Mechanistic Studies Related to the Metal- Catalyzed Reduction of

12 Mechanistic Studies Related to the MetalCatalyzed Reduction of Carbon Monoxide to Hydrocarbons

Downloaded by UNIV LAVAL on June 13, 2017 | http://pubs.acs.org Publication Date: May 5, 1979 | doi: 10.1021/ba-1979-0173.ch012

CHARLES P. CASEY and STEPHEN M. NEUMANN Department of Chemistry, University of Wisconsin, Madison, WI 53706

Anionic metal formyl complexes are produced upon reaction of K HB[OCH(CH ) ] - with metal carbonyls. The formyl compounds can be observed in solution by H NMR (14-16 δ) and have been isolated as stable solids in several cases: (CH CH ) N {[3,5-(CH ) -C H O]3P}(CO) FeCHO is kinetically quite stable but decomposes upon heating to 70°C to (CO) FeH (E = 29.7 ±2 kcal mol ). No metal formyl compound can be observed in equilibrium with the corre sponding metal hydride. In contrast, the equilibrium be tween L(CO) FeCOCH - and (CO) FeCH - lies entirely on the side of the acetyl iron compound. Metal formyl com pounds can act as hydride donors to ketones, alkyl halides, and metal carbonyls. Metal carbene complexes react with molecular hydrogen, leading to reductive cleavage of the carbene ligand. +

3 2 3

1

+

3

2

-

4

3

2

6

3

3

-

-1

4

a

3

Metal Formyl Ti/Tetal

3

4

3

Complexes

f o r m y l complexes h a v e b e e n p r o p o s e d as i m p o r t a n t i n t e r m e d i a t e s i n the metal-catalyzed reduction of C O b y H

2

(1,2,3,4).

While

the i n s e r t i o n o f C O i n t o a l k y l a n d a r y l c a r b o n - m e t a l b o n d s is w e l l k n o w n ( 5 ) , t h e i n s e r t i o n of C O i n t o a m e t a l - h y d r o g e n b o n d t o g i v e a m e t a l f o r m y l c o m p l e x has n o t b e e n

observed.

( T h e intermediacy of metal

f o r m y l c o m p o u n d s i n t h e s u b s t i t u t i o n reactions been considered.)

of m e t a l h y d r i d e s has

T o ascertain the reasons f o r t h e f a i l u r e to observe m e t a l

f o r m y l c o m p l e x e s i n t h e reactions of m e t a l h y d r i d e s w i t h C O , w e h a v e d e v e l o p e d a n e w synthesis of m e t a l f o r m y l complexes a n d h a v e s t u d i e d their properties. 0-8412-0429-2/79/33-173-131$05.00/0 © 1979 American Chemical Society King; Inorganic Compounds with Unusual Properties—II Advances in Chemistry; American Chemical Society: Washington, DC, 1979.

132

INORGANIC

COMPOUNDS

WITH

UNUSUAL

C

PROPERTIES

II

0

I M—H

M—C H

metal hydride

metal formyl At

Synthesis and N M R Observation of Metal Formyl Complexes.


t h e outset of o u r research, the o n l y r e p o r t e d m e t a l f o r m y l c o m p l e x w a s [ ( C H ) P ] 2 N ( C O ) F e C H O - , w h i c h h a d been prepared b y C o l l m a n a n d 6

5

+

3

4

W i n t e r i n 1973 ( 9 )

f r o m acetic f o r m i c a n h y d r i d e a n d

Na Fe(CO) . 2

4

A t t e m p t s to extend this synthetic route to the p r e p a r a t i o n of m e t a l f o r m y l complexes f r o m ( C H ) F e ( C O ) - , C r ( C O ) - , ( C H ) P M n ( C O ) - , a n d 5

5

2

2

5

6

5

[ ( C H ) P ] M n ( C O ) - uniformly met w i t h failure 6

5

3

2

3

4

(10).

3

W e h a v e d e v e l o p e d a n e w synthesis of m e t a l f o r m y l c o m p o u n d s f r o m the a d d i t i o n of m e t a l t r i a l k o x y b o r o h y d r i d e s to m e t a l c a r b o n y l s

(10,11).

