to the chromium sandwich complex (Tr6-C6H6)2Cr.14 A paramagnetic








adduct forms in which the R group is on the Cp ring endo to the metal. ENDOR studies

indicate a dynamic ring-to-ring migration mediated by the central metal atom. Thus, during

the migration of the R group, the site of the radical moves back and forth between the metal

center and the Cp ring. Merlic also reported addition of organic radicals to 18-electron

organometallic species to generate organometallic radicals.15 As shown in Scheme 1.B,

the organic radical adds to the double bond of an unsaturated Fischer carbene resulting in

an alkyl radical adjacent to the metal center. This radical is then trapped by Cp2TiCI;

subsequent acidic workup leads to the cyclized product.



Scheme 1.B. Radical addition of cyclohexene oxide to a chromium carbene.
Me @CICp2Ti
Me OMe
(CO)5 (CO)5Cr
[Cp2TiCI]2
Me 1, CICp2Ti
MeOMe
2 HCI ''^" =i <>
(CO)5Cr CICp2Ti Me


Demonstrating a slightly different reactivity, Stryker adds allyl radicals to a 17-

electron organometallic allyl species 1 (equation 1.1).16 Although metal-centered radical

reactivity would be expected, the radical addition occurs solely at the central carbon of the

allyl to produce the metallacyclic product 2. This regiochemistry could be indicative of

spin density at C2 in the original complex.


Cp*2T C3H5Br
1 THF


Cp 2Ti_

2


+ Cp*2TiBr2


(1.1)








Radical Generation at the Ligand



In addition to the above reactions in which an organic radical is added to a closed

shell organometallic system to generate an organometallic radical, there are also a few cases

in which the radical is generated selectively at the ligand. However, the exact role of the

metal in these systems is unclear. Although the free aryl ligand of the dicationic iridium

system 3 (Scheme 1.C) is stable, decomposition ensues upon complexation to the

metal.17 It is proposed that the O-N bond undergoes homolysis to produce a carboxyl

radical 4 which then loses CO2 to produce the alkyl radical 5. Hydrogen abstraction at the


Scheme 1.C. Formation of methyl arene via a radical decomposition pathway.

MeO 0 CH Me <-P CH2CO; MeO < -CH2





MeO- -CH3


0-- M e 5
6


ligand produces the final product 6. Another example by Merlic involves generation of the

samarium ketyl 7 at a chromium completed aryl ketone (Scheme 1.D).18 The

completed ketyl undergoes an intermolecular radical addition to an alkene to yield alkyl

radical 8. Reduction by samarium (II) then produces the corresponding anion. After protic

workup, cyclization yields the lactone 9.








Scheme 1.D. Intermolecular radical addition of a completed samarium ketyl to an alkene.


Sm(II) COCOZMeW 4'
0 ---- OSm(Iff) (OC)3C
(co()3 Cr(CO)3 "OSm(I)
7 Cr(CO) 3 0
8


Ligand Coupling



A more common mode for ligand-centered reactivity of odd-electron

organometallics is ligand-ligand coupling. Metal-centered radical reactivity is typical for

neutral 17-electron organometallic complexes such as CpM(CO),.3 However, ligand-

centered radical reactivity is often observed in 19-electron or cationic 17-electron

systems.19 Since aspects of this topic have been discussed,' this section of the review

focuses on the most recent literature although some earlier reports will be covered as well.

These reactions will be grouped according to the coupling process. First dimerization

through polyhapto ligands will be examined followed by coupling through monohapto

ligands. Finally, miscellaneous reactions involving coupling of other molecules to the

ligand radical will be considered.



Coupling through polyhapto ligands in 19-electron complexes


19-electron systems tend to have more radical density located on the ligand than 17-

electron complexes. This fact is a consequence of the need to relieve the metal of the extra

electron. Therefore, the most stable 19-electron complexes tend to have polyhapto ligands

in which the radical density can be evenly spread over a large number of atoms. The most

common reaction for 19-electron systems is dimerization through polyhapto ligands.

Dimerization results in a lowering of the electron count by decreasing the hapticity of the








attached ligand. For example, upon one electron reduction, rhodocenium cation 10

dimerizes through the Cp ring to form complex 11 (equation 1.2).20


= Rh
I + H
(1.2)

10 11 h


A more recent example involves the reduction of the mixed Cp rhodocenium

complex [(Trl-CMes)Rh(rl-C5H,)].21 Dimerization occurs as above; however, only one

isomer is observed in which one of the Cp ligands dimerizes with a Cp* ligand of another

rhodocene. Dimerization is also observed with cobaltocenium complexes through ligands

other than Cp. For example, [CpCo(rl5-C7H9)] (12) can be reduced chemically and

electrochemically to produce complex 13 (equation 1.3).19



I + + e-
(1.3)


12 13



There are a few cases of dimerization through open polyhapto ligands as well. For
example, reduction of cobaltocenium complex 14 results in dimerization through the

pentadiene ligand to produce 15 (equation 1.4).22 Dimerization was also observed upon
reaction of CrCl2(PEt), with two equivalents of KC5H7. The reaction occurs through the
pentadienyl ligand to yield the chromium dimer 16 shown in equation 1.5 with

spontaneous reduction of the metal from Cr(II) to Cr(I).23











0+ +e-
(1.4)

14 15 o







Et3P*"Or
CrCl2(PEt3)n + KCsH7 E- I 1 ^ (1.5)


16 j PEt3




As discussed above, neutral 17-electron complexes tend to react via metal-centered

reactions while 19-electron complexes are dominated by ligand-centered reactivity. The

example in Scheme 1.E demonstrates these differences within the same system.24 Upon

photolysis, the iron dimer 17 homolytically breaks the iron-iron bond to form the 17-

electron neutral radical species 18 which dimerizes at the metal to regenerate the starting

material. Photolysis in the presence of a ligand such as PPh, results in a dimerization at the

ligand to produce 20 following addition of phosphine to yield the intermediate 19-electron

radical 19.









Scheme 1.E. Reactivity of 17-electron vs. 19-electron species.


hu
+ 2 PPh3


oc/F9-CO
0


17

S 17e

Oc, co


Fe(CO)2PPh3



Fe(CO)2PPh3

20


18


Coupling through polyhapto ligands in 17-electron complexes


Unlike their neutral counterparts, 17-electron cationic complexes often demonstrate

ligand-centered reactivity. For example, Novikova observed the formation of dimer 22


I+ eMe
FeCp

21


MI Me

I+
22 FeCp


upon one-electron oxidation of the iron fluorenyl complex 21 (Equation 1.6).25 In a

related reaction, oxidation of the rhodium half-sandwich complex 23 produces dimer 25

presumably from loss of H2 from the expected dimerization product 24 (equation

1.7).26,27 The driving force for the reaction is the regeneration of the 115 Cp ligand.

Ph3P CO

R -e H H2
Ph3P CO O + (1.7)

23 Rh Ph3P OCPPh3
Ph3P Co
Ph3P CO


(1.6)








Surprisingly, it was found that changing the phosphine ligand in the above rhodium

complex 23 for either P(OPh)3 or PMe3 resulted in entirely different chemistry. As shown

in equation 1.8, the 17-electron radical cation generated from 26 reacts as a metal-centered

radical to form the metal dimer 27.28




SP(OPh 2+
S- e CO
Rh Rhr-R (1.8)
(PhO)3P/ \CO (PhO)3P"
OC
26 27


Like the 19-electron systems, there are also a few cationic 17-electron systems

which show coupling reactions with ligands other than Cp. Geiger has shown that the

rhodium cyclooctatetraene complex 28 yields the ligand-coupled dimer 29 upon oxidation

(equation 1.9).29 The proposed intermediate bears a cyclooctatetraene ring that is bound

rl5, with the remaining carbons comprising an allyl radical. Connelly observed an
analogous dimer when Ru(CO)2(PPh3)(rl4-C8H8) was oxidized with ferrocenium

tetrafluoroborate.30




I -e h +


8 2 (1.9)

28 29








Coupling through monohapto ligands



Although early examples of dimerization chemistry involved polyhapto ligands,

there is a growing body of literature encompassing the coupling of monohapto ligands.

One way to ensure ligand-centered radical reactivity is to increase the steric bulk around the

metal center. Metal-porphyrin systems have become popular for these studies. The odd-

electron complex (TMP)RhCO [TMP = tetramesitylporphyrin] behaves as an acyl radical,

coupling carbonyl ligands to form the diketone dimer (TMP)RhC(O)C(O)Rh(TMP) in the

absence of good H-donors.31 More recently, Wayland examined the reactivity of a

rhodium (II) porphyrin bimetalloradical complex, *RhO(CH2)6ORh-, in which 2

trismesitylphenylporphyrin units are bridged by a diether (O-(CH2)6-O) spacer. This

bimetalloradical complex reacts reversibly with CO to form the diketone complex 30

(equation 1.10).32


R

O-(CH2)6-- (CH2)6 O (.10)
C6D6
Rh
30


In a more common type of organometallic system, Waterman observed coupling of

allyl fragments to produce 32 upon one-electron oxidation of the iron allyl complex 31

(equation 1.11).33 Along similar lines, coupling of two allyl ligands on the same metal to




Fe -e" / (1.11)
SA co
CO O eC
-, CO









produce 1,5-hexadiene has been noted following one-electron oxidation of CpMo(nr3-

C3H5)2.34 Although the mechanism has not been elucidated, the reaction proceeds very

quickly without loss of propene, which suggests an intramolecular radical coupling

reaction. Finally, oxidation of vinyl ferrocene 33 with the aminium salt (4-

BrC6H4)3N+SbC16 was found to result in coupling at the vinyl ligand to produce complex

34 (equation 1.12).35


[(4-BrC6H4)3N]+SbC16


33


(1.12)


34


Iron vinyl complexes such as 35 have been shown to readily couple upon oxidation

to yield bis(alkylidene) dimers 36 (Scheme 1.F).36-38 The resonance structures in

Scheme 1.F explain the rationale for the observed reactivity.



Scheme 1.F. Formation of alkylidene dimers from radical reactivity at carbon.


Cp2Fe+PF6-


Lf
35


LI








Due to the recent interest in molecular wires,37,39,40 there has been an explosion in
the development of oxidative coupling chemistry for synthesis of conjugated carbon linkers
between two metals. Although the redox chemistry of the molecular wires will not be
discussed here, because no overall chemical reactions take place at the ligands, the
oxidative reactions used to make the dimers will be noted.
Lapinte has reported oxidation of the iron-alkynyl complex 37 with ferrocenium

hexafluorophosphate to yield the dicationic vinylidene dimer 38 (equation 1.13).41,42




C2CpePF6- +^ H
FPe- C-H 2...FFe= C~ +/1.13)
PhP2P"2P/ Ph2P CC F( / (13)
h2P 37 PPh2 38 H PPh2
^ 37 < 38 Ph2P \



A similar dimerization for molybdenum alkynyl complex 39 was described by Beddoes

(equation 1.14).43 An analogous reaction was found to occur upon one electron oxidation

of Cp(CO)3Cr(C=C-Ph) to produce [Cp(CO)2Cr=C=C(Ph)C(Ph)=C=Cr-(CO)2Cp]+2.44

Unlike most 17-electron neutral systems which display metal-centered reactivity, the
manganese alkynyl complex 40 produces vinylidene dimer 41 upon warming to ambient
temperature (equation 1.15).




Cp2Fe+PF6- /Ph Ph2P/'
.Mo-C=-C-Ph Mo=C =C + P
Ph2P"' Ph2P" / .C= Mo-"' 2 (1.14)









4?Me p? /Ph
Mn-C-= C-Ph .Mn=C=C / Me
MeP""/' I Me2P"" I C=C= Mn. (1.15)
M .PMe2 / PM e 41 Me n PMe2 (
40 41 Me2P



One-electron oxidation of iron vinylidene cation 42 with iodosobenzene yields the

dicationic vinylidene dimer 43 (equation 1.16).45 This complex is proposed to result from

dimerization of the 17-electron radical cation [Cp(dppe)Fe-C=CMe]+ produced after

spontaneous loss of H' from the oxidized vinylidene. In a similar reaction [Ru2,(-

C4TMS2)(PMe3)4Cp2]2, was produced after air oxidation of the cationic ruthenium

vinylidene [Cp(PMe3)2Ru=C=CH(TMS)]+.46




S H PhIO + /Me
F.e=C-- .Fe=C = +/
Ph2P"'I Me CH3CN PhP I =C-=F..- (1.16)
Ph2P 2P Me "PPh2
42 43 Ph-P


Coupling by deprotonation/oxidation sequences is also known. Deprotonation of
manganese carbene 44 yields anion 45, which couples via the carbene ligand to yield 46

upon oxidation with Cul (equation 1.17).47 Templeton has developed a similar route to

oxidatively couple carbyne complexes.48 Starting with the Tp' carbyne 47 (Tp' =
hydridotris(3,5-dimethyl-l-pyrazolyl)borate; M = Mo, W), deprotonation with "BuLi
followed by oxidation results in the coupled product 48 (equation 1.18). Analogously,
deprotonation of Cp{P(OMe)3)2Mo=CCH2tBu with "BuLi followed by oxidation with








ferrocenium tetrafluoroborate yields Cp { P(OMe)3 } 2Mo-CCR(H)CR(H)=Mo-

{P(OMe)3 ,Cp.49




Me OEt nBuLi Me OEt

oe' CH -60'C O 2.02
C OC 78"c
OC CH2R -78 C
44 45 Me (1.17)
/OEt


OC H MMe

46 EtO CO



Tp'\ BuLi Tp\-
.MsC-CH2R -M= C=CHR
OC"7 --C-60 C OC""/ (1.18)
OC 47OC e7
47
Tp' Tp'
.M C--C- -C=M..
OC""% rc-C-"'"CO
OC R R CO
48


H-Atom Abstraction


Although ligand-ligand coupling reactions are common radical ligand-centered

reactions for organometallic complexes, these radicals can also react intermolecularly with

other species in solution. For example, some of the above dimerization reactions occur in

competition with hydrogen atom abstraction. In the case of the manganese alkynyl

complex (l'-C5H4Me)(dmpe)Mn-C-CPh, hydrogen atom abstraction resulted in formation

of vinylidene 49 (equation 1.19).50 This reaction competed with dimerization to the extent

that the resulting mixtures were difficult to purify. In the presence of better hydrogen atom








donors, such as "Bu3SnH, the vinylidene could be made directly from the manganese
alkyne complex without any detectable amounts of dimerization products.


Me
Me /Ph
\Mrn--C-Ph -Mn-C- (1.19)
Me2P"e' MeP' H
./PMe2 39 PMe2 9



Lapinte found that if the iron alkynyl complex 37 were oxidized at 20 "C instead of at

temperatures below -50 "C, H atom abstraction at C2 of the alkynyl ligand became the

dominant reaction pathway and the vinylidene 50 resulted (equation 1.20).42



k;PCp2Fe+PF6 /H

SFe-C=C-H 2. *Fe=-C C\H (1.20)
Ph2' 20 C Ph2P" H
2P 37 2P 50



As mentioned previously, one electron oxidation of (717-C7H7)(dppe)Mo(C-CPh)

with ferrocenium hexafluorophosphate results in dimerization at C2 of the alkynyl ligand.43
However, when the alkyne is substituted with a tert-butyl group instead of a phenyl group,

oxidation results in the cationic vinylidene via hydrogen atom abstraction.51 In this case
dimerization is prevented by the steric bulk of the tert-butyl group. Similarly, Wayland
found that the radical (TMP)RhCO reacted selectively with "Bu3SnH by hydrogen atom

abstraction at the carbonyl ligand to form the formyl complex (TMP)RhC(O)H.31

As expected for 17-electron neutral radicals, Geiger found that reduction of
(COD)2Rh [COD = cyclooctadiene] in CH2Cl2 resulted in halogen atom abstraction from








the solvent at the metal center to produce [(COD)Rh(WC-C1)]2.52 Unexpectedly, reduction at

-45 "C in the absence of a halogenated solvent resulted in hydrogen atom abstraction at the

ligand to produce 52 (equation 1.21). It should be noted that the exact isomer of the

product is not known.




+^^ ^ r+ e)
Rh R (1.21)

51 52


Intermolecular Coupling Reactions with Unsaturated Substrates

Another type of intermolecular reaction involves the addition of organometallic

radicals to unsaturated species. (TMP)RhCO was found to form the adduct

(TMP)RhC(O)CH2CH(Ph)C(O)Rh(TMP) in the presence of styrene. This product results

from radical addition to the alkene followed by coupling to a second equivalent of

(TMP)Rh(CO).31 The bimetalloradical complex depicted in equation 1.10 also reacts with

alkenes such as 1,3-butadiene to produce the carbon-bridged molecule 53 (equation

1.22).32




O-(CH2)6- (C r2)6 (1.22)

Rh
53


Oxidation of vinyl ferrocene (32) with (4-BrC6H4)3N+SbCl6 in the presence of 1,1-

diphenylethylene results in formation of the adduct 54 (equation 1.23).35 A similar

coupling was noted upon oxidation of the iron allyl complex 55 in the presence of 1,3-








diphenylisobenzofuran. In this case oxidation was followed by treatment with I to remove

the metal from the benzofuran product 56 (equation 1.24).33




+ Ph [(4-BrC6H4)3N]+SbCI6 (Ph
Ph P h (1.23)
32 54





P 1. Ag Ph
C e P 2. I P" Ph .,CO (1.24)
CO CO
55 56


Metal and Ligand Reactivity Hapticity Changes


Because metal-centered organometallic radicals are generally more reactive than

ligand-centered organometallic radicals, a system that displays metal radical behavior rarely

exhibits ligand-centered reactivity as well. A fairly recent example by Strelet involves

chromium tricarbonyl anions completed to fluorenyl systems via the central Cp ring

(57).53 One-electron oxidation leads to generation of the corresponding radical which is in

equilibrium with the metal-metal bonded dimer 58 (Scheme 1.G). The major product

(59) results from H atom abstraction at the fluorenyl ligand, with the minor product

resulting from dimerization at the fluorenyl ligand to yield 60. These products result from

a facile haptotropic shift of the chromium tricarbonyl complex from rl5 to 16.









