Inorganic Compounds with Unusual PropertiesâII - American

8 Homogeneous Catalysis of the Water Gas

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Shift Reaction by Metal Carbonyls

1

PETER C. FORD , CHARLES UNGERMANN, VINCENT LANDIS, and SERGIO A. MOYA—Department of Chemistry, University of California, Santa Barbara, CA 93106 ROBERT C. RINKER—Department of Chemical Engineering, University of California, Santa Barbara, CA 93106 RICHARD M. LAINE—SRI International, Menlo Park, CA 94025 Summarized are our recent studies of the homogeneous catalysis of the water gas shift reaction. Characterization of the previously reported catalyst based on Ru (CO) in alkaline, aqueous ethoxyethanol solution indicates that the principal ruthenium components are tetraruthenium carbonyl hydride anions. A mechanism is proposed involving the attack of OH or H O on coordinated C O to give, after loss of C O2, a dihydride metal species MH . Reductive elimination of hydrogen and coordination of another C O regenerates the original metal carbonyl M C O . A number of other metal carbonyls proved to form active catalysts under analogous conditions. Active catalysts are also formed from H Ru (CO) in acidic aqueous diglyme solution and from H Ru (CO) or H Ru (CO) /Fe(CO) mixtures in organic amine solutions. 3

12

-

2

2

4

4

4

12

4

12

4

4

12

5

A n i m p o r t a n t route f o r t h e p r o d u c t i o n of h y d r o g e n f r o m w a t e r is t h e w a t e r gas shift r e a c t i o n ( R e a c t i o n 1 ) . Since w a t e r gas ( a m i x t u r e of C 0 , C O , H 0 , a n d H ) c a n b e o b t a i n e d f r o m t h e r e a c t i o n o f s t e a m 2

2

2

w i t h h o t coke, i t w i l l p l a y a n i m p o r t a n t r o l e i n m e t h o d s of i m p r o v i n g H 0 ( g ) + CO(g) ^ C0 (g) + H (g) 2

2

2

(1)

Address correspondence to this author at the Department of Chemistry, University of California, Santa Barbara, C A 93106. 1

0-8412-0429-2/79/33-173-081$05.00/0 © 1979 American Chemical Society In Inorganic Compounds with Unusual Properties—II; King, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1979.

82

INORGANIC

COMPOUNDS WITH UNUSUAL

PROPERTIES

the usefulness of c o a l as a p r i m a r y f u e l source i n this c o u n t r y .

II

Schemes

f o r t h e gasification a n d l i q u i f i c a t i o n of c o a l (i.e., t h e p r o d u c t i o n of r e l a tively light hydrocarbons) require copious, readily available hydrogen i n a d d i t i o n to that a l r e a d y p r o d u c e d . T h e e n o r m o u s q u a n t i t i e s of i n d u s t r i a l h y d r o g e n n o w u s e d (1976 p r o d u c t i o n i n the U n i t e d States w a s ~ 10

11

s t a n d a r d c u b i c meters {1,2))

are d e r i v e d l a r g e l y b y t h e steam

r e f o r m i n g or p a r t i a l o x i d a t i o n of h y d r o c a r b o n s . T h u s , e v e n w i t h o u t n e w , Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 29, 2013 | http://pubs.acs.org Publication Date: May 5, 1979 | doi: 10.1021/ba-1979-0173.ch008

h y d r o g e n - d e p e n d e n t m e t h o d s f o r t h e synthesis of h y d r o c a r b o n s , a m a j o r s a v i n g of this v a l u a b l e resource w o u l d b e one benefit f r o m t h e better u s e of other m e t h o d s f o r the p r o d u c t i o n of h y d r o g e n , e.g., t h e w a t e r - g a s shift r e a c t i o n . C o m m e r c i a l methods heterogeneous

f o r c a r r y i n g out the shift reaction i n v o l v e

m e t a l o x i d e catalysts

at e l e v a t e d t e m p e r a t u r e s

A c c o r d i n g to t h e t h e r m o d y n a m i c s of R e a c t i o n 1, A G ° = ( - 4 . 7 6 ) , AH° =

(3,4).

—6.81 k c a l / m o l

- 9 . 8 3 kcal/mol (0.68), a n d AS° =

- 1 0 . 1 e u (18.3)

[figures i n parentheses are f o r H 0 ( 1 ) r a t h e r t h a n H 0 ( g ) ] , greater p r o 2

2

d u c t i o n efficiency s h o u l d b e r e a l i z e d b y c a r r y i n g o u t this

exothermic

r e v e r s i b l e process at l o w e r t e m p e r a t u r e s . C o n s i d e r a b l e p r e c e d e n t exists f o r t h e use of H 0 / C O m i x t u r e s as 2

the source of h y d r o g e n i n t h e h o m o g e n e o u s r e d u c t i o n s of v a r i o u s o r g a n i c c o m p o u n d s . T h e h y d r o - h y d r o x y m e t h y l a t i o n o f olefins (5,6)

is one s u c h

e x a m p l e ( R e a c t i o n 2 ) w h e r e t h e e q u i v a l e n t of one C O a n d t w o h y d r o gens are a d d e d to t h e olefin i n a process w h i c h consumes three moles o f CO/H 0 2

RCH = C H

2

>R C H C H C H 0 H + R C H — C H | CH OH 2

Fe(CO) /NR 5

3

2

2

3

(2)

2

C O a n d t w o of H

2

0 a n d p r o d u c e s t w o moles of C 0 . H o m o g e n e o u s 2

catalysis of this r e a c t i o n c a n b e a c c o m p l i s h e d w i t h a n i r o n c a r b o n y l i n c o n j u n c t i o n w i t h a B r o n s t e d a c i d o r base. T h u s i t appears that c o n d i t i o n s m i g h t b e f o u n d w h e r e t h e s h i f t r e a c t i o n itself c a n b e effected g e n e o u s l y u s i n g m e t a l c o m p l e x catalysts.