T h e f o r m y l p r o t o n c h a r a c t e r i s t i c a l l y a p p e a r s at v e r y l o w f i e l d , 14-16 8, i n t h e * H N M R s p e c t r u m of m e t a l f o r m y l complexes.

T h i s l o w field reso-

n a n c e has a l l o w e d us to r a p i d l y survey the reactions of t r i a l k o x y b o r o h y d r i d e s w i t h a series of m e t a l c a r b o n y l s . I n i t i a l l y , N a H B ( O C H ) " w a s +

3

3

u s e d as the b o r o h y d r i d e r e d u c i n g agent, b u t w e h a v e s u b s e q u e n t l y f o u n d that K H B ( 0 - i - P r ) " is a m o r e r a p i d a n d effective h y d r i d e d o n o r +

(10).

3

W e h a v e o b t a i n e d N M R e v i d e n c e f o r the f o r m a t i o n of m e t a l f o r m y l c o m p l e x e s i n the reactions of K H B ( 0 - i - P r ) - w i t h F e ( C O ) +

(C H 0) PFe(CO) 6

5

/ =

3

24);

8).

Cr(CO)

4

3

(14.8 8, d , / — 4 4 ) ; (15.2 8 ) ; W ( C O )

6

(C H ) PFe(CO) 6

(15.9

G

5

3

(14.9

5

8);

(15.5 8, d ,

4

8); a n d R e ( C O ) 2

I n some cases w e h a v e i s o l a t e d the m e t a l f o r m y l complexes.

(16.0

1 0

I n other

cases, s u c h a C r ( C O ) , the m a x i m u m o b s e r v e d c o n v e r s i o n to ( C O ) C r 6

5

C H O ~ w a s 7 6 % after 25 m i n at r o o m t e m p e r a t u r e , a n d the f o r m y l c o m p l e x u n d e r w e n t subsequent d e c o m p o s i t i o n w i t h a h a l f - l i f e of 40 m i n at r o o m temperature. Isolation of Stable Metal Formyl Complexes. T o d a t e w e h a v e isol a t e d a n d c h a r a c t e r i z e d the f o l l o w i n g stable m e t a l f o r m y l c o m p l e x e s : [(C H ) P] N (CO) FeCHO-, 6

5

3

+

2

(CH CH ) N [(C H 0) P](CO) FeCHO-,

4

3

2

+

4

6

5

3

3

( C H C H ) N [ ( 3 , 5 ( C H ) C H 0 ) P ] ( C O ) F e C H O " , and 3

2

+

4

3

2

6

3

3

3

(CH CH ) 3

2

4

N (CO) Re CHO-. +

9

2

Kinetic Stability of Metal Formyl Complexes.

Metal formyl com-

plexes h a v e a p p r o x i m a t e l y the same k i n e t i c s t a b i l i t y as t h e c o r r e s p o n d i n g m e t a l a c e t y l complexes.

T h e r m a l d e c o m p o s i t i o n of ( C H C H ) N [ ( C 3

2

4

+

6

H 0 ) P ] ( C O ) F e C H O - i n T H F at 6 5 ° C gives a m i x t u r e of t w o m e t a l 5

3

3

h y d r i d e s i n a 4 : 1 r a t i o : ( C O ) F e H " , f o r m e d b y loss of p h o s p h i t e a n d 4

King; Inorganic Compounds with Unusual Properties—II Advances in Chemistry; American Chemical Society: Washington, DC, 1979.

12.

CASEY

Mechanistic

AND NEUMANN

133

Studies

h y d r i d e m i g r a t i o n , a n d [ ( C H 0 ) P ] ( C O ) F e H ' , f o r m e d b y loss of C O 6

5

3

3

a n d h y d r i d e m i g r a t i o n . T h e d e c a r b o n y l a t i o n of t h e r e l a t e d t r i - ( 3 , 5 - d i methylphenyl)phosphite complex

(CH CH )4N [(ArO) P](CO) FeCHO3

+

2

3

3

p r o c e e d e d b y e x c l u s i v e loss of p h o s p h i t e to g i v e ( C O ) F e C H O ~ a n d 4