Scheme 1.G. Hapticity changes and radical reactivity

-e
I I r(CO)3
Cr(CO)3 Cr(CO)3 r(CO)3

57 THF <^T
T + H* Cr(CO)3 H 59

THF-Cr(CO)3 Cr(CO)3 H
Cr(CO)3 H


60 (OC 3c
Miscellaneous Ligand-Centered Reactions



Green observed that upon addition of CF3I to the carbyne

Cp{P(OMe),}2Mo-CCH2'Bu (61), two different organometallic products resulted

(Scheme 1.H).54 These products are proposed to arise from initial electron transfer from

the carbyne 61 to CF3I to yield the 17-electron radical cation 62. H-atom abstraction from

the carbyne ligand followed by addition of r to the metal gives rise to the vinylidene 63.


Scheme 1.H. Various modes of reaction from a 17-electron cationic carbyne.


CF31
o C-CF3I MO C-CH2'Bu
(MeO)3P"M=C-C (MeO)3P"
(MeO)3P 61 (MeO)3P 62

-CH3* He



\ CH2tu
\P-P(OMe)2 (MeOhP" C CHtBu
(MeO)3P 4 (MeO)3P 63



The second product results from Arbuzov-type abstraction of CH3. from one of the

coordinated phosphite groups. The resulting complex adds I- followed by migration of the








phosphite to the carbyne carbon. Coordination of the oxygen to the metal yields the final

product 64. Thus, although radical reactivity is implicated in these processes, the radical

reactions are different from any of those previously described.


Seventeen Electron Cationic Carbynes


Over the past several years, the McElwee-White group has focused on the activation

of low valent carbyne complexes by photochemical electron transfer. In the presence of

halocarbons, the complexes CpL2M=CR [M = Mo, W; L = P(OMe),, CO and R = alkyl,

aryl] undergo photooxidation to give 17-electron cation radicals. Unlike the majority of the

reactions described above, depending on the reaction conditions and the carbyne

substituent, the 17-electron complexes exhibit both metal-centered and ligand-centered

reactivity without changing ligand binding modes. In the metal-centered mode, ligand

exchange and halogen abstraction (characteristic reactions of metal radicals) yield new

carbyne complexes. In the ligand-centered mode, hydrogen abstraction at the carbyne

carbon yields highly reactive cationic carbene complexes whose further rearrangements lead

ultimately to organic products. In order to better understand these processes, it is essential

that the structure and bonding in carbyne complexes be examined.

Since the discovery of the first carbyne complex in 1973 55, much work has been

done theoretically and experimentally to gain an understanding of the nature of metal-

carbon multiple bonded molecules. An electronic picture of carbyne complex

Cp(CO){P(OMe)3}W-C-Ph was described recently (Figure 1.1).56

Based on extended Hiickel calculations, the HOMO is mainly composed of a metal

dx2.y2 nonbonding orbital. Thus, it would be expected that upon one-electron oxidation the

unpaired electron would remain behind in a nonbonding-metal orbital and metal-centered

reactivity would result.













y



/-Z


d

-K'
.S
d(w-co)4CO(


Srt* (W-C)
S
%
* S








S S
II
t
r
t



r
l
%


n* (W-C-Ph)


\


(WC
*
S s di c


Figure 1.1. Orbital mixing diagram for Cp(CO){P(OMe) } W=C-Ph.


Early experiments involved irradiation of CHCI3 solutions of the carbynes


CpL2Mo-CR 65. When the reactions were run in the presence of PMe3 to stabilize any


unsaturated intermediates, new cationic carbyne complexes resulted as shown in Scheme


1.1.57,58 Mechanistic studies showed the primary photoprocess to be electron transfer


-65.










S -75-
-ra
U








85 -










95 .


P





p + Ph i


"-1+'-


r








from the excited state of the carbyne to the chloroform solvent. Upon reduction, the

solvent undergoes fragmentation to form chloride ion and dichloromethyl radical ensuring

an irreversible electron transfer. The resulting 17-electron cationic carbyne 65'. then

undergoes ligand exchange (66*) and halogen-atom abstraction to yield the final cationic

carbyne (67).



Scheme 1.I. Metal-centered reactivity of 17-electron cationic carbynes.


hv +
Mo-CR CH3 65 + Cl- + *CHC12
Lf" CHCI3
c' 65



+ PMe3 Me oCR Cl
65 Me3P "~C/
PMe3 +
66"


+ CHC13 \-
66 CHC3 C Me3I CR CI + .CHCI2
Me3P Y
PMe3
67


In the absence of strongly nucleophilic species such as PMe3, the results of the

photooxidation are quite different. For the complexes Cp(CO)LM=CR, where R is a

primary or secondary alkyl group, photooxidation results in organic products derived from

the carbyne substituent. If R is a tertiary alkyl group, a new carbyne species is the product

(Scheme 1.J).

Mechanistic studies have revealed that these products are derived from similar

intermediates. As shown for the proposed mechanism for the formation of olefins from

carbynes with 1 alkyl substituents (Scheme 1.K) the first step is one-electron oxidation

of the carbyne to form the 17-electron radical cationic carbyne A. H-atom abstraction at the







carbon results in an electrophilic carbene B followed by a 1,2 hydride shift to yield the final
olefin complex C. Under the oxidative conditions, the olefin is released from C. In
general, the fate of the carbyne radical A depends on the steric bulk of the carbyne
substituent. For 1 and 2" substituents on the carbyne, hydrogen atom abstraction is
standard. For 3" substituents, the 17-electron cationic carbyne undergoes ligand exchange
with chloride followed by halogen atom abstraction to form the new carbyne via metal-
centered radical reactions.


Scheme 1.J.


Products from the photooxidation of carbynes.

ZMO \ hu
(MeO),P O CDC13
3 CDCI


\w-C-- (MeO)" W'

CMo

(MeO)31 o


hu
CDC13


hu
CDC13


hu
CDCI3


(MeO)3I ;l


C.....Mo-C--
(MeO)3P


6


6








Scheme 1.K. Proposed mechanism for the formation of olefins from primary alkyl
susbstituents.


Mo= C-CHRIR2 hv (Me .Mo C-CHRIR2
(MeO)P/ CHC3 MeO)3P
CO CO
A

R


I H H-shift
(MeO)3P' Mo (MeO)3P o =C CHRR2
CO R, R2 ( COP
C L B J


As discussed above, because of the electronic structure of the neutral carbyne

complexes, H-abstraction at the carbyne carbon was unexpected. Extended Hiickel and

INDO calculations on the neutral carbyne complexes indicate that their HOMOs are

nonbonding metal d orbitals (dx2y2) (Figure 1.1).59 This suggests that one-electron

oxidation should yield radical cations whose spin density and positive charge are on the

metal, not the carbyne ligand. However, INDO calculations on the carbyne radical cation

[Cp(CO){P(OMe)3,Mo=CCH2CH3]" indicate stabilization upon bending the Mo-C-C

angle from 180" to 120'. This change in geometry places spin density on the carbyne

carbon in the radical cation although the initial oxidation occurs from an orbital that is
primarily nonbonding metal d in character. The oxidized carbyne is thus able to function as

a carbon-centered radical and abstract a hydrogen atom at the carbyne carbon.
As mentioned before, complexes with 3" substituents on the carbyne yielded new
carbyne species via metal-radical reactions. This is consistent with the additional steric
hindrance at the carbyne carbon rendering H abstraction at that site too slow to compete
with reaction at the metal atom of the radical cation. An alternative view is that the steric

bulk of the tert-butyl group hinders the bending of the Mo=C-C angle, preventing the shift








of spin density onto the carbyne carbon. The tert-butyl carbyne thus behaves as a typical

metal-centered 17-electron radical.

Although proposed as an intermediate in several carbyne photooxidation reactions,

the electrophilic carbene B generated upon H abstraction by the 17-electron radical cation

had not been directly observed. However, it was recently found that photooxidation of the

cyclohexenyl carbyne 68 in CHCI3 produced carbene complex 69 (Scheme 1.L).60 The

carbene moiety is proposed to form via electron transfer and H atom abstraction as with

other carbynes. However, the alkene moiety then coordinates to the metal and Cl-

exchanges for the carbonyl ligand to yield the final product. Carbene 69 is stable at -40 C

and has been characterized spectroscopically ('H NMR, "C NMR, IR and electrospray

MS). These results are significant because they represent the first direct observation of a

carbene complex in one of the photooxidation reaction mixtures, and provides

corroborating evidence that the carbyne radical cation produced upon oxidation does indeed

undergo the highly unusual H-abstraction process postulated on the basis of mechanistic

studies.



Scheme 1.L. Hydrogen atom abstraction at the carbyne ligand.
hv /CHC13

OC. Cl `--- ^ -
(MeO)3P HCI (MeOP /
we (MeO)3 /
68
69


Summary

Organometallic radicals have been studied for decades. However, there is still a

great deal to learn about these species. Most of the literature has focused on the more

common metal-centered reactions, yet there is a growing interest in ligand-centered radical

reactivity. Due to the variety of products observed in these reactions, current studies are








focused on understanding how small changes in the molecules result in different modes of

reactivity. In the future, selectively accessing some of these reaction modes, many of

which can not be accessed through traditional organometallic reactions, could greatly

enhance the generation and development of catalytic systems involving paramagnetic

species.

This dissertation will focus on the extended research of 17-electron cationic

carbynes. Although there is much already known about the activation of carbynes through

photooxidation to produce organic products, relatively little is known about the actual

electron transfer process responsible for generating these radicals. Even less is known

concerning the general reactivity of the 17-electron cationic carbynes, so that predictions of

expected reactivity repeatedly fall short. In this dissertation the formation of these

organometallic radicals as well as their general reactivity will be discussed.














CHAPTER 2
PHOTOPHYSICS AND PHOTOREDOX PROPERTIES OF LOW VALENT
CARBYNES


Introduction


The photochemistry of low-valent carbynes has been attracting increasing attention

due to the variety of reaction modes accessible. Generally, the photolysis of organometallic

compounds results in ligand loss as the primary photoprocess due to population of the M-L

antibonding orbital.61 In contrast, it was recently discovered that photolysis of

Cp { P(OR)3 (CO)Mo-CR' and Cp { P(OR)3 } (CO)W=CR' [R' = alkyl] in CHCl1 results in

conversion of the carbyne ligands to organic products.62 Carbyne complexes possess low-

lying MLCT bands which can be accessed with visible light and often have lifetimes on the

order of several hundred nanoseconds.63 The long-lived emissive excited states could

facilitate photochemical conversions to useful products.63-65 The photochemistry of these

carbyne complexes is dominated by these low-lying transitions. Because of the nature of

these excitations, in which the excited and ground electronic states are quite different, a

range of reactivity can be expected.

Photochemistry is a useful tool for activating complexes by inducing one-electron

oxidation. One-electron oxidation is a known method for increasing the reactivity of

organometallic species.2 The differences in the rates of reaction for 17-electron and 18-

electron species can be quite dramatic.2,3,7 For example, reaction manifolds unavailable to

18-electron species can become accessible to 17-electron counterparts. Previously,

photooxidation of a carbyne complex resulted in irreversible electron transfer from the

carbyne to a halogenated solvent.57 This process involved electron transfer from the

27








excited state of the carbyne to an electron acceptor, resulting in the generation of an

organometallic radical cation. Depending on the coordinating ligands and the nature of the

carbyne substituent, both metal-centered reactions typical of organometallic radicals and

unusual rearrangements of the carbyne ligand to give organic products have been observed.


Photochemistry of Organometallic Complexes


The carbynes Cp{P(OR)3}(CO)Mo-CR' and Cp{P(OR)3}(CO)W-CR' [R' =

alkyl], display a unique reactivity from other organometallic systems in that photolysis in

CHC13 results in organic products.62 In these reactions, the excited state of the carbyne

complex is proposed to undergo electron transfer to CHCl3 to produce a highly reactive

seventeen-electron species. Evidence for electron transfer can be found in the radical

reactions of the resulting carbyne complexes59,60 and the observation of side reactions

from the reduction of chloroform.57,62

The involvement of electron transfer in the photochemistry of metal carbyne

complexes has been unequivocally established by recent studies of photoinduced electron

transfer between a rhenium carbyne complex and a series of electron donors and

acceptors.66 However, in the case of the carbynes Cp{P(OR)3}(CO)Mo-CR' and

Cp{P(OR)3}(CO)W=CR' [R' = alkyl] relatively little is known about the actual electron

transfer from the excited state of the carbyne to the halogenated solvent. Even less is

understood about the excited state of the carbyne, or how its structure may induce the

reactivity observed after the formation of the radical cation.

In an effort to more fully investigate the role photochemical electron transfer67 plays

in the reactions of tungsten carbynes, a study of electron transfer from the excited state of

Cp{P(OPh)3}(CO)W=CPh (70) to a series of electron acceptors was undertaken. These

studies were were performed in conjunction with Carla Cavalheiro and Kirk Schanze. In








the course of this study, the quenching of the dn* excited state of 70 by a series of

pyridinium and nitroaromatic acceptors of varying reduction potential was examined. Laser

flash photolysis reveals that in every case quenching is accompanied by the appearance of

radical ion products, thereby demonstrating that quenching occurs via electron transfer.

The dependence of the bimolecular quenching rate constant on the reduction potentials of

the acceptors establishes that 70 is a potent reducing agent in the dn* excited state.

Moreover, a Marcus analysis of the rate data implies that oxidation of 70* is accompanied

by a comparatively low reorganization energy but that electron transfer within the encounter

complex may be weakly non-adiabatic.



Photophysics of Cp IP(OPh) I (CO)W=CPh



Previous photophysical studies of the carbynes Cp { P(OMe) } (CO)M=CR, where

M = Mo or W and R = aryl, allowed the assignment of the lowest lying absorption as

arising from a dn* transition.56,57 This absorption, although spin-allowed, has a low

extinction coefficient because the large contribution of d orbitals to the "n*" LUMO lends

the transition a significant degree of dd character. In addition to luminescence in solution,

the moderately long-lived dn* excited states feature a strong transient absorption by which

the excited state reactivity can be examined.

In previous studies of the photophysics of carbynes of the type

Cp{P(OR)3)(CO)M=CR',56,57 P(OMe)3 served as the ancillary ligand. However, the

alkyl phosphite participates in the Arbuzov reaction under electron transfer conditions.68.69

This problem has been alleviated by changing the ancillary ligand to P(OPh)3 in the present

investigation. The absorption spectrum of the carbyne complex Cp{P(OPh)3}(CO)W=CPh

(70) in CH3CN (Figure 2.1) is very similar to its P(OMe)3 analog in that it displays two

UV/visible bands ( = 322 nm, E = 9000 M- cm'; ma = 458 nm, E = 200 M-'cm').56






30

The lower energy band corresponds to the dt* transition while the high energy band is due

to the nrn* transition of the W=CPh chromophore.

10

7" 8


4A
X 1

"- / N.



0
300 400 500 600 700 800
Wavelength / nm


Figure 2.1. (- ) Absorption spectrum of 70 in CH3CN solution. (------
Luminescence spectrum of 70 in CH3CN solution.


Complex 70 features red luminescence similar to that of the structurally-related Mo

and W carbyne complexes that have been previously studied.56,57 In CH3CN solution at

298K, the luminescence appears as a broad, structureless band with Xm = 710 nm and a

lifetime (er,) of 192 ns (Figure 2.1). The emission from 70 at 77K in a 2-MTHF solvent

glass is similar in energy and bandshape to that observed in solution at 298K. Franck-

Condon bandshape analysis of the low temperature emission affords an estimate of 14,800

200 cm-' (1.85 eV) for Eo.70,71

Laser flash photolysis of 70 affords a strongly absorbing transient with Xm = 425

nm (Figure 2.2a). Because the spectrum of this transient is very similar to that assigned

to the dnt* state in Cp{P(OMe)3}(CO)M=CR (M = W and Mo), the transient absorption

observed for 70 is also attributed to that state.56 Global analysis of the transient absorption









data indicates that the dn* excited state absorption decays with a lifetime of 187 ns, in

excellent agreement with the emission lifetime.


0.12

0.09

0.06

0.03

0.00 .

-0.03

.n ni


v.w ,
0.12


0.09


0.06


0.03


0.00


350 400


a








b


450 500 550 600 650 700


Wavelength / nm


Figure 2.2. Transient absorption difference spectra following 355 nm laser excitation
(10 mJ/pulse, 10 ns fwhm). (a) Complex 70 (c = 1 x 10-4 M) in CH3CN, spectra at 40,
80, 120 and 160 ns delay after excitation. (b) Complex 70 (c = 1 x 104 M) and N,N'-
dimethyl-4,4'-bipyridinium (c = 0.02 M) in CH3CN solution, spectra at 0, 40 and 80 its
delay after excitation.


