Osmium Hydridoalkyls and Their Elimination Mechanisms

13 Osmium Hydridoalkyls and Their Elimination Mechanisms JACK R. NORTON, WILLIE J. CARTER, JOHN W. KELLAND, and STANLEY J. OKRASINSKI

Downloaded by UNIV OF SYDNEY on May 3, 2015 | http://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/ba-1978-0167.ch013

Department of Chemistry, Princeton University, Princeton, NJ 08540

Eliminations from Os(CO)RR' occur by dinuclear mecha nisms only if either R or R' is H. A hydride on one metal is necessary to interact with a vacant coordination site on the other in the dinuclear transition state. With Os(CO) H , the vacant site is created by dissociation of CO. With Os(CO) (H)CH , the vacant site is created by a facile rate-determining isomerization which we suggest is to an acetyl hydride. The unique instability of hydridoalkyl carbonyls thus is explained. The synthesis and properties of Os(CO) (H)C H and various polynuclear ethyl osmium derivatives show that β-hydrogens have no significant effect on these elimination mechanisms. Dinuclear hydridoalkyls are excellent starting points for the synthesis of more complex polynuclear alkyls. 4

4

2

4

3

4

2

5

'hree years ago, w h i l e w e were considering possible reasons for the A general inability of transition metals to insert into a n d activate C - H bonds, our attention turned to the question of the instability of transition metal a l k y l h y d r i d e complexes. W e have listed the f e w a l k y l h y d r i d e complexes of w h i c h we are aware (I ) (one a d d i t i o n a l case (2) recently c a m e to our attention) as w e l l as some of the only slightly more numerous cases of substituted a l k y l hydrides stabilized by chelation (3). In contrast, there are enormous numbers of polyalkyls (4, 5) a n d poly hydrides (6). W h i l e rarity does not logically i m p l y instability, it does suggest it, so w e considered possible mechanistic explanations for the as sumed r a p i d decomposition of c t s - M L ( R ) ( H ) relative to c i s - M L R and cisM L H . W e have focused on octahedral complexes since they are both more important and more numerous. n

n

n

2

2

Construction of an orbital correlation d i a g r a m (7) discloses that concerted cis e l i m i n a t i o n of R - R ' f r o m c i s - M L 4 R R is not f o r b i d d e n b y s y m m e t r y consid erations; thus, there appears to be no advantage for the a s y m m e t r i c e l i m i n a t i o n /

0-8412-0390-3/78/33-167-170/$05.00/0 © American Chemical Society In Transition Metal Hydrides; Bau, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1978.

13.

Osmium

NORTON ET AL.

171

Hydridoalkyls

R - H over the s y m m e t r i c eliminations R - R a n d H - H .

B o n d strength consider

ations suggest that if rates were determined entirely b y the strengths of the bonds made a n d broken, R - H e l i m i n a t i o n m i g h t be fastest.

If one assumes a constant

M - H bond strength X greater than a constant M - R bond strength Y and considers that the strength of the C - H b o n d b e i n g f o r m e d i n R - H (about 100 k c a l / m o l ) is more than halfway between the bond strengths of R - R (85 k c a l / m o l ) and H - H (104 k c a l / m o l ) , AH

(X + Y — 100) for R - H e l i m i n a t i o n can, for certain values

0

of X - Y , be lower and more favorable than AH

for R - R e l i m i n a t i o n (2Y — 85)

0

or H - H e l i m i n a t i o n (2X -

104).

This difference w o u l d be reflected i n Δ Η * and i n reaction rates only if the elimination transition state strongly resembled the products.

T o the extent that

the elimination transition state resembles the starting complex o s - M L R R ' , one Downloaded by UNIV OF SYDNEY on May 3, 2015 | http://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/ba-1978-0167.ch013

4

w o u l d expect relative rates to be largely a f u n c t i o n of the energies of the bonds being broken.