( A r O ) P as the o n l y o b s e r v e d p r o d u c t s . 3

[ ( C H 0 ) P ] ( C O ) F e C H O - -> ( C O ) F e H " + 6

5

8

3

4

[ ( C H 0 ) P ] (CO) F e H ~ 6

5

3

3

(1) [ ( A r 0 P ] ( C O ) F e C H O " -> ( C O ) F e H " + Downloaded by UNIV LAVAL on June 13, 2017 | http://pubs.acs.org Publication Date: May 5, 1979 | doi: 10.1021/ba-1979-0173.ch012

3

3

(ArO) P

4

(2)

3

A d e t a i l e d k i n e t i c s t u d y of R e a c t i o n 2 w a s c a r r i e d out. T h e rate of f o r m a t i o n of m e t a l h y d r i d e f r o m m e t a l f o r m y l c o m p l e x w a s f o l l o w e d b y * H N M R . F i r s t - o r d e r k i n e t i c s w e r e o b s e r v e d f o r R e a c t i o n 2 to m o r e t h a n t w o h a l f - l i v e s , i n d i c a t i n g that the rate of r e a c t i o n w a s i n d e p e n d e n t of t h e c o n c e n t r a t i o n of p h o s p h i t e . I n r e l a t e d experiments w e h a v e f o u n d t h a t t h e i n i t i a l rate of R e a c t i o n 2 is i n d e p e n d e n t of a d d e d p h o s p h i t e . O n l y the p h o s p h o r u s - c o n t a i n i n g species s h o w n i n R e a c t i o n 2 w e r e o b s e r v e d b y 3 1

P N M R . T h e h a l f - l i f e f o r d e c o m p o s i t i o n of

(CH CH ) N [(ArO) P]3

2

4

( C O ) F e C H O - i n T H F at 6 7 . 3 ° C w a s f o u n d to b e 1.1 h r . 3

+

3

Measurement

of the rate o f d e c o m p o s i t i o n of the m e t a l f o r m y l c o m p l e x over t e m p e r a t u r e r a n g e 4 7 ° - 7 9 ° C g a v e a n a c t i v a t i o n energy f o r the of 29.7 ±

2 kcal/mol. (Atf+ =

29.0 ±

the

process

1.5 k c a l , A S + — 7.9 ±

6.1 e u

at 6 3 ° C ) . T h e m e c h a n i s m of R e a c t i o n 2 is t h o u g h t to p r o c e e d b y

rate-deter-

m i n i n g phosphite dissociation followed b y r a p i d h y d r i d e migration f r o m the f o r m y l c a r b o n to i r o n . A n a l o g o u s m e c h a n i s m s f o r t h e d e c a r b o n y l a t i o n of m e t a l a c y l c o m p l e x e s h a v e b e e n d e m o n s t r a t e d ( 5 ) .

T h e fact that the

rate of R e a c t i o n 2 is i n d e p e n d e n t of p h o s p h i t e c o n c e n t r a t i o n

indicates

either that m i g r a t i o n of h y d r i d e f r o m the f o r m y l g r o u p to the m e t a l i n t h e c o o r d i n a t i v e l y u n s a t u r a t e d i n t e r m e d i a t e is either m u c h faster t h a n c a p t u r e of the i n t e r m e d i a t e b y p h o s p h i t e or that m i g r a t i o n of h y d r i d e f r o m t h e f o r m y l g r o u p to the m e t a l is c o n c e r t e d w i t h the loss of p h o s p h i t e f r o m starting material. CO

0

fast (CO) FeH"+ (ArO) P 4


3

134

INORGANIC

COMPOUNDS

WITH

UNUSUAL

PROPERTIES

II

T h e corresponding acetyl iron complex [ ( A r O ) P ] ( C O ) F e C O C H ~ 3

does n o t d e c a r b o n y l a t e

3

3

u n d e r the r e a c t i o n c o n d i t i o n s since the

acetyl

c o m p o u n d s are greatly f a v o r e d t h e r m o d y n a m i c a l l y r e l a t i v e to t h e m e t h y l i r o n c o m p o u n d ( C O ) F e C H " . H o w e v e r , the p h o s p h i t e e x c h a n g e of the 4