T o this e n d , w e h a v e

e x a m i n i n g t h e a c t i v i t y of v a r i o u s h o m o g e n e o u s

homobeen

catalysts f o r t h e s h i f t

r e a c t i o n , a n d o u r i n v e s t i g a t i o n s o f m e t a l c a r b o n y l cluster complexes a r e s u m m a r i z e d here. Catalysis

by Ruthenium

Carbonyl

in Alkaline

Solution

I n a p r e l i m i n a r y s t u d y (7) w e r e p o r t e d t h a t catalysis of t h e s h i f t r e a c t i o n is a c c o m p l i s h e d b y a h o m o g e n e o u s s o l u t i o n p r e p a r e d f r o m R u ( C O ) i . F o r t h e i n i t i a l e x p e r i m e n t s , t h e catalysis s o l u t i o n t y p i c a l l y c o n t a i n e d t h e f o l l o w i n g c o m p o n e n t s i n 15 m L of p u r i f i e d e t h o x y e t h a n o l solvent: R u ( C O ) (0.126 g, 2 X 10" m o l ) , K O H (0.5 g, 0.01 m o l ) , a n d 3

2

3

1 2

4

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

8.

FORD E T A L .

H 0

Water Gas Shift

( l . O g , 0.06mol).

2

83

Reaction

A t 100°C under about 1 atm C O

(occasionally

r e c h a r g e d ) , this s o l u t i o n p r o d u c e d a b o u t 3 X 10" m o l of H 2

m a t e l y a n e q u i v a l e n t a m o u n t of C 0

and approxi-

over a p e r i o d of 30 days. N o t a b l y ,

2

this q u a n t i t y represents a r a t i o of 150 moles of H a d d e d or three moles of H

2

2

p e r m o l e of R u ( C O ) i 3

2

p e r m o l e of K O H a d d e d . T h u s the system is

2

c a t a l y t i c b o t h i n r u t h e n i u m a n d i n base. W h e n this r e a c t i o n w a s c a r r i e d out i n a s o l u t i o n p r e p a r e d f r o m t h e d e u t e r a t e d solvent C H C H O C H C H O D p l u s D 0 , D Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 29, 2013 | http://pubs.acs.org Publication Date: May 5, 1979 | doi: 10.1021/ba-1979-0173.ch008

3

2

2

2

2

( > 9 0 % ) was

2

t h e h y d r o g e n p r o d u c t as m e a s u r e d b y mass s p e c t r o m e t r y ( s m a l l a m o u n t s of H D a n d H

f o u n d c o u l d be a t t r i b u t e d to the i s o t o p i c i m p u r i t y of t h e

2

solvent m i x t u r e ) . T h u s , the source of the d i h y d r o g e n p r o d u c t is w a t e r or w a t e r - e x c h a n g e a b l e h y d r o g e n s i n the s o l u t i o n ( 7 ) .

The homogeneity

of the r e a c t i o n s o l u t i o n is i n d i c a t e d b y its c l a r i t y w h e n e x a m i n e d w i t h a s t r o n g l i g h t a n d b y the fact that a n a c t i v e catalyst s o l u t i o n d i s p l a y e d t h e same rate of h y d r o g e n p r o d u c t i o n at 1 1 0 ° C before a n d after f i l t r a t i o n t h r o u g h a F l u o r o p o r e filter ( F H L P , 0.5 /x p o r e size) u n d e r a n inert atmosphere.

A d d i t i o n a l qualitative support for homogeneity

of the

active

c o m p o n e n t s derives f r o m the f a c t that the catalyst solutions s h o w r e l a t i v e l y h i g h r e p r o d u c i b i l i t y of a c t i v i t y w h e n p r e p a r e d a n u m b e r of d i f ferent times b y different i n d i v i d u a l s i n o u r laboratories. E x a m i n a t i o n of the a c t i v e r u t h e n i u m c a r b o n y l catalyst s o l u t i o n b y I R a n d N M R spectroscopy a n d b y i o n exchange c h r o m a t o g r a p h y i n d i c a t e that the s o l u t i o n contains at least three i o n i c r u t h e n i u m c o m p o n e n t s , t w o of w h i c h are major. I n a d d i t i o n , traces of a species w i t h a n I R s p e c t r u m consistent w i t h t h a t of R u ( C O ) i is seen.

T h e m a j o r i o n i c species

are

the t r i h y d r i d o tetraruthenium dodecacarbonyl anion, H R u ( C O ) i ~

(>

3

2

3

50%)

4

2

a n d a c o m p o n e n t ( X " ) h a v i n g s p e c t r a l p r o p e r t i e s different f r o m

those of k n o w n r u t h e n i u m c a r b o n y l species. i n d i c a t e the E t N 4

+

I R a n d * H N M R spectra

salt of X to b e c a r b o n y l h y d r i d e ( i ?

co

=

2072w, 2012s,

1987s, 1950s, b r , 1732w i n T H F ; h y d r i d e resonance at 22.53 r i n ^ - a c e tone).

T h e c h e m i c a l b e h a v i o r of this m a t e r i a l suggests that X " m a y b e

HRu (CO)i ". 4

Although

3

purification problems

o b t a i n i n g a g o o d e l e m e n t a l analysis of the E t N

+

4

the m a j o r species f o r m e d b y the H S 0 2

(CO)i

3

4

have

prevented

our

salt of X " , the f a c t that

n e u t r a l i z a t i o n of X " is H R u 2

4

is consistent w i t h this assignment.

W h e n the a c t i v e catalyst s o l u t i o n is n e u t r a l i z e d w i t h H S 0 2

4

before

i s o l a t i n g the c o m p o n e n t s , three k n o w n r u t h e n i u m species are f o u n d i n the r e a c t i o n m i x t u r e : R u ( C O ) 3

H Ru (CO)i 4

4

2

(~60%).