T h e r e is then no reason to expect e l i m i n a t i o n of R - H f r o m the

m i x e d species to be faster than e l i m i n a t i o n of both R - R f r o m M L 4 R 2 and H - H from ML4H2. W e thus began to question the traditional belief that concerted cis e l i m i nation of R - R ' (simple intramolecular reductive elimination) was i n fact the mechanism: ML RR' — R-R' + M L 4

4

of organic l i g a n d e l i m i n a t i o n f r o m M L R R ' . O u r first w o r k i n g hypothesis was that attention should be p a i d to the energy of the fragment complex M L that w o u l d r e m a i n after such an e l i m i n a t i o n . If this energy were sufficiently great, other e l i m i n a t i o n processes w o u l d be observed rather than simple intramolecular reductive e l i m i n a t i o n . 4

4

T h e literature already contained some results that supported this hypothesis. W h i l e o r g a n o p l a t i n u m ( I V ) complexes such as P t L I ( C H ) readily undergo 2

3

3

ethane elimination, leaving stable < r a n s - P t L ( C H ) I (8), the superficially similar ( 7 r - C 5 H 5 ) P t ( C H ) does not, g i v i n g m e t h y l radicals and eventually methane i n stead (9). T h e difference is explained reasonably as a consequence of the h i g h energy of the hypothetical C s H P t C H compared with the stable, square-planar fragment f r a n s - P t L ( C H ) I . 2

3

3

3

5

2

3

3

PtLJ(CH ) : J

C H

3

2

(^C H )Pt(CH. ), 5

5

(

-A#+

8

+

/raw.s-PtL (CH )I

C,H \

2

6

+

;J

C H PtCH, 5

* · CH

5

: t

CH

4

T o investigate the v a l i d i t y of this hypothesis, we looked at the series of complexes, c i s - O s ( C O ) R R . 4

/

Several of its m e m b e r s were reported, and even

an apparent h y d r i d o m e t h y l complex was observed spectroscopically i n small quantities (JO, J J ).

Furthermore, there was reason to believe that O s ( C O ) would 4

be a very h i g h energy fragment a n d hence that mechanisms other than simple

In Transition Metal Hydrides; Bau, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1978.

172

TRANSITION M E T A L HYDRIDES

i n t r a m o l e c u l a r reductive e l i m i n a t i o n m i g h t be observed.

O s ( C O ) 4 h a d been

generated i n matrix isolation experiments and gave behavior qualitatively similar to that of the m o r e extensively studied F e ( C O ) 4 .

T h e latter appears to be ex-

t r e m e l y reactive t o w a r d various inert m a t r i x materials a n d has a C

structure

2v

i n most of t h e m (12, IS).

A l t h o u g h the question of whether such M ( C O ) 4

fragments are singlets or triplets is under active discussion (14,15), it is clear that they are not stable, square-planar d

complexes like £rans-PtL,2(CH )I.

8

3

A p r e l i m i n a r y investigation showed that Os(CO)4H2, O s ( C O ) 4 ( C 2 H ) , and 5

2

O s ( C O ) 4 ( C H ) 2 do not decompose appreciably below 100°C whereas O s ( C O ) 4

3

(H)CH

3

decomposes r a p i d l y at 4 0 ° C .

In a d d i t i o n to p r o v i d i n g a concrete ex-

a m p l e of the relative instability of a l k y l hydrides, these results suggested strongly


that m o r e than one e l i m i n a t i o n m e c h a n i s m was operating i n this series of c o m pounds a n d thus that something other than simple i n t r a m o l e c u l a r reductive e l i m i n a t i o n must be o c c u r r i n g .

Elimination

Mechanisms of Os(CO) (CH )2 4

and

3

Os(CO) H 4

2

F u r t h e r w o r k has shown that the most obvious alternative, m e t a l - c a r b o n b o n d homolysis to f o r m free radicals, occurs w i t h O s ( C O ) ( C H ) . 4

3

The methyl

2

radicals that were produced (slowly even at 162.5°C) attack a variety of solvents. F u r t h e r , q u a n t i t a t i v e v e r i f i c a t i o n of their i n t e r m e d i a c y was obtained by m e a s u r i n g ku/kr> i n mixtures of n - C i 2 H 6 a n d n - C i 2 D 6 . 2

T h e ratio, 5.3, is charac-

2

teristic of the k n o w n selectivity for m e t h y l radicals at that temperature T h e first h y d r i d e e x a m i n e d was naturally O s ( C O ) 4 H . 2

(16).