3

acetyl complex proceeds

v i a a coordinatively unsaturated

intermediate

v e r y s i m i l a r to t h a t p r o p o s e d i n the r a t e - d e t e r m i n i n g step of the d e c o m p o s i t i o n of the m e t a l f o r m y l c o m p l e x . T h e rate of e x c h a n g e of

(C H 0) P 6

5

3

exchange w i t h [ ( A r O ) P ] ( C O ) F e C O C H ~ (Reaction 3) was measured


3

(C H O) P + c

s

3

3

[(ArO) P](CO) FeC^

3

3

v

3

CH

(3)

(CO) Fe 8

CH

3

3

0 AarO) P + 3

[(C H O) P](CO) FeC c

s

3

3

*CH

by

3 1

3

P N M R . P r e l i m i n a r y k i n e t i c d a t a i n d i c a t e that the rate of R e a c t i o n

3 is a b o u t 20 times s l o w e r t h a n the rate of d e c o m p o s i t i o n of m e t a l f o r m y l complex i n Reaction

2

(kinetics

of the

ligand exchange reaction

of

L ( C O ) F e C O C H - h a v e b e e n m e a s u r e d ( 1 2 ) . ) T h u s , the f o r m y l g r o u p 3

6

5

a n d the a c e t y l g r o u p affect the l a b i l i t y of p h o s p h i t e l i g a n d s i n these i r o n complexes i n very similar ways. Equilibrium between Metal Formyl Complexes and Metal Hydrides. N o w that w e h a v e a n efficient route to m e t a l f o r m y l c o m p l e x e s , w e c a n s t u d y the t h e r m o d y n a m i c s t a b i l i t y of these c o m p l e x e s .

W e have f o u n d

that m e t a l f o r m y l s are m u c h less t h e r m o d y n a m i c a l l y stable t h a n corresponding metal hydrides.

T h u s , m e t a l f o r m y l species h a v e

the

never

b e e n o b s e r v e d i n the reactions of m e t a l h y d r i d e s w i t h C O because of t h e t h e r m o d y n a m i c i n s t a b i l i t y of the f o r m y l c o m p l e x e s a n d not b e c a u s e of their kinetic instability. The

equilibrium between

(CH CH ) N [ (ArO) P](CO) FeCHO3

2

4

+

3

a n d ( C H C H ) N ( C O ) F e H - w a s s t u d i e d b y 270 M H z 3

2

4

+

4

3

X

H N M R . At

e q u i h b r i u m , e v e n i n the p r e s e n c e of 1 . 5 M ( A r O ) P , there w a s no observ3


12.

CASEY

Mechanistic

AND NEUMANN

able metal f o r m y l complex.

135

Studies

Since 1 %

of the m e t a l f o r m y l c o m p o u n d

c o u l d h a v e b e e n detected, a l i m i t o n the e q u i l i b r i u m constant f o r R e a c t i o n 4 c a n be e s t i m a t e d : K

e q

=

{[(ArO) P](CO) FeCHO-}/[(CO)4FeH-]3

3

[ ( A r O ) P ] < 1.7 X 1 0 " M . T h i s corresponds to a free e n e r g y difference 2

3

_ 1

of at least 3.1 k c a l m o l " i n f a v o r of the m e t a l h y d r i d e . I n contrast,

the

1

equilibrium +

between

[ ( A r O ) P ] ( C O ) F e C O C H - and 3

3

3

(CO) FeCH " 4

8

( A r O ) P s t r o n g l y favors the a c y l i r o n c o m p o u n d . 3

( C O ) F e H - + (ArO) P^± [(ArO) P](CO) FeCHO"


4

3

3

(4)

3

T h e greatly different t h e r m o d y n a m i c stabilities of m e t a l a c y l a n d m e t a l f o r m y l c o m p o u n d s is p r o b a b l y a t t r i b u t a b l e to the greater strength of the M - H b o n d ( e s t i m a t e d 5 0 - 6 0 k c a l m o l " ) c o m p a r e d w i t h the M - C 1

b o n d ( e s t i m a t e d 3 0 - 4 0 k c a l m o l " ) . W e are n o w a t t e m p t i n g to measure 1

the heat of r e a c t i o n f o r the c o n v e r s i o n of a m e t a l - f o r m y l c o m p o u n d to a m e t a l h y d r i d e . T h i s w i l l a l l o w a m u c h better estimate

of the

energy

difference b e t w e e n a m e t a l f o r m y l c o m p l e x a n d a m e t a l h y d r i d e since the e n e r g y difference w a s too large to m e a s u r e b y e q u i l i b r a t i o n of the species. H y d r i d e Transfer Reactions of Metal Formyl Complexes. W e h a v e f o u n d that m e t a l f o r m y l complexes c a n act as h y d r i d e donors to electrop h i l e s s u c h as ketones, a l k y l h a l i d e s , a n d m e t a l c a r b o n y l s .

