Mechanisms of Inorganic Reactions

8 Insertion Reactions of Metal Complexes RICHARD F. HECK

Downloaded by UNIV OF MICHIGAN ANN ARBOR on February 18, 2015 | http://pubs.acs.org Publication Date: January 1, 1965 | doi: 10.1021/ba-1965-0049.ch008

Hercules Powder Co., Wilmington,

Del., 19899

The

insertion reaction

is e n c o u n t e r e d

with

surprising frequency in organometallic c h e m istry.

Many

undergo metal

types

the

compounds.

containing

of unsaturated molecules

reaction

with

For

many

example,

metal-hydrogen,

different compounds

metal-carbon,

metal-oxygen, metal-nitrogen, metal-halogen, a n d metal-metal bonds have reacted or

more

of t h e

pounds:

carbon

acetylenes,

with

one

following unsaturated commonoxide,

carbonyl

olefins, dienes,

compounds,

and

cya-

n i d e s . T h e r e are still m a n y g a p s i n o u r k n o w l e d g e o f t h e i n s e r t i o n r e a c t i o n , but a l r e a d y i t has

been

applied in

numerous

unusual

and

useful chemical syntheses.

J h e r e a c t i o n m e c h a n i s m of t h e v a r i o u s m e t a l c o m p l e x e s c l e a r l y h a v e m u c h i n common.

T h e r e c e n t l y recognized

i n s e r t i o n r e a c t i o n a p p e a r s t o be a p a r t i

c u l a r l y g o o d e x a m p l e of a r e a c t i o n w h i c h is g e n e r a l a m o n g t h e m e t a l

compounds.

I n t h e f o l l o w i n g d i s c u s s i o n I i n t e n d t o p o i n t o u t t h e g e n e r a l i t y of t h e i n s e r t i o n reaction w i t h examples from the literature a n d from our o w n work. c o m p l e t e series of s u b s t a n t i a t e d c a r b o n y l complexes,

insertion reactions

involves

T h e most

the

organocobalt

a n d these r e a c t i o n s w i l l f o r m t h e n u c l e u s of t h e d i s c u s s i o n .

T h e i n s e r t i o n r e a c t i o n is t h e a d d i t i o n of a c o v a l e n t m e t a l c o m p o u n d , M - X , t o a neutral unsaturated molecule,

: Y , forming a new complex where the unsaturated

m o l e c u l e h a s i n s e r t e d i t s e l f between t h e m e t a l a n d t h e a t o m w h i c h w a s i n i t i a l l y bonded to the metal. M-Z T h e unsaturated molecule

+

:Y

->

(1)

M - Y - Z

: Y m a y be c a r b o n m o n o x i d e , a n olefin, a

diene, a n acetylene, a carbonyl compound,

various unsaturated

c o m p o u n d s , o r p r o b a b l y a n y of s e v e r a l o t h e r u n s a t u r a t e d m a t e r i a l s . p a r t of t h e c o v a l e n t m e t a l c o m p o u n d

is u s u a l l y a m e t a l - h y d r o g e n ,

metal-oxygen, metal-halogen, metal-nitrogen, or metal-metal group.

conjugated

carbon-nitrogen T h e reactive metal-carbon, T h i s reaction

181

In Mechanisms of Inorganic Reactions; Kleinberg, J., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1965.

M E C H A N I S M S O F I N O R G A N I C REACTIONS

182

i s a c t u a l l y a s p e c i a l case of a n a d d i t i o n r e a c t i o n i n w h i c h t h e m o l e c u l e t h a t i s a d d i n g is a covalent metal compound.

Since the covalent m e t a l c o m p o u n d is completely

a d d e d i n one s t e p , a c i s a d d i t i o n i s e x p e c t e d . T h e i n s e r t i o n r e a c t i o n i s u s u a l l y m o r e c o m p l i c a t e d t h a n e q u a t i o n (1) w o u l d indicate.

T h e e v i d e n c e n o w a v a i l a b l e suggests t h a t M - X m u s t be c o o r d i n a t e l y

unsaturated i n order t o react w i t h : Y .

T h e r e f o r e , before t h e i n s e r t i o n r e a c t i o n c a n

occur, a p r e l i m i n a r y step is often required to f o r m M - Z f r o m a coordinately s a t u r a t e d species.

F u r t h e r m o r e , t h e i n s e r t i o n r e a c t i o n m a y n o t go t o c o m p l e t i o n o r


m a y n o t e v e n go a t a l l , unless t h e r e i s a n o t h e r l i g a n d m o l e c u l e p r e s e n t t o f o r m a s t a b l e , c o o r d i n a t e l y s a t u r a t e d c o m p o u n d f r o m M - Y - Z as t h e final p r o d u c t .

Carbon

Monoxide

Insertion

Metal H y d r i d e s . reduction

Reaction

T h e simplest reactions i n this group are the various catalytic

reactions

of

carbon

monoxide.

Methane

or

higher

hydrocarbons,

m e t h a n o l o r h i g h e r a l c o h o l s , a n d a v a r i e t y of o t h e r o x y g e n a t e d o r g a n i c c o m p o u n d s m a y be f o r m e d , d e p e n d i n g u p o n t h e c a t a l y s t a n d r e a c t i o n c o n d i t i o n s (23).

There

i s l i t t l e e v i d e n c e a b o u t t h e m e c h a n i s m of these r e a c t i o n s , b u t t h e i n i t i a l s t e p i n e v e r y example is p r o b a b l y a carbon monoxide insertion i n t o a m e t a l hydride, followed b y reduction reactions. Ο ΜΗ

+

CO

^±

Ο

M C H

M H

+

H C H

(2)

O M H

+

H C H

^±

MCH OH — ^

M H

2

+

(3)

CH3OH

T h e h y d r i d e i n v o l v e d i s p r o b a b l y o n t h e s u r f a c e of t h e c a t a l y s t . A s i m i l a r m e c h a n i s m m a y e x p l a i n t h e f o r m a t i o n of f o r m a t e esters i n t h e h y d r o f o r m y l a t i o n r e a c t i o n (90, 64). Ο

I HCo(CO)

4

+

CO

^

Ο

HCCo(CO)

(4)

4

Ο

II

li

HCCo(CO)

4

-f

ROH

Metal-Carbon Compounds.

-»

HCOR

+

HCo(CO)

(S)

4

T h e e x i s t e n c e of t h e i n s e r t i o n r e a c t i o n a n d , i n

f a c t , t h e first c o n v i n c i n g e x a m p l e of i t , w a s r e p o r t e d b y C o f f i e l d a n d c o - w o r k e r s i n 1957.

T h e y showed that alkylmanganese pentacarbonyls would absorb

monoxide,

sometimes

reversibly, to

form acylmanganese

T h e y f u r t h e r s h o w e d i n 1959 (17), b y m e a n s of C

1 4

carbon

pentacarbonyls

(16).

labeled C O , t h a t w i t h m e t h y l -

manganese pentacarbonyl, a coordinated carbon monoxide inserted rather t h a n the incoming carbon monoxide. / - C O

/

I

CH —Mn(CO) 8

4

+

C*0

-

CH COMn(C*0) 3

5


(6)

8.

HECK

Insertion

Reaction*

183

These reaction rates have been measured, but the d a t a do not distinguish between t w o l i k e l y m e c h a n i s m s (14).

A n i m p o r t a n t q u e s t i o n , therefore, i s u n a n s w e r e d :

does t h e c o o r d i n a t e d c a r b o n y l g r o u p i n s e r t before t h e n e w C O is a d d e d o r does t h e i n c o m i n g C O push the coordinated c a r b o n y l i n t o the a c y l position? T h e m e c h a n i s m of t h e reverse r e a c t i o n , t h e e l i m i n a t i o n of C O f r o m a n a c y l m e t a l c a r b o n y l to form a n a l k y l m e t a l c a r b o n y l , is also not clear.

T w o possibilities exist:

the acylmetal carbonyl m a y s i m p l y dissociate into a coordinately unsaturated a c y l m e t a l complex a n d C O a n d then rearrange to the a l k y l m e t a l c a r b o n y l :


-co RCOMn(CO)

^ ~

5

RCOMn(CO)

4

->

RMn(CO)

(7)

5

or, t h e a c y l c a r b o n y l m a y b e c o m e a c o o r d i n a t e d c a r b o n y l as a n o t h e r c a r b o n y l g r o u p departs.

i f RCOMn(CO) ^^-"^

— R M n ( C O )

4

T h e a l k y l c o b a l t tetracarbonyls react completely monoxide, forming acylcobalt tetracarbonyls RCo(CO)

+

4

T h e r e a c t i o n is r e v e r s i b l e (33).

CO

(8)

6

analogously w i t h

carbon

(43).

^±

RCOCo(CO)

(9)

4

T h e cobalt derivatives are considerably more

reactive t h a n the corresponding manganese compounds.

Acetylcobalt tetracar-

b o n y l dissociates a b o u t 2250 times more r a p i d l y t h a n the corresponding a c e t y l m a n g anese p e n t a c a r b o n y l does (33). T h e g e n e r a l i t y of t h e c a r b o n m o n o x i d e i n s e r t i o n r e a c t i o n is c l e a r f r o m r e p o r t s t h a t m e t h y l c y c l o p e n t a d i e n y l i r o n d i c a r b o n y l (16), num

t r i c a r b o n y l (66),

ethylcyclopentadienylmolylbde-

alkylrhenium pentacarbonyls

c a r b o n y l b i s p h o s p h i n e s (34),

alkylrhodium dihalo

(50),

a l l y l n i c k e l d i c a r b o n y l h a l i d e s (35),

and

mono-and

d i - a l k y l d e r i v a t i v e s of t h e n i c k e l , p a l l a d i u m , a n d p l a t i n u m b i s p h o s p h i n e h a l i d e s (9), also undergo the reaction.

T h e r e a c t i o n of G r i g n a r d reagents (24), a n d of b o r o n

a l k y Is (51) w i t h c a r b o n m o n o x i d e p r o b a b l y t a k e s p l a c e b y t h e same m e c h a n i s m . W h e t h e r c o o r d i n a t i o n of t h e c a r b o n m o n o x i d e is r e q u i r e d before i n s e r t i o n c a n t a k e p l a c e i n a l l these e x a m p l e s is n o t c l e a r .

B u t since i t is r e q u i r e d i n t h e a l k y l -

m a n g a n e s e p e n t a c a r b o n y l r e a c t i o n , i t is n o t u n r e a s o n a b l e t o e x p e c t t h e same t o be t r u e i n t h e o t h e r cases. A s expected, coordinating molecules other t h a n C O can react a n d result i n the s h i f t of a c o o r d i n a t e d C O t o a n a c y l C O . with

alkylmanganese pentacarbonyls

to

C y c l o h e x y l a m i n e , for e x a m p l e , r e a c t s produce acylmanganese

tetracarbonyl

c y c l o h e x y l a m i n e c o m p l e x e s (59). RMn(CO)

6

+

C H NH 6

U

->

2

RCOMn(CO) (C H NH ) 4

6

u

2

(10)

S i m i l a r l y , a l k y l c o b a l t t e t r a c a r b o n y l s r e a c t w i t h t r i p h e n y l p h o s p h i n e (44, 45)

or

w i t h p h o s p h i t e s (36) t o g i v e h i g h y i e l d s of a c y l c o b a l t t r i c a r b o n y l t r i p h e n y l p h o s phines or phosphites. RCo(CO)

4

+

PR

3

—

RCOCo(CO) PR 3

3


(11)

184

M E C H A N I S M S O F I N O R G A N I C REACTIONS Metal-Oxygen Compounds.

A

few

examples

of t h e

m o n o x i d e i n t o m e t a l - o x y g e n g r o u p s h a v e been r e p o r t e d .

i n s e r t i o n of

carbon

T h e best k n o w n i s t h e

r e a c t i o n of m e c u r i c a c e t a t e i n m e t h a n o l s o l u t i o n w i t h c a r b o n m o n o x i d e , f o r m i n g m e t h o x y c a r b o n y l m e r c u r i c a c e t a t e (83) w h i c h p r o b a b l y i n v o l v e s t h e f o l l o w i n g s t e p s (32): CH COOHgOCOCH 3

+

3

CH OH 3

CH COOHgOCH 3

+

3

—

CH COOHgOCH 3

CO

->

+

3

HOCOCH

CH COOHgCOOCH 3

(12)

3

(13)

3


T h e f o r m a t i o n of f o r m a t e esters i n t h e h y d r o f o r m y l a t i o n r e a c t i o n (90, 64) m a y b e e x p l a i n e d b y a C O - a l k o x i d e i n s e r t i o n r e a c t i o n as w e l l a s b y t h e C O - h y d r i d e insertion mechanism mentioned above.

A l d e h y d e s formed i n the h y d r o f o r m y l a t i o n

r e a c t i o n c a n be r e d u c e d b y c o b a l t h y d r o c a r b o n y l (27) p r e s u m a b l y b y w a y of a n a d d i t i o n of t h e h y d r i d e t o t h e c a r b o n y l g r o u p (90, 2).