1 2

( 2 0 - 3 0 % ), H R u ( C O ) i 2

4

( 1 0 % ), a n d

3

T h e f o r m a t i o n of these species

is c e r t a i n l y

n o t u n e x p e c t e d u n d e r the r e a c t i o n c o n d i t i o n s g i v e n t h e observations b y L e w i s et a l . ( 8 ) H Ru (CO)i 4

4

2

t h a t the reactions of R u ( C O ) i 3

and H R u ( C O ) 2

4

1 3

2

w i t h w a t e r leads t o

a n d b y Kaesz a n d co-workers (9)

that

the f o r m e r species c a n b e d e p r o t o n a t e d b y base to g i v e H R u ( C O ) ~ . 3

4


i2

84

INORGANIC


PROPERTIES

I n this context, i t is p a r t i c u l a r l y i n t e r e s t i n g t o note that catalysis u n d e r t h e same c o n d i t i o n s , b u t u s i n g H R u ( C O ) 4

4

i 2

II

runs

as t h e i n i t i a l source,

h a v e a c t i v i t y i n d i s t i n g u i s h a b l e f r o m that of runs s t a r t i n g w i t h R u ( C O ) i . 3

2

I n a d d i t i o n , t h e s p e c t r a l p r o p e r t i e s of t h e a c t i v e solutions f r o m these t w o sources are i n d i s t i n g u i s h a b l e . L a s t l y i t is also n o t a b l e that activity (RuCl

3

is seen

with

solutions

prepared

with

comparable

ruthenium trichloride

• n H 0 ) as t h e i n i t i a l r u t h e n i u m source. 2


C l o s e r e x a m i n a t i o n of t h e r e a c t i o n s o l u t i o n reveals t h a t t h e n a t u r e of t h e base species changes m a r k e d l y i n t h e e a r l y stages of t h e catalysis r u n s . C a r b o n m o n o x i d e is k n o w n t o react w i t h aqueous a l k a l i h y d r o x i d e t o f o r m t h e analogous a l k a l i f o r m a t e (10,11).

T h i s r e a c t i o n occurs u n d e r

t h e i n i t i a l s o l u t i o n c o n d i t i o n s of t h e catalyst runs d e s c r i b e d here a n d is r e l a t i v e l y fast c o m p a r e d w i t h t h e shift r e a c t i o n (12).

N o t a b l y , t h e pres-

e n c e o f t h e r u t h e n i u m catalyst has l i t t l e i f a n y effect o n t h e rate of f o r m a t e formation.

T h u s , f o r t h e t y p i c a l catalysis

runs at 1 0 0 ° C ,

titrimetric

studies i n d i c a t e t h a t w i t h i n a p e r i o d of h o u r s v i r t u a l l y a l l t h e K O H first a d d e d has b e e n c o n s u m e d a n d that > 9 0 % of t h e base e q u i v a l e n t s a r e present i n t h e guise of p o t a s s i u m f o r m a t e .

T h e r e m a i n i n g base e q u i v a -

lents are l a r g e l y a m i x t u r e of p o t a s s i u m b i c a r b o n a t e a n d p o t a s s i u m carbonate.

I n this context, i t is n o t a b l e t h a t R u ( C O ) i 3

solutions p r e p a r e d u s i n g K C 0 2

plus K H C 0

3

3

2

and H R u ( C O ) i 4

4

2

as t h e i n i t i a l bases g i v e

c o m p a r a b l e c a t a l y t i c a c t i v i t y t o those p r e p a r e d u s i n g K O H ( T a b l e I ) . "Possible Mechanisms for

Catalysis

A t this p o i n t i t c a n b e of v a l u e t o speculate

o n the mechanisms

w h i c h m i g h t b e c a t a l y z i n g t h e shift r e a c t i o n . O n e m e c h a n i s m is d e s c r i b e d i n S c h e m e 1. I n this scheme i n i t i a l a c t i v a t i o n of c a r b o n m o n o x i d e i n v o l v e s n u c l e o p h i l i c attack of O H " o r H complex M - C 0 H \

0 o n M - C O to f o r m t h e h y d r o x y c a r b o n y l

2

A m p l e p r e c e d e n t exists f o r this r e a c t i o n .

2

F o r ex-

a m p l e , several m e t a l c a r b o n y l c o m p l e x e s h a v e b e e n r e p o r t e d t o u n d e r g o oxygen exchange w i t h

l s

O - l a b e l e d w a t e r i n s o l u t i o n (13,14),

a n d the

r e v e r s i b l e f o r m a t i o n of h y d r o x y c a r b o n y l species has b e e n p o s t u l a t e d i n l o g i c a l m e c h a n i s m s f o r this exchange.

S u c h species h a v e i n d e e d b e e n

i s o l a t e d , e.g., R e a c t i o n 3 ( 1 5 ) . H 0 — IrCl (PhPMe ) (CO) (-C0 H) dry HC1 2

IrCl (PhPMe ) (C0) 2

2

2

2

+

2

2

2

2

(3)

T h e d e c a r b o x y l a t i o n of t h e h y d r o x y c a r b o n y l species H M - C 0 H s h o u l d b e f a c i l e a n d has b e e n p r o p o s e d f o r other conversions of c o o r d i n a t e d c a r b o n y l t o h y d r i d e , e.g., R e a c t i o n 4 (16). Subsequent reductive e l i m i n a t i o n o f d i h y d r o g e n f r o m M H has p r e c e d e n c e f o r a n u m b e r o f 2

2


8.

FORD E T A L .