Et^Wtrans-

[ ( C H 0 ) P ] ( C O ) F e C H O " reacts w i t h 2 - b u t a n o n e o v e r n i g h t at a m b i e n t 6

5

3

3

t e m p e r a t u r e to g i v e a 9 5 % y i e l d of 2 - b u t a n o l . T h e p o s s i b i l i t y that 2-butan o n e is r e d u c e d b y ( C O ) F e H " f o r m e d i n s i t u f r o m d e c o m p o s i t i o n of the 4

m e t a l f o r m y l c o m p l e x is e x c l u d e d since the m e t a l f o r m y l c o m p l e x reacts w i t h 2-butanone

m u c h faster t h a n i t decomposes

to

( C O ) F e H " and 4

since no r e a c t i o n b e t w e e n ( C O ) F e H " a n d 2-butanone w a s o b s e r v e d b y 4

I R spectroscopy. R e a c t i o n of a T H F s o l u t i o n of E t N [ ( C H 0 ) P ] ( C O ) F e C H O " +

4

with C F C 0 H 3

2

(10 e q u i v a l e n t s )

6

5

3

3

l e d to the f o r m a t i o n of 2 7 %

and no observable formaldehyde ( < 5 % ) .

CH OH 3

M e t h a n o l m i g h t arise f r o m a c i d

c l e a v a g e of the m e t a l f o r m y l c o m p l e x to g i v e f o r m a l d e h y d e , w h i c h is s u b s e q u e n t l y r e d u c e d to m e t h a n o l b y h y d r i d e d o n a t i o n f r o m a s e c o n d e q u i v a l e n t of m e t a l f o r m y l c o m p l e x . A l t e r n a t i v e l y , m e t h a n o l c o u l d arise via

O - p r o t o n a t i o n to g i v e a h y d r o x y c a r b e n e c o m p l e x , w h i c h is

subse-

q u e n t l y r e d u c e d to a h y d r o x y m e t h y l c o m p l e x b y a s e c o n d e q u i v a l e n t of metal f o r m y l complex.

C l e a v a g e of the h y d r o x y m e t h y l c o m p l e x b y a c i d

w o u l d g i v e m e t h a n o l . E i t h e r of the t w o routes leads to a m a x i m u m 5 0 % y i e l d of m e t h a n o l . C o l l m a n a n d W i n t e r h a v e r e p o r t e d that

[(C H ) P]2N (CO) FeCHO-

reacts w i t h 1-iodo-octane to g i v e o c t a n e ( 7 5 % )

6

5

3

+

4

a n d a t r a c e of n o n a n a l ;

o c t a n e f o r m a t i o n w a s a t t r i b u t e d to d e c a r b o n y l a t i o n of [ ( C H i ) ( C H O ) 8

7


136

INORGANIC

COMPOUNDS

H

WITH

0 || C

+

>

/

5

3

H

>

II

+

>CH OH 3

4v

H

H

:0

Et N* [ (C H O) P] (CO) Fe-C 0

l

PROPERTIES

\

H

4

UNUSUAL

+

3


H

0-H

0H1 * —>[ ( C H 0 ) P ] ( C O ) F e - C H

/

[ (C H 0) P] (CO) Fe=C 6

5

3

3

c

5

3

3

2

F e ( C O ) ] , f o l l o w e d b y h y d r i d e m i g r a t i o n a n d r e d u c t i v e e l i m i n a t i o n of 4

octane ( 9 ) . (Ar =

W e h a v e f o u n d that E t N f m r w - [ ( A r O ) 3 P ] ( C O ) F e C H O +

4

3

3 , 5 - d i m e t h y l p h e n y l ) reacts w i t h n - C H i I w h e n s t i r r e d o v e r n i g h t 7