If the intermediate i n the

reduction is a n a l k o x y c o b a l t c a r b o n y l , carbon monoxide

insertion followed

by

h y d r o g é n a t i o n w o u l d g i v e f o r m a t e esters (90, 64). RCHO

+

RCH OCHO

+

2

HCo(CO)

HCo(CO)

^±

RCH OCo(CO) II llCO

(CH ) COCo(CO) 3

3

4

|CO (CH ) COCOCo(CO) P(C H ) 3

3

3

6

5

3

+

C O

2

CO

ROH

CH2=CHC00R

+

2

~CH =CHCONi(CO) X

CO

CH2=CHC0X

(53)

HNi(CO) X

+

Ni(CO)

CH2=CHC0X

2

2

4

+

ROH

CH2=CHCOOR

+

H X

(54)


I t h a s been v e r y d i f f i c u l t t o o b t a i n d i r e c t e v i d e n c e o n t h e m e c h a n i s m of t h e a c r y l a t e s y n t h e s i s because t h e i n t e r m e d i a t e c o m p o u n d s a r e e x t r e m e l y r e a c t i v e . B o r o n (13) a n d a l u m i n u m h y d r i d e s (104) a d d cis t o a c e t y l e n e s , f o r m i n g s u b stituted vinylmetal compounds.

H y d r o l y s i s of these c o m p o u n d s p r o v i d e s a r o u t e

t o cis-olefins. "" B He

+

2

2

1

6C HÔC=CC H5 2

C H5~]

C2H5

/

2B — C = C

*

2

\ H

I

(55)

H+

C H§

C2H5

2

\

/

/

c=c

\

H

H

Metal-carbon compounds

Metal-Carbon Compounds. also.

J;

add

to

acetylenes

A l k y l - or acyl-cobalt carbonyls undergo insertion reactions readily w i t h a

large v a r i e t y of a c e t y l e n e s .

D i s u b s t i t u t e d acetylenes a n d highly branched mono-

a c e t y l e n e s g i v e m a i n l y a single t y p e of p r o d u c t , τ τ - b u t e n o l a c t o n y l c o b a l t t r i c a r b o n y l d e r i v a t i v e s (34).

F o r example, acetylcobalt t e t r a c a r b o n y l a n d 3-hexyne react i n a

few h o u r s a t r o o m t e m p e r a t u r e t o g i v e a g o o d y i e l d of 2,3-diethyl-x-(2, 4 ) - p e n t e n o 4-lactonyl cobalt tricarbonyl, I X .

T h e r e a c t i o n seems t o i n v o l v e t h e i n s e r t i o n

of t h e a c e t y l e n e b e t w e e n t h e a c e t y l a n d c o b a l t t r i c a r b o n y l g r o u p s , p e r h a p s b y w a y of a n i n t e r m e d i a t e ττ-complex ( V ) , t o g i v e c o m p l e x V I .

T h i s complex can then undergo

a C O i n s e r t i o n r e a c t i o n , f o r m i n g V I I w h i c h p r o b a b l y e x i s t s as t h e 7 r - a c r y l y l t y p e complex ( V I I I ) .

T h e latter c o m p o u n d can then cyclize b y a t h i r d insertion reac

tion ; this t i m e the terminal a c y l c a r b o n y l inserts between the other a c y l group a n d the cobalt tricarbonyl group, producing the observed product, I X .

CH COCo(CO) 3

^

4

CH COCo(CO) 3

3

+

(56)

CO

C H§C= CC He 2

2

1 CH COCo(CO) 3

3

+

C H C=CC H 2

6

2

6

^

|_CH COCo(CO) J 3

3

V


196

M E C H A N I S M S O F I N O R G A N I C REACTIONS (57) C2H5C2H5

CH COC=C—Co(CO) 3

3

VI C H5C Hg

C2H5C2H5

2

CH COC=CCo(CO) 3

+

3

CO

^

2

CH COC=CCOCo(CO) 3

3


VII Ο COCH

C2H5 QHg

1

/ 0 Ηδ

CH

2

3

/ l \ CO

c

\

C H C 2

Co(CO)

5

Co CO

3

\ /

\ CO

3

/

c

IX

(58)

ο

T h e final p r o d u c t c a n be i s o l a t e d e a s i l y as t h e t r i p h e n y l p h o s p h i n e c o m p l e x . VIII T h i s r e a c t i o n is a l s o general as f a r as t h e a c y l c o b a l t c a r b o n y l is c o n c e r n e d , b u t t h e y i e l d s v a r y w i d e l y d e p e n d i n g u p o n w h i c h a c e t y l e n e i s u s e d (34).

Presumably, the

presence of s u b s t i t u e n t s o n t h e a c e t y l e n e f a v o r s t h e c y c l i z a t i o n step r a t h e r t h a n t h e f o r m a t i o n of l i n e a r p r o d u c t s . t h e c y c l i z a t i o n becomes. compounds formed.

T h e larger t h e s u b s t i t u e n t s t h e m o r e f a v o r a b l e

If c y c l i z a t i o n does n o t t a k e place r e l a t i v e l y r a p i d l y , l i n e a r

a n d p o l y m e r s of a c e t y l e n e ,

o r of a c e t y l e n e

a n d C O are

probably

T h u s , these r e a c t i o n s d e m o n s t r a t e t h e i n s e r t i o n r e a c t i o n of b o t h a c e t

ylenes a n d ketonic c a r b o n y l groups. A n o t h e r c l e a r e x a m p l e of a n a c e t y l e n e i n s e r t i o n r e a c t i o n w a s r e p o r t e d C h i u s o l i (15).

H e observed

by

t h a t a l l y l i c halides react c a t a l y t i c a l l y w i t h n i c k e l

c a r b o n y l i n a l c o h o l i c s o l u t i o n , i n t h e presence of C O a n d a c e t y l e n e , t o f o r m esters of cis-2,5-hexadienoic

acid.

T h e intermediate i n this reaction is v e r y p r o b a b l y a

i r - a l l y l n i c k e l c a r b o n y l h a l i d e , X , w h i c h t h e n undergoes a c e t y l e n e i n s e r t i o n f o l l o w e d b y C O i n s e r t i o n a n d a l c o h o l y s i s o r a c y l h a l i d e e l i m i n a t i o n (35).

Acetylene is

o b v i o u s l y a c o n s i d e r a b l y b e t t e r i n s e r t i n g g r o u p t h a n C O i n t h i s r e a c t i o n since w i t h a c e t y l e n e a n d C O , t h e h e x a d i e n o a t e is t h e o n l y p r o d u c t , w h e r e a s , w i t h o n l y C O , t h e 3 - b u t e n o a t e ester is f o r m e d (15).

[See R e a c t i o n 59].

R e a c t i o n 59 differs f r o m t h e c o b a l t - a c e t y l e n e i n s e r t i o n m e n t i o n e d a b o v e b e cause t h e c o b a l t prefers t o i n s e r t C O before t h e a c e t y l e n e , a n d t h e n i c k e l t h e reverse. W h e t h e r o r n o t t h i s difference results f r o m specific effects of t h e i r - a l l y l n i c k e l s y s t e m is n o t k n o w n ; b u t i t is a g o o d p o s s i b i l i t y since t h e a l l y l i c d o u b l e b o n d i s p r o b a b l y c o o r d i n a t e d t o t h e n i c k e l t h r o u g h o u t the r e a c t i o n .


8.

HECK

Insertion

CH2=CHCH X

+

2

Reactions

Ni(CO)

197

^±

4

CH2==CHCH Ni(CO) X 2

+

2

2C0


—CO H

CH —CH=CH 2

\

2

/ CH

2

X/

CO

\

CH

2

X

X

CH2=CH—CH

COOR

2

2COI

\

/

/

c=c

Η CH =CH- CH 2

r

+

HX

+

Ni(CO)

\ Η

COX

2

\

/ G=C

Η

+

Ni(CO)

4

Η

IROH CH2=CH—CH

COOR

2

\ / Η

c=c

+

HX

/ \ Η


4

(59)

198

M E C H A N I S M S O F I N O R G A N I C REACTIONS T h e f o r m a t i o n of t h e b u t e n o l a c t o n e c o m p l e x , X I I , b y t h e a c t i o n of c a r b o n

m o n o x i d e o n a c e t y l e n e d i c o b a l t h e x a c a r b o n y l c o m p l e x e s , X I , (89) seems t o be a closely related reaction.

I t p r o b a b l y involves the following steps :

R (CO) Co-

-Co(CO)


3

3

+

R

I I

3CO

(CO) CoCOC=CCOCo(CO) I* 4

c

8

ι ι

R

(60)

XI R R—C-

-C=0

I

_ R — C

R—C

• \

Ο

\ /

R—C

c

c

Co(CO)

/ \

(CO) Co

Co(CO)

3

Co(CO)

3

3

c I ο

/ \

(CO) Co

4

c

-c=o

R—C-

I

COCo(CO)

4

3

\ /

cο XII U n d e r more vigorous conditions, complex X I I can a p p a r e n t l y a d d more acetyl ene a n d c a r b o n m o n o x i d e , f o r m i n g a b i f u r a n d i o n e , X I I I ( I , 79, 82).

A reasonable

m e c h a n i s m for t h e d i o n e f o r m a t i o n w o u l d be a C O i n s e r t i o n , t h e n a n a c e t y l e n e i n sertion, a n d another C O insertion, followed b y cyclization b y ketone insertion, a n d finally

a Co2(CO) elimination. 8

XII

+

CO

H—cH—c

H—C

-c=o b

C H 2

(co)^^ \:ocorco)8

C=0

« 2

H—C

A O

y

(CO)4Co

^ COCH=CHCo(CO)t CO

-c=o

H—C-

II H—C Cos(CO)

8

+

\

C

/

H—C-

(CO)4Co^C

c

XIII

/ /

C—Co(CO)4

ο / \ co=
CH

(62)

3

I 1,3,5-(CH ) C H C=CHCH 3

3

6

2

3

Trimethylchromium reacts with diphenylacetylene to give hexaphenylbenzene and tetraphenylcyclopentadiene.

T h e latter compound may have been formed by

insertions and a cyclization reaction (97).


Several cyclopentadienyl (alky 1)metal carbonyl derivatives have reacted with acetylenes. the

In some examples, insertion reactions may also be involved, although

mechanisms

have

not

been

investigated.

Cyclopentadienyl (methyl)iron

dicarbonyl with diphenylacetylene gave a 1 0 % yield of cyclopentadienyltetraphenylcyclopentadienyliron (71). CO

I Fe—CH

3

+

C H C=CC H e

5

e

6

-

I CO CeHi

,

y

CgHe

\

I

/ CeHs Similarly, acetylene itself gave ferrocene.

(63)

ι CeHs

Cyclopentadienyl(methyl)molybdenum

tricarbonyl reacted with diphenylacetylene to produce some tetraphenylcyclopen tadiene.

T h e corresponding ethylmolybdenum derivative gave some tetraphenyl-

methylcyclopentadiene.

T h e cyclizations involved in these reactions and

the

trimethylchromium reaction above are quite unusual and certainly deserve further study. Wilke has shown that aluminum alkyls add readily to acetylenes, giving the expected adducts (105). (CîHe),Al

+

HC==CH

->

(C H )2A1CH=CHCH CH 2

5

2

3

(64)

T h e reported addition of triphenylaluminum to diphenylacetylene to form 1, 2, 3triphenylbenzaluminole (22) is another clear example of an acetylene insertion, this one being followed by a cyclization reaction. C H —C— e

C H CsCC H 6

6

e

6

+

(C H ) Al e

6

3

-

6

C H —C e

II

6

I

(65)

\ / V Al

I CeHg T h e polymerization of acetylene by Ziegler catalysts very likely involves metal alkyl-acetylene insertion reactions also (26).


M E C H A N I S M S O f I N O R G A N I C REACTIONS

200

#-Butyllithium has been added to diphenylacetylene, but the reaction is com


plicated by metalation of the aromatic system (69).

COt 2-n-C H»Li 4

+

C H C=CC H 6

6

e

5

(66)

C H 4

9

Ο

COOH

^X/Vc.H.

+

V

Metal-Oxygen Compounds.

Clear examples of the addition of transition

metal alkoxides to acetylenes are not known; however, the addition of trialkyltin alkoxides has been reported.

Triethyltin methoxide,

for example, reacts with

dimethyl acetylenedicarboxylate to give the vinyltin derivative X V I (C H )3SnOCH3 2

6

+

CH OCOC=CCOOCH 3

(63).

-*

3

COOCH

8

(C H ) SnC=C—COOCH3 2

5

8

OCH, (67)

XIV Metal-Halogen Compounds.

Mercuric salts react readily with acetylenes,

forming various products, depending upon the salt and reaction conditions.

Mer

curic chloride appears to undergo a clean insertion reaction with acetylene, giving aj-2-chlorovinylmercuric chloride in the vapor phase (72,

73).

CI 120°C. HgCl

2

+

HC=CH

HgCl \

•

/

(68)

c=c / Η

\ Η


8.

HECK

Insertion

Reactions

201

In solution, the trans isomer is produced, presumably because external chloride ion is adding to the acetylene-mercuric chloride x-complex (72, Compounds

with M e t a l — M e t a l Bonds.

metal-metal bonds to acetylenes are rare.

Additions

of

73). compounds

with

Perhaps the addition of acetylenes to

cobalt octacarbonyl (29) should be considered an insertion reaction even though the metal-metal bond is not broken since the acetylene finally is bonded to both metal


atoms.

RC=CR

+

Co (CO) 2

/ \

(CO) Co-

8

8

\

-Co(CO)

-1-

8

2C0

(69)

c I R

Similar acetylene

addition reactions

carbonyl dimer (93).

take place with bis-cyclopentadienylnickel

Changing from carbonyl to cyanide ligands seems to allow

the formation of a true vinyl derivative.

T h u s , potassium

pentacyanocobaltate,

which may react as a dimer with a cobalt-cobalt bond (20), reacts with acetylene to give the adduct X V (31).

T h e product was thought to be the trans isomer, but

the data were not conclusive. (CN) Co

H

B

\ K [Co(CN) ] e

6

+

2

HC^CH

K

/ C (70)

e

C

/ \ H

Co(CN) J 6

XV If it is the trans isomer, the product m a y be formed b y a radical rather than insertion reaction.