Electron Transfer Ouenching


The transient absorption assigned to the dn* state of 70 is quenched by the addition

of various pyridinium and nitroaromatic electron acceptors to the solutions. For each


' .' i ' "'I""' "~'"








electron acceptor, dn* quenching is accompanied by the formation of a long-lived transient

(T > 20 ms, vide infra) which can be assigned to the radical ion produced by reduction of

the electron acceptor. For example, Figure 2.2b illustrates the transient absorption

spectrum of a solution of 70 with 20 mM dimethylviologen (MV2+). The spectrum is

clearly dominated by the viologen radical cation, as evidenced by the characteristic

absorptions at 395 and 605 nm.72 Based on these laser flash photolysis observations, the

quenching is attributed to photoinduced electron transfer in which the excited state carbyne

complex reduces the acceptor A to generate A" (equation 2.1).



(70*) + A -+ (70+*) + A- (2.1)



Transient absorption due to the oxidized carbyne complex 70+' was not observed in

these experiments, in spite of many efforts directed towards its detection. Although the

failure to observe 70*" could be attributed to low absorptivity, it is likely that this 17-

electron species undergoes rapid secondary reactions. Moreover, several observations

support the premise that 70*" reacts very rapidly after being formed. First, in most cases

the transient absorption due to A" persists out to very long time scales, which suggests that

second-order charge recombination (equation 2.2) does not occur. Second, photochemical

studies of related tungsten and molybdenum carbyne complexes indicate that the metal

center in 17-electron radical cations such as 70'* rapidly engages in ligand exchange and

atom abstraction reactions.62


(70+') + A- (70) + A


(2.2)








Table 2.1. Rate constants for electron transfer quenching of tungsten carbyne complex
70"

Quencher El2/Vb kq/l09 M-s-'
N,N'-dimethyl-4,4'- -0.45c 5.1
bipyridinium
N-methyl-4,4'-bipyridinium -0.54c 4.7
p-dinitrobenzene -0.69d 9.6
o-dinitrobenzene -0.81 d 5.4
p-nitrobenzaldehyde -0.86d 4.9
m-dinitrobenzene -0.90d 4.9
N-methyl isonicotinamide -0.93c 3.2
cation
nitrobenzene -1.15d 0.53
N-methyl pyridinium -1.33ce 0.15
N-methyl-4-tert- -1.45c.e 0.028
butylpyridinium
a Estimated error in E,, values is 0.05 V for reversible waves
and 0.1 V for irreversible waves. Estimated error in rate
constants is 10%. b V vs. SCE reference. c The laboratory
of Kirk Schanze unpublished results. d From ref. 74.
e Cathodic peak potential for irreversible wave.


In order to explore the effect of the thermodynamic driving force on the electron

transfer quenching kinetics of 70, Stem-Volmer quenching studies were carried out with a

series of five pyridinium ion and four nitroaromatic electron acceptors. The reduction

potentials of the electron acceptors73 and corresponding Stem-Volmer quenching rate

constants (kq) are compiled in Table 2.1. Figure 2.3 illustrates the correlation between

kq and E,2(A/A"). As expected for an electron transfer mechanism, kq increases as the

reduction potential of the electron acceptor becomes less negative.










101 Ei(70*/70) = -1.45 V --
S= 0.25 eV
wn 109
"/ E,1(70*/70+) = -1.85 V
12 X= 0.40 eV
108


C0 107 i


106
-1.8 -1.5 -1.2 -0.9 -0.6 -0.3 0.0

E,1/(A/A") / V vs SCE


Figure 2.3. Plots of log kq vs. E,/2(AIA) for electron acceptors listed in Table 2.1.
A: Data for nitroaromatic quenchers; *: Data for pyridinium quenchers. Solid lines
calculated as described in text.


Finally, in order to obtain information regarding the overall efficiency for the

production of electron transfer products, the cage escape yield (ri) was determined for the

quenching of 70 with dimethylviologen. This experiment revealed that rlTes = 0.26,

indicating that electron transfer products are produced in comparatively high yield as a

result of the quenching process. Interestingly, the cage escape yield for quenching of 70*

by MV2' is very similar to that for the oxidative quenching of the excited state Ru(bpy)32+

by MV2+.74-77 Moreover, the cage escape yield for both metal complex systems is

considerably larger than observed when the singlet excited state donors are quenched by

pyridinium acceptors.78 The relatively high cage escape yield in the Ru(bpy)32+/ MV2'

system has been attributed to arise (in part) because Ru(bpy),2+* has a large degree of

triplet spin character.74-77,79,80








Thermodynamics and Kinetics of Photoinduced Electron Transfer


The free energy for photoinduced electron transfer from the dn* state of 70 to an

electron acceptor can be estimated as shown in equation 2.3a,



AGET = E,1(70*/70+') E/12(A/A-) (2.3a)

E112(70*/70+') = E,12(70/70+') E0o (2.3b)


where E,,(70*/70'') is the oxidation potential of the dn* state of 70 and E,,(A/A') is the

reduction potential of the acceptor.73 (Because 70 is a neutral species, it is assumed that

the work term is negligible.) The excited- and ground-state oxidation potentials of 70 are

related by equation 2.3b, where Eo is the energy of the relaxed dn* excited state.73 Cyclic

voltammetry of 70 in CH3CN solution reveals a single irreversible anodic wave at Epa =

+0.34 V vs. SCE. This wave arises from one-electron oxidation of the complex to afford

the radical cation, 70', which reacts rapidly on the electrochemical time scale. Although

the peak of an irreversible voltammetric wave does not necessarily correspond to the

thermodynamic potential for the reversible electrode process (i.e., E,/2), typically the peak

potential is within several hundred millivolts of E/2'.81,82 Thus, by assuming Ea =

E1/2(70/70'') = +0.34 V, and using the E0o value obtained from luminescence

spectroscopy, equation 2.3a affords an estimate of E,2(70*/70+') = -1.5 V. This estimate

suggests that photoinduced electron transfer is exothermic for acceptors with reduction

potentials positive of -1.5 V, and therefore 70* will be quenched efficiently by these

acceptors. Inspection of Figure 2.3 clearly indicates that this qualitative analysis is

consistent with the experimental observations in that acceptors with E,2 > -1.5 V quench

70* at rates in excess of 107 MA's-'.








The correlation between the kinetics and thermodynamics of photoinduced electron

transfer can be placed on a more quantitative basis by subjecting the quenching rate data to

analysis by using Marcus semi-classical electron transfer theory.83,84 This analysis relies

on the mechanism shown in Scheme 2.A where kd and kd are the rate constants for

formation and dissociation of the encounter complex, k,, and k,, are the rate constants for

the forward and back excited state electron transfer reactions in the encounter complex, kes

is the rate of dissociation of the geminate ion pair and kb, is the rate of back electron

transfer within the geminate pair. The pathway with rate krxu is added to include the

possibility that 70'' reacts rapidly to form a metal complex cation radical product (X') at a

rate that is competitive with back electron transfer and cage escape.



Scheme 2.A. Mechanism of electron transfer

kd kel
70* + A [70*, A] [70, A-'] kesc 70+' + A`
k-d kel kbet

4X X + A-
70 + A


Some years ago Balzani and co-workers showed that for Scheme 2.A in the limit

where k.d = (kesc + kbt + krx), equation 2.4 provides the relationship between the observed

electron transfer quenching rate constant, kq, and the parameters AGET and AG*ET"83 In

equation 2.4, kq is the experimentally determined quenching rate constant (see Table 2.1

for values) and the other rate constants are as defined above. The parameter k0e is the rate

kq AGE k-d AGEI (2.4)
1 + exp + I + exp+
SRT kel t RT J








constant for electron transfer within the encounter complex when the reaction is

activationless. In the context of Marcus theory, activationless electron transfer occurs
when -AGr = X, where is the total reorganization energy for electron transfer. Marcus

theory defines the relationship between AG*E and the reaction driving force and the

reorganization energy (AGr and X, respectively):85



AGET 1 + AG (2.5)



Now, by substituting equation 2.5 into equation 2.4, and replacing AG. with

E,12(70*/70'') EI,(A/A") (equation 2.3a) we arrive at equation 2.6 which defines the
dependence of kq on the rate constants in Scheme 2.A, as well as on the important

parameters ke, E/,2(70*/70'), E,,(A/A"') and X. This equation is useful because it allows

one to compute the dependence of kq on E,2(A/A'), by assuming values for kd, k-d, k,e, X

and E,/2(70*/70+).


kd
kq = 1 ep(E(70/70) E./2(A/A-))+ d exp E/2(A/A (2.6)
I RT j kEel [14RT I I I



Figure 2.3 illustrates two plots of the calculated dependence of kq on E/(A/A-').
Both lines were calculated by using equation 2.6 with kd = 1 x 1010 M-'s', k.d = 2 x 1010 s'~

and k0e = 5 x 10" s'.70,83 The two differ in that the solid line was computed using X =
0.25 eV and E/2(70*/70+') = -1.45 V while the broken line was computed with X = 0.40
eV and E,,2(70*/70+') = -1.85 V. Although both calculations fit the experimental

quenching data reasonably well, the broken line provides a better fit. Moreover, the value

of X = 0.25 eV is unreasonably small for a charge shift reaction in a polar solvent.86 We








conclude that the parameters used for the broken line fit are better estimates of the "true

values" for electron transfer quenching of 70*. An interesting outcome of this analysis is

that it implies that E,/2(70*/70+) is approximately 350 mV more negative than the value

estimated by using equation 2.3b assuming that Epa = E,12(70/70''). Thus, we conclude

that the ground state oxidation potential of 70 must be negative of Epa = +0.34 V, and the

analysis suggests a value for Ei2(70/70') = 0 V.

Interestingly, the quenching data for the nitroaromatic and pyridinium quenchers

follow the same correlation, despite the fact that the nitroaromatics are neutral while the

pyridiniums are cations. Different charges in the quencher ions will lead to differences in

the cage escape rates (kesc, Scheme 2.A).73,83 Thus, the observation that all of the

quenchers follow the same correlation implies that the electron transfer step is irreversible

(i.e., ke, << kb, + kesc + kxn).


Photoinduced Electron Transfer and Photochemical Reactivity in Carbyne Complexes


An interesting question concerns the relationship between the well-defined

photoinduced electron transfer documented herein and the previously reported

photochemical reactions of related carbyne complexes in CHCl1.57,62 These processes are

attributed to initial photoinduced electron transfer to CHC1,, followed by reactions of the

resulting 17-electron cationic carbyne complexes. Although the reduction potential of

CHC13 is poorly defined due to the reactivity of the anion radical, polarographic and

voltammetric studies suggest that Et2(CHCl3/CHCl3') lies between -1.7 and -2.0 V.87

Given the uncertainty of this estimate for the reduction potential of CHC13 and the

uncertainty in the excited state oxidation potential of 70 videe supra), it is possible that

photoinduced electron transfer from excited state 70 (and related carbyne complexes) to

CHC13 could be slightly to moderately endothermic. If so, the process could be








comparatively inefficient. This prediction is consistent with a previous study in which it

was observed that the emission lifetime of Cp{P(OMe)3}(CO)W-C-Ph was only slightly

shorter in CHC13 than in THF (134 ns in CHC13 vs. 141 ns in THF).56 Nonetheless, even

if photoinduced electron transfer from the excited state carbyne complex to CHC13 is

inefficient, the substantial reactivity of CHC13" and/or the 17-electron carbyne complexes

could render the electron transfer step irreversible and net photochemistry could occur with

modest overall quantum efficiency.

Summary


Photoinduced electron transfer from the dn* state of carbyne complex 70 to a series

of nitroaromatic and pyridinium electron acceptors with well-defined reduction potentials

has been examined. The study confirms that electron transfer occurs, moreover,

correlation of k, with E,2(A/A") demonstrates that the dn* state of 70 is a potent reducing

agent, with E,2(70*/70'') = -1.7 0.2 V. Marcus analysis of the correlation of kq with

E,,(A/A-') suggests that photoinduced electron transfer is accompanied by a relatively low

reorganization energy (X = 0.4 eV). Furthermore, comparatively low electron transfer rates

are observed for the strongest acceptors, a feature which implies that the photoinduced

electron transfer reaction may be weakly nonadiabatic (ko, = 5 x 10" s-1).














CHAPTER 3
FORMATION OF a,co-DIENES UPON PHOTOOXIDATION OF ALKENYL
CARBYNE COMPLEXES


Introduction

As described in the first chapter, photolysis of carbynes of the type

Cp(Co){P(OR)3}M-CR' [R = OMe, OPh; R' = alkyl, aryl; M = W, Mo] in the presence of

CHC13 results in a variety of products depending on the substituent at the carbyne carbon.

1 alkyl substituents lead to H atom abstraction at the carbyne carbon followed by

rearrangement to yield organic products. For example, photooxidation of the butenyl

carbyne 71a yields cyclohexenone (Scheme 3.A).88

Mechanistic studies on cyclohexenone formation were consistent with a pathway

initiated by electron transfer from the carbyne complex to yield a radical cation. Hydrogen

abstraction at the carbyne carbon then generates a cationic carbene (72a) that undergoes an

intramolecular ene reaction to form the metallacycle 73a.88 Next, CO insertion into the

metallacycle ring of 73a, reductive elimination and hydride shift yield cyclohexenone.








Scheme 3.A. Formation of cyclohexanone and 1,4-pentadiene from the photooxidation
of butenyl carbyne (71a).



oc2) + RH ocO M H
(MeO)3P (MeO)3P / H

71a 72a


intramolecular
ene reaction


(MeO)3P

73a











(40%)
(40%)


H-shift





Mo

(MeO)3P

74a


(7%)


The minor organic product of this reaction is 1,4-pentadiene (Scheme 3.A). The
diene undoubtedly arises from an alternative pathway for carbene 72a. Hydride shift from

C2 to Cl of the carbene ligand would yield the T12-diene complex 74a, which would be








prone to diene loss under oxidative conditions. A related process has been observed in

complexes such as butyl carbyne 75 (equation 3.1).59




< 9hv

CCc CHC3, (3.1)
(MeO)3P
75


Formation of cyclohexenone from the butenyl carbyne 71a suggested that other

alkenyl carbynes might also form cyclic products via the mechanism in Scheme 3.A. For

example, if the homologous series (rl-C5Hs)(CO){P(OMe)3}Mo=CCH2(CH2),CH=CH2

[n = 2 (71b), 3 (71c), and 4 (71d)] were to undergo the same sequence of reactions as

71a, the products would be cycloheptenone, cyclooctenone and cyclononenone,

respectively.





\ H (3.2)
Y Y


The crucial step in the Scheme 3.A mechanism is the intramolecular ene reaction

72a -- 73a. In the rearrangement of 72a, the carbene moiety functions as the enophile.

This is an extremely unusual mode of metal participation in the ene reaction. In the

extensively studied "metallo-ene reaction," the metal either serves as the migrating group89

or catalyzes the ene reaction in an organic substrate.90 The reaction of 72a -- 73a, in

which the metal is a part of the enophile moiety, is more closely related to purely organic

cases. For the organic intramolecular ene reaction, three types have been classified








according to the pattern of connectivity between ene and enophile.91 The conversion of

72a to 73a represents a rare example of the type III ene reaction (equation 3.2), in which

the enophile is attached to the allylic terminus of the ene.



Scheme 3.B. Formation of cycloalkenones from alkenyl carbynes.
P +
1) hv/CHCl3 \

OC 2) + RH OC/
(MeO)3P R(MeO)3P / "H
H
71a n= 1
71b n = 2 72a n = 1
71c n=3 72b n=2
71d n=4 72c n=3
72d n=4

known for n = 1
unknown for
n = 2-4

-+

S----(CH2)n

(CH2)n (MeO)3Pq1


73a n = 1
73b n=2
73c n=3
73d n=4
Type m intramolecular ene reactions are unusual, but known examples include ring

closure of a,o-dienes to yield 7-, 8-, and 9-membered rings.91,92 If the ring size

dependence of the organometallic system were similar, the homologous alkenyl carbynes

71b-d could access the 7-, 8-, and 9- membered metallacycles 73b-d, respectively.

Completion of the Scheme 3.A pathway would then yield larger cycloalkenones

(Scheme 3.B). This work is an examination of the photooxidation of the alkenyl

carbynes 71b-d. Although the chemistry of these complexes exhibits significant








differences from that of 71a, the results lead to significant insight into the radical cations

arising from one-electron oxidation of metal carbynes.



Synthesis of (nsCr H )(CO) P(OMe)}Mo-CCH,(CH)CH=CH, [n = 2 (71b). 3 (71c).
and 4 (71d)1


The alkenyl carbynes (1rS-C5H5)(CO){P(OMe)3}Mo=CCH2(CH2),CH=CH2 [n = 2

(71b), 3 (71c), and 4 (71d)] were synthesized by a deprotonation/alkylation strategy first

reported by Green and Templeton.49,93,94 Deprotonation of methyl carbyne 76 with "BuLi

and subsequent alkylation of the resulting vinylidene anion with the alkenyl iodides

I(CH2)nCCH=CH2 [n = 2-4] yielded the carbyne complexes 71b-d (Scheme 3.C). In

order to obtain good yields of pure products, care must be taken to ensure that the alkenyl

iodides are free of protic impurities. In the presence of proton sources, reprotonation of the

vinylidene anion 77 results in regeneration of methyl carbyne 76 which is virtually

inseparable from the alkylated products. If the amount of 76 in the reaction mixtures is

minimal, 71b-d can be purified by chromatography on neutral alumina. The pure carbyne

complexes 71b-d are yellow oils at room temperature and are thermally sensitive, thus

requiring storage in dry ether at -40 C to avoid decomposition.