Water Gas Shift

85

Reaction

Scheme 1 O H " (or H 0 )

OH

2

/

M—CO

- •

M —C = 0


i{

CO

(+H ) +

•H 0 2

C

J

OH-

' OH

/ HM—C = 0

CO,

"M"

H

f

3

2

2

(Et P) (CO) C l

transit

MH

+

+ O H " - » Pt (Et P) C 1 H + C 0 3

2

(4)

2

m o n o n u c l e a r a n d p o l y n u c l e a r systems (17). T h i s last step f o r m s 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 species " M " w h i c h undergoes r a p i d r e a c t i o n w i t h free C O to r e f o r m M - C O . ( A s i m i l a r c y c l i c scheme has also b e e n p r o p o s e d r e c e n t l y b y E i s e n b e r g (18)). A m o d i f i c a t i o n of this s c h e m e w o u l d b e to h a v e C O assist i n t h e d e h y d r o g e n a t i o n step i n some m a n n e r , p e r h a p s b y c o o r d i n a t i o n w i t h M H p r i o r t o loss of h y d r o g e n . 2

T h e c o m p o s i t i o n of t h e r u t h e n i u m catalyst s o l u t i o n is consistent w i t h t h e steps p r o p o s e d i n S c h e m e 1, i f w e v i s u a l i z e M - C O as H R u ( C O ) - ( o r H R u ( C O ) ) a n d M H as H R u ( C O ) - ( o r H R u ( C O ) i ) . C o n s i d e r a b l y m o r e i n f o r m a t i o n ( k i n e t i c s , etc.) needs a c c u m u l a t i o n t o s u p p o r t o r d i s p r o v e this m e c h a n i s m , b u t at present i t serves as a reasonable w o r k i n g h y p o t h e s i s . W i t h r e g a r d t o t h e details of S c h e m e 1, it is n o t a b l e that n u c l e o p h i l i c attack o n c o o r d i n a t e d c a r b o n y l s is o f t e n q u i t e f a c i l e (13-16,19,20). I n a d d i t i o n , w e h a v e f o u n d t h e react i o n of R u ( C O ) i w i t h base i n aqueous a l c o h o l i c s o l u t i o n t o o c c u r at l o w e r t e m p e r a t u r e a n d m o r e r a p i d l y t h a n t h e shift r e a c t i o n catalysis. T h u s i t appears that C O a c t i v a t i o n is n o t rate l i m i t i n g b u t another step, p e r h a p s t h e r e d u c t i v e e l i m i n a t i o n of h y d r o g e n , i s . 4

1 3

2

4

1 3

2

3

4

1 2

2

3

2


4

4

86

INORGANIC


PROPERTIES

II

Scheme 2 C O + O H " (or H 0 ) -> H C 0 " (or H C O O H ) 2

H C 0 ~ (or H C O O H ) + 2

(5)

2

catalyst H 0 -> H 2

2

+ C0

2

+

O H " (or H 0 )

(6)

2


A n o t h e r p o s s i b l e m e c h a n i s m f o r t h e shift r e a c t i o n w o u l d b e i n v o l v i n g f o r m a t e or f o r m i c a c i d as a n i n t e r m e d i a t e ( S c h e m e 2 ) .

one The

f a c i l e r e a c t i o n of C O w i t h s t r o n g base a n d the r e s u l t i n g presence of formate i n the reaction solution initially prepared w i t h K O H make c o m p e l l i n g the c o n s i d e r a t i o n of this m e c h a n i s m . O t h e r p l a t i n u m m e t a l catalysts h a v e b e e n r e p o r t e d f o r R e a c t i o n 6 ( 2 1 ) .

H o w e v e r , w e a n d others

h a v e d e m o n s t r a t e d catalysis of the shift r e a c t i o n i n a c i d i c s o l u t i o n ( v i d e i n f r a ) . I n a d d i t i o n , w e h a v e f o u n d that a d d i n g s i g n i f i c a n t c o n c e n t r a t i o n s of s o d i u m f o r m a t e to a n a c t i v e r u t h e n i u m catalyst s o l u t i o n h a d l i t t l e effect o n the rate of H

2

a n d C O o p r o d u c t i o n . T h e s e observations

against the i m p o r t a n c e of S c h e m e 2 f o r this system. ( 7 ) that H C O o " is r a p i d l y d e c o m p o s e d to H

2

argue

( O u r earlier r e p o r t

p l u s C O o b y the r u t h e n i u m

catalyst i n a l k a l i n e s o l u t i o n is a p p a r e n t l y i n c o r r e c t .

I n that s t u d y , f o r -

m a t e w a s a d d e d as f o r m i c a c i d i n q u a n t i t i e s sufficient to a c i d i f y t h e s o l u t i o n to g i v e c o n d i t i o n s u n d e r w h i c h the system does

decompose

f o r m a t e . W e are e v a l u a t i n g the r e a c t i o n i n a c i d s o l u t i o n f u r t h e r . ) Other Catalysts

in Alkaline

Alcoholic

Solution

W e also h a v e s t u d i e d other m e t a l c a r b o n y l c o m p l e x e s i n a l k a l i n e e t h o x y e t h a n o l to s u r v e y the

g e n e r a l i t y of the s h i f t - r e a c t i o n

catalysis.

U n d e r c o n d i t i o n s (0.9 a t m C O , 1 0 0 ° C ) c o m p a r a b l e w i t h those u s e d f o r the r u t h e n i u m catalyst d e s c r i b e d a b o v e , i r o n , r h o d i u m , o s m i u m , a n d i r i d i u m c a r b o n y l s a l l p r o v e d a c t i v e b u t r h e n i u m c a r b o n y l d i d not. systems

starting w i t h the

activities (see

Initial

For

normalized catalytic

Activities of Various Catalysts for Water—Gas Shift Reaction Complex

A l k a l i n e solutions (low p r e s s u r e ) H FeRu (CO) Ir (CO)i2 H Ru (CO) 2

3

1 3

4

4

the

T a b l e I; n o r m a l i z e d a c t i v i t y is b a s e d o n the n u m b e r of

Table I.

A.

listed complexes,

4

1 2

Initial

the

Solution

Activity

c c c d e

10.3 5.3 2.5 3.3 2.5

0

6


8.

FORD E T A L .

Water

Table I . Initial Ru (CO)


3

87

Gas Shift Reaction Continued

Complex

Initial

Solution

1 2

Fe(CO) Rh (CO) Ru C(CO) H Re (CO)i2 Re (CO) Ru (CO) /Fe(CO) 5

6

1 6

G

3

B.

1 7

3

2

1 0

3

1 2

5

A l k a l i n e solutions (high pressure) Rh (CO)i Ru (CO) Ru (CO) /Fe (CO) Fe,(CO)i* Ir (CO)i2 Os (CO) (Ir(CO) Cl) Re (CO)i 0

0

3

1 2

3

1 2

3

1 2

i

4

3

1 2

3

2

2

C.