Insertion

Reactions

of Carbonyl

Metal Hydrides.

Compounds.

It is likely that the reduction of aldehydes to alcohols by

cobalt hydrocarbonyl (27) is an example of a carbonyl insertion reaction with a metal hydride.

It is not clear which way the hydrocarbonyl adds to the carbonyl groups

—whether it forms a cobalt-carbon bond (2), or a cobalt-oxygen bond Ο

OH

I

RCH

(90).

HCo(CO)4

I

+

HCo(C0)

8

^

R—C—Η

>

I Co(CO)

8

RCH OH 2

+

Co (CO) 2


7

(71)

202


or Ο

OCo(CO)

I

RCH

+

HCo(CO)

—

4

3

HCo(CO)4

I

R—C—Η

>

Η RCH 0H

+

2

Co (CO) 2

(72)

7

A k n o w n r e a c t i o n of c o b a l t h y d r o c a r b o n y l suggests t h a t t h e c o b a l t - c a r b o n m a y be p r e f e r r e d .

bond

I t has been reported that, under rather vigorous conditions,


acetaldehyde or formaldehyde react w i t h C O a n d a cobalt catalyst to give α-hydroxy a c i d s o r esters i n a l c o h o l s o l u t i o n (7).

T h e intermediate w i t h the

carbon-cobalt

b o n d p r o b a b l y is u n d e r g o i n g a C O i n s e r t i o n r e a c t i o n , f o l l l w e d b y a h y d r o l y s i s o r alcoholysis reaction. OH

OH

I

I

R—C—H

+

CO

—

ROH

R—C—Η

I

•

I

Co(CO)

CO

3

I Co(CO)

3

OH

I R—CHCOOR

+

HCo(CO)

(73)

3

If t h e f o r m a t i o n of f o r m a t e esters u n d e r h y d r o f o r m y l a t i o n c o n d i t i o n s i n v o l v e s t h e c a r b o n y l a t i o n of a n a l k o x y c o b a l t c a r b o n y l as suggested p r e v i o u s l y (90),

this

w o u l d be e v i d e n c e t h a t c o b a l t h y d r o c a r b o n y l a d d s t h e reverse w a y t o a c y l g r o u p s . S i n c e t h e f o r m a t i o n of f o r m a t e esters c a n be e x p l a i n e d as w e l l b y a C O i n s e r t i o n i n t o a c o b a l t - h y d r o g e n g r o u p f o l l o w e d b y a l c o h o l y s i s , h o w e v e r , t h e d a t a w o u l d be e x p l a i n e d best i f a c o b a l t - c a r b o n b o n d w a s f o r m e d i n t h e h y d r i d e r e d u c t i o n of a c y l compounds. O f course, m a n y p t h e r n o n t r a n s i t i o n m e t a l h y d r i d e s w h i c h reduce

carbonyl

c o m p o u n d s a r e k n o w n ; b u t t h e r e is l i t t l e c o n c l u s i v e e v i d e n c e o n t h e m e c h a n i s m o f these r e a c t i o n s . Metal-Carbon Compounds.

W e l l - k n o w n e x a m p l e s of t h e i n s e r t i o n r e a c t i o n of

a c y l c a r b o n y l groups between m e t a l a n d a l k y l groups include the G r i g n a r d reaction a n d a l k y l l i t h i u m reactions.

T h e r e is evidence t h a t the c a r b o n y l c o m p o u n d a n d

t h e G r i g n a r d reagent c a n f o r m a 1:1 c o m p l e x before r e a c t i n g .

T h u s , 4-methoxy-2',

é ' - d i m e t h y l b e n z o p h e n o n e f o r m e d a 1:1 c o m p l e x w i t h m e t h y l m a g n e s i u m b r o m i d e w h i c h was observed spectroscopically.

T h e r a t e of d i s a p p e a r a n c e of t h e c o m p l e x

w a s e q u a l t o t h e r a t e of a p p e a r a n c e of G r i g n a r d r e a c t i o n p r o d u c t

(87),

Ο C H

3

- ^

/

>

~

C

CH

~

H

\

^ — O C H

+

3

CH MgBr

->

3

1:1 c o m p l e x

(74)

3

OMgBr

c

h

°

-

0

—

CH,

?

— C

H

^

s


C

H

i

8.

HECK

Insertion Reactions

203

A s t r u c t u r e for t h e i n t e r m e d i a t e has n o t been p r o p o s e d , b u t a c a r b o n y l ττ-complex is a good possibility. T w o e x a m p l e s of t h e a d d i t i o n of c o b a l t - c a r b o n c o m p o u n d s t o c a r b o n y l g r o u p s were g i v e n a b o v e u n d e r a c e t y l e n e r e a c t i o n s , s u g g e s t i n g t h i s r e a c t i o n is a l s o g e n e r a l l y important. Metal-Oxygen Compounds.

T r i a l k y l t i n a l k o x i d e s a r e r e m a r k a b l e for

the

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

B l o o d w o r t h a n d D a v i e s h a v e r e p o r t e d r e a c t i o n s of t r i - w - b u t y l t i n a l k o x i d e s


w i t h isocyanates, carbon dioxide, sulfur dioxide, isothiocyanates, carbon bisulfide, chloral, a n d ketene.

T h e r e a c t i o n s o b s e r v e d were as follows : R

I (w-C H ) SnOCH 4

9

3

+

3

(w-C H ) SnOCH 4

9

3

3

(w-C H ) SnOCH 4

9

R N = C = 0

3

3

->

(w-C H ) SnNC0 CH 4

9

3

2

+

C0

2

->

(w-C H ) SnOC0 CH

+

S0

2

->

(w-C H ) SnOS0 CH

4

9

4

3

9

2

3

2

(75)

3

(76)

3

(77)

3

R

I (n-C H ) SnOCH 4

9

3

+

3

(w-C H ) SnOCH 4

9

3

R N = C = S +

3

CS

2

—

-+

(w-C H ) SnNCSOCH 4

9

3

(w-C H ) SnSCSOCH 4

9

3

(78)

3

(79)

3

OCH

3

I («-C H ) SnOCH 4

9

3

(w-C H ) SnOC H 4

9

3

2

5

+

3

+

CC1 CH0

(«-C H ) SnOCHCCl

3

CH2=C=0

4

->

9

3

(80)

3

(n-C H ) SnCH C0 C H 4

9

3

2

2

2

5

(81)

S i n c e these r e a c t i o n s t a k e p l a c e i n n o n p o l a r s o l v e n t s u n d e r m i l d c o n d i t i o n s , i n s e r t i o n m e c h a n i s m s m a y be o p e r a t i n g (8). Metal-Nitrogen Compounds. r e a c t i o n s of

V e r y l i t t l e w o r k has been d o n e o n a d d i t i o n

metal-nitrogen compounds.

The

trimethyltin

dimethylamide ap

p a r e n t l y does u n d e r g o r e a c t i o n s a n a l o g o u s t o t h o s e of t h e t r i a l k y l t i n a l k o x i d e s j u s t discussed.

F o r e x a m p l e , t h e f o l l o w i n g r e a c t i o n s were o b s e r v e d w i t h c a r b o n d i o x i d e ,

c a r b o n d i s u l f i d e , a n d p h e n y l i s o c y a n a t e (57) : (CH ) SnN(CH ) 3

3

3

(CH ) SnN(CH ) 3

3

3

+

2

2

C0

+

CS

-*

2

2

(CH ) SnOCON(CH ) 3

3

3

(CH ) SnSCSN(CH ) 3

3

3

(82)

2

(83)

2

CeHs

I

S i m i l a r r e a c t i o n s h a v e been r e p o r t e d for t h e r e l a t e d s i l i c o n c o m p o u n d s , t h e d i a l k y l (CH ) SnN(CH ) + C H N=C=0 -+ (CH ) SnNCON(CH ) (84) a m i n o t r i m e t h y l s i l i c o n e s (10). S i n c e these r e a c t i o n s a r e c a t a l y z e d b y a m i n e s , t h e y 3

3

3

2

6

5

3

3

are p r o b a b l y ionic.


3

2

204

MECHANISMS OF INORGANIC

Insertion

Reactions

of Carbon-Nitrogen

REACTIONS

Groups

M e t a l Hydrides a n d M e t a l - C a r b o n C o m p o u n d s .

Numerous

examples

of

r e d u c t i o n s a n d a d d i t i o n s of m e t a l h y d r i d e s o r a l k y l s t o u n s a t u r a t e d c a r b o n - n i t r o g e n compounds are k n o w n .

I shall mention only two examples pertinent to this discus

sion. T h e S c h i f f bases f r o m s u b s t i t u t e d b e n z a l d e h y d e s a n d a n i l i n e s w i l l c a r b o n y l a t e i n t h e presence of c o b a l t c a r b o n y l , as c a t a l y s t a t 225°C. p r o d u c i n g p h t h a l i m i d i n e


d e r i v a t i v e s , X V I , i n g o o d y i e l d (70, 52).

T h i s r e a c t i o n m a y be e x p l a i n e d as a n

C H = N

+

CO (85)

a d d i t i o n of c o b a l t h y d r o c a r b o n y l , f o r m e d b y d e h y d r o g e n a t i o n r e a c t i o n s , t o t h e carbon-nitrogen double bond t o give a cobalt-nitrogen b o n d w h i c h then undergoes C O insertion.

T h e c a r b o n y l cobalt derivative then m a y a d d to the a r o m a t i c system

and eliminate cobalt hydrocarbonyl, giving the observed product, X V I .

A related

Co(CO) C H = N

4

CH —Ν 2

+

HCo(CO)

4

(86)

CO

COCo(CO)

4

Ν—CH —Ν 2

xvi

4

m e c h a n i s m i n v o l v i n g t h e a d d i t i o n of c o b a l t o c t a c a r b o n y l t o t h e c a r b o n - n i t r o g e n d o u b l e b o n d as t h e i n i t i a l s t e p has been p r o p o s e d b y S t e r n b e r g a n d W e n d e r


(90).

8.

HECK

Insertion

Reactions

205

S i m i l a r r e a c t i o n s a r e p r o b a b l y i n v o l v e d i n t h e c a r b o n y l a t i o n r e a c t i o n s of o x i m e s (80), o x i m e ethers (53), n i t r i l e s (81), a n d of d i a z o c o m p o u n d s (53). T h e w e l l - k n o w n a l k y l a t i o n of f e r r o c y a n i d e i o n t o f o r m i s o c y a n i d e i r o n c o m p l e x e s (48) c a n be e x p l a i n e d b y a n i n s e r t i o n m e c h a n i s m i f t h e m e t a l i s a l k y l a t e d i n i t i a l l y , a n d t h e n m e t a l a l k y l a d d s across a c y a n i d e g r o u p .

T h i s mechanism also explains

h o w e x t e r n a l r a d i o a c t i v e c y a n i d e i o n c a n e n t e r t h e i s o c y a n i d e l i g a n d s (48). [Fe(CN ]6

+

4

R X

->

[RFe(CN) ]~ 6

+

2

R


I Ν II II C 6

Carbene Insertion

I

^

2

+

C N ~

R 1 1 Ν π II C

1

[RFe(CN) ]-

X "

CN"

[Fe(CN) ]4

^

2

J-

[Fe(CN) ]5

8

Reactions

D i a z o m e t h a n e i s k n o w n t o r e a c t w i t h a large v a r i e t y of m e t a l h a l i d e d e r i v a t i v e s , to

produce

halomethylmetal compounds

These

(107).

reactions

m a y well be

methylene insertion reactions. MX*

+

wCH N 2

->

2

M(CH X)» 2

+

(88)

nN

2

M o r e r e c e n t l y , d i c h l o r o c a r b e n e h a s been a d d e d t o d i i s o p r o p y l m e r c u r y t o g i v e a n i n s e r t i o n p r o d u c t , l , l - d i c h l o r o - 2 - m e t h y l - l - p r o p y l ( i s o p r o p y l ) m e r c u r y (62). CI

I [(CH ) CHj Hg 3

2

2

+

C 1 C : -> 2

(CH ) CHCHgCH(CH ) 8

2

3

2

(90)

I CI Conclusion T h e l i s t of g r o u p s o r m o l e c u l e s f o r w h i c h s o m e e v i d e n c e e x i s t s t h a t i n s e r t i o n r e a c t i o n s c a n t a k e place, i n c l u d e s c a r b o n m o n o x i d e , olefins, dienes, a c e t y l e n e s , a c y l g r o u p s , c e r t a i n c a r b o n - n i t r o g e n g r o u p s , a n d carbenes.

Perhaps the list should be

e x t e n d e d t o i n c l u d e m o l e c u l a r o x y g e n since s e v e r a l m e t a l a l k y l s a r e k n o w n t o f o r m peroxides w i t h o x y g e n .

R e c e n t l y oxygen has even been shown t o f o r m a coordina

t i o n c o m p o u n d w i t h a t r a n s i t i o n m e t a l , i r i d i u m (100).

T h e examples

discussed

s t r o n g l y suggest t h a t t h e i n s e r t i o n r e a c t i o n i s v e r y g e n e r a l l y i m p o r t a n t a m o n g transition metals as w e l l as nontransition m e t a l compounds. w o r k r e m a i n s t o s u b s t a n t i a t e t h e g e n e r a l i t y of t h e r e a c t i o n .

Obviously, much

B u t t h e r e a l v a l u e of

t h i s c l a s s i f i c a t i o n i s t h a t i t suggests n e w c h e m i s t r y t o i n v e s t i g a t e .