T h e cis structure

presumed for this c o m p o u n d (and for all the other O s ( C O ) R r V ) f r o m i r data was 4

c o n f i r m e d by R a m a n observation (methylcyclohexane solution) of i>ç>s-H at 1971 (A i) a n d 1942 (B ) c m 2

i n the gas phase (17).

a n d by an electron d i f f r a c t i o n study on the c o m p o u n d

- 1

T h e structure departs only slightly f r o m octahedral ge-

ometry, w i t h the C O ( a x i a l ) - O s - C O - ( e q u a t o r i a l ) angle being 96.3 ± 0.7°.

The

structure of the O s ( C O ) unit is similar to those of the same units i n O s ( C O ) i 4

3

2

(Ιβ). D e u t e r i u m l a b e l i n g experiments proved that the i n i t i a l reaction upon thermolysis at 125.8°C: 2 O s ( C O ) H --> H O s ( C O ) + H 4

2

2

2

8

2

does not proceed via simple intramolecular reductive elimination to form Os(CO)4 (which might then insert i n an O s - Η bond in O s ( C O ) 4 H ) , but rather is dinuclear, 2

i.e., a m i x t u r e of O s ( C O ) H and O s ( C O ) D gives H D as w e l l as H and D 4

2

4

2

2

(19).

2

D i n u c l e a r e l i m i n a t i o n is d e f i n e d as b e i n g the formation of R - R ' f r o m M L R R ' 4

w i t h R a n d R ' o r i g i n a t i n g on different molecules of M L R R ' . 4

T h e process can

be i d e n t i f i e d o n l y b y l a b e l i n g studies of the type described. W i t h O s ( C O ) 4 H 2 a n d other complexes to be discussed later, d i n u c l e a r e l i m i n a t i o n is k i n e t i c a l l y first order.

T h e detailed mechanism for O s ( C O ) H

appears (19) to be:


4

2

13.

Osmium

NORTON ET AL

173

Hydridoalkyls

O s ( C O ) H — O s ( C O ) H + C O (rate determining) 4

2

3

2

fast

Os(CO) H + Os(CO) H — > 3

2

4

H Os (CO) + H

2

2

2

7

2

(the actual d i n u c l e a r e l i m i n a t i o n step) fast

H Os (CO) + C O — • H Os (CO) 2

2

7

2

W h e n the reaction is r u n i n the presence of

1 3

2

8

C O and stopped after one half-life,

not only is the label incorporation into recovered starting m a t e r i a l negligible, as predicted by the mechanism, but the label incorporation into H O s ( C O ) s 2


exceeds that r e q u i r e d b y the mechanism.

2

T h i s shows that it is undergoing car

b o n y l exchange under the reaction conditions a n d suggests that such dinuclear species are m u c h more labile than their mononuclear counterparts. In view of the structural similarity between the O s ( C O ) units i n O s ( C O ) H 4

4

2

a n d O s ( C O ) i noted above, it is interesting to c o m p a r e the O s ( C O ) H ther 3

2

4

2

molysis rate, for w h i c h we said c a r b o n y l dissociation is rate d e t e r m i n i n g , w i t h the k n o w n rate of dissociative c a r b o n y l exchange for O s ( C O ) i (20). 3

4

5

2

s e c " ; the rate

- 5

of O s ( C O ) H thermolysis at that temperature is 6 X 1 0 ~ s e c " . 4

T h e ex

2

change rate per O s ( C O ) unit extrapolated to 125.8°C is 25 Χ 1 0

1

T h e similarity

1

of these numbers is final evidence that c a r b o n y l dissociation f r o m O s ( C O ) H 4

does occur i n the r a t e - d e t e r m i n i n g step.