0

A c i d i c solutions (low p r e s s u r e ) Ru (CO) H Ru (CO)io 3

4

c d e / d c c c c h

2.3 2.6 ^ I 3 2 ~1 3.4' 1.5 -0.15 I r ( C O ) i 2

(CO)

-

1 2

Ru (CO) 3

H Re (CO)i 3

3

2

>

1 2

-

Fe(CO)

Re (CO)i . 2

3

3

> Rh (CO)

5

G

4

>

1 G

2

>

Ru C(CO) 6

H Ru 4

4

>>

1 7

A s o m e w h a t different o r d e r w a s seen f o r

0

the catalysts s t u d i e d u n d e r c o n d i t i o n s w h e r e C O pressure a n d t e m p e r a t u r e w e r e m u c h h i g h e r a n d m e t h a n o l w a s the p r i n c i p a l solvent ( T a b l e

I).

H o w e v e r , i t s h o u l d be n o t e d that the latter d a t a are l a r g e l y f r o m s i n g l e Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 29, 2013 | http://pubs.acs.org Publication Date: May 5, 1979 | doi: 10.1021/ba-1979-0173.ch008

d a y runs i n p r e s s u r i z e d b o m b s i n contrast to the c o n t i n u o u s l y m o n i t o r e d , p e r i o d i c a l l y flushed runs i n the l o w pressure glass vessels.

It is p a r t i c u -

l a r l y n o t a b l e that u n d e r the h i g h e r pressure a n d t e m p e r a t u r e

conditions

the catalyst solutions b a s e d o n R u ( C O ) i

are

3

2

and R h ( C O ) G

1 G

quite

a c t i v e f o r the h y d r o f o r m y l a t i o n a n d h y d r o h y d r o x y m e t h y l a t i o n , respect i v e l y , of olefins b y C O p l u s H 0

(22).

2

A p a r t i c u l a r l y i n t e r s t i n g o b s e r v a t i o n is the h i g h a c t i v i t y seen f o r H FeRu (CO)i . 2

3

Since this is c o n s i d e r a b l y h i g h e r t h a n that seen f o r

3

either r u t h e n i u m c a r b o n y l or i r o n c a r b o n y l alone, these metals a p p a r e n t l y act i n a synergistic m a n n e r .

S i m i l a r enhancements

of a c t i v i t y are n o t e d

w h e n the i r o n a n d r u t h e n i u m are a d d e d together i n the f o r m s F e ( C O ) a n d R u ( C O ) i respectively ( T a b l e I ) . 3

m a l i z e d ) w a s o b s e r v e d w h e n the F e ( C O ) : R u ( C O ) i 5

( a F e : R u ratio of 2 : 3 ) .

The

J

5

O p t i m a l catalytic activity (nor-

2

3

2

r a t i o is a b o u t 2 : 1

H N M R a n d I R spectra of these i r o n /

r u t h e n i u m r e a c t i o n solutions i n d i c a t e d the presence of a n u m b e r of species.

A m o n g these, F e ( C O )

5

and H R u ( C O ) i 3

4

2

could be identified.

_

N e u t r a l i z a t i o n of the r e a c t i o n s o l u t i o n w i t h s u l f u r i c a c i d f o l l o w e d b y s i l i c a g e l c h r o m a t o g r a p h y l e d to the i d e n t i f i c a t i o n of H R u ( C O ) i 4

H FeRu (CO)i 2

3

4

2

and

as the m a j o r cluster species as w e l l as m i n o r amounts of

3

the t r i a n g u l a r c a r b o n y l s R u ( C O ) 3

possibly F e ( C O ) 3

1 2

i 2

, R u F e ( C O ) i , R u F e ( C O ) i , and 2

2

2

2

.

O u r observations a n d those of others h a v e l e d us to v i e w these s o l u tions i n the f o l l o w i n g m a n n e r .

F i r s t , it appears that u n d e r the r e a c t i o n

c o n d i t i o n s ( a l k a l i n e s o l u t i o n at 1 0 0 ° C u n d e r a n atmosphere both H

2

containing

a n d C O ) i n t e r c o n v e r s i o n b e t w e e n the cluster species is r e l a -

t i v e l y f a c i l e . T h u s , w i t h i n h o u r s or p e r h a p s less, a s o l u t i o n p r e p a r e d b y mixing F e ( C O )

5

and R u ( C O ) i 3

2

i n a 1:1 m o l a r r a t i o m a y n o t b e d i s -

t i n g u i s h a b l e f r o m one p r e p a r e d f r o m H F e R u ( C O ) i . C l u s t e r species, 2

3

3

s p e c i f i c a l l y h y d r i d o c a r b o n y l anions, are the p r o m i n e n t reservoirs of t h e metals i n the s o l u t i o n , b u t o u r m e c h a n i s t i c studies are too u n d e v e l o p e d to e s t a b l i s h w h e t h e r the clusters are the p r o b a b l e catalysts. w e f o l l o w the course of the e a r l i e r m e c h a n i s t i c

H o w e v e r , if

speculation based

on

S c h e m e 1, t h e n H F e R u ( C O ) i a n d H F e R u ( C O ) i or t h e i r d e p r o t o 4

3

2

2

3

3

n a t e d analogs m a y b e M H a n d M - C O r e s p e c t i v e l y i n the m i x e d m e t a l 2

catalysts.

K a e s z (23)

has r e p o r t e d the synthesis of H F e R u ( C O ) i , b u t 4

3

2

this species is r e l a t i v e l y u n s t a b l e i n s o l u t i o n , d e c o m p o s i n g to g i v e the


8.

FORD E T A L .

more

Water

Gas Shift

stable H F e R u ( C O ) i 2

3

a m o n g other

3

89

Reaction species.

This

observation

t e m p t s one t o suggest that t h e s y n e r g i s t i c effect of t h e t w o m e t a l catalysts m i g h t b e a t t r i b u t e d t o t h e i n s t a b i l i t y of t h e p r o p o s e d M H

intermediate

2

toward reductive elimination (Reaction 7) ( 8 ) .