One can imagine

t h e e v e n t u a l d e v e l o p m e n t of s y n t h e t i c m e t h o d s , b a s e d u p o n t h e i n s e r t i o n m e c h a n i s m , f o r c o m b i n i n g c a r b o n m o n o x i d e , olefins, dienes, acetylenes, k e t o n e s , e t c . , i n a v a r i e t y of l i n e a r a n d c y c l i c c o m b i n a t i o n s .

C l e a r l y , t h e r e a c t i o n offers t h e p o s s i

b i l i t y of d i s c o v e r i n g m a n y n e w c a t a l y t i c syntheses of o r g a n i c c o m p o u n d s a s w e l l a s new methods for t h e p r e p a r a t i o n of organometallic

complexes.


206

MECHANISMS


Literature

O F I N O R G A N I C REACTIONS

Cited

(1) A l b a n e s i , G., T o v a g l i e r i , M., Chim. Ind. (Milan) 41, 189 (1959). (2) A l d r i d g e , C. L., Jonassen, H. B., J. Am. Chem. Soc. 85, 886 (1963). (3) A n d e r s o n , M. M., H e n r y P . M., Chem. and Ind. (London) 1961, 2053. (4) B a r t l e t , P . D., F r i e d m a n , S., Styles, M., J. Am. Chem. Soc. 75, 1771 (1953). (5) B a w n , C . Ε. H., Chem. and Ind. (London) 1960, 388. (6) B e s t i a n , H., Clauss, K., Angew. Chem. 75, 1068 (1963). (7) B h a t t a c h a r y y a , S. K., " A c t e s d u Deuxieme Congres I n t e r n a t i o n a l de C a t a l y s e , " p. 2401, E d i t i o n s T e c h n i p , P a r i s , 1961. (8) B l o o d w o r t h , A. J., D a v i e s , A. G., Proc. Chem. Soc. 1963, 315. (9) B o o t h , G., C h a t t , J., Ibid. 1961, 67. (10) B r e e d e r v e l d , H., Rec. Trav. Chim. 81, 276 (1962). (11) B r o w n , H. C., S u b b a R a o , B. C., J. Org. Chem. 2 2 , 1136 (1957). (12) B r o w n , H. C., Zweifel, G., J. Am. Chem. Soc. 81, 5832 (1959). (13) B r o w n , H. C., Zweifel, G . , Ibid. 81, 1512 (1959). (14) C a l d e r a z z o , F., C o t t o n , F. Α., Inorg. Chem. 1, 30 (1962). (15) C h i u s o l i , G. P., Chim. Ind. (Milan) 41, 503 (1959); Angew. Chem. 72, 74 (1960). (16) Coffield, T. H., K o z i k o w s k i , J., Closson, R . D., J. Org. Chem. 22, 598 (1957). (17) Coffield, T. H., K o z i k o w s k i , J., Closson, R . D., Chem. Soc. (London) Spec. Publ. No. 13, 126 (1959); Coates, G. E., " O r g a n o m e t a l l i c C o m p o u n d s , " p. 281, 2 n d e d . , W i l e y , N e w Y o r k , 1960. (18) C o o k e , D. J., N i c k l e s s , G., P o l l a r d , F. H., Chem. and Ind. (London) 1963, 1493. (19) C r o w e , B. F., Chem. and Ind. (London) 1960, 1000. (20) D e V r i e s , B., J. Cat. 1, 489 (1962). (21) D o z o n o , T., S h i b a , T., Bull. Japan. Petrol. Inst. 5, 8 (1963); C. Α. 59, 5829 (1963). (22) E i s c h , J. J., Kaska, W. C., J. Am. Chem. Soc. 84, 1501 (1962). (23) E m m e t t , P. H., "Catalysis," Vol. III, C h a p t e r 8, Vol. V, C h a p t e r 3, R e i n h o l d , N e w Y o r k , 1957. (24) Fischer, F. G., Stoffers, O . , Ann. 500, 253 (1933). (25) G a y l o r d , N. G., Mark, H. F., "Linear a n d Stereoregular P o l y m e r s , " p. 66, I n t e r science, N e w York, 1959. (26) Ibid., p. 219. (27) G o e t z , R . W . , O r c h i n , M., J. Org. Chem. 27, 3698 (1962). (28) G o l d f a r b , I. J., O r c h i n , M., " A d v a n c e s i n C a t a l y s i s , " Vol. IX, A d a l b e r t F a r k a s , Ed., p. 609, A c a d e m i c , New York, 1957. (29) Greenfield, H., Sternberg, H. W., F r i e d e l , R. Α., W o t i z , J . Α., M a r k b y , R . , W e n d e r , I., J. Am. Chem. Soc. 78, 120 (1956). (30) Greenfield, H., W o t i z , J. Α., W e n d e r , I., J. Org. Chem. 22, 542 (1957). (31) G r i f f i t h , W. P., W i l k i n s o n , G., J. Chem. Soc. 1959, 1629. (32) H a l p e r n , J., Kettle, S. F. Α., Chem. and Ind. (London) 1961, 668. (33) H e c k , R. F., J. Am. Chem. Soc. 85, 651 (1963). (34) H e c k , R. F., U n p u b l i s h e d results. (35) H e c k , R. F., J. Am. Chem. Soc. 85, 2013 (1963). (36) Ibid., p. 1220. (37) Ibid., p. 3116. (38) Ibid., p. 1460. (39) Ibid., p. 3381. (40) Ibid., p. 3383. (41) Ibid., p. 3387. (42) H e c k , R. F., Breslow, D. S., Ibid., p. 2779. (43) Ibid., 84, 2499 (1962). (44) Ibid., 82, 4438 (1960). (45) Ibid., 84, 2499 (1962). (46) Ibid., 83, 4023 (1961). (47) Ibid., p. 1097. (48) H e l d t , W . Z . , ADVAN. CHEM. SER. No. 37, 99 (1963). (49) H e n r y , P. M., U n p u b l i s h e d results. (50) H i e b e r , H., B r a u n , G., B e c k , W . , Chem. Ber. 93, 901 (1960). (51) H i l l m a n , M. E. D., J. Am. Chem. Soc. 84, 4715 (1962). (52) H o r i i e , S., M u r a h a s h i , S., Bull. Chem. Soc. Japan 33, 247 (1960). (53) H o r r i e , S., M u r a h a s h i , S., Ibid., p. 88. (54) I m p a s t a t o , F., I h r m a n , K. G., J. Am. Chem. Soc. 83, 3726 (1961). (55) Johnson, M., J. Chem. Soc. 1963, 4859. (56) Johnson, A. W., M e r v y n , L., S h a w , N., S m i t h , E. L., Ibid., p. 4146.


8. HECK Insertion Reactions


CHEM.

T.,

C.A.

207

(57) Jones, K., L a p p e r t , M. F., Proc. Chem. Soc. 1962, 358. (58) K a a b e , H. J., Ann. 656, 204 (1962). (59) K e b l y s , Κ. Α., F i l b e y , A. H., J. Am. Chem. Soc. 82, 4204 (1960). (60) K o s t e r , R., Angew. Chem. 71, 520 (1959). (61) K w i a t e k , J., M a d o r , I. L., Seyler, J. K., J. Am. Chem. Soc. 84, 304 (1962); ADVAN. SER. N o . 37, 201 (1963). (62) L a n d g r e b e , J. Α., M a t h i s , R. D., J. Am. Chem. Soc. 86, 524 (1964). (63) L u t s e n k o , I. F., P o n o m a r e v , S. V., P e t r i i , O. P., Zh. Obshch. Khim. 32, 896 (1962); C.A. 5 8 , 3455 (1963). (64) Markó, L., Chem. and Ind. (London) 1962, 2 6 0 ; Proc. Chem. Soc. 1962, 67. (65) M c C l e l l a n , W. R., H o e h n , H. H., C r i p p s , Η. N., M u e t t e r t i e s , E. L., H o w k , B. W., J. Am. Chem. Soc. 83, 1601 (1961). (66) M c C l e v e r t y , J. Α., W i l k i n s o n , G., J. Chem. Soc. 1963, 4096. (67) M e t l e s i c s , W., W h e a t l e y , P. J., Zeiss, H., J. Am. Chem. Soc. 84, 2327 (1962). (68) M e t l e s i c s , W., Zeiss, H., Ibid. 81, 4117 (1959). (69) M u l v a n e y , J. E., G a r d l u n d , Z. G., G a r d l u n d , S. L., J. Am. Chem. Soc. 85, 3897 (1963). (70) M u r a h a s h i , S., H o r i i e , S., J o , T., Bull. Chem. Soc. Japan 33, 81 (1960). (71) N a k a m u r a , Α., Mem. Inst. Sci. Ind. Res., Osaka Univ. 19, 81 (1962); C.A., 59, 8786 (1963). (72) N e s m e y a n o v , A. N., Bull. Acad. Sci. U.S.S.R., Classe Sci. Chim. 1945, 2 3 9 ; C.A. 40, 2122 (1946). (73) N e s m e y a n o v , A. N., F r e i d l i n a , R. K., B o r i s o v , A. E., Ibid., p. 137; C.A. 40, 3451 (1946). (74) P i n o , P . , M i g l i e r i n a , Α., J. Am. Chem. Soc. 74, 5551 (1952). (75) P i n o , P., P u c c i , P., P i a c e n t i , F., Chem and Ind. (London) 1963, 294. (76) P o d a l l , Η. E., Foster, W. E., J. Org. Chem. 23, 1848 (1958). (77) Quane, D., B o t t e i , R. S., Chem. Rev. 63, 403 (1963). (78) R e p p e , W., Ann. 582, 1 (1953). (79) R e p p e , W., G e r m a n P a t e n t 1,071,077 (1950). (80) R o s e n t h a l , Α., A s t b u r y , R. F., H u b s c h e r , Α., J. Org. Chem. 23, 1037 (1958); R o s e n t h a l , Α., Can. J. Chem. 38, 457, 2025 (1960). (81) R o s e n t h a l , Α., G e r v a y , J., Chem. and Ind. (London) 1963, 1623. (82) Sauer, J. C., C r a m e r , R. D., E n g l e h a r d t , V. Α., F o r d , T. Α., H o l m q u i s t , Η. E., H o w k , B. W., J. Am. Chem. Soc. 81, 3677 (1959). (83) Schoeller, W., S c h r a u t h , W., Essers, W., Ber. 46, 2864 (1913). (84) S c h u l t z , R. G., Tetra. Letters 6, 301 (1964). (85) S h a w , B. L., Chem. and Ind. (London) 1962, 1190. (86) S h a w , B. L., J. Chem. Soc. 1963, 4806. (87) S m i t h , S. G., Tetra. Letters 7, 409 (1963). (88) S t a i b , J. H., G u y e r , W. R. F., a n d Slotterbeek, O. C., U.S. P a t e n t 2,864,864 (1958). (89) Sternberg, H. W., S h u k y s , J. G., D o n n e , C. D., M a r k b y , R., F r i e d e l , R. Α., W e n d e r , J. Am. Chem. Soc. 81, 2339 (1959). (90) Sternberg, H. W., W e n d e r , I., Chem. Soc. (London) Spec. Publ. N o . 13, 35 (1959). (91) Sternberg, H. W., W e n d e r , I., F r i e d e l , R. Α., O r c h i n , M., J. Am. Chem. Soc. 75, 3148 (1953). (92) S t i l l e , J. K., Chem. Rev. 58, 541 (1958). (93) T i l n e y - B a s s e t t , J. F., Mills, O. S., J. Am. Chem. Soc. 81, 4757 (1959). (94) T r a y l o r , T. G., B a k e r , A. W., Ibid. 85, 2746 (1963). (95) T r e i c h e l , P. M., P i t c h e r , E., Stone, F. G. Α., Inorg. Chem. 1, 511 (1962). (96) T s u j i , J., M o r i k a w a , M., Kiji, J., Tetra. Letters 16, 1061 (1962). (97) T s u t s u i , M., Zeiss, H., J. Am. Chem. Soc. 81, 6090 (1959). (98) V a n D e r K e r k , G. J. M., L u i j t e n , J. G. Α., N o l t e s , J. G., Chem. and Ind. (London) 1956, 352; J. Appl. Chem. 7, 356 (1957); Angew. Chem. 70, 298 (1958). (99) V a r g a f t i k , M. N., M o i s e e v , Ι. I., S y r k i n , Y. K., Izv. Akad. Nauk. SSSR 1963, 1147; 59, 5830 (1963). (100) V a s k a , L., " P r o c e e d i n g s 7th ICCC," p. 266, J u n e 2 5 - 2 9 , 1962, S t o c k h o l m a n d U p p s a l a , Sweden. (101) W a r d , G., H e n r y , P. M., U n p u b l i s h e d results. (102) W a t t e r s o n , K. F., W i l k i n s o n , G., Chem. and Ind. (London) 1960, 1358; J. Chem. Soc. 1961, 2738. (103) W i l f o r d , J. B., T r e i c h e l , P. M., Stone, F. G. Α., Proc. Chem. Soc. 1963, 218. (104) W i l k e , G., Müller, M., Chem. Ber. 89, 444 (1956). (105) W i l k e , G., Müller, M., Ann. 629, 222 (1960). (106) W i t t e n b e r g , D., Angew. Chem. 75, 1124 (1963).


208


(107) W i t t i g , (108) Ziegler, (109) Ziegler, (110) Ziegler, (111) Ziegler, (112) Ziegler, (1954).