5

at a m b i e n t t e m p e r a t u r e i n T H F to g i v e n - C H i 7

( O A r ) ; less t h a n 0 . 2 % 3

6

(71% ) and ( C O ) F e P 4

n - C H i C H O was observed. 7

Since f o r m y l com-

5

plexes a p p e a r to f u n c t i o n as h y d r i d e donors, w e p r o p o s e that h e p t a n e is f o r m e d b y n u c l e o p h i l i c d i s p l a c e m e n t of i o d i d e b y the f o r m y l h y d r o g e n atom. Transformylation Reactions.

M e t a l f o r m y l complexes can

transfer

h y d r i d e to m e t a l c a r b o n y l c o m p o u n d s to p r o d u c e n e w m e t a l f o r m y l c o m plexes.

T h e s e " t r a n s f o r m y l a t i o n " reactions c a n b e u s e d to d e t e r m i n e the

r e l a t i v e s t a b i l i t y of a series of m e t a l f o r m y l complexes. E t N [ ( C H 0 ) P ] ( C O ) F e C H O - with R e ( C O ) 4

+

6

5

3

3

2

1 0

T h e r e a c t i o n of

i n T H F - 4 was fol-

l o w e d b y * H N M R . T h e characteristic d o u b l e t at 14.9 8 c a u s e d b y the i r o n f o r m y l c o m p l e x is r a p i d l y r e p l a c e d b y a singlet at 16.04 8 a t t r i b u t e d to E t N d s - ( C O ) R e C H O ~ , f o r m e d i n 8 2 % 4

+

9

N M R integration.

2

y i e l d as d e t e r m i n e d

by

( C O ) F e [ P ( O C H ) ] w a s d e t e c t e d b y I R as a co4

6

5

3

p r o d u c t of the r e a c t i o n . The

rhenium f o r m y l complex was

independently synthesized

r e a c t i o n of K H B ( C M - P r ) " w i t h R e ( C O ) i +

3

2

0

by

i n T H F at 0 ° C , f o l l o w e d b y

a q u e o u s basic w o r k u p a n d c a t i o n e x c h a n g e w i t h E t N B r " . 4

crystallized f r o m T H F - h e x a n e , and isolated i n 3 2 %

+

It w a s re-

y i e l d as a y e l l o w ,

air-stable s o l i d . T r a n s f o r m y l a t i o n reactions b e t w e e n v a r i o u s m e t a l f o r m y l a n d m e t a l c a r b o n y l c o m p o u n d s i n d i c a t e the f o l l o w i n g o r d e r o f s t a b i l i t y of f o r m y l


12.

CASEY

complexes

Mechanistic

AND NEUMANN

137

Studies

relative to their metal carbonyl precursors:

[(C H ) P] N 6

5

3

+

2

(CO) FeCHO- > Et N (CO) Re CHO- > Et N fmrw-[(C H 0) P](CO)34

+

4

FeCHO".

9

2

+

4

T h e possibility that

these

6

5

transformylations

3

proceed v i a

d e c a r b o n y l a t i o n to g i v e a m e t a l h y d r i d e , w h i c h t h e n transfers h y d r i d e t o a m e t a l c a r b o n y l , is e x c l u d e d since t h e r e a c t i o n of E t N [ ( C H 0 ) P ] +

4

( C O ) F e C H O - with R e ( C O ) i 3

2

or F e ( C O )

0

6

5

3

is faster t h a n its d e c o m -

5

p o s i t i o n t o ( C O ) F e H " a n d since E t N ( C O ) F e H " does n o t r e a c t w i t h 4

4

R e ( C O ) i o or ( C O ) F e P ( O C H ) 2

4

6

5

3

+

4

under the reaction conditions.

[ ( C H 0 ) P ] (CO) F e C H O " + R e (CO) 6

5

3

3

2

1 0


It (C H 0) PFe(CO) 6

5

3

4

+

(CO) Re CHO- + 9

Fe(CO)

2

5

It Re (CO)i + 2

Hydrogenation

of Metal Carbene

0

(CO) FeCHO" 4

Complexes

W e h a v e s t u d i e d t h e r e a c t i o n of m o l e c u l a r h y d r o g e n w i t h t r a n s i t i o n m e t a l c a r b e n e complexes

as a m o d e l f o r t h e t e r m i n a t i o n step i n t h e

synthesis of h y d r o c a r b o n s a n d alcohols f r o m C O a n d h y d r o g e n ( 1 3 ) .