2

A vacant coordination site apparently

is needed before the actual d i n u c l e a r e l i m i n a t i o n step can occur. Synthetic Aspects of Os(CO) (H)(R)

Chemistry

4

Next our interest focused on o s - O s ( C O ) ( H ) C H . 4

3

First it was necessary

to devise a synthesis capable of producing this rather unstable complex pure and in high yield. Initial attempts to methylate [ H O s ( C O ) ] ~ were thwarted by side 4

reactions caused by proton transfer from the product O s ( C O ) ( H ) C H onto anion 4

not yet methylated.

3

T h e use of C H O S 0 F to increase the m e t h y l a t i o n rate 3

2

solved this p r o b l e m (1) a n d p e r m i t t e d the synthesis of 99% pure c i s - O s ( C O ) 4

( H ) C H i n yields u p to 90% 3

W e recently extended this approach to the synthesis of the e t h y l analog cw-Os(CO) (H)C H . 4

2

5

CF3CO2H

Na Os(CO) 2

4

— •

Na [HOs(CO) ]" +

4

tetraglyme C2H5OSO2F

Na+[HOs(CO) ]4

— •

tetraglyme

cw-Os(CO) (H)(C H ) 4

2

5

T w o equivalents of ethyl fluorosulfonate must be used (one ethylates the t r i f l u oroacetate ion) to avoid complications arising f r o m ethylation of ether oxygens i n the tetraglyme solvent. T h e product must be distilled out of the reaction m i x t u r e on a v a c u u m line w i t h i n 5 m i n after a d d i t i o n is complete. T h e h y d r i -


174


H N M R Spectra of E t h y l O s m i u m C o m p l e x e s *

T a b l e I.

X

Coupling Constants (Hz)

Complex a\s-Os(CO) (H)(C H ) 4

2

5

C H O s ( C O ) O s ( C O ) C H 4

4

3

2

4

2

5

4

4

3

In comparison, O s ( C O ) H does not react w i t h ethylene while O s ( C O ) ( H ) C H , 4

2

4

3

rather than f o r m i n g an e t h y l o s m i u m complex, reacts w i t h ethylene to f o r m O s ( C O ) ( C H ) a n d methane i n a reaction to be discussed below. 4

2

4

T h e most important question about the reactivity of H O s ( C O ) O s ( C O ) C H 4

is whether or not it can f o r m methane by a 1,2 e l i m i n a t i o n .

4

3

It does evolve

methane; after several days at 7 4 ° C , analysis of the gaseous products f r o m its decomposition shows approximately one equivalent of C H and one equivalent


4

of C O .

However, the reaction is extremely complicated.

and O s ( C O ) ( H ) C D 4

Via Os(CO) (D)CH 4

3

(described below), it is possible to prepare D O s ( C O ) -

3

4

O s ( C O ) C H and H O s ( C O ) O s ( C O ) C D separately; w h e n they are m i x e d and 4

3

4

4

3

heated to 7 4 ° C , C D is found i n the resulting methane.

Therefore, the reaction

4

is intermolecular, and there is no evidence for a 1,2-elimination.

It can be argued

that it is unreasonable to expect a concerted 1,2-elimination ever to occur i n a system of this sort where the methyl group and hydrogen are attached to osmium atoms almost 3 A apart, a n d where m i g r a t i o n or b r i d g i n g b y C H or H seems 3

likely to be r e q u i r e d prior to e l i m i n a t i o n . P r e l i m i n a r y investigation suggests once again that the presence of

-hy

drogens makes little difference a n d that c i s - O s ( C O ) ( H ) C H has a chemistry 4

2

5

like that of its m e t h y l c o u n t e r p a r t — i t evolves ethane i n a few hours at room temperature.

Its decomposition products appear to be O s ( C O ) i ( C H s ) a n d 3

HOs(CO) Os(CO) (C Hs). 4

4

2

2

2

T h e latter has not been isolated, but its presence is

2

inferred f r o m the fact that treatment of the reaction mixture w i t h C C 1 permits 4

the isolation of C l O s ( C O ) O s ( C O ) ( C H s ) (characterized b y mass spectrometry). 4

4

2

T h e ir spectra of C l O s ( C O ) O s ( C O ) C H and O s ( C O ) i ( C H ) appear in Table 4

4

2

5

3

2

2

5

2

II.