RECEIVED

REACTIONS

G., Scharzenback, K., Ann. 650, 1 (1961). K., Angew. Chem. 6 4 , 323 (1952); Ibid., 6 8 , 721 (1956). K., Bähr, Κ., Chem. Ber. 6 1 , 253 (1928). K., Crössmann, F., K l e i n e r , H., Schäfer, O., Ann. 4 7 3 , 1 (1929). K., G e l l e r t , H. G., U . S . P a t e n t 2,699,457 (1955). K., G e l l e r t , H. G., M a r t i n , H., N a g e l , K., Schneider, J., Ann. 589, 91

A p r i l 3, 1964.

Discussion R i c h a r d F. H e c k :

T h e p u r p o s e of m y p a p e r h a s been t o p o i n t o u t a r e a c t i o n

w h i c h appears more w i d e l y i n the periodic table t h a n most people realize.

This

g e n e r a l r e a c t i o n i s t h e i n s e r t i o n r e a c t i o n a n d i t m i g h t be u s e d m o r e w i d e l y t o m a k e s o m e o r g a n o m e t a l l i c c o m p o u n d s w h i c h are n o t a v a i l a b l e n o w . T h e m e c h a n i s m of t h i s r e a c t i o n i s n o t w e l l u n d e r s t o o d . or four-center a d d i t i o n . [L M

-

n

L

I t i s a k i n d of t h r e e -

S o m e v a r i a t i o n s of t h i s m e c h a n i s m a r e : Ζ

= Ligand,

M

=

L

+

= Metal,

L

n

-

M

1

-

Z]

Ζ = M o n o v a l e n t group

Y

i

L L

[L

n

-

1

n - 1

M

M

-

—

Ζ

+

n

-

1

M

Y:

-

=

Ζ

L

n

-

1

M

-

Υ

Y:

= U n s a t u r a t e d molecule

Y

—

Z

+

L

=

L

n

M

-

-

Ζ

Υ

-

Ζ]

Y

I orL _jM n

-

Ζ

+

L

Figure A.

;=±

L

n

M

-

Y

-

Ζ

The insertion reaction

T h e r e is c o n s i d e r a b l e e v i d e n c e t h a t a t l e a s t m a n y of t h e s e r e a c t i o n s r e q u i r e coordinately unsaturated compounds

to proceed.

s t e p m a y be t h e first p a r t of t h e r e a c t i o n .

I n t h o s e cases, a d i s s o c i a t i o n

T h e n these c o o r d i n a t e l y u n s a t u r a t e d

c o m p o u n d s r e a c t w i t h a n u n s a t u r a t e d m o l e c u l e — i t c a n be m o s t a n y t h i n g a s l o n g a s i t h a s a n a v a i l a b l e p a i r of e l e c t r o n s — a n d t h i s i n s e r t i n g m o l e c u l e goes i n b e t w e e n t h e m e t a l a t o m a n d one of t h e g r o u p s i n i t i a l l y b o n d e d t o t h e m e t a l . m a t e r i a l is c o o r d i n a t e l y u n s a t u r a t e d , so i s t h e p r o d u c t .

If t h e s t a r t i n g

A final s t e p m u s t be t h e

f o r m a t i o n of a c o o r d i n a t e l y s a t u r a t e d p r o d u c t b y s o m e final r e a c t i o n , e i t h e r w i t h a n o t h e r l i g a n d o r b y d e c o m p o s i t i o n of t h i s i n s e r t i o n p r o d u c t . T h e r e is c o n s i d e r a b l e c o n t r o v e r s y as t o w h e t h e r o r n o t t h i s r e a c t i o n i n v o l v e s a TT-complex as a t r u e i n t e r m e d i a t e .

T h e r e seems t o be n o r e a l p r o o f t h a t ττ-com-

plexes a r e t r u e i n t e r m e d i a t e s a l t h o u g h i t seems c l e a r t h a t t h e y are p r e s e n t i n these


8.

HECK

Discussion

reaction mixtures. more

209

I f these x - c o m p l e x e s a r e r e a l l y i n t e r m e d i a t e s , t h e m e c h a n i s m i s

complicated.

I t i s p o s s i b l e t h a t t h e s e c a n be f o r m e d d i r e c t l y f r o m

co-

o r d i n a t e l y s a t u r a t e d c o m p o u n d s b y a d i s p l a c e m e n t of one of t h e o r i g i n a l l i g a n d s b y this Y molecule.

I t i s a l s o p o s s i b l e t h a t i n s e r t i o n w i l l n o t t a k e p l a c e unless

a n o t h e r l i g a n d is present t o m o v e t h i s Y group i n t o the insertion p o s i t i o n .

T h e r e is

o n l y one case t h a t I k n o w of i n t h e l i t e r a t u r e w h e r e i t h a s b e e n s h o w n c o n c l u s i v e l y t h a t a c o o r d i n a t e d l i g a n d i s t h e one t h a t i n s e r t s .

T h i s is the well k n o w n manganese

carbonyl carbonylation,


CO CH —Mn(CO) 3

Figure B.

4

+

CO

?±

CH COMn(CO) 3

The manganese carbonyl carbonylation

6

(5)

T h i s is well k n o w n d a t a b u t u n f o r t u n a t e l y i t has never been p u b l i s h e d . given at the L o n d o n C o o r d i n a t i o n Conference.

It was

T h e reaction involved the addition

of r a d i o a c t i v e c a r b o n m o n o x i d e t o m e t h y l m a n g a n e s e p e n t a c a r b o n y l .

T h e carbon

m o n o x i d e e n t e r i n g d i d n o t go i n t h e a c y l p o s i t i o n b u t w e n t e x c l u s i v e l y i n a c o o r d i n a tion position.

I t seems t h a t a t l e a s t i n t h i s one e x a m p l e i t i s a c o o r d i n a t e d l i g a n d

that is inserting. I a m i n c l i n e d t o t h i n k t h a t t h i s s a m e k i n d of m e c h a n i s m i s o p e r a t i n g i n m a n y o t h e r cases, t h a t i s , t h a t t h e i n s e r t i n g m o l e c u l e m u s t be c o o r d i n a t e d a n d t h e n i t c a n insert.

B u t I k n o w of n o e v i d e n c e f o r t h i s i n a n y o t h e r cases.

In the

figures

I h a v e s u m m a r i z e d s o m e of t h e i n s e r t i o n r e a c t i o n s f r o m t h e

literature w h i c h we s t u d i e d . H—M

R—M

RMo(CO) Cp RMn(CO) RRe(CO)* RFe(CO) Cp RCo(CO)4 RRhX (CO)(PR's)

HCo(CO)4(?)

3

6

2

Figure C.

6

RPdX(PR's) RPtX(PR' ) RLi RMgX RsB 3

2

2

RiN—M

RO—M

[τγ—C H NiX]t

8

2

ROCo(CO)4 ( [τ—C8H4CH 0]Fe (CO)s} 2

2

[ R 2 N — C o (CO) 4]

Fe Cu

Carbon monoxide insertion reactions

Figure C shows carbon monoxide insertion reactions.

T h e r e a r e a n u m b e r of

r e d u c t i o n r e a c t i o n s of c a r b o n m o n o x i d e c a t a l y z e d b y t r a n s i t i o n m e t a l s , a n d these, I b e l i e v e , a l l i n v o l v e a n i n s e r t i o n of c a r b o n m o n o x i d e i n t o a m e t a l h y d r i d e as a n initial step.

C o b a l t h y d r o c a r b o n y l r e a c t s w i t h c a r b o n m o n o x i d e t o give f o r m a t e

derivatives.

T h i s is p r o b a b l y a n insertion reaction also.

M a n y t r a n s i t i o n m e t a l a l k y l s react w i t h c a r b o n monoxide to give a c y l c o m pounds.

I n a l l t h e s e cases t h e a c y l d e r i v a t i v e s c a n be d e t e c t e d a t l e a s t b y i n f r a r e d

m e t h o d s a n d i n m o s t cases i s o l a t e d .

M o l y b d e n u m , manganese, r h e n i u m , iron,

cobalt, r h o d i u m , n i c k e l , p a l l a d i u m , a n d p l a t i n u m a l k y l s , G r i g n a r d reagents, a n d b o r a n e s , a l l r e a c t w i t h c a r b o n m o n o x i d e , a n d one c a n e x p l a i n t h e p r o d u c t s f r o m these o n t h e b a s i s of c a r b o n m o n o x i d e i n s e r t i n g i n t o t h e m e t a l a l k y l . T w o a l k o x i d e d e r i v a t i v e s a l s o seem t o i n s e r t c a r b o n m o n o x i d e .

T h e products

o b t a i n e d w h e n these a l k o x i d e s a r e f o r m e d i n t h e presence of c a r b o n m o n o x i d e h a v e C O inserted between the oxygen a n d the m e t a l .

T h e s e t w o p r o d u c t s c a n a l s o be



210

e x p l a i n e d o n t h e b a s i s of t h e a l k o x i d e a t t a c k i n g a c o o r d i n a t e d c a r b o n

monoxide.

H e n c e , these cases c e r t a i n l y are n o t c l e a r . T h e r e are a n u m b e r of a m i n e - c a t a l y z e d c a r b o n y l a t i o n r e a c t i o n s w h i c h a r e catalyzed by cobalt carbonyl and iron carbonyl.

I t seems t o m e t h a t these a r e i n

s e r t i o n r e a c t i o n s of m e t a l a m i d e s , w h e r e c a r b o n m o n o x i d e is i n s e r t e d a n d t h e n s o m e k i n d of a r e d u c t i o n o r s u b s e q u e n t r e a c t i o n gives t h e o b s e r v e d p r o d u c t s , u r e a d e r i v a tives or carbamates i n alcohols.

W e d o n o t k n o w t h e s t r u c t u r e of t h e i r o n c o m

p o u n d ; i t i s p r o b a b l y s i m i l a r t o t h e c o b a l t species s h o w n .


C o p p e r s a l t s , c u p r i c O r c u p r o u s a l s o w i l l c a t a l y z e t h e c a r b o n y l a t i o n of a m i n e s . P i p e r i d i n e , for e x a m p l e , gives a u r e a d e r i v a t i v e w i t h c a r b o n m o n o x i d e , a n d i t , t o o , is p r o b a b l y a m e t a l a m i d e — c a r b o n monoxide insertion reaction. H—M Η Μη ( C O ) s HCo(CO) H Mg H B HA1R HGeR (?) HSnR (?)

R—M RTiCl R Cr RMn(CO) RCOCo(CO) RLi RK R Mg RsAl

4

6

2

2

3

3

X—M X Pd X Hg

2

3

2

6

RO—M Pd+ T1+* (RCOO) Hg

3

M—M Co (CO)

2

2

8

2

2

4

2

Figure D.

Olefin insertion reactions

F i g u r e D s h o w s s o m e olefin i n s e r t i o n r e a c t i o n s . have been k n o w n for a long w h i l e .

H y d r i d e a d d i t i o n s t o olefins

A m o n g these m a n y e x a m p l e s ,

manganese

hydrocarbonyl, and cobalt hydrocarbonyl, magnesium hydride, diborane, a l k y l a l u m i n u m h y d r i d e s , g e r m a n i u m a n d t i n h y d r i d e s a l l a d d q u i t e r e a d i l y t o olefins. T h e s e l a s t t w o cases are q u e s t i o n a b l e because t h e m e c h a n i s m i s n o t c l e a r .

S o m e of

these a d d i t i o n s o c c u r w i t h o u t a c a t a l y s t ; s o m e a r e s p e e d e d u p b y u l t r a v i o l e t l i g h t ; some are catalyzed b y G r o u p V I I I metals.

S o i t i s n o t c l e a r w h e t h e r a l l these

r e a c t i o n s are t h e s a m e o r w h e t h e r t h e r e are s e v e r a l different m e c h a n i s m s . A n u m b e r of m e t a l a l k y l s a d d r e a d i l y t o d o u b l e b o n d s .

These include the

titanium alkyls, c h r o m i u m aryls and alkyls, the alkylmanganese carbonyls, a c y l cobalt carbonyls, a l k a l i m e t a l a l k y l s , the magnesium a l k y l s , a n d a l u m i n u m a l k y l s . A m o n g some m e t a l oxygen compounds w h i c h a d d , p a l l a d i u m and t h a l l i u m ion b o t h o x i d i z e olefins a n d a p p a r e n t l y t h e i n i t i a l s t e p i s t h e a d d i t i o n of a m e t a l h y d r o x i d e across t h e olefin d o u b l e b o n d .

T h e i n t e r m e d i a t e s h a v e n o t been i s o l a t e d

because t h e y go o n t o o t h e r p r o d u c t s ; b u t k i n e t i c a n d o t h e r e v i d e n c e i n d i c a t e s t h a t t h e a d d i t i o n of t h e h y d r o x i d e i s t h e i n i t i a l s t e p .

I n the well k n o w n mercury acetate

a d d i t i o n t o olefins i n a l c o h o l s o l u t i o n one c a n i s o l a t e t h e / S - h y d r o x y o r a l k o x y ethylmercury derivatives. T w o m e t a l h a l i d e s h a v e been f o u n d t o r e a c t w i t h olefins b y w h a t a p p e a r s t o be insertion reaction. olefins.

P a l l a d i u m chloride a n d mercury chloride both will a d d

to

T h e p a l l a d i u m a l k y l s c a n o t be i s o l a t e d , b u t t h e y go o n t o p r o d u c t s w h i c h

c a n be a c c o u n t e d for b y a n i n i t i a l a d d i t i o n . O n e c o m p l e x w i t h a m e t a l — m e t a l b o n d t h a t h a s been a d d e d t o a n olefin i s cobalt octacarbonyl.