H

R'

W e h a v e f o u n d that r e a c t i o n o f ( C O ) W C ( C H ) w i t h H 5

at 1 0 0 ° C

gives

CH (C H ) 2

(CO) WC(C H ) 5

6

5

2

e x c h a n g e studies. atm)

6

5

2

6

i n 4 0 % yield.

5

2

U n d e r these

2

(69 a t m )

conditions,

undergoes r a p i d C O d i s s o c i a t i o n as s h o w n b y Similarly ( C O ) W C ( O C H ) C H 5

3

6

5

reacts w i t h H

at 1 4 0 ° C t o g i v e m e t h y l b e n z y l ether i n 9 2 % y i e l d .

1 3

2

CO

(1.8

Alkenes a n d

ketones present as s i d e - c h a i n g r o u p s i n t h e m e t a l - c a r b e n e c o m p l e x e s a r e n o t r e d u c e d u n d e r these r e a c t i o n c o n d i t i o n s . Apparently, the reaction

does n o t i n v o l v e a m e t a l

hydrogenation

catalyst b u t i n v o l v e s a s t o i c h i o m e t r i c r e a c t i o n of m o l e c u l a r h y d r o g e n w i t h CeH (CO) W=/ 5

CeH

5

H

\

CeHs

a

>

5

C H , 2 C H 6

5


INORGANIC

COMPOUNDS

WITH

UNUSUAL PROPERTIES


138


II

12.

CASEY

A N D NEUMANN

a coordinatively unsaturated

Mechanistic

Studies

139

metal carbene complex. T h i s implies that

photochemical hydrogenation of carbene complexes c a n b e accomplished u n d e r m i l d c o n d i t i o n s since p h o t o l y s i s o f t h e m e t a l c a r b e n e c o m p l e x c a n lead to the same coordinatively unsaturated

intermediate.

Preliminary

e x p e r i m e n t s i n d i c a t e that p h o t o c h e m i c a l h y d r o g e n a t i o n c a n o c c u r b e l o w room temperature.

Acknowledgment S u p p o r t f r o m t h e D i v i s i o n o f B a s i c E n e r g y Sciences o f t h e D e p a r t -


m e n t o f E n e r g y is g r a t e f u l l y a c k n o w l e d g e d .

Literature Cited 1. Henrici-Olivé, G., Olivé, S., Angew. Chem. Int. Ed. Engl. (1976) 15, 136. 2. Vannice, M. A., J. Catal. (1975) 37, 449, 462. 3. Storch, H. H., Golumbic, N., Anderson, R. B., "The Fischer-Tropsch and Related Synthesis," Wiley, New York, 1951. 4. P. H. Emmett, Ed., "Catalysis," Vol. 4, Reinhold, New York, 1956. 5. Calderazzo, F., Angew. Chem., Int. Ed. Engl. (1977) 16, 299. 6. Byers, B. H., Brown, T. L., J. Organomet. Chem. (1977) 127, 181. 7. Berry, A., Brown, T. L., J. Organomet. Chem. (1971) 33, C67. 8. Basolo, F., Pearson, R. G., "Mechanisms of Inorganic Reactions," 2nd ed., p. 555, Wiley, New York, 1967. 9. Collman, J. P., Winter, S. R., J. Am. Chem. Soc. (1973) 95, 4089. 10. Casey, C. P., Neumann, S. M., J. Am. Chem. Soc. (1976) 98, 5395. 11. Winter, S. R., Cornett, G. W., Thompson, E . A., J. Organomet. Chem. (1977) 133, 339. 12. Conder, H. L., Darensbourg, M. Y., Inorg. Chem. (1974) 13, 506. 13. Casey, C. P., Neumann, S. M., J. Am. Chem. Soc. (1977) 99, 1651. RECEIVED February 22, 1978.


Mechanistic Studies Related to the Metal- Catalyzed Reduction of

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