Scheme 3.C. Synthesis of alkenyl carbynes.


n-BuLi [ (
MC,, C--Me OC.Mo C-CH2
(MeO)3P THF (MeO)3P
76

/ a) (CH2)2--
b) (CH2)3 -I
C) / (CH2)4-I


C M C-CH2(CH2)n -
(MeO)3P
n = 2 (71b), 3 (71c), 4 (71d)


Photooxidation of (nrl-CH )(CO)IP(OMe) }Mo=CCH2(CH CH=CHz fn = 2 (71b). 3
(71c), and 4 (71d)1

Photolysis of 71b-d resulted in the production of both organic and organometallic
products. In order to identify the organic products, GC and 'H NMR data for the
photolysis mixtures were compared with those from corresponding authentic samples of
the anticipated enone and diene products. However, the GC and 'H NMR data for the
products from 71b-d were not consistent with the presence of enones. Instead, the dienes
CH2=CH(CH2),CH=CH2 were the only identifiable organic products that were derived
from the original carbyne substituents. They were accompanied by the
dichloromolybdenum carbynes 78b-d (Scheme 3.D). Carbynes 78b-d were identified
by comparison to 'H NMR and "P NMR spectra of authentic samples generated by
reaction of the alkenyl carbynes 71b-d with PCI Due to the ability of 78b-d, pure








samples could not be isolated. However, the spectral data were in strong agreement with

the data from other (Trl-CsHs)Cl2{P(OMe)3}Mo=C-R complexes59, including the 1-

methylcyclopropyl derivative, for which a crystal structure was obtained.95


Scheme 3.D. Formation of dichloromolybdenum carbynes and dienes from
photooxidation of alkenyl cabynes.


M mCCH2(CH2)
OC" A
(MeO)3P
n = 2 (71b), 3 (71c), 4 (71d)


hv
CHCI3


n = 2 (79b), 3 (79c), 4 (79d)


C'-


H abstraction


n = 2 (80b), 3 (80c), 4 (80d)



CHCI3



C Mo CCH2(CH2)
(MeO)3hP
C1
n = 2 (78b), 3 (78c), 4(78d)


n = 2 (72b), 3 (72c), 4 (72d)


H-shift




oc%'/ Ao-
(MeO)3P (CH2)


n = 2 (74b), 3 (74c), 4 (74d)


(CH2)n---








The photooxidation of (n5-C5sH)(CO){P(OMe)3) Mo-C-CH,(CH2)2CH=CH2

(71b) was carried out by irradiation in CDCI3 at 0 C. During the photolysis, the extent of

starting material loss was monitored by 'H NMR. At about half conversion of 71b, 1,5-

hexadiene had been formed in 72% yield as determined by GC analysis. Integration of the

'H NMR spectrum of the reaction mixture indicated a diene yield of 73%, in excellent

agreement with the GC value. The corresponding dichloromolybdenum carbyne complex

78b was formed in 17% yield as determined by integration of the 'H NMR spectrum. The

yields are reported at half-conversion of the carbyne because both the dichloromolybdenum

carbyne 78b and 1,5-hexadiene are sensitive to the photolysis reaction conditions. For

example, at 33% conversion, the carbyne 71b had produced the dichloromolybdenum

carbyne 78b in 25% overall yield. By the time 47% conversion of 71b had been reached,

the yield of 78b had dropped to 17%. The carbyne 71c was oxidized under the same

conditions to form 1,6-heptadiene in 72% yield and the dichloromolybdenum carbyne 78 c

in 21% yield as determined by integration of the 'H NMR spectrum of the reaction mixture.

Likewise, 71d formed 1,7-octadiene in 67% yield and 78d in 17% yield. The presence of

methyl chloride was also observed in all of the reaction mixtures by 'H NMR. Methyl

chloride has been detected in previous reactions of related complexes and is a product of

Arbuzov reaction of the P(OMe)3 ligands.68



Mechanistic Considerations

Formation of the diene products upon photooxidation of the alkenyl carbynes 71b-

d is precedented by formation of 1,4-pentadiene as a minor product from the photolysis of

the butenyl carbyne 71a in CHC13 (Scheme 3.A and equation 3.1). Prior mechanistic

studies on the formation of organic products upon photooxidation of metal carbynes are

consistent with single electron transfer from the carbyne excited state to the solvent as the

first step on the pathway (Scheme 3.D).62 Next, the 17-electron radical cation 79








abstracts hydrogen from the reaction medium to form the cationic carbene complex 72.59

Diene formation results from 1,2-H-shift in the intermediate 72 to produce the 1l2-diene

complex 74, in a process related to Wagner-Meerwein shifts in organic carbocations. Such

rearrangements have previously been observed in electrophilic carbene complexes.96

Under the oxidative conditions of the photolysis, the 12-diene complex 74 would be prone

to loss of diene to yield the free organic product.

In the chemistry of butenyl carbyne 71a (Scheme 3.A), the fate of cationic

carbene complex 72a determines the partitioning between diene and cycloalkenone

products. Although enone formation predominates from butenyl carbyne 71a, the reaction

fails for the longer alkenyl chains derived from 71b-d. Formation of cycloalkenones from

71b-d would require intramolecular ene reactions from 72b-d. Although this process is

favorable for 72a, which produces the 6-membered metallacycle 73a, the ene reaction is

slower for systems which would form larger rings. In these cases, the ene reaction cannot

compete with the fast [1,2]-H shift that leads to diene products.

Formation of the dichloromolybdenum carbynes 78b-d is also precedented.

Dichloromolybdenum carbynes are minor products of most photolyses of similar carbynes

in CHCI3 and result from reactivity of the initial 17-electron radical cation species 79 at the

metal center (Scheme 3.D). Rapid ligand exchange and halogen atom abstraction are

characteristic reactions of metal-centered radicals.1-3,7 If 79 undergoes these processes

instead of H-abstraction at the carbyne carbon, dichloromolybdenum carbyne 78 is the

final product. It arises from chloride exchange at the metal center of 79 to yield the radical

compound 80 which undergoes halogen abstraction to form 78. Although revising the

order of the ligand exchange and halogen atom abstraction steps would yield the same

product, consideration of the relative rates of these processes in other metal radical systems

suggests the sequence shown in Scheme 3.D.2








The formation of both the dienes and the dichloromolybdenum carbynes stems from

partitioning of the 17-electron radical cation species 79b-d between "metal radical" and

"organic radical" behavior. Which product is produced from this common intermediate

depends on the reactivity of the metal toward ligand exchange with Cl vs. the tendency of

the carbyne carbon to abstract hydrogen. Because at least 85% of the starting material can

be accounted for in the form of organic dienes or the dichloromolybdenum carbynes, these

product ratios allow an estimate of the preference for 79b-d to undergo reaction at the

metal vs. the carbyne carbon. Under these reaction conditions, the dienes are produced

preferentially over the dichloromolybdenum carbynes by a factor of about 4 to 1. Thus,

hydrogen abstraction at the carbyne carbon is faster than ligand exchange at the metal center

for the radical cations 79b-d, which have sterically unhindered 1 alkyl substituents on the

carbyne ligands. These results can be contrasted with carbynes bearing 3" substituents, for

which H-abstraction is significantly slowed by steric hindrance and Cl1 exchange to yield

dichloromolybdenum carbynes dominates the reactivity.59,95



Summary

Although the photooxidation of the alkenyl carbynes 71b-d did not produce

cycloalkenones, this chemistry provides an interesting opportunity to assess the reactivity

of the 17-electron radical cation species that are produced upon photooxidation of metal

carbynes. The organic dienes and the dichloromolybdenum carbynes produced in these

photooxidations result from reactivity of those radicals at the carbyne carbon and the metal

respectively. The organic product is favored over the organometallic one by about 4:1

under these reaction conditions. The fact that both products are produced provides a rare

example in which both metal and carbon radical reaction manifolds can be accessed from

the same species.














CHAPTER 4
OXIDATION OF METAL CARBYNES IN THE PRESENCE OF ALKYNES. ALKYNE
ADDITION VS. H-SHIFT IN THE CARBENE INTERMEDIATE


Introduction

As explained in the previous chapters, photooxidation of the carbyne complexes

(015-C5H5)(CO){P(OPh)3}M-CR [M = Mo, W; R = alkyl],62 results in formation of

reactive 17-electron complexes that abstract hydrogen at the carbyne carbon to form cationic

metal carbenes.59,60,97 When R is a primary alkyl group, hydride shift in the carbene

complex yields an alkene as the final organic product. This chapter will discuss the

development of the chemical oxidation of carbynes and the resulting reactivity of the radical

cations in the presence of phenylacetylene. For the case of the alkyl carbynes, the H-shift

pathway of the metal carbene intermediate is suppressed. Instead, addition of the alkyne

and nucleophilic trapping with phosphite yields the l'i2-allyl complex (ir5-

C5H5)(CO) {P(OPh)3 Mo[rl': rl2-CH {P(OPh)3} C(Ph)=CH(R)].


Chemical Oxidation

In prior studies, oxidations to form the reactive seventeen-electron cationic carbynes

were carried out by photochemical electron transfer from the carbyne complexes to CHC13.

However, there are aspects of this method that make it difficult to obtain products in high

yield. Upon reduction, CHC13 fragments to CI and *CHC12.98 Evidence for side reactions

involving the *CHCl2 radical can be found in the formation of CH3C168 by Arbuzov

reaction of P(OMe)3 ligands.69 The use of outer sphere chemical oxidants99 at low








temperatures provides an alternative approach in which side reactions from *CHCI, can be

avoided and the radical cation can be generated selectively.

Initially, the butyl carbyne 81a was examined by cyclic voltammetry in order to

determine its oxidation potential. The cyclic voltammogram taken in 0.1 M

Bu4NSO3CF3/C2H4CI2 under nitrogen revealed two oxidation peaks. The first at +0.87V

vs. NHE is completely irreversible regardless of scan speed or the size of the scan

window, and the second peak at +1.77V is also irreversible. The complete irreversibility

of the first oxidation peak indicates that the radical cation is a very reactive species that

undergoes chemical reaction on the cyclic voltammogram time scale. Based on the

oxidation potential of the carbyne, acetyl ferrocenium with an oxidation potential of

+0.82V99 appears to be a good match for chemical oxidation of the carbyne.

To confirm that chemical oxidation generates the same intermediates as

photooxidation, butyl carbyne 81a was reacted with acetylferrocenium tetrafluoroborate

(AcFc*BF4). Photolysis of 81a in the presence of CDC13 is known to result in the

formation of 1-pentene (Scheme 4.A) in a process involving H-abstraction by the

oxidized carbyne followed by a facile 1,2-hydride shift in the resulting carbene complex

(83a).59,97 Observation of 1-pentene after oxidation of 81a is thus a marker for the H-

abstraction/H-shift sequence that is typical of these 17-electron alkyl carbynes. In the test

reaction, a solution of 81a in CD2Cl2 at -95"C was slowly mixed with a dilute solution of

AcFc'BF4- in CD2Cl2 to yield a dark purple reaction mixture. Warming to ambient

temperature produced an orange-brown solution whose color is characteristic of

acetylferrocene. Analysis of the volatile components by 'H NMR spectroscopy revealed

the presence of 1-pentene, as also seen following photooxidation.








Scheme 4.A. Formation of 1-pentene from the oxidation of butyl carbyne.

S1)hv/CHC13 +
or AcFc BF4 _H
OC"'/ 2) + RH OC"
(PhO)3P 81a RH (PhO)3P
83a


HBF4 I


4+


oc-" / -
(PhO)3P H 84




Oxidation in the Presence of Alkynes

Once it had been established that oxidation of 81a with AcFc'BF4 yields the same
product as photooxidation, attempts were made to obtain evidence of organic-radical
reactivity from the 17-electron cationic carbynes. As described in Chapter 1, some
organometallic radicals react like organic radicals in that they can be trapped
intermolecularly with unsaturated substrates such as alkenes and alkynes. Although only
hydrogen atom abstraction leading to the formation of 1-pentene was observed when the
chemical oxidation of 81a was run in the presence of alkenes, very different results were
obtained when the oxidation was performed in the presence of phenylacetylene. A mixture
of butyl carbyne 81a plus 10 equivalents of phenylacetylene was dissolved in CD2C12. A
dilute solution of acetylferrocenium tetrafluoroborate was then added at -95"C to yield a
dark purple solution. Upon slow warming to ambient temperature, the reaction mixture
became an orange-brown color similar to that observed in the absence of alkyne.








Examination of the volatile components by 'H NMR confirmed that no 1-pentene had been

formed and thus, in the presence of the alkyne, the expected H-abstraction/H-shift

sequence had been suppressed. Instead, compound 82a was isolated in 25% yield

(Scheme 4.B). In subsequent experiments where 1 equiv P(OPh)3 was added to the

reaction mixtures, the isolated yield of 82a rose to 51%.


Scheme 4.B. Oxidation



..M C-R

(PhO)3P
R' = Bu (81a), Ph (81b)


1) AcFc+ BF4
2) + RH, R-


of carbynes in the presence of alkynes.

R1

AcFc+ BF4 "
P(OPh)3 OC"' \R2
-2 (PhO)3P
II 2 ( P H P(OPh)3

R = Bu, R2 = Ph (82a)
R1 = Ph, R2 = Ph (82b)
Rl =Bu, R2 =Bu(82c)


P(OPh)3


H -=-R

R2= Bu, Ph


R1


H

(PhO)3P H
85a-c


X-ray Structure of (n5-CH)(CO) P(OPhjMol' L:n2-
CHI P(OPh) 3 C(Ph)=H(CHiCHzCHCHCH3)] (82a)

Slow recrystallization of 82a in CH2Cl/toluene (1:2) resulted in golden-orange

crystals that were suitable for X-ray crystallography. A thermal ellipsoids diagram appears

in Figure 4.1. The crystal structure shows clearly that the C2-C3 bond of the allyl ligand

resulted from carbon-carbon bond formation between the carbyne carbon and


BF4


83a,b








phenylacetylene. The allyl ligand also bears a P(OPh), moiety derived from addition of a

second phosphite to Cl. Because the C1-C2 [1.476(5) A] and C2-C3 [1.427(5) A] bond

lengths differ as do the Mo-Cl [2.297(3) A] and Mo-C3 [2.363(4) A] distances, the

coordination of the allyl ligand is best described as Tr':r12. In solution, complex 82a exists

as a mixture of exo and endo isomers in an 87:13 ratio, as determined by 'H NMR

spectroscopy. NOE enhancement between the protons on the C2 phenyl substituent and

the Cp ring allows assignment of the major isomer as exo.


C84


Figure 4.1. Thermal ellipsoids diagram of 82a showing the crystallographic numbering
scheme. Thermal ellipsoids are drawn at the 40% probablility level. The majority of the
hydrogens are removed for clarity.








Reaction with Other Alkynes

A similar reaction occurred between the phenyl carbyne 81b and phenylacetylene in

the presence of 1 equiv of free P(OPh)3 to produce 82b in 39% isolated yield (Scheme

4.B). In addition, 81a reacted with 1-hexyne under similar conditions to furnish 82c in

28% yield. The structures of these compounds were assigned by comparison of their

spectral data to that of 82a. Butyl carbyne 81a also reacted with other terminal alkynes

such as trimethylsilylacetylene under similar conditions to produce the l'r 2 adducts.

However, many of these adducts were difficult to obtain in analytically pure form.

Reaction of butyl carbyne 81a with internal alkynes resulted in the formation of 1-pentene

which indicates the absence of reactivity of the alkyne with the oxidized carbyne.



Mechanistic Considerations

Since control experiments have established that the carbynes 81a,b do not react

with alkynes in the absence of an oxidant, the first step in formation of 82a-c must be

generation of the 17-electron carbyne. The structures of the adducts require hydrogen

abstraction, addition of the alkyne and addition of the phosphite. Mechanistically, it is

difficult to discern the order of these steps. First, in order to determine whether the

phosphite on the carbon atom of the allyl originated from the carbyne or intermolecular

attack, the oxidation of 81a with phenyl acetylene was performed in the presence of

triphenyl phosphine (equation 4.1). Based on spectral characterization, the resulting adduct

86 has a triphenyl phosphite group on the metal center and a triphenylphosphine group at

the carbon on the allyl. This result implies an intermolecular nucleophilic attack of the

phosphine. It is important to note that the original r'11r2 complex containing two triphenyl

phosphite groups does not exchange with triphenyl phosphine. Thus, the phosphine does

not exchange for phosphite at the metal or carbon center and thus blur the results of the

initial product formation. Because phosphines often react differently than phosphites due








to their increased nucleophilicity, the same oxidation reaction was performed in the

presence of trimethyl phosphite (equation 4.1). Unfortunately, the product could not be

obtained in analytically pure form. Side reactions due to radical reactions of P(OMe)3

produced impurities inseparable from the product. However, comparison of spectral data

with an authentic sample of the adduct 87 with the P(OMe)3 on the carbon of the allyl

indicates that this same adduct is present as the major product in the oxidation chemistry.

Thus, it appears that the phosphite at the carbon of the allyl results from nucleophilic attack

at the carbon.




AcFc BF4 B p BF4
Moc C-Bu PMo3 B\ (4.1)
OCj7 PR3 OC71 Ph
(PhO)3P HI Ph (PhO)3P H PR
+
R = Ph (86)
R = OMe(87)


It is not clear whether the 17-electron radical cation or the cationic carbene produced

from hydrogen atom abstraction at the carbyne carbon reacts with the alkyne. When the

oxidation of 81a is carried out with only one equivalent of phenyl acetylene, the nT112

adduct is formed along with 1-pentene. Therefore, it is reasonable to postulate initial H-

abstraction, then subsequent chemistry derived from the 16-electron cationic carbenes 83a-

b. Insertion of the alkyne into the Mo=C double bond100-106 would produce vinylcarbene

complexes 85a-c, which could undergo nucleophilic attack by the phosphite107-"11 to

yield 82a-c (Scheme 4.B).