I t r e a c t s w i t h t e t r a f l u o r o e t h y l e n e a n d i t seems reasonable

t h a t t h i s i s a n i n s e r t i o n r e a c t i o n ; b u t a g a i n i t has n o t been p r o v e d . F i g u r e Ε s h o w s s o m e c o n j u g a t e d diene i n s e r t i o n r e a c t i o n s . compounds

A s e x p e c t e d , these

r e a c t s i m i l a r l y t o t h e o l e f i n s — t h e same reagents a d d .

Manganese


8.

HECK

211

Discussion RO—M

X—M

(RCOO) Hg

X Pd

R—M

H—M HMn(CO) HCo(CO) HCo(CN) HeB HSnR (?)

RCOCo(CO) [R2C0]

5

4

4

2

2

4

3

2

3

Figure E.

Conjugated diene insertion reactions


hydrocarbonyl, cobalt h y d r o c a r b o n y l , the cobaltpentacyanide hydride, diborane, and, again, the a l u m i n u m a n d t i n hydrides a d d . e x a m p l e s is s t i l l u n c e r t a i n .

T h e mechanism i n the last two

T w o a l k y l - o r a c y l - c o b a l t c o m p o u n d s h a v e been a d d e d .

T h e a c y l c o b a l t t e t r a c a r b o n y l s a d d t o give 7 r - a l l y l c o b a l t d e r i v a t i v e s .

Dialkylcobalt

c o m p o u n d s , w h i c h h a v e n o t been i s o l a t e d b u t p r o b a b l y are p r e s e n t i n t h e r e a c t i o n m i x t u r e , a d d t o dienes i n a s i m i l a r w a y , p r o b a b l y g i v i n g ττ-allyl i n t e r m e d i a t e s . M e r c u r y a c e t a t e a d d s t o dienes j u s t as i t does t o olefins, a n d so does p a l l a d i u m chloride.

H e r e a g a i n a ? r - a l l y l d e r i v a t i v e is o b t a i n e d .

T h e f o r m a t i o n of t h e i r - a l l y l

d e r i v a t i v e , I t h i n k , o c c u r s a f t e r t h e i n i t i a l a d d i t i o n a n d p r o b a b l y has n o t h i n g t o d o w i t h t h e first i n s e r t i o n s t e p . II—M

RO—M

R—M

HMn(CO) HCo(CO) [HNi(CO) X] HeB HA1R 5

4

2

2

2

RMo(CO) Cp R Cr RFe(CO) Cp RCOCo(CO) [*—C H NiX] RLi R A1

M—M

X—M

Co (CO) K [Co(CN)5] (?)

X Hg

ROSnR'a

3

2

2

8

e

3

2

2

4

3

5

2

3

Figure F.

Acetylene insertion reactions

Figure F shows some acetylene insertion reactions. the olefin i n s e r t i o n r e a c t i o n s . add.

T h e s e , t o o , are s i m i l a r t o

T h e manganese a n d cobalt hydrocarbonyls again

C h l o r o n i c k e l c a r b o n y l h y d r i d e , w h i c h I b e l i e v e is a n i n t e r m e d i a t e i n m a n y of

t h e n i c k e l c a r b o n y l - c a t a l y z e d r e a c t i o n s , a d d s t o olefins.

Diborane a n d the a l u m i

n u m hydrides also a d d . A g a i n several alkyls a d d — m o l y b d e n u m , c h r o m i u m , iron, cobalt, nickel, the alkali metal a l k y l s and a l u m i n u m a l k y l s react.

A t i n a l k o x i d e h a s r e c e n t l y been

studied b y R u s s i a n workers a n d found to add to acetylenes.

M e r c u r y c h l o r i d e , of

course, adds a n d t w o c o b a l t — c o b a l t bonded c o m p o u n d s a d d to acetylene.

The

s e c o n d i s q u e s t i o n a b l e because i t d i s s o c i a t e s i n s o l u t i o n a n d t h e r e a c t i o n m a y be a r a d i c a l r e a c t i o n , one c o b a l t a d d i n g t o e a c h e n d of t h e t r i p l e b o n d . H—M HCo(CO) H B HA1R 6

4

2

2

R—M

RO—M

RLi RMgX R*A1

ROSnR'

Figure G. RCHO,

2

2

2

Carbonyl insertion reactions;

R C = 0, R—N 2

R N—M R N—SnR' ( R N ) As

3

= C = 0, C0

2l

CII = C = 0 2


3

3

212

M E C H A N I S M S O F I N O R G A N I C REACTIONS F i g u r e G s h o w s s o m e i n s e r t i o n r e a c t i o n s of c a r b o n y l c o m p o u n d s .

I n the iso-

c y a n a t e a n d k e t e n e cases, t h e a d d i t i o n t a k e s p l a c e , n o t t o t h e c a r b o n y l d o u b l e b o n d , b u t to the carbon—nitrogen or the c a r b o n — c a r b o n double b o n d . C o b a l t h y d r o c a r b o n y l , d i b o r a n e , a n d a l u m i n u m h y d r i d e s a d d , I t h i n k , t o a l l of these c a r b o n y l c o m p o u n d s .

O f course, there is t h e w e l l k n o w n G r i g n a r d reagent

a n d the a l k y l l i t h i u m additions to carbonyl compounds.

Aluminum alkyls add,

a n d we c o u l d h a v e l i s t e d a l l t h e o t h e r a l k a l i m e t a l a l k y l s .

R e c e n t w o r k has s h o w n

t h a t t h e t i n a l k o x i d e s a d d r e a d i l y t o a l l these d e r i v a t i v e s , a n d s i m i l a r l y , a t i n a m i d e


a d d s t o m o s t of these c a r b o n y l c o m p o u n d s . R e c e n t l y a n arsenic amide d e r i v a t i v e has reacted w i t h a n isocyanate, a d d i n g across t h e c a r b o n — n i t r o g e n d o u b l e b o n d .

I t h i n k t h i s is t h e first e x a m p l e of a

g r o u p V e l e m e n t w h i c h seems t o be u n d e r g o i n g a n i n s e r t i o n r e a c t i o n .

\ C=N—

\ C=S

/

/

\

—C=N

/

o

— N = N Figure H.

s=o 2

Miscellaneous insertion reactions

F i n a l l y , i n F i g u r e H a r e s o m e a d d i t i o n a l u n s a t u r a t e d g r o u p s for w h i c h s o m e evidence exists t h a t t h e y undergo insertion reactions also: the c a r b o n — n i t r o g e n double bond, the nitrile group, the azo group, the carbon—sulfur double bond, the sulfur oxide group, a n d the oxygen molecule. t h a t t h i s is a g e n e r a l r e a c t i o n .

I t h i n k i t i s c l e a r f r o m these e x a m p l e s

Perhaps the mechanisms don't a l l involve insertion

r e a c t i o n s , b u t t h e y a r e s i m i l a r e n o u g h t o l o o k as i f t h e y b e l o n g i n t h e s a m e g r o u p . T h i s r e a c t i o n h o l d s p r o m i s e for m a k i n g m a n y n e w , u n u s u a l , a n d u s e f u l c o m p o u n d s , a n d I t h i n k i t w i l l be u s e d c o n s i d e r a b l y i n t h e f u t u r e . R a y m o n d Dessy:

I w o u l d l i k e t o focus o n three p r o b l e m s .

D r . H e c k has a l

r e a d y m e n t i o n e d one, t h e i m p o r t a n c e of c o m p l e x i n g these c a r b o n y l m e t a l h y d r i d e c o m p o u n d s w i t h olefins, o r f o r t h a t m a t t e r , t h e i m p o r t a n c e of c o m p l e x i n g a n y olefin w i t h these t r a n s i t i o n m e t a l c a t a l y s t s i n l e a d i n g t o final p r o d u c t .

Does a four-center

t r a n s i t i o n s t a t e of s o m e t y p e o c c u r d i r e c t l y , o r i s a n o t h e r m e c h a n i s m i n v o l v e d ?

I

also hope t h a t s o m e b o d y w o u l d c o m m e n t on w h a t D r . H e c k has called coordinative unsaturation.

H i s v i e w , I t h i n k , is t h a t t h e first s t e p i n m a n y of t h e c a r b o n y l r e a c

t i o n s w i t h c o b a l t i n v o l v e s loss of e n o u g h C O t o give a 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 cobalt.

F i n a l l y , I w o u l d like to consider some d a t a from a paper t h a t D r . H e c k

p u b l i s h e d i n 1961 (6) c o n c e r n i n g t h e r e a c t i o n s of i s o b u t y l e n e w i t h t h e c o b a l t h y d r o c a r b o n y l u n d e r t w o t y p e s of c o n d i t i o n s .

O n e c o n d i t i o n , t h e so c a l l e d o x o c o n d i t i o n

w h i c h is a b o u t 120°C. u n d e r a f a i r l y h i g h pressure of h y d r o g e n , gave p r o d u c t s w h i c h he q u o t e d d i r e c t l y f r o m t h e l i t e r a t u r e .

T h i s leads t o a l d e h y d e m a t e r i a l .

T h e a l d e h y d e g r o u p i n t r o d u c e d o c c u p i e s w h a t m i g h t be c a l l e d a p r i m a r y c a r b o n . I n h i s o w n w o r k a t 0 ° C , w h e r e t h e i s o l a t i o n t o o k place b y r e a c t i o n w i t h t r i p h e n y l p h o s p h i n e , t h e n m e t h y l a l c o h o l a n d i o d i n e , t h e p r o d u c t i s , of course, n o t a n a l d e h y d e b u t a n a c i d ester.

T h e skeletal arrangement would indicate that the tertiary


8.

HECK

Discussion

213

c a r b o n a t o m i s u s e d for t h e a t t a c h m e n t site of t h e c o b a l t . about 2 0 % .

O v e r a l l y i e l d s were

T h i s i s t o be c o m p a r e d w i t h t h e r e a c t i o n of t h e c o r r e s p o n d i n g e p o x i d e

w i t h h y d r o c a r b o n y l o r c a r b o n y l a n i o n t h a t he r e c e n t l y r e p o r t e d (7).

T h i s gives a

p r o d u c t d e r i v e d f r o m o p e n i n g t h e e p o x i d e ring i n a w a y w h i c h uses t h e p r i m a r y c a r b o n a g a i n as t h e p o i n t of a t t a c h m e n t for t h e c o b a l t .

T h e r e i s one o t h e r r e a c

t i o n i n t h i s v e i n , w h i c h leads t o t h e q u e s t i o n t h a t I w o u l d l i k e t o a s k .

T h e reac

t i o n s of a c r y l i c esters u n d e r o x o c o n d i t i o n s gives a s k e l e t a l a r r a n g e m e n t i n t h e p r o d u c t , w h i c h p u t s t h e a l d e h y d e g r o u p o n t h e t e r m i n a l c a r b o n a t o m of t h e a c r y l i c


e s t e r ; w h i l e u n d e r c o n d i t i o n s of 0 ° C , f o l l o w e d b y i s o l a t i o n of a p r o d u c t b y t r i p h e n y l p h o s p h i n e / m e t h y l alcohol/iodine reaction, the skeletal arrangement i n the product indicates t h a t the cobalt attaches itself to carbon atom-2.

Although 2 0 %

of t h e o t h e r p r o d u c t i s t h e r e , t h i s i s t h e m a i n p r o d u c t . I w o u l d l i k e t o r e a d f r o m t w o of D r . H e c k ' s p a p e r s : " T h e h i g h e l e c t r o n d e n s i t y of t h e d o u b l e b o n d i n i s o b u t y l e n e r e s u l t s i n a n acid type a d d i t i o n , while the low electron density i n m e t h y l acrylate leads pre d o m i n a n t l y to a h y d r i d i c addition.

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

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

T h u s , if t h e a d d i t i o n is r e v e r s i b l e , t h e p r o d u c t s a t e l e

v a t e d t e m p e r a t u r e s c o u l d reflect t h e r e l a t i v e s t a b i l i t i e s of t h e a d d u c t s r a t h e r t h a n their initial concentrations"

(6).

A p p a r e n t l y t h e e x p l a n a t i o n for these t w o d i f f e r e n t r e s u l t s , i n t e r m s of t h e c a r b o n s k e l e t o n of a p r o d u c t , w a s a s c r i b e d t o t h e s t a b i l i t i e s of t h e i n t e r m e d i a t e s a t these t w o t e m p e r a t u r e s ; t h e difference

i n d i r e c t i o n of

a d d i t i o n between

the

methyl

acrylates a n d the isobutylene was caused b y the electron density a t the double b o n d . F i n a l l y , f r o m a p a p e r i n 1963 o n t h e e p o x i d e w o r k w e h a v e a q u o t a t i o n : " T h e m e c h a n i s m m o s t c o n s i s t e n t w i t h a l l t h e d a t a is a n i o n i c a c i d o p e n i n g of t h e e p o x i d e " — a p p a r e n t l y w h e r e t h e h y d r o c a r b o n y l is u s e d a s a n a c i d t o a t t a c k t h e e p o x i d e — " w h i c h i s m o r e s e n s i t i v e t o s t e r i c effects t h a n t o e l e c t r o n i c f a c t o r s . T h i s c o n c l u s i o n m a y a t first a p p e a r t o be i n c o n s i s t e n t w i t h o u r p r e v i o u s

finding

t h a t i s o b u t y l e n e r e a c t e d w i t h c o b a l t h y d r o c a r b o n y l t o g i v e e x c l u s i v e l y a d d i t i o n of the cobalt to the t e r t i a r y position.