Mechanism of Dinuclear

Elimination

from

cisOs(CO)4(H)CHs

T h e diagnostic reaction, thermolysis of a O s ( C O ) ( D ) C H and O s ( C O ) 4

3

4

( H ) C D m i x t u r e , yields C D a n d C H as w e l l as C H D a n d C D H . 3

4

4

3

Therefore,

3

this is classified as a d i n u c l e a r e l i m i n a t i o n reaction.

A p p r o p r i a t e l y labeled

starting materials are easily obtained by using C F C 0 D or C D O S 0 F at the 3

appropriate place i n φ β synthesis.

2

3

2 O s ( C O ) ( H ) C H --> C H + H O s ( C O ) O s ( C O ) C H 4

3

2

T h e rate of the e l i m i n a t i o n reaction: 4

4

4

3

is, as w i t h the analogous reaction w i t h O s ( C O ) H , first order: 4

2


13.

Osmium Hydridoalkyls

N O R T O N E T AL.

w i t h ki = 1.38 X 1 0 " s e c " 4

at 4 9 ° C .

1

177

However, unlike O s ( C O ) H , carbonyl 4

dissociation is not the r a t e - d e t e r m i n i n g step. w h e n the reaction is carried out under

1 3

2

T h e value of A S * is —8 eu, a n d

C O , no label is incorporated into the

product or the recovered starting m a t e r i a l (3). O u r presumption that the rate-determining step somehow produced a vacant coordination site led to our investigating the reaction i n the presence of t r i e t h ylphosphine.

M e t h a n e is still e l i m i n a t e d , Os(CO)4(Et3P) is f o r m e d , a n d the

disappearance rate of O s ( C O ) ( H ) C H is still first order i n that material, but the 4

rate constant (6.4 X 1 0

5

3

s e c ) is one-half that observed i n the absence of E t P . - 1

3

T h e rate is completely independent of the concentration of E t P .

Furthermore,

3

reaction of a O s ( C O ) ( H ) C D and O s ( C O ) ( D ) C H mixture w i t h E t P gives only 4

C D H and C H D .


3

3

4

3

3

These observations require the f o l l o w i n g m e c h a n i s m (3):

3

where [ O s ( C O ) ( H ) C H ] * is an isomerized, reactive form of the starting material. 4

3

T h e course of the reaction reflects the outcome of the competition for this i n termediate between external nucleophiles L a n d the o r i g i n a l h y d r i d o m e t h y l compound. Several considerations (such as the activation parameters and small solvent dependence of the reaction i n w h i c h it is formed) suggest that [ O s ( C O ) ( H ) C H ] * 4

is the unsolvated, five-coordinate a c y l h y d r i d e O s ( C O ) ( H ) 3

CH . 3

3

Attempts

to trap this intermediate w i t h the a c y l l i g a n d intact were not successful—either d i n u c l e a r e l i m i n a t i o n or r a p i d methane evolution occurs.

O n e observes the re

action: c i s - O s ( C O ) ( H ) C H + L --> O s ( C O ) L + C H 4

3

4

for L = E t P , ( C H 0 ) P , pyridine, and C H . 3

3

3

2

4

4

T h e compound, O s ( C O ) ( C H ) , 4

2

4

has ir bands i n pentane at 2111(w), 2023(s), a n d 1993(s) a n d a H N M R signal l

at 8.56 τ ( C D ) . 6

6

If the intermediate is a five-coordinate a c y l hydride, the above observations require that:


178


be faster than the reaction of L with the intermediate.

W h i l e the thermodynamic

d r i v i n g force for methane e l i m i n a t i o n is obvious [Os(CO)4L can be generally isolated as stable complexes, whereas acetaldehyde e l i m i n a t i o n w o u l d leave the high-energy fragment O s ( C O ) L ] , a m e c h a n i s m for methane e l i m i n a t i o n is not 3

readily apparent.