An adduct similar to 82a was previously observed by Geoffroy following

protonation of (Tl-C5sH)(CO)2W-CTol with HBF4 in the presence of diphenylacetylene

and PBu3.112 Although the intermediate derived from the initial protonation could not be








directly observed, it was postulated to be the cationic carbene [(qr5-C5Hs)(CO)2W=CHTol]

(88). Given the analogy between intermediates 88 and 83a-b, an attempt was made to

independently generate 83a by protonation of 81a with HBF4. However, this control

experiment did not produce 1-pentene, as expected if cationic carbene 83a were formed

(Scheme 4.A). As a result of this discrepancy, the product of the protonation was

characterized by low temperature 'H NMR. This experiment revealed that protonation of

la results in the face protonated carbyne complex [(r'-C5H5)(CO){P(OPh)3}-

(H)Mo=CBu]' (84) as evidenced by the proton signal at -2.96 ppm and a C-H coupling

constant of 73 Hz at the carbyne carbon.113-117 At no time during the warming of the

sample from -85 "C to room temperature could signals corresponding to 83a be detected.

Interestingly, reaction of the carbyne 81a with HBF4 in the presence of

phenylacetylene at low temperature does result in formation of 82a. However, since

protonation of 81a yields the face-protonated complex instead of 83a, it is not yet clear

what relationship this pathway bears either to the oxidation chemistry of 81a or the

Geoffroy results.'18 In other protonation studies of Cp{P(OMe) 3}2Mo=C-CH2tBu,119

results have been interpreted in terms of initial protonation at the carbyne carbon followed

by irreversible conversion to the metal hydride. If 81a were to initially protonate at the

carbyne carbon to form 83a, rearrangement of 83a to 84 would have to be faster than

formation of 1-pentene from 83a under these conditions. This conversion is highly

unlikely since 84 has never been observed following the generation of 83a under oxidative

conditions.

The protonation of 81a with HBF4 in the presence of alkynes and phosphite results

in the r1'lI2 adducts in over 90% isolated yield. The reaction of trimethylsilylacetylene with

81a, which yielded an impure rl'rl2 adduct in the oxidative chemistry, provided the pure

adduct 89 in nearly quantitative yield under the protonation conditions (equation 4.2).

Internal alkynes did not react with the protonated carbynes. The mixed ri'12 adducts which

result from the protonation of carbynes with alkynes in the presence of a different








phosphine or phosphite from the one on the carbyne all have the added phosphine or

phosphite located on the carbon of the allyl group. The protonation chemistry involving

P(OMe)3 ligands is much cleaner than the radical chemistry indicating radical side reactions

occur with these ligands under one-electron oxidation conditions on the same time scale as

other reactions. For example, protonation of the butyl P(OMe)3 carbyne 75 with phenyl

acetylene in the presence of P(OMe)3 produces the adduct 90 in over 90% yield (equation

4.2), whereas the chemical oxidation chemistry yields none of the adduct.





C-Bu HBF4 Mo\ BF4
OC'/ P(OR)3 OC/ (4.2)
(RO)3P -- R' (RO)3P H (OR)3

R=Ph (81a) R = Ph;R'=TMS (89)
R = Me (75) R = OMe; R' = Ph (90)


In previous cases where intermediates of the type (115-

C5H5)(CO){P(OR)3}M=CHR' have been generated via oxidation of carbyne complexes,

intramolecular rearrangement of the carbene ligand has been the dominant process.62

These examples are the first where the carbene could be intercepted in a bimolecular

reaction. Competition between H-shift and intermolecular trapping has also been observed

for the related electrophilic carbenes Cp(CO)LFe=CHCH2CH3, in which cyclopropanation

of olefins is slower than the H-shift to yield propene,120 but insertion into Si-H bonds is

faster than the H-shift.121 Such competition between H-shift and bimolecular reactivity is

rare in highly electrophilic carbenes with alkyl groups larger than methyl because the H-

shift is accelerated by increasing electron density at the migration origin.96,120,121






59


Summary


One-electron oxidation of molybdenum carbynes in the presence of terminal alkynes

results in H-abstraction and addition of the alkyne to produce rl'l2-allyl complexes as the

final products. Under these conditions, the expected H-shift in the cationic carbene

intermediate is not observed.














CHAPTER 5
EFFECT OF LIGAND VARIATION ON THE SITE OF PROTONATION IN THE
METAL CARBYNES CpL2Mo-CBu AND TpL2Mo-CBu [L = CO, P(OR)3]

Introduction

Protonation of carbyne (alkylidyne) complexes has been a topic of long-standing

interest due to the variety of observed products and the difficulty of predicting which will

be obtained.122,123 In addition, complications arise in discerning kinetic vs.

thermodynamic protonation sites.118 On the basis of computational studies that assigned a

net negative charge to the carbyne carbon, kinetic protonation has been assumed to involve

charge controlled addition of the proton at that site.124-127 However, the final

thermodynamic outcome is variable. The protonation product is dependent on the metal,

the ancillary ligands and the counterion of the acid.

For example, protonation of {HB(pz)3}(CO)2W=CC6H4OMe-2 91 with

HBF4*Et2O produces carbene (alkylidene) 92 (equation 5.1) whose structure was

determined by x-ray crystallography.128 Similar protonations resulting from addition of

the proton to the alkylidyne carbon were observed with other alkylidynes.129-134



H HR
B 9 .B ? H+ BF4
HBF4
SHB H OM (5.1)
o W-C C oC,/ WO
OC MeO OC
91 92







In contrast, carbyne 93 yields the hydrido carbyne 94 upon protonation with

HBF4*(MeCO)20 (equation 5.2)119 as a result of addition of the proton to the metal center.

Similar examples are known in the literature.135-138



S 7BF4
(MeO) "M C t HBF4*(MeCO)20, (MeO),3Pc CCH2But (5.2)
(MeO)3P, CCHBut
(MeO)3P 93 (MeO)3P 94


Yet another example can be found in the protonation of alkylidyne 95 with HBF4 to yield

alkylidene 96 (equation 5.3).115 Complex 96 is a "face-protonated" alkylidyne whose C-
H bond is engaged in agostic interaction with the metal. Similar examples have been

observed for other alkylidynes.113,114,122


Ph2
Ph CO Ph2 7 +BF
r C HBF, co
H3C WT -C HBF4 (5.3)
KH3C-L--W-
PhP PPh2 H
95 Ph PPh2
95 ^96

In the presence of coordinating anions, several different outcomes have been
observed. Protonation of carbyne 97 with two equivalents of HCI results the in t2-acyl

complex 98 (equation 5.4).139 Other examples involving the formation of iT2-acyl

complexes are known.59,68.140,141 There are even a few examples in which protonolysis

results in the loss of the original alkylidyne ligand, 119,137 such as the formation of

complex 100 upon protonation of carbyne 99 with trifluoroacetic acid (equation 5.5).119










SHCI
OC'00.W-CR CI'.J "'Cl (5.4)
MMe3P e3P y-- CH2R
97 98




CF3CO2H
a=C CCH2But MtOCCF3 (5.5)
(MeO)3P' 2(MeO)3P' "'O
(MeO)3P (MeO)3P O H
99 C-OH
100 CF3
CF3


In alkylidyne complexes that bear no n-acid ligands, thermodynamic protonation

occurs either on the alkylidyne face or at the metal. Steric considerations have been

invoked to explain the preference. 116,117,122,135,136 However, in the presence of n-acid

ligands, electronic effects appear to be the overriding factor in determining the ultimate site

of protonation. It has been suggested that alkylidene (face-protonated) complexes that bear

i-acid ligands do not rearrange into the corresponding alkylidyne hydride species because

the resulting oxidation of the metal center would interfere with backbonding.122 A noted

absence in the discussion is a closely related series of compounds where all three

protonation outcomes (alkylidene, face-protonated alkylidyne and alkylidyne hydride) are

available.

Protonation of the Fischer carbynes CpL2Mo-CBu and TpL2Mo=CBu [L = CO,

P(OR)3] with HBF4 results in a systematic shift of the thermodynamic protonation product
from the alkylidyne hydride to the face-protonated alkylidyne to the non-agostic alkylidene

as the number of carbonyl groups increases from zero to two. These results are consistent

with determination of the final protonation site by the electron density at the metal. As n-

backbonding to the carbonyl ligands decreases the electron density at the metal, the








protonation site shifts from the metal toward the carbyne carbon, consistent with earlier

calculations which assign negative charge to the alkylidyne carbon in cationic

complexes. 124-127



Protonation of Cp P(OPh) } (CO)Mo=CBu (81a)


As discussed previously, oxidation of the butyl carbyne

Cp{P(OPh)3}(CO)Mo-CBu (81a) with acetyl ferrocenium results in the formation of 1-

pentene.142 In the proposed mechanism, electron transfer generates a 17-electron complex

that undergoes H-atom abstraction to yield the electrophilic carbene

[Cp {P(OPh)3 (CO)Mo=CHBu]' (83a). Carbene 83a then undergoes a facile 1,2-hydride

shift followed by decomplexation to yield the free alkene.59 Although carbene 83a has

never been directly observed in these studies, its presence is implied by the formation of 1-

pentene. Subsequent observation that the formation of 1-pentene is suppressed upon

oxidation of 81a in the presence of alkynes142 raised the question of whether the alkyne

had reacted with carbene 83a or with the 17-electron cationic carbyne prior to hydrogen

abstraction. In conjunction with mechanistic studies on oxidation of 81a in the presence of

alkynes, ways were explored to generate carbene 83a independently.

In a formal sense, carbene 83a results from addition of H* to carbyne 81a.

Although the protonation chemistry of metal carbynes is complex, it seemed possible that

employing an acid with a noncoordinating anion could provide an independent generation

of 83a. However, protonation of butyl carbyne 81a with HBF4 at low temperature

resulted in an unstable species whose 'H NMR spectra were not consistent with the

expected carbene. While the protons on electrophilic carbenes are known to exhibit 'H

NMR signals between 10-18 ppm,60,143 the newly generated species showed a new

resonance at -2.96, with JP = 10 Hz.








Although the 'H NMR spectrum appeared to rule out a carbene product, the 3C

NMR spectrum of the product contained two deshielded carbons at 276.8 and 226.8 ppm,

consistent with carbene and carbonyl carbons. Elucidation of the structure was carried out

by 2D NMR. Of the two deshielded carbons at 226.8 ppm and 276.8 ppm, the latter is Ca

of the original alkylidyne ligand as indicated by its long-range coupling to the protons on

Cp and C, (1.44, 1.52, 2.07 and 2.33 ppm) observed in the HMBC144 spectrum. The

carbon at 276.8 ppm is coupled to the proton at -2.96 ppm as indicated by the HMQC145

spectrum. The value of the coupling constant was then measured more accurately in a ID

HMQC spectrum optimized for the J value observed in the 2D HMQC. The value 'JCH =

73.4 0.7 Hz indicates that the proton is centered neither on the metal nor on the carbon.

Instead, the complex is face-protonated carbyne 84, in which the hydrogen participates in

an agostic interaction with the metal center (equation 5.6). Similar JCH values in the range

of 45-84 Hz have been reported for other face-protonated alkylidynes.113-117




HBF4 B -
M O Mo-C (5.6)
Ocy ( oC'/ 'H
(PhO)3P 81a (PhO) 84



Protonation of Cp{P(OMe) j.lMo=CBu (103)

Generation of the agostic alkylidene species 84 upon protonation of 81a was

intriguing. Complex 84 was clearly not the species generated in the previously reported

oxidative chemistry of 81a because it did not produce 1-pentene upon decomposition.

Face-protonation was also a different outcome from what we had obtained by protonation

of the related complex Cp{P(OMe)3}2Mo=C(c-C3H,) (101) with HBF4.138 The








protonation of 101 occurred at the metal center to yield the hydrido carbyne species

[Cp{P(OMe)3}2(H)Mo=C(c-CH,)]'[BF4] (102). The 'H NMR spectrum of complex
102 had also exhibited an upfield resonance at -2.42 ppm but the much larger JPH = 64.7
Hz clearly identified the complex as a metal hydride. In addition, the carbyne carbon of

102 was shifted downfield to 344 ppm as compared to 299.5 ppm for the neutral carbyne
101 and 276.8 ppm for the face-protonated alkylidyne 84.




HBF44 7 BF4
c(Me --C (MeO)3C-C (5.7)

(MeO)3P 103 (MeO)3P 104


Cyclopropyl carbyne 101 and butyl carbyne 81a differ both in the alkyl substituent
and the ancillary ligand set (two phosphites for 101 vs. one phosphite and one carbonyl
for 81a). In order to differentiate the effects on the site of protonation, the bis(phosphite)

butyl carbyne complex Cp{P(OMe),}2Mo-CBu (103) was synthesized. Reaction of 103

with HBF4 at -78 *C (equation 5.7) results in protonation at the metal center to yield the
hydrido carbyne species [Cp{P(OMe)3}2(H)Mo=CBu]'[BF4]- (104) as characterized by

the 'H NMR resonance at -2.6 ppm with JPH = 64 Hz. Carbyne 104 exhibits a downfield
shift of the carbyne carbon to 347 ppm in the "3C NMR, similar to what is observed for the

related hydrido carbyne complex 101. As further evidence that the proton resides at the

metal center, JCH between the carbyne carbon and the added proton was determined to be
less than 6 Hz.
As discussed above, kinetic protonation of alkylidyne complexes has been
postulated to be charge-controlled, which should result in protonation at the carbyne
carbon. Consistent with this interpretation, a different species was observed upon reaction
of carbyne 103 with HBF4 at low temperature. 'H NMR spectra recorded at -50 C








exhibited a resonance at -5 ppm with the small JpH indicative of a face-protonated carbyne.

Upon warming, this species converted irreversibly to hydrido carbyne 104.



Protonation of Cp(CO)XMo-CBu (105)

The difference in protonation behavior between butyl carbynes 81a and 103 can be

attributed to the change in ancillary ligands. The carbyne with two phosphite ligands (103)

was protonated at the metal. In the related complex with one carbonyl and one phosphite

(81a), the site of thermodynamic protonation was shifted toward the carbyne carbon to

yield the face-protonated alkylidyne. This change is consistent with withdrawal of electron

density from the metal by the it-acid carbonyl, rendering the metal less basic with respect to

the carbyne carbon. If this were the case, a second carbonyl ligand might be expected to

decrease the electron density at the metal to the point where the protonation site would shift

completely to the carbon. As a test of this hypothesis, the dicarbonyl carbyne

Cp(CO)2Mo-CBu (105) was prepared by reaction of the bis(pyridine) complex

Cl(C5HsN)2(CO)2Mo=CBu with NaCp.

Reaction of carbyne 105 with HBF4 at low temperature resulted in the dinuclear

species [Mo2(i-H){ -C2(nBu)2)(CO)4Cp2][BF4] (106) (equation 5.8). Complex 106 is

structurally equivalent to a product previously prepared by protonation of Cp(CO)2W-CTol

with HBF4129 and could be identified by the characteristic 'H NMR resonance at -15.7

ppm for the bridging hydride. In the original report on the tungsten analogue of 106, it

was proposed that protonation of the carbyne carbon produced the corresponding cationic

carbene. Reaction of the carbene with starting material then yielded the binuclear alkyne

complex. However, the carbene intermediate was not directly observed. In order to verify

that the dicarbonyl complexes did indeed undergo protonation at the carbon, the analogous

but more sterically encumbered complex Tp(CO)2Mo=-CBu (107) in which dimerization

would be inhibited was prepared.












0McECBu
OC 105
OC 105


HBF4


Bu Bu + BF4

45 CO
OCc
oc 106


Protonation of Tp(CO)2Mo-CBu (107)

Protonation of 107 with HBF4 at -78 "C resulted in a species which was difficult to

characterize spectroscopically due to poor solubility at low temperatures. However, the

structure could be assigned as carbene 108 (equation 5.9) on the basis of certain

resonances in its 'H and '3C spectra. A proton signal at 12.6 ppm and a carbon resonance

at 260 ppm are in agreement with similar Tp carbene complexes, one of which was

characterized by X-ray crystallography.128


H HBF4

Ma C
OC"'/ L
OC 107


BH + BF4-


MOC
oc" 0 -
OC 108


(5.9)


Protonation of Tp P(OMe) } (CO)Mo=CBu (10 9)


Although protonation of the Tp carbyne 107 at the carbon was as expected on the

basis of its two carbonyl ligands, concerns about the electronic differences between the Tp

and Cp ligands led us to prepare Tp{P(OMe)3}(CO)Mo=CBu (109) in order to confirm

that the same protonation trend held for the Tp carbynes as for the Cp derivatives. As

predicted, protonation of the Tp carbyne 109 results in face-protonation to yield complex


(5.8)








110 (equation 5.10) just as protonation of its Cp analogue 81a yields 84 (equation 5.6).

Assignment of 110 as the face-protonated species was possible via its 'H and "C NMR

spectra which exhibited a proton resonance at 0.45 ppm that is coupled to the carbon at 253
ppm with JH = 91.0 0.4 Hz. Hence, despite the electronic difference between Tp and
Cp ligands, the protonation site once again shifted from the carbon to the alkylidyne face
upon replacement of a strong n-acid carbonyl with a phosphite.