MH Catalysis in Acidic

2

-» M + H

(7)

2

Solution

O u r i n i t i a l forays i n t o the s h i f t - r e a c t i o n catalysis

(7) focussed o n

a l k a l i n e c o n d i t i o n s o w i n g t o t h e p r e j u d i c e t h a t i n i t i a l a c t i v a t i o n of coord i n a t e d C O w o u l d b e p a r t i c u l a r l y f a c i l e v i a h y d r o x i d e attack o n C O ( R e a c t i o n 8 ) . H o w e v e r , w a t e r itself m a y b e a c t i v e ( R e a c t i o n 9 ) .

To

M - C O + O H "*± M - C 0 H "

(8)

M - C O + H 0 *± H M - C 0 H

(9)

2

2

2

e v a l u a t e this p o s s i b i l i t y , w e also h a v e s t u d i e d t h e r u t h e n i u m clusters i n acidic solution. N o t a b l y Eisenberg r e a c t i o n catalyst

based

has r e c e n t l y r e p o r t e d a shift-

(18)

o n the R h ( I ) complex

(Rh(CO) Cl) 2

2

i n an

a q u e o u s a c e t i c a c i d / H C l / N a l m e d i u m , c o n f i r m i n g t h e v i a b i l i t y of s u c h an approach. W h e n t h e r e a c t i o n w a s r u n u s i n g 0.1N H S 0

i n aqueous

ethoxy-

as t h e i n i t i a l m e t a l l i c

species,

2

e t h a n o l as t h e solvent a n d H R u ( C O ) i 4

4

2

4

the a c t i v i t y first seen w a s a f a c t o r of six h i g h e r t h a n that f o u n d i n t h e alkaline solution (Table I ) .

H o w e v e r , after several days t h e a c t i v i t y

d e c r e a s e d m a r k e d l y , o w i n g t o t h e s u b l i m a t i o n of t h e r u t h e n i u m f r o m t h e s o l u t i o n i n t o t h e cooler n e c k of the all-glass r e a c t i o n vessel. T h e orange s o l i d c o l l e c t i n g at this l o c a t i o n w a s i d e n t i f i e d as R u ( C O ) i 3

s p e c t r u m b u t m a y h a v e c o n t a i n e d traces of H R u ( C O ) 2

4

tempts w e r e m a d e t o effect t h e catalysis w i t h R u ( C O ) i 3

1 3

2

2

b y its I R

. W h e n atitself i n t h e

same a c i d i c m e d i u m , l i t t l e r e a c t i o n w a s seen o w i n g t o t h e r e l a t i v e l y r a p i d s u b l i m a t i o n of this m a t e r i a l f r o m t h e s o l u t i o n . S i m i l a r l y t h e c a r b i d e cluster R u C ( C O ) i 7 d i s p l a y e d i n i t i a l a c t i v i t y m u c h h i g h e r i n a c i d i c t h a n 6

i n a l k a l i n e s o l u t i o n b u t a g a i n w a s u n s t a b l e t o w a r d s u b l i m a t i o n of R u 3

(CO)

1 2

.

D e s p i t e t h e i n s t a b i l i t y of these r u t h e n i u m c a r b o n y l solutions i n a c i d , the h i g h i n i t i a l a c t i v i t y e n c o u r a g e d t h e search f o r other solvents i n w h i c h Ru (CO)i 3

2

m a y prove more soluble.

D i g l y m e meets this c r i t e r i o n , a n d

preliminary data indicate that H R u ( C O ) 4

4

i 2

in I N H S 0 2

4

aqueous d i -

g l y m e is r o u g h l y one o r d e r of m a g n i t u d e m o r e active as a s h i f t - r e a c t i o n catalyst t h a n i n a l k a l i n e e t h o x y e t h a n o l ( T a b l e I ) .


90

INORGANIC COMPOUNDS W I T H UNUSUAL PROPERTIES

II

V a r i o u s r a t i o n a l e c a n b e offered f o r t h e e n h a n c e d c a t a l y t i c a c t i v i t y i n a c i d . T h e k e y steps i n S c h e m e 1 are l i k e l y t o b e t h e a c t i v a t i o n of C O b y n u c l e o p h i l i c attack o n M - C O a n d t h e r e d u c t i v e e l i m i n a t i o n o f H from M H . 2

species

I f M - C O is either H R u ( C O ) i " o r H R u ( C O ) 4

3

2

4

1 3

2

, t h e latter

( w h i c h is f a v o r e d b y l o w e r i n g t h e p H ) s h o u l d b e t h e m o r e

s u s c e p t i b l e one t o n u c l e o p h i l i c attack.

I n a c i d i c s o l u t i o n t h e m o r e reac-

t i v e n u c l e o p h i l e O H " is at a n i n c o n s e q u e n t i a l c o n c e n t r a t i o n , b u t i t is Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 29, 2013 | http://pubs.acs.org Publication Date: May 5, 1979 | doi: 10.1021/ba-1979-0173.ch008

w o r t h w h i l e t o r e m e m b e r t h a t t h e c o n c e n t r a t i o n of H experiments)

2

0 ( 6 M i n these

is a l w a y s m u c h l a r g e r t h a n ( O H " ) regardless of t h e p H .

W i t h r e g a r d t o t h e r e d u c t i v e e l i m i n a t i o n of h y d r o g e n ( R e a c t i o n 7 ) , i t is e n t i r e l y p o s s i b l e that a n e u t r a l species (e.g., H R u ( C O ) i ) c a n b e m o r e 4

4

2

r e a c t i v e t h a n its d e p r o t o n a t e d a n a l o g (e.g., H R u ( C O ) i " ) . T h e s e are 3

4

2

m e c h a n i s t i c aspects of these systems i n n e e d o f greater e x p l o r a t i o n a n d under study i n our laboratory.