It cannot involve C O dissociation—carrying out the reaction

of O s ( C O ) ( H ) C H w i t h L = E t P under 4

3

3

1 3

C O leaves neither the product

(Os(CO)4L) nor the recovered starting m a t e r i a l w i t h any label incorporation. Ο

II C o n c e i v a b l e mechanisms for methane e l i m i n a t i o n f r o m O s ( C O ) ( C C H ) ( H ) L 3

3

involve either a seven-coordinate transition state or direct migration of C H onto 3


H. T h e relative ability of various nucleophiles to compete for the reactive i n termediate requires comment.

T h e reactivity of O s - Η i n O s ( C O ) 4 ( H ) C H (or 3

in O s ( C O ) 4 H — s e e below) is so h i g h that only strong nucleophiles such as E t P 2

3

can compete successfully w i t h it. ( C H 0 ) P is somewhat less reactive a n d p y r 3

3

i d i n e is m u c h less reactive than E t P , as measured by their ability to divert the 3

reaction f r o m H O s ( C O ) 4 0 s ( C O ) C H p r o d u c t i o n into O s ( C O ) L production. 4

3

4

T h e low reactivity of C O that m i g h t be i n f e r r e d f r o m the results of the labeling experiments (lack of of 1 3

1 3

1 3

C O incorporation) is incorrect since the partial pressure

C O i n such experiments is m u c h less than 1 a t m , a n d the concentration of

C O i n solution is < 1 0 ~ M . 3

T h e O s - Η bonds i n starting m a t e r i a l are present

at concentrations of > 1 0 ~ M ; therefore, their concentration relative to that of 2

1 3

C O is h i g h enough that no conclusions can be d r a w n r e g a r d i n g the relative

reactivity of O s - Η and C O t o w a r d the intermediate.

T h e proposed a l k y l m i

gration i n the r a t e - d e t e r m i n i n g step accounts nicely for the instability of Os(CO) (H)C H 4

2

5

c o m p a r e d w i t h O s ( C O ) ( H ) C H , as e t h y l groups generally 4

3

migrate onto carbonyls more r a p i d l y than m e t h y l groups

(22).

Conclusion P r o p o s e d G e n e r a l E x p l a n a t i o n for A l k y l H y d r i d e I n s t a b i l i t y . T h e a d vantage of suggesting a five-coordinate a c y l h y d r i d e as the reactive intermediate i n O s ( C O ) ( H ) C H thermolysis is that it leads to a general explanation of e l i m i 4

3

nation processes of this type.

T h a t general explanation contains the f o l l o w i n g

elements: (1) D i n u c l e a r e l i m i n a t i o n processes are possible only w h e n at least one of the ligands to be e l i m i n a t e d is a h y d r i d e . T h i s is supported b y our observations (dinuclear e l i m i n a t i o n f r o m O s ( C O ) ( H ) C H and O s ( C O ) H but not f r o m O s ( C O ) ( C H ) ) and is explained reasonably by the u n i q u e ability of a h y d r i d e to bridge a pair of transition metal atoms. Trie interaction of O s - Η with a vacant coordination site on another Os to f o r m a dinuclear species appears to be an es sential part of the dinuclear e l i m i n a t i o n process. (2) A l k y l carbonyl complexes can create vacant coordination sites by a l k y l m i g r a t i o n to give acyls far more readily than h y d r i d e c a r b o n y l complexes can 4

4

3

3

4

2

2


13.