T h e i n h i b i t o r y effect of c a r b o n m o n o x i d e o n

that reaction, however, indicated t h a t i t was probably

cobalt hydrotricarbonyl

t h a t w a s a c t u a l l y a d d i n g t o t h e o l e f i n a n d s t e r i c effects w o u l d be e x p e c t e d t o be m u c h less i m p o r t a n t w i t h t h e t r i c a r b o n y l t h a n w i t h t h e t e t r a c a r b o n y l " (7)* A p p a r e n t l y he feels n o w t h a t t h e f o r m e r r e a c t i o n s r e a l l y i n v o l v e t h e t r i c a r b o n y l , loss of C O b e i n g i m p o r t a n t t o get t h e r e a c t i o n r u n n i n g ; w h e r e a s e p o x i d e a t t a c k p e r h a p s i n v o l v e s a t e t r a c a r b o n y l , s t e r i c f a c t o r s are m o r e i m p o r t a n t here. T h e p r o b l e m I w o u l d l i k e t o focus o n p e r h a p s c a n best be e x p r e s s e d

by

a n a n a l o g y w i t h s o m e of P r o f . P e a r s o n ' s c o m m e n t s . T h e a n a l o g y c o m e s f r o m s o m e o n e w h o w a s i m p r e s s e d b y t h e soft a c i d — s o f t base w o r k .

A s a m a t t e r of f a c t , he felt t h a t a c i d s a n d bases r e a c t t o g i v e s a l t s , a n d

s o a p i s a s a l t , a n d so w e h a v e soft s o a p . S i n c e w o r d s s o m e t i m e s h i d e m e a n i n g , w e h a v e t o be c a r e f u l t h a t w e d o n ' t s u b stitute words w h i c h d o n ' t mean m u c h for ideas.

I a m very troubled at the moment

o v e r w h a t D r . H e c k m e a n t b y a c i d base, h o w e l e c t r o n d e n s i t y i n t h e olefin c o u l d l e a d t o t h e o r i e n t a t i o n he m e n t i o n s . this.

I w o u l d l i k e t o a s k w h e t h e r o r n o t he c a n e x p l a i n

F i n a l l y , i f t h i s p r o v e s d i f f i c u l t , h a s he t h o u g h t a b o u t r a d i c a l processes i n t h i s

t y p e of t h i n g ?


214

MECHANISMS OF INORGANIC Jack Halpern:

REACTIONS

P e r h a p s I h a v e m o r e r e a s o n t h a n a n y o n e else t o be

disposed

t o t h e v i e w t h a t π - c o m p l e x i n g i s a n i m p o r t a n t s t e p of t h e i n s e r t i o n r e a c t i o n , b e cause I t h i n k t h a t p o s s i b l y w e h a v e t h e o n l y r e a s o n a b l y c l e a r c u t case of a n olefin insertion reaction where a complex is clearly i m p l i c a t e d .

T h i s is the r u t h e n i u m

c h l o r i d e - c a t a l y z e d hydrogénation of c e r t a i n olefins, w h i c h a l m o s t c e r t a i n l y i n v o l v e s t h e i n s e r t i o n of t h e o l e f i n i n t o a r u t h e n i u m h y d r o g e n b o n d a n d w h e r e c e r t a i n l y a r u t h e n i u m olefin c o m p l e x is i n v o l v e d as a n o b s e r v a b l e r e a c t a n t . N e v e r t h e l e s s , I a m n o t a t a l l sure t o w h a t e x t e n t t h i s is a g e n e r a l o r n e c e s s a r y feature of s u c h i n s e r t i o n reactions.

T h e i m p o r t a n t q u e s t i o n i s w h e t h e r one o r t w o c o o r d i n a t i o n p o s i t i o n s


o n t h e m e t a l i o n are i n v o l v e d i n t h e t r a n s i t i o n s t a t e of t h e i n s e r t i o n r e a c t i o n .

For

e x a m p l e , i f one c o n s i d e r s t h e i n s e r t i o n of a n o l e f i n , s a y i n t o a n M — X b o n d , t h e n the transition state m a y look something like :

ι

]

M - - X T h e r e i s p a r t i a l b o n d i n g b e t w e e n t h e m e t a l a n d t h e olefin (or p e r h a p s one c a r b o n of t h e olefin) a n d b e t w e e n t h e m e t a l a n d X , a n d t h i s uses t w o c o o r d i n a t i o n p o s i t i o n s of t h e m e t a l .

O t h e r w i s e o n l y one c o o r d i n a t i o n p o s i t i o n is i n v o l v e d , a n d

t h e t r a n s i t i o n s t a t e is n o t a p p r e c i a b l y s t a b i l i z e d b y b o n d i n g b e t w e e n t h e m e t a l a n d X.

I f t h i s i s t h e case, t h e n t h e r e i s less r e a s o n t o p o s t u l a t e t h e olefin as i n i t i a l l y

i n v o l v e d , s a y as a τ - b o n d e d l i g a n d .

Perhaps i t just comes i n from the outside.

I n m a n y of these s y s t e m s , t h e p o s t u l a t e d olefin c o m p l e x i n t e r m e d i a t e w o u l d be labile.

T h e r e f o r e , i t s role as a p r e - e q u i l i b r i u m i n t e r m e d i a t e i s n o t t e r r i b l y r e l e v a n t

to the kinetic problem.

I t h i n k t h e r e l e v a n t feature is w h e t h e r t h e f a v o r a b l e p a t h s

i n these i n s e r t i o n r e a c t i o n s i n v o l v e t h e first o r s e c o n d t y p e of t r a n s i t i o n s t a t e . perhaps de-emphasizes

This

t h e q u e s t i o n of w h e t h e r o r n o t a 7r-bonded i n t e r m e d i a t e

i s i n v o l v e d b u t c e r t a i n l y does focus a t t e n t i o n o n t h e q u e s t i o n of w h e t h e r a c o o r d i n a t e d u n s a t u r a t e d species i s i n v o l v e d as a r e a c t a n t .

T h i s i s because t h e

first

t y p e of t r a n s i t i o n s t a t e w i l l r e q u i r e t w o c o o r d i n a t i o n p o s i t i o n s a n d hence i n v o l v e t h e e l i m i n a t i o n of s o m e o t h e r l i g a n d before i t c a n f o r m , w h e r e a s t h e s e c o n d w i l l n o t . I d o n ' t k n o w t h e a n s w e r t o t h i s q u e s t i o n b u t t h i s is h o w I w o u l d f o r m u l a t e t h e problem. W e are c u r r e n t l y t r y i n g t o a n s w e r s p e c i f i c a l l y t h e q u e s t i o n of w h e t h e r ττ-bonded c o m p l e x e s d o o c c u r i n c e r t a i n cases w h e r e i n s e r t i o n r e a c t i o n s are o b s e r v e d .

I

t h i n k t h e y d o because I believe t h a t t h e s a m e f a c t o r s w h i c h f a v o r s t a b i l i z a t i o n of t h i s t y p e of t r a n s i t i o n s t a t e w i l l a l s o t e n d t o f a v o r f o r m a t i o n of 7r-bonded olefin c o m plexes, w h i c h a r e o n l y s l i g h t l y r e m o v e d f r o m t h i s .

A t the m o m e n t B e r n T i n k e r is

e x a m i n i n g t h e i n s e r t i o n of olefins i n m e r c u r i c c o m p l e x e s t o see w h e t h e r t h e r e is a n y i n d i c a t i o n of 7r-bonded i n t e r m e d i a t e s .

I n h i s p a p e r , D r . H e c k referred t o s o m e

unpublished work relevant to this theme.

I w o u l d c e r t a i n l y be i n t e r e s t e d i n a n y

t h i n g m o r e he c a n t e l l us a b o u t t h a t . Dr. Dessy:

M a n y workers have

felt t h a t s u c h 7 r - c o m p l e x i n g , because

of

d i r - p i r - b a c k - b o n d i n g i n t o t h e w* of t h e o l e f i n , c a n a c t i v a t e t h e olefin f o r t h e s u b sequent attack.

W h a t r e a l i t y does t h a t have?

Dr. Halpern:

I t h i n k t h e d e s c r i p t i o n c a n be f o r m u l a t e d i n a s o m e w h a t d i f

ferent w a y e m p h a s i z i n g t h e p o i n t t h a t y o u r a i s e ; n a m e l y , t h a t f o r m a t i o n of a m e t a l olefin c o m p l e x , b y v i r t u e of t h e b a c k - b o n d i n g process, p u t s m e t a l e l e c t r o n s i n t o


8.

HECK

Discussion

215

a n t i - b o n d i n g o r b i t a l s of t h e o l e f i n .

T h i s r e d u c e s t h e b o n d o r d e r of t h e o l e f i n , a n d

i n t h i s sense c o u l d l e a d t o a v i e w t h a t t h e olefin i s a c t i v a t e d .

If y o u prefer, a

v a l e n c e b o n d r e p r e s e n t a t i o n , a p e r f e c t l y s a t i s f a c t o r y d e s c r i p t i o n of a i r - o l e f i n c o m p l e x w o u l d be one i n w h i c h t h e r e i s s u b s t a n t i a l o p e n i n g of t h e d o u b l e b o n d a n d f o r m a t i o n of p a r t i a l b o n d s b e t w e e n t h e c a r b o n s a n d t h e m e t a l .

I t h i n k most people

w o u l d t e n d t o v i e w t h i s t y p e of species as p r o b a b l y h a v i n g h i g h e r r e a c t i v i t y t o w a r d s a d d i t i o n t h a n the uncômplexed olefin. Dr. Heck:

I believe t h i s c a n b e s t be d e s c r i b e d as a c o m p r o m i s e b e t w e e n t h e


e l e c t r o n i c effects a n d s t e r i c effects. R. J . Mawby:

D i s c u s s i n g t h e i n s e r t i o n r e a c t i o n s of m e t h y l m a n g a n e s e p e n t a -

c a r b o n y l , D r . H e c k w r i t e s , " A n i m p o r t a n t q u e s t i o n , therefore, is u n a n s w e r e d . D o e s t h e c o o r d i n a t e d c a r b o n y l g r o u p i n s e r t before t h e n e w C O is a d d e d o r does t h e i n c o m i n g C O push the coordinated c a r b o n y l i n t o the a c y l p o s i t i o n ? " I h a v e been i n v e s t i g a t i n g t h i s p r o b l e m a t N o r t h w e s t e r n U n i v e r s i t y , u n d e r P r o f s . B a s o l o a n d P e a r s o n (8).

F . C a l d e r a z z o a n d F . A . C o t t o n (/) h a d p r e v i o u s l y

showed t h a t Reaction 1 : CH Mn(CO) 3

was

first-order

+

B

CO

-

CH COMn(CO) 3

(1)

5

i n b o t h C H M n ( C O ) e a n d C O o v e r t h e r a n g e of c a r b o n

monoxide

3

concentrations used.

H o w e v e r , t h i s range was severely l i m i t e d b y the low s o l u

b i l i t y of C O i n t h e s o l v e n t s w h i c h t h e y e m p l o y e d . B y s t u d y i n g r e a c t i o n s of t y p e (2) : CH Mn(CO) 3

+

5

L

->

CH COMn(CO) L 3

(2)

4

where L is some l i g a n d other t h a n C O , we c o u l d w o r k w i t h considerably greater ligand concentrations.

T h e first r e a c t i o n w e s t u d i e d w a s C H M n ( C O ) 3

hexylamine i n tetrahydrofuran.

6

with cyclo-

W e found that the reaction rate was independent

of a m i n e c o n c e n t r a t i o n o v e r t h e concentration*" r a n g e s t u d i e d — f r o m 2.5 χ 10~ M

to

2

5 χ 10 lf.

T h i s r u l e d o u t t h e m e c h a n i s m suggested b y D r s . C a l d e r a z z o a n d C o t

- 1

t o n for R e a c t i o n s 1 a n d 2, w h i c h i n v o l v e d a n a t t a c k b y t h e l i g a n d C O o r L , s i m u l taneous w i t h a n intromolecular rearrangement to form the a c e t y l group. W e t h e n s t u d i e d t h e r e a c t i o n s of C H M n ( C O ) 5 w i t h t r i p h e n y l p h o s p h i n e a n d 3

triphenylphosphite, using the same solvent, t e t r a h y d r o f u r a n .

I n these cases t h e

o b s e r v e d r a t e c o n s t a n t rose w i t h l i g a n d c o n c e n t r a t i o n t o w a r d s a l i m i t i n g v a l u e , w h i c h w a s close t o t h e r a t e c o n s t a n t o b t a i n e d u s i n g c y c l o h e x y l a m i n e ( F i g u r e I ) . T o e x p l a i n these o b s e r v a t i o n s , w e p o s t u l a t e d a t w o - s t e p m e c h a n i s m : CH Mn(CO) 3

5

^

CH COMn(CO) 3

+L ^ - L

4

CH COMn(CO) L 3

4

(3)

T h e first s t e p i n v o l v e s a n i n t r a m o l e c u l a r r e a r r a n g e m e n t t o f o r m t h e a c e t y l g r o u p ; t h e s e c o n d is t h e r e a c t i o n of t h e i n t e r m e d i a t e w i t h t h e l i g a n d t o give t h e product.

final

I t is possible t h a t a m o l e c u l e of s o l v e n t is c o o r d i n a t e d t o t h e i n t e r m e d i

ate s h o w n i n E q u a t i o n 3.

S i n c e i t w o u l d h a v e n o effect o n t h e f o r m of t h e r a t e

e x p r e s s i o n for t h e r e a c t i o n , we c a n n o t s a y c o n c l u s i v e l y w h e t h e r o r n o t t h i s i s so. E q u a t i o n 3 c a n be c o n v e n i e n t l y a b b r e v i a t e d a s f o l l o w s : M

— k—l

MS

^±

M L

k—i


(4)



216

.3 .4 moles/liter Figure

I.