Catalysis in Amine

Solution

T h e r e is c o n s i d e r a b l e p r e c e d e n t f o r the reactions of o r g a n i c amines w i t h metal carbonyls, i n particular w i t h iron carbonyls. a m i n e s react d i r e c t l y w i t h F e ( C O ) h y d r o g e n (6,19),

5

N o t only do

to f o r m various products i n c l u d i n g

b u t they are c o m p o n e n t s of t h e i r o n c a r b o n y l c o n t a i n i n g

catalysts f o r t h e h y d r o f o r m y l a t i o n of olefins w i t h C O a n d H

2

0

(5,6,24).

T h u s , catalysis of t h e shift r e a c t i o n u n d e r analogous c o n d i t i o n s is n o t u n e x p e c t e d , e s p e c i a l l y i n t h e context of t h e a c t i v i t y d i s p l a y e d b y t h e m e t a l c a r b o n y l s i n a l k a l i n e solutions ( a b o v e , et a l . (25),

Indeed, Imyanitov

(7)).

i n a study of the hydrogenation a n d hydrocarboxylation of

dienes w i t h C O a n d H

2

0 catalyzed b y C o ( C O ) 2

8

and by R h ( C O ) i 6

6

plus organic amines, noted the formation of h y d r o g e n a n d C 0 . I n t h e 2

absence of olefins, R h ( C O ) i 6

6

plus pyridine apparently catalyzed the

s h i f t r e a c t i o n u n d e r h i g h pressure ( 2 5 0 a t m o f C O ) a n d e l e v a t e d t e m p e r a t u r e ( 2 1 0 ° C ) ; h o w e v e r , r e d u c t i o n of t h e p y r i d i n e t o p i p e r i d i n e is a serious side r e a c t i o n . V a r i o u s a m i n e s i n c l u d i n g p y r i d i n e also h a v e b e e n r e p o r t e d as c o m p o n e n t s i n t h e p u r p o r t e d h o m o g e n e o u s catalysis of t h e s h i f t r e a c t i o n b y systems c o n t a i n i n g g r o u p V I I I m e t a l salts ( 2 6 ) , a n d v e r y r e c e n t l y there has b e e n a r e p o r t (27)

of b o t h t h e h y d r o f o r m y l a t i o n o f

olefins a n d t h e w a t e r gas shift r e a c t i o n c a t a l y z e d b y s e v e r a l m e t a l carb o n y l s p l u s t r i m e t h y l a m i n e i n p r e s s u r i z e d autoclaves. O u r studies h a v e f o c u s s e d l a r g e l y o n t h e catalysis o f t h e s h i f t r e a c t i o n b y ruthenium carbonyl a n d b y the ruthenium carbonyl/iron carbonyl m i x t u r e s i n t h e presence of o r g a n i c a m i n e s u n d e r l o w pressures o f C O . R e p r e s e n t a t i v e studies are i n d i c a t e d i n T a b l e I I w h e r e i t is n o t a b l e t h a t r u t h e n i u m a l o n e is a c o n s i d e r a b l y b e t t e r catalyst t h a n is i r o n

alone.

A m o n g t h e r u t h e n i u m systems, p y r i d i n e solutions a r e s o m e w h a t

more


8.

FORD E T A L .

Water Gas Shift

Table II.

Catalysis i n A m i n e Solutions ( L o w Pressure) °

Complex

Amine

H Ru (CO)i2 (0.04 m m o l ) H Ru (CO)i2 (0.02 m m o l ) Fe(CO) (0.16 m m o l ) H Ru (CO) :Fe(CO) (0.02 m m o l :0.08 m m o l )

Solvent

Activity * 1

4

4

pyridine

c

13

4

4

piperidine

d

8

piperidine

d

0.9

piperidine

d

5


91

Reaction

4

4

1 2

5

e

10'

Peo = 0.9 atm, T = 100°C, initial solutions contained 0.022 mol H 0 . Activity is number of moles of H2 produced per day per mole of the initial complex added ( H R u ( C O ) i plus F e ( C O ) ) . P y r i d i n e (3 m L ) . Piperidine (1.5 mL):ethoxyethanol (2.8 m L ) . * Low CO2 :H2 ratios. Normalized activity is 12 mol H2/day/g-atcm of metal added ( R u + Fe). a

2

b

4

4

2

5

e

d

1

a c t i v e t h a n p i p e r i d i n e solutions. H o w e v e r , t h e most a c t i v e systems a m o n g these are d e r i v e d f r o m i r o n / r u t h e n i u m m i x t u r e s , w h i c h a r e m u c h m o r e a c t i v e t h a n catalysts p r e p a r e d u n d e r s i m i l a r c o n d i t i o n s f r o m t h e i n d i v i d u a l metal carbonyls.

( I f t h e n o r m a l i z e d c a t a l y t i c activities are c o m -

p a r e d f o r p i p e r i d i n e solutions, t h e F e ( C O ) / H R u ( C O ) i system is a 5

4

f a c t o r of six m o r e a c t i v e t h a n t h a t of H R u ( C O ) i 4

m o r e a c t i v e t h a n that b a s e d o n F e ( C O )

5

4

4

2

2

a n d a f a c t o r of 13

alone).

T h e e n h a n c e d a c t i v i t y of t h e r u t h e n i u m a n d t h e r u t h e n i u m / i r o n catalysts i n t h e a m i n e solutions o v e r those i n a l k a l i base solutions m a y b e t h e result of several p e r t u r b a t i o n s . C e r t a i n l y , t h e solvent effects a l o n e c a n p l a y a role i n this case g i v e n that t h e a m i n e concentrations are suffic i e n t t o c h a n g e m a r k e d l y t h e p r o p e r t i e s of t h e m e d i u m . T h u s s o l v a t i o n effects o n a r a t e - d e t e r m i n i n g step o r k e y e q u i l i b r i u m i n a c y c l e s u c h as S c h e m e 1 w o u l d h a v e m a j o r consequences o n t h e c a t a l y t i c a c t i v i t y .