H K B -. B
/B + BF4'
HBF4 H BF4 /- (5.10)
M owC- 00' 'C
O0"''fM>C (MeO)3O
(MeO)3P 109 P 110


Summary

The site of protonation in metal carbynes can be shifted from the carbon to the metal
by manipulation of the ancillary ligand set. In the absence of n-acid ligands, the metal is
sufficiently basic for the thermodynamic protonation product to be the alkylidyne hydride
complex. Replacing one phosphite with a ni-acid carbonyl results in a loss of electron-
density at the metal and a shift to face-protonation of the carbyne. Carbynes bearing two
carbonyl ligands selectively react with HBF4 at the carbyne carbon to produce cationic
carbenes. These carbenes undergo secondary reactions unless the remaining ligands are
sufficiently sterically encumbered to prevent dimerization.














CHAPTER 6
EXPERIMENTAL PROCEDURES

General

Standard inert atmosphere techniques were used throughout. Hexane, petroleum

ether, chloroform, and methylene chloride were distilled from CaH,. Diethyl ether and

THF were distilled from Na/Ph2CO. All NMR solvents were degassed by three freeze-

pump-thaw cycles. Benzene-d6 was vacuum transferred from Na/Ph2CO. CDCI3 was

stored over 3A molecular sieves. Triphenyl phosphite was purified by rinsing an ethereal

solution with 10% KOH and then brine. After drying over Na2SO4 and removal of

solvent, pure triphenyl phosphite was obtained by vacuum distillation. Phenyl acetylene

and 1-hexyne were vacuum distilled from NaBH4. W(CO), was purified by column

chromatography on silica using pentane as the eluent. 4-Iodo-l-butene, 5-iodo-l-pentene

and 6-iodo-1-hexene were prepared from the corresponding tosylates using the Finkelstein

reaction.146,147 Authentic samples of 1,5-hexadiene, 1,6-heptadiene, 1,7-octadiene, and

2-cyclohepten-l-one were purchased from Aldrich. All other starting materials were

purchased in reagent grade and used without further purification.

The acyl complex [(CO),WC(O)(Ph)][NMe4] was prepared by addition of phenyl

lithium to tungsten hexacarbonyl.148 (15-CsHs)(CO){P(OPh)3}Mo-CC6H, (81b) was

synthesized by adaptations of previously reported methods.68 (r'1-CH,)(CO){P(OMe)3)-

Mo=CCH3 (76),88,149,150 Cl{P(OMe)3,}(CO)Mo=CBu (116),59 and (j'-C5H.)(CO)-

{P(OMe)3}Mo=C"Bu (75)59 were made as reported previously.








Equipment and Instrumental Methods


General Instrumentation


'H, 3P, and "C NMR spectra were recorded on Gemini-300, VXR-300, and

UNITY 500 NMR spectrometers. IR spectra were recorded on a Perkin-Elmer 1600

spectrometer. High resolution mass spectrometry was performed by the University of

Florida analytical service. A Hewlett-Packard 8452A diode array spectrophotometer was

used to obtain UV-Visible absorption spectra.



Photophysical Methods


Corrected emission and excitation spectra were obtained with a Spex Industries

Fl 12-A spectrophotometer. Emission correction factors were generated by using a 1000

W tungsten primary standard lamp. Emission quantum yields are reported relative to

aqueous Ru(bpy)32' (Xem = 0.055).151 All room temperature measurements for emission

were carried out on nitrogen-degassed acetonitrile solutions and studies at low temperature

were conducted on nitrogen-degassed 2-methyltetrahydrofuran (MTHF) solutions.

Laser flash photolysis was carried out on a system that has been described

previously.152 All experiments were performed by using the third harmonic output of a

Nd:YAG laser for excitation (355 nm, 10 ns fwhm, 10 mJ/pulse). Samples were contained

in a recirculating flow cell that was deaerated with N2. Global analysis of the

multiwavelength transient absorption data was effected using the SPECFIT factor analysis

software. 153

The cage escape yield for photoinduced electron transfer from 70 to

dimethylviologen (Tri,) was determined by laser flash photolysis using the excited state of

the complex (2,2'-bipyridine)ReI(CO)3(4-benzylpyridine) as an actinometer.

Dimethylviologen radical cation was monitored at 605 nm (e = 10,060 M'cm'-) and the








excited state of the Re complex at 370 nm (E = 11,300 M"'cm'). The concentration of

dimethylviologen was 20 mM to insure that the dt* excited state of 70 was quenched with

> 95% efficiency; therefore, it was unnecessary to correct for incomplete quenching. A

plot of AA60 nm (for the solution of 70 + dimethylviologen) versus AA370 nm (for the

actinometer) was linear for doses ranging from 1 10 mj-cm2-pulse1. The slope of the

plot was used to determine rie.


2D NMR Methods


HMQC and HMBC spectra were recorded at -50 "C, on a Varian UNITY 500

spectrometer equipped with a 5 mm indirect detection probe. The HMQC spectra were

optimized for a 'JcH = 71 Hz (measured in a scouting run) and run in phase-sensitive

mode. BIRD nulling (null = 0.5 s), a relaxation delay of 0.2 s and no "C decoupling

during acquisition were used. For the 2D spectrum, the full proton region (6525 Hz

covering the region from -4.2 to 8.6 ppm) was taken in f2 and a spectral width of 12583

Hz, covering the region from 200 to 300 ppm, infl. The 2D FID had 2K points inf2 and

64 increments infl and were acquired with 64 scans per increment. A Gaussian function

with a time constant of 0.09 s was used for weighting inf2. Zero-filling to 256 points,

followed by a shifted Gaussian with a time constant of 0.001 s and a shift of 0.001 s was

applied infl prior to the Fourier transform. The ID HMQC spectrum was recorded with

256 points over a spectral width of 363 Hz centered about the signal at -2.98 ppm, in 1024

transients. Zero-filling twice and a shifted Gaussian window function with a time constant

of 0.126 s and a shift of 0.084 s were applied prior to the Fourier transform, affording a

precision of 0.7 Hz for the coupling constant. The HMBC spectrum was optimized for a

"JcH of 8 Hz. The spectral width, number of points, relaxation delay and apodization in f2

were the same as for the 2D HMQC experiment. Infl, 64 increments (128 transients each)

were collected for a spectral width of 39024 Hz, covering the region -20 300 ppm. Zero-








filling twice and multiplication with a Gaussian with a time constant of 0.001 s were

applied prior to the Fourier transform.


Syntheses


Cl P(OPh)l CoCQ)zWCPh (111)


[(CO),WC(O)(Ph)][NMe] (2.55 g, 5.06 mmol) was dissolved in 35 mL CH2CI2
and cooled to -95'C. Oxalyl chloride (442 iL, 5.06 mmol) was added dropwise, and gas

evolution was observed as the solution was allowed to warm to -20'C. After cooling the

solution to -50C, triphenyl phosphite (6.63 mL, 25.3 mmol) was added. The mixture was

warmed to ambient temperature and then refluxed for 2 1/2 hr. The solvent was removed

in vacuo to leave a dark brown oil, which was dissolved in 10 mL THF and filtered

through Celite to remove NMe4Cl. Excess P(OPh)3 was washed away with pentane (8 x 5

mL). Upon addition of 5 mL of Et2O, a tan precipitate formed. The golden solution was

removed by filter cannulation and the remaining tan solid was rinsed with 5 mL of Et2O.

The remaining solvent was removed in vacuo to leave a tan powdery solid (4.30g, 86.2%

yield) which was a mixture of 111, the tris(triphenyl phosphite) carbyne

ClIP(OPh)3}3(CO)W=CPh (112) and free P(OPh)3 (40% by 3'P NMR). The crude solid

was used in the preparation of 70 without further purification. For 111: 31P{ 'H) NMR

(CDC13) 8 128.1. For 112: 31P{'H} NMR (CDCIl) 8 126.4 (d, Jp = 43 Hz), 119.1 (t,

J,, = 43 Hz) ppm. For the mixture: IR (CH2Cl2) 1987 cm-' (vco).


Cp I P(OPh) I (CO)W-CPh (70)

The tan solid from above was dissolved in 30 mL THF and solid CpNa (0.768 g,

8.73 mmol) was added. The mixture was refluxed for 12 hours, then the solvent was

removed in vacuo to leave an orange-brown oil, which was chromatographed on alumina








using Et2O as eluent. A bright red fraction was collected and the solvent was removed in

vacuo to leave a dark red oil. After addition of 10 mL of pentane, a pink precipitate

formed. The orange solution was removed by filter cannulation, and the pink solid was

rinsed with pentane (8 x 8 mL). The remaining solvent was removed in vacuo to yield 70
as a pink powder (0.488g, 14.2% yield overall from [(CO)sWC(O)(Ph)][NMe4). 'H

NMR (CDC13) 7.10 7.31 (m, 20 H, P(OPh)3, Ph ), 4.90 (s, 5H, Cp) ppm; 3"C {H)

NMR (CDC3) 8 290.5 (d, Jc = 20 Hz, W=C), 231.1 (d, Jpc = 11 Hz, CO), 152.5 (d,

Jrc= 5 Hz), 151.9, 129.5, 128.3, 127.9, 127.2, 124.6, 122.5 (d, Jpc = 5 Hz), 90.2 (Cp)

ppm; 3"P{'H} NMR (CDC3) 8 160.5 (Jp, = 706 Hz) ppm; IR (CH2CI2) 1912 cmn' (vco);
HRMS (FAB) m/z calcd for M' (C3MH2sO4PW) 676.1005, found 676.0998.



(t1'-CH )(CO)1P(OMe)l}Mo=CCH2(CH2):CH=CHz (71b)

Methyl carbyne 76 (175 mg, 0.514 mmol) was dissolved in 15 mL of THF and
reacted with a 2.3 M hexane solution of n-butyllithium (335 LL, 0.771 mmol) at -78 "C.
After 25 min, 4-iodo-l-butene (374 mg, 2.05 mmol) was added. The solution was reacted
for 15 min at -78 "C and then warmed to room temperature. Following removal of solvent

in vacuo, the residue was extracted with ether and chromatographed on neutral alumina

using 4:1 hexane/ether as eluent followed by 1:1 hexane/ether after the 4-iodo-1-butene was
eluted. The product 71b was obtained as a yellow oil (145 mg, 71.5%) after removal of
solvent. For 71b: 'H NMR (C6,D) 8 5.71 (m, 1 H, =CH), 5.26 (d, 5 H, C5H5, JH = 1
Hz), 4.99 (m, 2 H, =CH2), 3.38 (d, 9 H, OMe, JPH = 12 Hz), 2.27 (m, 2 H, CH2), 2.10

(q, 2 H, CH2), 1.63 (p, 2 H, CH2) ppm; 3C{1H} NMR (C6D,) 8 315.9 (d, Mo=C, Jpc =

28 Hz), 241.8 (d, CO, JPc = 18 Hz), 138.5 (=CH), 115.1 (=CH2), 91.0 (C5H5), 51.2

(OMe), 49.4 (Mo-CC), 33.3, 27.9 ppm; P1{ 'H) NMR (CDC13) 8 203.8 ppm; IR








(CH2Cl2) 1901 cm' (vco); HRMS (FAB) m/z calcd for MW (CsH2398MoO4P) 396.0392,

found 396.0387.

(nH-C )(CO)IP(OMe), Mo-CCH2(CH.jCH=CH (71c)

Methyl carbyne 76 (232 mg, 0.682 mmol) was dissolved in 15 mL of THF and
reacted with a 2.3 M hexane solution of n-butyllithium (445 jIL, 1.02 mmol) at -78 'C.

After 25 min, 5-iodo-l-pentene (535 mg, 2.73 mmol) was added. The solution was

reacted for 15 min at -78 "C and then warmed to room temperature. Following removal of

solvent in vacuo, the residue was extracted with ether and then chromatographed on neutral

alumina using 4:1 hexane/ether as eluent followed by 1:1 hexane/ether after the 5-iodo-1-

pentene was eluted. The product 71c was obtained as a yellow oil (198 mg, 71.1%) after

removal of solvent. For 71c: 'H NMR (C6D6) 8 5.76 (m, 1 H, =CH), 5.27 (d, 5 H,

CHs, JP = 1 Hz), 4.99 (m, 2 H, =CH2), 3.39 (d, 9 H, OMe, Jp, = 12 Hz), 2.27 (m, 2
H, CH2), 1.94 (q, 2 H, CH2), 1.56 (p, 2 H, CH2), 1.43 (p, 2 H, CH,) ppm; 3CI'H}

NMR (C6D6) 316.2 (d, Mo=C, Jpc = 28 Hz), 241.7 (d, CO, Jpc = 19 Hz), 138.9 (=CH),

114.6 (=CH2), 91.0 (CH,), 51.2 (OMe), 49.9 (Mo=CC), 33.8, 28.5, and 28.1 ppm;

31P{'H} NMR (CDC1) 8 203.8 ppm; IR (CH2Cl2) 1900 cm' (vco); HRMS (FAB) m/z

calcd for M' (C,6H259MoO4P) 410.0549, found 410.0557.



(L-CH)(CO) ( P(OMe), Mo-CCH_(CH_ CH=CH (71d)

Methyl carbyne 76 (180 mg, 0.529 mmol) was dissolved in 15 mL of THF and
reacted with a 2.3 M hexane solution of n-butyllithium (346 pL, 0.795 mmol) at -78 "C.

After 25 min, 6-iodo- -hexene (446 mg, 2.12 mmol) was added. The solution was reacted

for 15 min at -78 'C and than warmed to room temperature. Following removal of solvent

in vacuo, the residue was extracted with ether and then chromatographed on neutral

alumina using 4:1 hexane/ether as eluent followed by 1:1 hexane/ether after the 6-iodo-1-








hexene had eluted. The product 71d was obtained as a yellow oil (169 mg, 75.6%) after
removal of solvent. For 71d: 'H NMR (C6D6) 8 5.76 (m, 1 H, =CH), 5.28 (d, 5 H,

C5H, JPH = 1 Hz), 5.00 (m, 2 H, =CH2), 3.40 (d, 9 H, OMe, JpH = 12 Hz), 2.27 (m, 2
H, CH2), 1.97 (q, 2 H, CH,), 1.57 (p, 2 H, CH2), 1.30 (m, 4 H, CH2) ppm; '3C{ H}

NMR (C6D6) 316.4 (d, Mo=C, JPc = 27 Hz), 241.7 (d, CO, Jpc = 20 Hz), 139.1 (=CH),

114.5 (=CH2), 91.0 (C5H,), 51.2 (OMe), 50.0 (Mo=CC), 34.0, 31.9, 29.0, 28.5 ppm;

31P{ 'H} NMR (CDC1,) 8 203.9 ppm; IR (CH2C12) 1900 cm-' (vco); HRMS (FAB) m/z

calcd for (M+H) (C,,H2,98MoO4P) 425.0784, found 425.0799.



HK1_-C 1 i{ P(OMe) }Mo=CCHz(CHiCH=CHz (78b)

Alkenyl carbyne 71b (38.5 mg, 0.0976 mmol) was dissolved in 0.5 mL CDCI3
and reacted with PC15 (20.0 mg, 0.0976 mmol) at 0 "C. The solution reacted for 1 min
producing effervescence and was characterized by NMR spectroscopy without further
purification. The resulting 'H NMR spectrum indicated a mixture of compounds
containing the dichloromolybdenum carbyne as the major component. Due to the liability of
78b, it could not be purified further. The NMR signals of 78b were identified by

comparison to the spectral data of related compounds.59,95 For 78b: 'H NMR (CDCI,) 6

5.95 (d, 5 H, CH,, J, = 3 Hz), 5.78 (m, 1 H, =CH), 5.01 (m, 2 H, =CH2), 3.92 (d, 9

H, OMe, JPH = 11 Hz), 3.18 (m, 2 H, CH2) ppm; "P{ 'H} NMR (CDC1,) 8 144.2 ppm.



Lnis-r )Cl i P(OMe)1 IMo-=CCHzCHz3CH=CH= CH(78

Alkenyl carbyne 71c (11.5 mg, 0.0281 mmol) was dissolved in 0.5 mL CDCI, and
reacted with PCI, (5.90 mg, 0.0281 mmol) at 0 "C. The solution reacted for 1 min
producing effervescence and was characterized by NMR spectroscopy without further








purification. The resulting 'H NMR spectrum indicated a mixture of compounds

containing the dichloromolybdenum carbyne as the major component. Due to the liability of

78c, it could not be purified further. The NMR signals of 78c were identified by

comparison to the spectral data of related compounds.59,95 For 78c: 'H NMR (CDC13) 8

5.95 (d, 5 H, C5H,, JP = 3 Hz), 5.79 (m, 1 H, =CH), 4.97 (m, 2 H, =CH2), 3.91 (d, 9

H, OMe, JpH = 11 Hz), 3.17 (m, 2 H, CHI) ppm; 31"P{H) NMR (CDC13) 144.3 ppm.



L--'HC )CIl I P(OMe) } Mo=CCH IzLCHz CH=CHz 78d)

Alkenyl carbyne 71d (33.5 mg, 0.0793 mmol) was dissolved in 0.5 mL CDCl1

and reacted with PCI, (16.5 mg, 0.0793 mmol) at 0 "C. The solution reacted for 1 min

producing effervescence and was characterized by NMR spectroscopy without further

purification. The resulting 'H NMR spectrum indicated a mixture of compounds

containing the dichloromolybdenum carbyne as the major component. Due to the liability of

78d, it could not be purified further. The NMR signals of 78d were identified by

comparison to the spectral data of related compounds.59,95 For 78d: 'H NMR (CDCI3) 6

5.94 (d, 5 H, CsH,, JPH = 3 Hz), 5.79 (m, 1 H, =CH), 4.95 (m, 2 H, =CH2), 3.91 (d, 9

H, OMe, JH = 11 Hz), 3.16 (m, 2 H, CH2) ppm; 3P{'H} NMR (CDCI3) 6 144.3 ppm.