Reaction

of

CHzMn(CO)s

with

plot of observed rate constant against

.5

REACTIONS

.6

triphenylphosphite triphenylphosphite

in

tetrahydrofuran;

concentration.

w h e r e M represents t h e s t a r t i n g m a t e r i a l , M S t h e i n t e r m e d i a t e , a n d M L t h e product.

final

I n d i s c u s s i n g t h e k i n e t i c s of these r e a c t i o n s I s h a l l i g n o r e £-2 because

a l l t h e r e a c t i o n s m e n t i o n e d here w e n t t o c o m p l e t i o n . If t h e first s t e p of t h i s r e a c t i o n were r a t e c o n t r o l l i n g , t h e r e a c t i o n r a t e w o u l d be c o m p l e t e l y i n d e p e n d e n t of l i g a n d c o n c e n t r a t i o n , a n d e v i d e n t l y t h i s i s t h e case for c y c l o h e x y l a m i n e i n t e t r a h y d r o f u r a n .

T h e r a t e e x p r e s s i o n for t h i s r e a c t i o n

then becomes: 4ML] dt

-

MM]

(5)

H o w e v e r , i f t h e first s t e p i s n o t c o m p l e t e l y r a t e c o n t r o l l i n g , t h e r e w i l l be c o m p e t i t i o n for t h e i n t e r m e d i a t e , M S , b e t w e e n t h e s e c o n d f o r w a r d s t e p t o give t h e

final

p r o d u c t , a n d t h e reverse of t h e first s t e p , w h i c h l e a d s b a c k t o t h e s t a r t i n g m a t e r i a l .


8.

HECK

Discussion

217

W e b e l i e v e t h i s i s t h e ease for t h e r e a c t i o n s of C H 3 M n ( C O ) 5 w i t h t r i p h e n y l p h o s p h i n e and triphenylphosphite in tetrahydrofuran. U n d e r these c o n d i t i o n s , a s s u m i n g t h e s t e a d y s t a t e a p p r o x i m a t i o n for t h e c o n c e n t r a t i o n of t h e i n t e r m e d i a t e , t h e r a t e e x p r e s s i o n b e c o m e s :

4ML]

WM][L]

dt

+

kJL]

(

}

F r o m t h i s one c a n o b t a i n a n e x p r e s s i o n r e l a t i n g t h e o b s e r v e d r a t e c o n s t a n t t o


the ligand concentration: — &obs

=

+ [L]

k\

(7)

I f t h e m e c h a n i s m i s c o r r e c t , E q u a t i o n 7 s h o w s t h a t a p l o t of t h e r e c i p r o c a l of t h e o b s e r v e d r a t e c o n s t a n t a g a i n s t t h e r e c i p r o c a l of t h e l i g a n d c o n c e n t r a t i o n s h o u l d be l i n e a r f o r t h e r e a c t i o n s of C H M n ( C O ) 5 w i t h t r i p h e n y l p h o s p h i n e a n d t r i p h e n y l 3

phosphite.

T h i s w a s f o u n d t o be t h e case for b o t h r e a c t i o n s ( F i g u r e J ) , a n d p r o

vides good evidence t h a t the postulated m e c h a n i s m is indeed correct.

8

liters/mole Figure

J.

Reaction

of CHzMn(CO)§

in tetrahydrofuran.

with

Plot of

triphenylphosphite

reciprocals.

In addition, E q u a t i o n 7 predicts that b y extrapolating to a reciprocal concen t r a t i o n of z e r o , one s h o u l d o b t a i n a v a l u e f o r k\ t h e r a t e of f o r m a t i o n of t h e i n t e r y

mediate from C H 3 M n ( C O ) 6 .

T h i s s h o u l d be i n d e p e n d e n t of t h e l i g a n d u s e d , d e

pending only on the solvent.

F i g u r e Κ s h o w s t h e v a l u e s for k\ o b t a i n e d for t h e

r e a c t i o n s of C H M n ( C O ) 5 w i t h t h r e e d i f f e r e n t l i g a n d s i n t e t r a h y d r o f u r a n , w h i c h a r e 3

i n r e a s o n a b l e a g r e e m e n t w i t h one a n o t h e r . T h e o b s e r v a t i o n s of D r s . C a l d e r a z z o a n d C o t t o n (1) c a n a l s o be e x p l a i n e d o n t h e b a s i s of t h i s m e c h a n i s m .

I n t h e v e r y l o w l i g a n d c o n c e n t r a t i o n s t o w h i c h these


218

MECHANISMS OF INORGANIC Ligand

ki(sec.—l)

cyclohexylamine triphenylphosphine triphenylphosphite Figure

K.

REACTIONS

9.6 Χ Ι Ο " 9.0 Χ Ι Ο " 9.9 Χ Ι Ο "

Values of k\ for the reaction of CHzMn(CO)s

4 4 4

with various

ligands

in

tetrahydrofuran

a u t h o r s were r e s t r i c t e d b y t h e p o o r s o l u b i l i t y of C O i n t h e s o l v e n t s u s e d , t h e s e c o n d


s t e p of t h e r e a c t i o n (the r e a c t i o n of t h e i n t e r m e d i a t e w i t h C O ) w o u l d b e c o m e r a t e controlling, leading to the rate expression : d\ML]

[M][L]

dt w h i c h agrees w i t h t h e o b s e r v e d

first-order

(8)

dependence on b o t h C H 3 M n ( C O ) g a n d

CO. I w o u l d l i k e t o a s k D r . H e c k i f he believes t h a t t h e i n s e r t i o n r e a c t i o n s of CHgCo(CO)4

proceed

by

a

similar

two-step

mechanism,

or

by

a

concerted

mechanism? Dr. Heck:

W e h a v e p r o p o s e d m a n y t i m e s t h a t t h e a c y l g r o u p i s f o r m e d before

t h e l i g a n d c o m e s i n , b u t t h e r a t e s i n t h e c o b a l t series are t o o f a s t t o m e a s u r e .

I

t h i n k cobalt and manganese react similarly. H a v e y o u measured this rate i n a hydrocarbon solvent b y a n y chance—one that wouldn't coordinate? Dr. Mawby: was

first-order

I n w-hexane, t h e r e a c t i o n of C H 3 M n ( C O ) e w i t h c y c l o h e x y l a m i n e

i n both reactants, suggesting t h a t a concerted mechanism, i n v o l v i n g

s i m u l t a n e o u s a t t a c k b y t h e a m i n e a n d r e a r r a n g e m e n t t o f o r m t h e a c e t y l g r o u p , is operating.

I n mesitylene, w h i c h has a s l i g h t l y higher dielectric constant,

o b s e r v e d a m o r e c o m p l i c a t e d s t a t e of affairs.

we

B o t h mechanisms appeared to oper

a t e side b y s i d e , a n d we o b t a i n e d r a t e c o n s t a n t s for b o t h t h e t w o - s t e p a n d t h e c o n certed mechanisms.

C e r t a i n l y a nonpolar solvent appears to favor the concerted

mechanism. Alan J . Chalk:

I should like t o c o m m e n t on the p o i n t raised b y D r . D e s s y

on coordinately unsaturated catalysts a n d on some points i n the paper. J o h n H a r r o d a n d I h a v e been l o o k i n g a t t h e s i l i c o n h y d r i d e a d d i t i o n t o olefins catalyzed by Pt(II)

W e d i s c u s s e d t h i s c a t a l y s i s r e c e n t l y (141st N a t i o n a l M e e t i n g of t h e A m e r i c a n C h e m i c a l S o c i e t y , M a r c h 1962) i n t e r m s of a n olefin i n s e r t i o n r e a c t i o n i n v o l v i n g a P t ( I I ) olefin c o m p l e x ( J ) .

W e found that catalysis was only accomplished b y p l a t i n u m

c o m p o u n d s c a p a b l e of c o o r d i n a t i n g olefins.

F o r example, substitution b y tertiary

p h o s p h i n e s b l o c k s c o o r d i n a t i o n b y olefins a n d g r e a t l y reduces t h e c a t a l y t i c a c t i v i t y of P t ( I I ) .

T h e s u b s t i t u t i o n b y p h o s p h i n e s does n o t affect t h e a b i l i t y of t h e c o m

plexes t o c l e a v e t h e S i — H b o n d , h o w e v e r .

T h e h i n d e r i n g of a c a t a l y t i c r e a c t i o n

b y b l o c k i n g c o o r d i n a t i o n sites is a c o m m o n o c c u r r e n c e a n d i s , I t h i n k , a p e r s u a s i v e


8.

HECK

Discussion

219

a r g u m e n t f a v o r i n g t h e n e c e s s i t y for a c o o r d i n a t e l y u n s a t u r a t e d o r

coordinately

labile catalyst. C o n c e r n i n g D r . H e c k ' s e x p e c t a t i o n of a cis a d d i t i o n for t h e i n s e r t i o n r e a c t i o n , we h a v e f o u n d t h a t t h e reverse r e a c t i o n , a n e l i m i n a t i o n , a l s o r e s u l t s i n a cis p r o d u c t . T h u s , t h e i s o m e r i z a t i o n of t e r m i n a l olefins, c a t a l y z e d b y m e t a l i o n s w h i c h f o r m trcomplexes,

p r o d u c e s t h e cis-2 olefin first (4).

S u b s e q u e n t l y , t h e t r a n s - 2 olefin i s

formed, however, w h i c h requires explanation.

P o s s i b l y t h e h y d r i d e i s , i n t h i s case,

p u l l e d off t h e a l k y l g r o u p b y a n o t h e r c o o r d i n a t e d olefin r a t h e r t h a n b y t h e m e t a l itself.


M y l a s t c o m m e n t c o n c e r n s t h e r e a c t i o n of p a l l a d i u m olefin c o m p l e x e s w i t h carbon monoxide discovered b y T s u j i .

I agree t h a t t h i s is m o s t l i k e l y t o p r o c e e d b y

an insertion rather than an ionic mechanism. is r a r e h o w e v e r .

C h l o r i d e a t t a c k o n c o o r d i n a t e d olefin

C h l o r i d e i o n i s a n i n h i b i t o r , for e x a m p l e i n t h e p a l l a d o u s c h l o r i d e

c a t a l y z e d h y d r a t i o n of e t h y l e n e (Ρ).

I , therefore, w o n d e r e d w h e t h e r c a r b o n m o n

oxide w a s a f f e c t i n g t h e ease w i t h w h i c h c h l o r i d e a t t a c k s o l e f i n .

One can postulate

t h a t c a r b o n m o n o x i d e p a r t i c i p a t e s i n t h i s i n s e r t i o n e i t h e r as a gas phase r e a c t a n t o r b y first f o r m i n g a c a r b o n y l olefin c o m p l e x .

S u c h c o m p l e x e s of t h e n o b l e

metals

were u n k n o w n , b u t e x a m i n i n g t h e r e a c t i o n b e t w e e n c a r b o n m o n o x i d e a n d t h e h a l o gen b r i d g e d olefin c o m p l e x e s of p l a t i n u m r e v e a l e d t h a t t h e y are f o r m e d v e r y r e a d i l y (2).

A n a t t e m p t w a s a l s o m a d e t o p r o d u c e β - i o d o a c y l i o d i d e s b y t h e r e a c t i o n of

iodine, carbon monoxide chloride.

a n d olefins i n t h e presence of p a l l a d i u m o r p l a t i n u m

T h i s i s , i n effect, a n a t t e m p t t o m a k e D r . T s u j i ' s r e a c t i o n c a t a l y t i c

rather than stoichiometric. monoxide.

N o c a r b o n y l i n s e r t i o n o c c u r r e d a t 1 a t m . of

carbon

H o w e v e r , i t w a s f o u n d t h a t i o d i n a t i o n of t h e olefin w a s c a t a l y z e d b y

p l a t i n u m olefin c o m p l e x e s a n d t h a t a n a d d i t i o n a l increase i n c a t a l y t i c a c t i v i t y a c c o m p a n i e d t h e presence of c a r b o n m o n o x i d e .

T h e r e has been m u c h s p e c u l a t i o n

a t t h i s conference c o n c e r n i n g t h e p o s s i b i l i t y of a f f e c t i n g c a t a l y t i c a c t i v i t y b y c h a n g i n g t h e l i g a n d s i n t h e c o o r d i n a t i o n sphere of t h e c a t a l y s t .

T h i s would appear to

be s u c h a case.

Literature

Cited

(1) C a l d e r a z z o , F., C o t t o n , F. Α., Inorg. Chem. 1, 30 (1962). (2) C h a l k , A. J., Tetrahedron Letters 37, 2627 (1964). (3) C h a l k , A. J., H a r r o d , J. F., J. Am. Chem. Soc. i n press. (4) C h a l k , A. J., H a r r o d , J. F., J. Am. Chem. Soc. 86, 1776 (1964). (5) Coffield, T. H., K o z i k o w s k i , J., Closson, R. D., " I n t e r n a t i o n a l Conference o n C o o r d i n a t i o n C h e m i s t r y , London, April 1959. (6) H e c k , R. F., Breslow, D. S., J. Am. Chem. Soc. 8 3 . , 4023 (1961). (7) H e c k , R i c h a r d F., J. Am. Chem. Soc. 85, 1460 (1963). (8) M a w b y , R. J., Basolo, F r e d , Pearson, R a l p h , J. Am. Chem. Soc. 86, 3994 (1964). (9) S c h m i d t , J., Chem. and Ind. 54, 1962.


Mechanisms of Inorganic Reactions

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