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179

Osmium Hydridoalkyls

by forming formyl complexes. The chemical literature does not contain a single example of the direct generation of a formyl complex from a hydridocarbonyi(3) Combination of both of the above elements in a single molecule such as Os(CO)4(H)CH3 gives rise to facile dinuclear elimination. The dihydride is capable of dinuclear elimination but must rely on the comparatively high-energy process of carbonyl dissociation to provide the necessary vacant coordination site. The dimethyl compound has the necessary vacant site easily available but no hydride to interact with it. The hydridomethyl compound has both elements and is uniquely unstable. We conclude that our working hypothesis is valid, and that when ML4 is a sufficiently unstable fragment, both dinuclear elimination and metal-carbon bond homolysis can occur instead of simple reductive elimination of R-R' from ML RR'. We conclude further that the involvement of a hydride ligand is necessary for dinuclear elimination from such ML^RR'. On that basis, we pro pose the above general mechanism to explain the instability of hydridoalkyls of this type. The above conclusions and suggestions, if valid, require than an alkyl car bonyl (because it can easily generate a vacant coordination site) and a hydride should be able to carry out a facile dinuclear alkane elimination. Thus we predict that dinuclear eliminations between Os(CO)4H and Os(CO)4(CH3) should occur more rapidly than the decomposition of either compound separately, and we have confirmed this prediction.


4

2

2

Os(CO) H + Os(CO) (CH ) — HOs(CO) Os(CO) CH + C H 4

2

4

3

2

4

4

3

4

Some acetaldehyde is formed with prolonged heating of the reaction mixture in a sealed tube. Similarly, we predict that the Os-Η bonds in Os(CO)4H should be able to compete with those in Os(CO) (H)CH3 for the reactive acyl hydride intermediate formed in the decomposition of the latter. We have also confirmed this pre diction. 2

4

Os(CO) H + Os(CO) (H)CH — H Os (CO) + C H 4

2

4

3

2

2

8

4

We are now examining other hydride and methyl complexes to see whether or not the reactions predicted on the basis of our conclusions and proposals actually occur.

Literature Cited 1. Evans, J., Okrasinski, S. J., Pribula, A. J., Norton, J. R., J. Am. Chem. Soc. (1976) 98, 4000. 2. Strope, D., Shriver, D. F., J. Am. Chem. Soc. (1973) 95, 8197. 3. Okrasinski, S. J., Norton, J. R., J. Am. Chem. Soc. (1977) 99, 295. 4. Schrock, R. R., Parshall, G. W., Chem. Rev. (1976) 76, 243. 5. Davidson, P. J., Lappert, M. F., Pearce, R., Chem. Rev. (1976) 76, 219. 6. "Transition Metal Hydrides," Muetterties, E. L., Ed., Marcel Dekker, Inc., New York 1971.


180 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.


17. 18. 19. 20. 21. 22.

TRANSITION METAL HYDRIDES

Braterman, P. S., Cross, R. J., Chem. Soc. Rev. (1973) 2, 271. Ruddick, J. D., Shaw, B. L., J. Chem. Soc. A (1969) 2969. Egger, K. W., J. Organomet. Chem. (1970) 24, 501. L'Eplattenier, F., Pelichet, C., Helv. Chim. Acta (1970) 53, 1091. George, R. D., Knox, S. A. R., Stone, F. G.A.,J. Chem. Soc., Dalton (1973) 972. Poliakoff, M., Turner, J. J., J. Chem. Soc., Dalton (1973) 1351. Poliakoff, M., Turner, J. J., J. Chem. Soc., Dalton (1974) 2276. Burdett, J. K., Chem. Soc., Faraday 2 (1974) 70, 1599. Elian, M., Hoffman, R., Inorg. Chem. (1975) 14, 1058. Evans, J., Okrasinski, S.J.,Pribula, A. J., Norton, J. R., J. Am. Chem. Soc. (1977) 99, 5835. Robiette, A. G., Hedberg, K., unpublished data. Churchill, M. R., DeBoer, B. G., Inorg. Chem. (1977) 16, 878. Evans, J., Norton, J. R., J. Am. Chem. Soc. (1974) 96, 7577. Cetini, G., Gambino, O., Sappa, E., Vaglio, G. Α., Atti Accad. Sci. Torino (1967) 101, 855. Cook, N., Smart, L., Woodward, P., J. Chem.Soc.,Dalton Trans. (1977) 1744. Wojcicki, Α., Adv. Organomet. Chem. (1973) 11, 88.

RECEIVED July 18, 1977. We thank the National Science Foundation for supporting this work.


Osmium Hydridoalkyls and Their Elimination Mechanisms

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