Cl P(OPh),2ziCOl_ Mo=CBu (113)


Mo(CO)6 (2.408 g, 9.122 mmol) was dissolved in 30 mL Et2O and cooled to 0'C.
A solution of n-butyllithium (2.0 M in hexane, 4.56 mL, 9.12 mmol) was added dropwise.

After 1 h, the solution volume was reduced to 5 mL in vacuo. The solution was filtered

through Celite and the solvent removed in vacuo to leave a golden-tan powdery solid. This

solid was dissolved in 30 mL CH2C12. After cooling to -95"C, oxalyl chloride (0.637 mL,

7.30 mmol) was added dropwise ensuring the temperature remained below -90"C. After








the addition was complete, the bath was removed and the solution warmed to -300C.

During this time effervescence was observed. After cooling the solution below -50"C,

excess P(OPh), (9.56 mL, 36.5 mmol) was added. The solution was allowed to stir at

room temperature for 2 h. The solvent was removed in vacuo to leave a golden-brown oil

and excess P(OPh)3 was extracted with pentane (4 x 10 mL). The resulting residue was

dissolved in Et2O and filtered through Celite. The remaining solvent was removed in vacuo

to leave a golden-brown oil (6.010 g, 75.1% yield) which was a mixture of 113, the

tris(triphenyl phosphite) carbyne Cl{P(OPh)3)3(CO)Mo=CBu (114) and free P(OPh)3

(50% by 31P NMR). The crude solid was used in the preparation of 81a without further

purification. For 113: 3"P{'H} NMR (CDCI,) 8 148.4 ppm. For 114: "'P{'H} NMR

(CDC,1) 8 146.6 (d, Jpp = 56 Hz), 140.2 (t, Jpp = 56 Hz) ppm. For the mixture: IR

(CH2CI2) 1997 (s), 1924 (w) cm (vco).



Cp IP(OPh), (CO)Mo=CBu (81a)


The golden-brown oil from above was dissolved in 40 mL THF and solid CpNa

(1.206 g, 13.70 mmol) was added. The mixture was stirred at ambient temperature for 3

h. The solvent was removed in vacuo to leave a dark brown oil, which was

chromatographed on alumina using Et2O as eluent at -78'C. A bright orange-yellow

fraction was collected and the solvent was removed in vacuo to leave a bright orange oil.

After three successive columns eluting with hexane/EtO2 (4:1) at -78'C, 81a was obtained

as a bright yellow powder (0.964 g, 18.6% yield overall from Mo(CO)6). 'H NMR

(C6D6) 8 7.36 (d, JHH = 7.8 Hz, 6H), 7.06 (t, JH = 7.8 Hz, 6H), 6.87 (t, Ja = 7.2 Hz,
3H), 4.81 (s, 5H, Cp), 2.12 (m, 2H), 1.52 (pentet, 2H), 1.32 (sextet, 2H), 0.81 (t, 3H)

ppm; C{'H} NMR (CD2CI2) 8 323.8 (d, Jc = 31 Hz, Mo=C), 238.9 (d, Jc = 19 Hz,

CO), 152.7 (d, Jpc = 4 Hz), 130.0, 125.1, 122.9 (d, Jpc = 4 Hz), 91.3 (Cp), 50.0, 30.4,








22.43, 13.8 ppm; "P{'H} NMR (CDC13) 8 192.3 ppm; IR (CH2Cl2) 1917 cm-' (vco);
HRMS (FAB) m/z calcd for M' (C9H2998MoPO4) 570.0865, found 570.0863.


T(I-CH)(CO) IP(OPh) IMo[':r12-CH {P(OPh), C(Ph)=CH(CHCH2CH2CH.(BF4
(82a)

Butyl carbyne 81a (140 mg, 0.245 mmol) was mixed with phenylacetylene (270
gL, 2.45 mmol) in 20 mL CH2ClI. The solution was cooled to -95'C. A solution of
acetylferrocenium tetrafluoroborate (73.4 mg, 0.233 mmol) in 25 mL CH2CI2 was slowly
cannulated into the carbyne solution keeping the temperature below -90'C. A dark violet-
purple solution resulted. After 10 min triphenyl phosphite (64.3 gL, 0.245 mmol) was
added. After 15 min, the solution was warmed to -78'C for 35 min. The bath was
removed and the solution was allowed to warm to ambient temperature upon which the
solution changed color to orange-brown. Following removal of solvent in vacuo,
acetylferrocene was extracted with ether (3 x 8 mL). Addition of 2 mL CH2CI2 followed
by 10 mL ether resulted in the formation of a brown powder. Removal of the filtrate
afforded crude product (193 mg, 73.7%). Analytically pure product could be obtained
after three successive recrystallizations from CH2CI/ether (134 mg, 51.0%) For 82a
(exo:endo 87:13): 'H NMR (CDCI,) 8 6.59-7.02 (m, 35H, Ph), 5.12 (s, 5H, CsH5,
endo), 4.32 (s, 5H, C5H,, exo), 3.72 (dd, 1H, CHP(OPh)3, Jp = 3, 7.5 Hz), 2.83 (m,
1H, CHCH2CH2CH2CH3), 2.21 (m, 1H, CHCH2CH2CH2CH3), 1.69 (m, 1H,
CHCH2CH2CH2CH3) 1.58 (m, 2H, CH,), 1.39 (m, 2H, CH2), 0.95 (t, 3H, CH3) ppm;
'3C{'H} NMR (CD2C12) 237.1 (d, CO, Jpc = 30 Hz), 151.2 (d, Ph, Jc = 9 Hz), 149.6

(d, Ph, Jpc = 12 Hz), 140.7 (d, Ph, J.c = 8 Hz), 131.3, 131.0, 130.5, 129.8, 128.7,
128.2, 128.1, 127.7, 126.5, 126.2, 125.2, 121.4 (d, Ph, Jc = 4 Hz), 120.7, 120.0 (d,
Ph, JPc = 4 Hz), 95.5 (CH,5, exo), 91.4 (CH,, endo), 84.0 (d, CPh, Jc = 6 Hz), 62.3
(d, CHCH2CH2CH2CH3, Jpc = 6 Hz), 34.4 (CHCH2CH2CH2CH3), 34.2 (dd,
CHP(OPh)3, Jc = 161, 20 Hz), 33.1, 22.9, 14.0 ppm; 31P{'H} NMR (CDC1,) 6 178.4








(d, Jpp = 13 Hz, exo), 162.5 (d, Jpp = 22 Hz, endo), 52.5 (d, Jpp = 21 Hz, endo), 49.8 (d,

Jpp = 13 Hz, exo) ppm; IR (CH2C12) 1881 cm' (vco); HRMS (FAB) m/z calcd for MW
(C55Hs98MoO7P2) 983.2179, found 983.2163.

(nS-C H)(CO) P(OPh) .Moln' :2-CH P(OPh)} C(CIH)=CH(C H ](BF) (82b)

Phenyl carbyne 81b (122 mg, 0.207 mmol) was mixed with phenyl acetylene (228
pL, 2.07 mmol) in 30 mL CH2Cl2. The solution was cooled to -95"C. A solution of
acetylferrocenium tetrafluoroborate (62.0 mg, 0.197 mmol) in 20 mL CH2CI2 was slowly
cannulated into the carbyne solution keeping the temperature below -90C. A dark-brown
violet-purple solution resulted. After 10 min triphenyl phosphite (54.3 gL, 0.207 mmol)
was added. After reacting for 10 min, the solution was warmed to -780C for 2 hr. The
bath was removed and the solution was allowed to warm to ambient temperature upon
which the solution changed color to orange-brown. Following removal of solvent in
vacuo, acetylferrocene was extracted with ether (3 x 8 mL). Addition of 2 mL CH2Cl2
followed by 10 mL hexane resulted in the formation of a brown powder of the crude
product (165 mg, 73.2%). Analytically pure product could be obtained after two
successive recrystallizations from CH2Cl2ether (88.0 mg, 39.0%) For 82b (exo:endo
90:10): 'H NMR (CD2CI2) 6.59-7.47 (m, 40H, Ph), 5.03 (s, 5H, CH,, endo), 4.45
(s, 5H, CsH5, exo), 3.61 (s, 1H, CHPh), 3.45 (dd, 1H, CHP(OPh)3, JPH = 4, 9 Hz) ppm;
'"C{'H} NMR (CD2C2) 5 237.7 (d, CO, Jpc = 31 Hz), 151.1 (d, Ph, Jpc = 9 Hz), 149.6
(d, Ph, Jc = 12 Hz), 140.3 (d, Ph, Jc = 6 Hz), 137.9, 131.1, 130.6, 130.5, 130.2,
130.0, 128.9, 128.4, 127.9, 127.7, 126.3, 121.5 (d, Ph, Jc = 5 Hz), 119.7 (d, Ph, Jpc =
5 Hz), 96.9 (CH,, exo), 92.0 (C,H,, endo), 82.1 (CCH,), 59.4 (CHC6H,), 35.0 (dd,
CHP(OPh)3, Jc = 159, 20 Hz) ppm; 3'P{'H} NMR (CDC13) a 177.1 (d, Jp, = 23 Hz),
49.9 (d, Jpp = 23 Hz) ppm; IR (CH2CI2) 1885 cm-' (Vco); HRMS (FAB) m/z calcd for M'
(C57H4798MoOAP2) 1003.187, found 1003.195.








r(n'CH)(CO) P(OPh) Morn' :2-CH P(OPhl), C(H zCHCH CHI)=CH-
(CH2CH2iCHiCH)1(BF) (82c)

Butyl carbyne 81a (101 mg, 0.177 mmol) was mixed with 1-hexyne (204 gL, 1.77

mmol) in 20 mL CH2Cl2. The solution was cooled to -95"C. A solution of

acetylferrocenium tetrafluoroborate (53.0 mg, 0.168 mmol) in 25 mL CH2C12 was slowly

cannulated into the carbyne solution keeping the temperature below -90C. A dark violet-

purple solution resulted. After 20 min triphenyl phosphite (46.5 gL, 0.177 mmol) was

added. The solution was warmed to -78"C for 20 min. The bath was removed and the

solution was allowed to warm to ambient temperature upon which the solution changed

color to orange-brown. Following removal of solvent in vacuo, acetylferrocene was

extracted with ether (3 x 8 mL). Addition of 2 mL CH2CI2 followed by 10 mL hexane

resulted in the formation of a brown powder. Dissolving the solid in 2 mL CH2CI2

followed by 15 mL ether yielded the crude product (117 mg, 62.8%). Analytically pure

product could be obtained after two successive recrystallizations from CH2Cl/hexanes

(52.3 mg, 28.1%) For 82c (exo:endo 60:40): 'H NMR (CD2CI2) 6 6.98-7.52 (m, 30H,

Ph), 5.08 (s, 5H, CsH,, endo), 4.62 (d, 5H, C5Hs, JPH = 1.5 Hz, exo), 4.22 (m, 1H,

CHCH2CH2CH2CH3, endo), 3.26 (dd, 1H, CHP(OPh)3, JPH = 4, 14 Hz, exo), 3.17 (m,

1H, CHCH2CH2CH2CH3, exo), 2.73 (d, 1H, CHP(OPh)3, Jp, = 12 Hz, endo) 2.21-2.51

(m), 2.10 (m), 1.94 (m), 1.77 (m), 1.60 (m), 1.34-1.49 (m), 0.98 (m), 0.63 (t, 3H, CH3)

ppm; 13C IH} NMR (CD2C2) 8 245.0 (d, CO, Jpc = 33 Hz, endo), 238.9 (d, CO, Jpc =
33 Hz, exo), 152.1 (d, Ph, Jc = 14 Hz, endo), 151.6 (d, Ph, Jpc = 9 Hz, exo), 150.4 (d,

Ph, Jpc = 12 Hz, exo), 149.8 (d, Ph, Jpc = 11 Hz, endo), 131.8, 131.3, 130.7, 130.5,
128.6, 127.9, 126.2, 125.9, 121.6 (d, Ph, Jpc = 4 Hz), 121.4, 120.1 (d, Ph, Jpc = 5 Hz),

103.2 (CH{P(OPh)3)CCH2CH2CH2CH3, endo), 93.8 (CAHs, exo), 91.3 (CH,, endo),

89.4 (CH { P(OPh)3 CCH2CH2CH2CH3, exo), 66.1 (CHCH2CH2CH2CH3), 38.4, 34.6,

34.3, 33.7, 32.6, 31.7, 31.1, 28.1 (dd, CHP(OPh)3, Jc = 166, 18 Hz, exo), 23.2, 23.0,

21.4 (d, CHP(OPh)3, Jpc = 145 Hz, endo), 14.0, 13.7 ppm; 31p{ H} NMR (CD2CI2) 8








181.1 (s, exo), 168.3 (d, Jpp = 18 Hz, endo), 49.4 (d, Jpp = 18 Hz, endo), 46.2 (s, exo)

ppm; IR (CH2CI2) 1876 cm-' (vco); HRMS (FAB) m/z calcd for M' (C53H5598MoO7P2)
963.2492, found 963.2503.



Lf(I-Cl)(CO) { P(OPhY) HMo-CBul(BF) (84)

Butyl carbyne 81a (201 mg, 0.353 mmol) was mixed with a 54% solution of
HBF4 in ether (48.7 gL, .353 mmol) in 10 mL of CH2CI2 at -95 TC. After 10 minutes, 30

mL of hexane at -95 *C was added and an orange oil precipitated from solution. The oil
was rinsed with hexanes at -78 C and some of the remaining solvent was removed in

vacuo at -78 C. Keeping the temperature below -78 C, 1 mL of CD2CI2 was added. The
resulting solution was cannulated into an NMR tube for spectral characterization at -40"C.

For 84: 'H NMR (CDC12) 8 7.20 7.50 (m, 15H, Ph), 5.40 (s, 5H, C5H,), 2.33 (m,

1H), 2.07 (m, 1H), 1.52 (m, 1H), 1.44 (m, 1H), 1.21 (m, 2H), 0.79 (m, 3H), -2.82 (d,

1H, JpH = 10 Hz) ppm; "3C{'H} NMR (CD2C2) 8 276.8 (d, Jpc = 12 Hz, MoC, JcH =
73Hz), 226.8 (d, Jpc = 22 Hz, CO), 149.9 (d, Jpc = 6Hz), 130.8, 126.7, 121.2 (d, Jac = 4

Hz), 96.9 (Cp), 47.2, 30.4, 22.0, 13.5 ppm.



r(nH-CH)(CO) P(OPh)3 IMo[' :112-CH { PPhLC.C H )=CH(CHCfHzCF CH1(BF,
(86)

Butyl carbyne 81a (75.1 mg, 0.132 mmol) was mixed with phenyl acetylene (145
gL, 1.32 mmol) in 15 mL CH2CI2. The solution was cooled to -95"C. A 54% solution of
HBF4 in ether (30.4 pL, 0.132 mmol) was added dropwise. The solution changed color to
bright orange. After 20 min triphenyl phosphine (69.3 mg, 0.264 mmol) was added.
After reacting for 5 min, the solution was warmed to -78'C for 20 min during which the
solution changed color to bright yellow. The bath was removed and the solution was
allowed to warm to ambient temperature. Following removal of solvent in vacuo, the








remaining oily solid was rinsed with Et2O and then hexanes. The oil was dissolved in 1

mL of CH2C2 and the solid precipitated with the addition of 3 mL of (2:1) hexanes/Et2O.
The solution was removed via filter cannulation and the resulting solid rinsed with Et20 and

the hexanes. Removal of remaining solvent in vacuo yielded 86 as a golden powder (133

mg, 98.7%). For 86 (exo:endo 11:89): 'H NMR (CDC13) 8 6.59-7.72 (m, 35H, Ph),

4.83 (s, 5H, CsH,, endo), 4.24 (d, 5H, CsH,, exo), 3.64 (s, 1H, CHCH2CH2CH2CH,,

endo), 3.45 (m, 1H, CHCH2CH2CH2CH3, exo), 2.47 (m, 1H, CHCH2CH2CH2CH3),
2.26 (m, 1H, CHCH2CCH2CHCH), 1.08-1.24 (m, 4H), 0.78 (t, 3H, CH3) ppm;
3C {'H} NMR (CD2C2) 8 245.9 (d, CO, Jpc = 32 Hz), 151.9 (d, Ph, Jc = 15 Hz),

141.1, 134.7, 134.4, 134.2, 133.8 (d, Jpc = 10 Hz), 130.3, 130.1, 130.0, 129.8, 129.2,

128.1, 127.4, 126.2, 125.1, 124.3, 123.2, 121.2, 120.7 (d, Ph, Jp = 4 Hz), 100.0

(CH(PPh3)CPh, endo), 95.2 (C5H5, exo), 90.4 (CH5,, endo), 65.4

(CHCH2CH2CH2CH3), 34.6, 31.8, 30.9 (d, CHPPh,, Jpc = 45 Hz), 23.1, 14.0 ppm;
31P{'H} NMR (CD2C2) 8 181.4 (s, exo), 163.2 (s, endo), 35.5 (s, exo), 34.0 (s, endo)

ppm; IR (CH2C2) 1885 cm (vco); HRMS (FAB) m/z calcd for M+ (C55H1,98MoO7P2)
935.2332, found 935.2319.



(n'-C H)(CO) P(OPh) I}Mor :n2-CH P(OMe)l C(rC 1H=CH-
(CH2CHCH2CHC3)1(BF.) (87)

Butyl carbyne 81a (52.4 mg, 0.0921 mmol) was mixed with phenyl acetylene (101
gL, 0.921 mmol) in 12 mL CH2Cl2. The solution was cooled to -950C. A 54% solution of
HBF4 in ether (21.2 uL, 0.0921 mmol) was added dropwise. The solution changed color
to bright orange. After 20 min trimethyl phosphite (21.7 gL, 0.184 mmol) was added.
After reacting for 5 min, the solution was warmed to -78"C for 25 min during which the
solution changed color to bright yellow. The bath was removed and the solution was
allowed to warm to ambient temperature. Following removal of solvent in vacuo, the
remaining oily solid was rinsed with Et2O and then hexanes. The oil was dissolved in 1








mL of CIHCl2 and the solid precipitated with the addition of 3 mL of hexanes. Removal of
remaining solvent in vacuo yielded 87 as a golden powder (78.0 mg, 95.9%). For 87
(exo:endo 92:8): 'H NMR (CD2C2) 6 6.66-7.49 (m, 20H, Ph), 5.10 (s, 5H, CsH5,
endo), 4.40 (d, 5H, CH5, JPH = 1.5 Hz, exo), 3.91 (d, 9H, P(OMe),, JPH = 11 Hz, endo),
3.83 (d, 9H, P(OMe)3, JP, = 11 Hz, exo), 3.14 (m, 1H, CHCHCH2CH2CHCH ), 2.53 (m,
1H), 2.36 (m, 1H), 1.69 (m, 3H), 1.42 (m, 2H), 0.98 (t, 3H, CH3) ppm; '3C{ 'H} NMR

(CD2C12) 8 235.9 (d, CO, Jpc = 30 Hz), 151.4 (d, Ph, Jc = 9 Hz), 141.7 (d, Ph, JPc = 7
Hz), 130.5, 129.8, 129.5, 129.1, 128.3, 127.2, 126.0, 125.1, 121.3 (d, Ph, Jpc = 5 Hz),
120.8 (d, Ph, Jc = 5 Hz), 95.1 (CH, exo), 91.2 (C5H5, endo), 84.4 (d, CC6H5, Jc = 6

Hz), 61.6 (CHCH2CH2CH2CH3), 57.4 (d, P(OMe)3, Jpc = 8 Hz), 34.6, 35.0 (dd,
CHP(OPh)3, JPc = 172, 21 Hz), 33.2, 23.1, 14.1 ppm; 31P('H} NMR (CD2CI2) 8 178.8
(s, exo), 164.6 (s, endo), 64.4 (s, endo), 63.5 (s, exo) ppm; IR (CH2C2) 1878 cm-' (vco);
HRMS (FAB) m/z calcd for M' (C4H4598MoO7P2) 797.1704, found 797.1657.



(nu-C H )(CO) P(OPh) IMoMln :2-CHI P(OPh)} C(SiMe3)=CH-
-CH zCH -i CHCH~)1BFj) (8 9)

Butyl carbyne 81a (45.5 mg, 0.0800 mmol) was dissolved in 2 mL of CH2C12 and
cooled to -95"C. A 54% solution of HBF4 in ether (18.4 gL, 0.0800 mmol) was added
dropwise. The solution changed color to bright orange. After 10 min, 10 mL of hexanes
at -95 "C was added and an orange oil precipitated from solution. The solution was

removed by filter cannulation to yield an orange oil which was rinsed with hexane at -95
"C. The oil was mixed with trimethylsilylacetylene (113 gL, 0.0800 mmol) in CH2Cl2 at
-95C. The solution darkened in color to an orange-brown. After 15 minutes, triphenyl
phosphite (105 iL, 0.400 mmol) was added. After reacting for 5 min, the solution was
warmed to -78'C for 25 min during which the solution changed color to bright yellow.
The bath was removed and the solution was allowed to warm to ambient temperature.
Following removal of solvent in vacuo, the remaining oily solid was rinsed with 5 mL of








hexanes. The oil was dissolved in 1 mL of CH2Cl2 and the solid precipitated with the

addition of 3 mL of hexanes. Removal of remaining solvent in vacuo yielded 89 as a
golden powder (85.1 mg, 99.8%). For 89 (exo:endo 98:2): 'H NMR (CD2Cl2) 8 6.82-

7.40 (m, 35H, Ph), 5.01 (s, 5H, CH,, endo), 4.82 (d, 5H, CH5, JPH = 1.8 Hz, exo),

3.05 (m, 1H, CHCH2CH2CH2CH3), 2.81 (dd, 1H, CHP(OPh)3, JPH = 5, 21 Hz), 1.85
(m, 2H), 1.74 (m, 2H), 1.52 (sextet, 2H), 1.01 (t, 3H, CH3), 0.35 (s, 9H, TMS, exo),

0.08 (s, TMS, endo) ppm; '3C{ 'H NMR (CD2C2) 8 236.8 (d, CO, Jc = 31 Hz, exo),

151.1 (d, Ph, Jc = 10 Hz), 150.5 (d, Ph, Jpc = 13.3 Hz), 131.0, 130.4, 129.8, 127.6,
126.0, 121.1 (d, Ph, Jpc = 5 Hz), 119.5 (d, Ph, Jc = 5 Hz), 115.6 92.2 (CH,, exo),

90.9 (CsH5, endo), 68.8 (d, Jpc = 6 Hz, CHCH2CCH2CH 3CH), 68.3 (d, Jpc = 8 Hz,

CHP(OPh)3C(TMS)) 35.4, 35.0, 28.4 (d of d, CHP(OPh)3, Jc = 178, 21 Hz, exo), 23.1,

14.1, 1.80 (TMS, exo), 1.13 (TMS, endo) ppm; 3'P{'H} NMR (CDCl2) 8 178.4 (s,

exo), 166.6 (s, endo), 49.4 (s, endo), 48.8 (s, exo) ppm; IR (CH22C) 1874 cm-' (vco);

HRMS (FAB) m/z calcd for M' (C52H5598MoO7P2Si) 979.2260, found 979.2292.



i(n-C H )(CO) I P(OMe) 1Mo T' :12-CH P(OMe)3j C(C,H.)=CH-
(CHzCHiH2CHCHfi)BF-) (90)

Butyl carbyne 75 (133 mg, 0.348 mmol) was mixed with phenyl acetylene (382
jgL, 3.48 mmol) in 20 mL CH2C12. The solution was cooled to -950C. A 54% solution of

HBF4 in ether (80.0 gL, 0.348 mmol) was added dropwise. The solution changed color to
bright orange. After 20 min trimethyl phosphite (205 pL, 1.74 mmol) was added. After

reacting for 5 min, the solution was warmed to -78"C for 20 min during which the solution
changed color to bright yellow. The bath was removed and the solution was allowed to
warm to ambient temperature. Following removal of solvent in vacuo, the remaining oily

solid was rinsed with Et2O and then hexanes. The oil was dissolved in 2 mL of CH2CI,
and a golden oil precipitated with the addition of 5 mL of (1:1) Et2O/hexanes. After rinsing








the golden oil with hexanes, removal of remaining solvent in vacuo yielded 90 as a golden
powder (223 mg, 92.1%). For 90 (exo:endo 77:19): 'H NMR (CD2CI2) 8 7.14-7.68 (m,

5H, Ph), 5.21 (s, 5H, CH5,, Jn = 0.6 Hz, endo), 4.91 (d, 5H, CH5 JPH = 1.8 Hz, exo),
3.89 (d, 9H, P(OMe)3, JPH = 11 Hz, endo), 3.86 (d, 9H, P(OMe)3, JPH = 11 Hz, exo),
3.76 (d, 9H, P(OMe)3, JPH = 11 Hz, exo), 3.32 (d, 9H, P(OMe)3, JPH = 11 Hz, endo),
2.86 (m, 1H, CHCH2CH2CH2CH3, exo), 2.65 (d, 1H, CHCH2CH2CH2CH3, JH = 5

Hz, endo), 2.52 (m, 1H), 2.33 (m, 1H), 2.18 (m), 1.74 (m, 2H), 1.45 (m, 2H), 0.97 (t,
3H, CH3) ppm; 3C{I'H} NMR (CD2C2) 8 246.8 (d, CO, Jpc = 33 Hz, endo), 238.4 (d,

CO, Jpc = 31 Hz, exo), 142.6 (d, Ph, Jpc = 6 Hz), 129.4, 128.8, 128.3, 128.0, 100.6

(CCH5, endo), 95.4 (CH,5, exo), 91.1 (CH,, endo), 82.6 (d, CC6H,, Jpc = 5 Hz, exo),
61.2 (d, CHCH2CH2CH2CH3, JPc = 4 Hz), 57.4 (d, P(OMe)3, JP, = 8 Hz, endo), 57.2 (d,

P(OMe)3, JPc = 8 Hz, exo), 53.6 (d, P(OMe)3, JPc = 11 Hz, exo), 53.3 (d, P(OMe)3, Jpc =
11 Hz, endo), 34.7, 33.5, 32.0 (dd, CHP(OMe)3, JPc = 168, 21 Hz, exo), 23.3 (d,
CHP(OMe),, Jc = 148 Hz, endo), 23.0, 14.0 ppm; 31P{ 'H) NMR (CD2C12) 8 183.8 (s,
exo), 173.6 (s, endo), 66.0 (s, endo), 64.6 (s, exo) ppm; IR (CH2Cl2) 1866 cm (vco);
HRMS (FAB) m/z calcd for M+ (C25H3998MoO7P2) 611.1232, found 611.1233.



ClIP(OMe)1,,Mo-CBu (115)

Cl{P(OMe)3}3(CO)Mo-CBu (116) (2.897g, 4.824 mmol) was dissolved in
trimethyl phosphite (5.69 mL, 48.2 mmol). The mixture was refluxed 12 h and some of
the excess phosphite removed in vacuo. Impurities were extracted into a minimal amount
of hexanes (3 x 5 mL) and the remaining solvent was removed to yield 115 as a gray-tan
oil (2.135 g, 63.5% yield) which was used in the preparation of 103 without further
purification. 'H NMR (C6D6) 8 3.79 (virtual t, 36H), 2.28 (m, 2H), 1.65 (pentet, 2H),
1.22 (sextet, 2H), 0.87 (t, 3H) ppm.








Cp P(OMe)3,_Mo-CBu (103)

Cl{P(OMe)3 4(CO)Mo-CBu (2.135 g, 3.065 mmol) was dissolved in 25 mL THF.
After addition of solid NaCp (0.404 g, 4.60 mmol), the mixture was heated to 55 C for 15
h. The solvent was removed in vacuo and the resulting residue was filtered through
alumina eluting with Et20 at -780C. After removal of the solvent, the golden-brown oil
was chromatographed on alumina at -78 "C with hexane as the eluent. Increasing amounts

of Et2O were added to obtain a bright yellow fraction. Removal of the solvent in vacuo
yielded 103 as a bright yellow oil (619 mg, 42.2% yield). 'H NMR (C6D6) 8 5.29 (s,
5H), 3.52 (virtual t, 18 H), 2.30 (m, 2H), 1.60 (pentet, 2H), 1.41 (sextet, 2H), 0.89 (t,

3H) ppm; '3C{'H} NMR (CD6) 8 310.4 (t, Jc = 29 Hz, Mo=C), 89.0 (Cp), 50.8

(P(OMe)3), 49.1, 31.6, 22.6, 14.1 ppm; 31PI'H} NMR (CDC13) 8 214.3 ppm; HRMS
(FAB) m/z calcd for M+ (C,6H3298MoP206) 480.0733, found 480.0725.



Cp {P(OMe), zHMo-CBul BF11 (104)

Butyl carbyne 103 (245 mg, 0.512 mmol) was dissolved in 8 mL of CH2C12 at -78
"C and mixed with a 54% solution of HBF4 in ether (70.6 LL, 0.512 mmol). After 25 min,
30 mL of pentane at -78 "C was added and a red-orange oil formed. The solution was
removed by filter cannulation to yield a solid which was rinsed with pentane at -78 "C.

Some of the remaining solvent was removed in vacuo at -78 C. Keeping the temperature
below -78 "C, 1 mL of CD2C12 was added. The resulting solution was cannulated into an
NMR tube for spectral characterization at -50C. For 104: 'H NMR (CD2CI2) 8 5.67 (s,
5H), 3.67 (d, JPH = 12 Hz, 18 H), 2.47 (m, 2H), 1.47 (pentet, 2H), 1.27 (sextet, 2H),
0.82 (t, 3H), -2.60 (t, JPH = 64 Hz, 1H) ppm; '"CI 'H NMR (CD2Cl2) 8 347.0 (t, Jc =
33 Hz, Mo=C), 96.2 (Cp), 53.5 (P(OMe)3), 51.4, 29.5, 22.2, 13.5 ppm.








Cl(CjH 1 (CO)_zMo-CBu (117)


Mo(CO)6 (2.248 g, 8.515 mmol) was dissolved in 30 mL EtO2 and cooled to 0OC.
A 2.3 M hexane solution of n-butyllithium (3.70 mL, 8.51 mmol) was added dropwise.

After 1.5 h, the solution volume was reduced to 5 mL in vacuo. The solution was filtered

through Celite and the solvent removed in vacuo to leave a golden-tan powdery solid. This

solid was dissolved in 30 mL CH2CI2. After cooling to -95C, oxalyl chloride (0.669 mL,

7.66 mmol) was added dropwise ensuring the temperature remained below 900C. After

the addition was complete, the bath was removed and the solution was allowed to warm to

-30'C. During this time effervescence was observed. After cooling the solution to -78C,

excess pyridine (2.15 mL, 25.5 mmol) was added. After 5 min the bath was removed and

the solution was allowed to stir 25 min before the solvent was removed in vacuo. The

residue was dissolved in 5 mL CH2Cl2 and filtered through Celite. The solvent was

removed in vacuo to leave a sticky brown solid which was dissolved in 5 mL CH2C12.

After addition of 5 mL Et2O and 10 mL hexanes, the solution was concentrated until a

golden precipitate formed. The solid was isolated by filtration and rinsed with hexanes (2 x

15 mL). Evaporation of the remaining solvent in vacuo yielded 117 as a golden brown

powder (3.200 g, 90.6% yield). This crude solid was used in the preparation of 105 and

107 without further purification. For 117: 'H NMR (C6D6) 8 9.05 (d, JH = 4.8 Hz,

4H), 6.68 (t, JHH = 6.6 Hz, 2H), 6.35 (t, JH = 6.6 Hz, 4H), 2.39 (t, 2H), 1.54 (pentet,

2H), 1.27 (sextet, 2H), 0.78 (t, 3H) ppm ; IR (CH2C2) 1998 (s), 1912 (s) cm-' (vco).



Cp(CO):MosCBu (105)


Cl(C5H,N)2(CO)2Mo=CBu (117) (417 mg, 1.00 mmol) was dissolved in 20 mL

THF. After addition of solid NaCp (133 mg, 1.51 mmol) the mixture was stirred for 1.5 h

at ambient temperature. The solvent was removed in vacuo and the resulting residue was








filtered through alumina eluting with Et2O at -78'C. After removal of solvent, the golden

oil was chromatographed on alumina at -78 C with hexane as the eluent. A bright yellow

fraction was collected. Removal of solvent in vacuo yielded 105 as a bright yellow oil

(170 mg, 59.0% yield). 'H NMR (C6D6) 8 5.05 (s, 5H), 2.19 (t, 2H), 1.42 (pentet, 2H),

1.25 (sextet, 2H), 0.75 (t, 3H) ppm; "3C{H} NMR (C6D6) 8 332.7 (Mo=C), 229.9 (CO),

92.1 (Cp), 50.5, 29.7, 21.9, 13.3 ppm; IR (CH2C12) 1992 (s), 1913 (s) cmn1 (vco); HRMS

(FAB) m/z calcd for M' (C,2HI498MoO2) 288.0051, found 288.0074.



[Moz(u-H) f i-Cz(Bu)l CO),CpD1 BF41 (10 6)

Butyl carbyne 105 (210 mg, 0.735 mmol) was dissolved in 8 mL of CH2Cl2 at -78

"C and mixed with a 54% solution of HBF4 in ether (101 gL, 0.735 mmol). After 25 min,

30 mL of pentane at -78 C was added and a red crystalline solid precipitated from solution.

The solution was removed by filter cannulation to yield a solid which was rinsed with

pentane at -78 C. Some of the remaining solvent was removed in vacuo at -78 'C.

Keeping the temperature below -60 C, 2 mL of CDCI3 was added. The resulting solution

was cannulated into an NMR tube for spectral characterization at -50'C. For 106: 'H

NMR (CDCl3) 8 5.54 (s, 10H, C5H5), 2.92 (m, 2H), 2.70 (m, 2H), 1.40 (m, 8H), 0.83

(m, 6H), -15.67 (s, 1H) ppm; "3C{'H) NMR (CDC13) 8 220.6, 219.6, 91.4 (Cp), 77.2,

69.8, 37.9, 22.4, 13.2 ppm.



Tp(CO)Mo-CBu (107)

CI(C5HN)2(CO)2Mo=CBu (117) (823 mg, 1.98 mmol) was dissolved in 25 mL

THF. After addition of solid KTp (750 mg, 2.97 mmol) the mixture was stirred for 30 min

at ambient temperature. The solvent was removed in vacuo and the resulting residue was

filtered through alumina eluting with Et2O at -78"C. After removal of solvent, the golden-

brown oil was chromatographed on alumina at -78 "C with hexane as the eluent.