If

C O a c t i v a t i o n i n steps s u c h as R e a c t i o n s 8 o r 9 c a n b e affected i n s t e a d b y other n u c l e o p h i l e s ( f o r e x a m p l e , R e a c t i o n s 10, 11, 1 2 ) , t h e n t h e h i g h concentrations of t h e amines, h i g h e r e v e n t h a n [ H 0 ] u n d e r these c o n 2

d i t i o n s , p l u s t h e r e l a t i v e n u c l e o p h i l i c i t y of these species m a y accelerate t h e C O a c t i v a t i o n step.

M - C O + B «=> M - C — O B

+

M - C — O + H 0 *± H M - C — O 2

I B

+

(10)

I B

+


(11)

92

INORGANIC COMPOUNDS W I T H UNUSUAL

HM-C — 0 + H B

2

0*± H M C 0 H + H 2

+

+ B

+

2


II

(12)

+

or « ± M H + B — C 0 " -> B + C 0

Concluding

PROPERTIES

a

2

Remarks

I n this c h a p t e r w e h a v e d e m o n s t r a t e d that m e t a l c a r b o n y l c o m p l e x e s c a n b e a c t i v e catalysts f o r t h e w a t e r - g a s shift r e a c t i o n u n d e r a v a r i e t y o f conditions.

F o r example, H R u ( C O ) i 4

4

2

f o r m s active catalysts i n either

a c i d i c o r b a s i c s o l u t i o n a n d f o r t h e latter t h e base c a n b e a n a l k a l i hydroxide or carbonate or a n organic amine.

S o m e differences

between

different m e t a l c a r b o n y l s are a p p a r e n t ; h o w e v e r , i n b a s i c s o l u t i o n t h e m o s t a c t i v e catalysts are those p r e p a r e d f r o m t h e m i x e d m e t a l F e / R u systems either b y s t a r t i n g w i t h t h e H F e R u ( C O ) 2

(or H R u ( C O ) i ) / F e ( C O ) 4

4

2

5

mixtures.

3

i 2

or w i t h R u ( C O ) i 3

2

A logical mechanism for the

catalysis w o u l d i n v o l v e t h e a c t i v a t i o n of C O b y n u c l e o p h i l i c attack o n the c o o r d i n a t e d c a r b o n m o n o x i d e f o l l o w e d b y h y d r o l y t i c steps l e a d i n g t o f o r m a t i o n of a m e t a l d i h y d r i d e .

A k e y a n d p e r h a p s r a t e - l i m i t i n g step

w o u l d b e t h e r e d u c t i v e e l i m i n a t i o n of d i h y d r o g e n f r o m this

species.

M e c h a n i s t i c studies c u r r e n t l y i n progress i n these laboratories are d i r e c t e d t o w a r d t h e e v a l u a t i o n of this a n d other p o s s i b l e c a t a l y t i c cycles a n d t o w a r d t h e o p t i m i z a t i o n of c a t a l y t i c a c t i v i t y .

Experimental

Procedures

C a t a l y s i s runs u n d e r l o w (0.9 a t m ) C O pressures w e r e c a r r i e d o u t i n glass reactors. T h e catalysis solutions w e r e p r e p a r e d b y d i s s o l v i n g t h e a p p r o p r i a t e components i n the solvent u n d e r a n i n e r t a t m o s p h e r e at a m b i e n t t e m p e r a t u r e . T h e r e s u l t i n g solutions i n t h e r e a c t i o n vessels w e r e t h e n degassed b y a f r e e z e / t h a w t e c h n i q u e a n d t h e d e s i r e d pressure of C O gas c o n t a i n i n g 6 % m e t h a n e as a n inert m a r k e r gas w a s i n t r o d u c e d to t h e b u l b at a m b i e n t t e m p e r a t u r e . T h e glass reactors w e r e t h e n s u s p e n d e d i n a n o i l b a t h a n d h e a t e d at a constant t e m p e r a t u r e . I n this c o n f i g u r a t i o n the r e a c t i o n s o l u t i o n w a s a g i t a t e d v i g o r o u s l y b y a m a g n e t i c s t i r r i n g b a r . T h e gas phase above t h e catalyst s o l u t i o n w a s s a m p l e d p e r i o d i c a l l y b y gas syringe, a n d t h e gas samples w e r e a n a l y z e d b y h i g h - r e s o l u t i o n gas c h r o m a t o g r a p h y o n a c a l i b r a t e d H e w l e t t P a c k a r d 5830A p r o g r a m m a b l e G C . Q u a n t i t i e s of C O c o n s u m e d a n d of C 0 a n d H p r o d u c e d w e r e d e t e r m i n e d b y c o m p a r i s o n w i t h t h e m a r k e r gas s i g n a l . T h e r e a c t i o n vessels w e r e p e r i o d i c a l l y r e c h a r g e d b y f r e e z e / t h a w degassing f o l l o w e d b y r e f i l l i n g w i t h t h e C O / m a r k e r gas m i x t u r e . S o m e runs u n d e r h i g h e r C O pressures w e r e c a r r i e d o u t i n P a r r stainless steel b o m b s e q u i p p e d w i t h T e f l o n liners. 2

2


8.

FORD E T A L .

Water

Gas Shift

Reaction

93

Acknowledgment T h i s w o r k was supported b y the D e p a r t m e n t of E n e r g y , D i v i s i o n of B a s i c E n e r g y Sciences.

H o w a r d W a l k e r a n d R a l p h G . Pearson

con-

t r i b u t e d s i g n i f i c a n t l y t o t h e d i s c u s s i o n a n d i n t e r p r e t a t i o n o f these results.


Literature Cited 1. Farbsman, G. H., NASA-CR-134918, JA 76. 2. K. E . Cox, K. D. W. Williamson, Jr., Eds., "Hydrogen Production Technology," Vol. I, CRC Press, 1977. 3. Thomas, C. L., "Catalytic Processes and Proven Catalysts," p. 104, Academic, New York, 1970. 4. Aldridge, C. L., U.S. Patent 3,850,840 (1974). 5. Reppe, W., Vetter, H., Justus Liebigs Ann. Chem. (1953) 582, 133. 6. von Kutepow, N., Kindler, H., Angew. Chem. (1960) 72, 802. 7. Laine, R. M., Rinker, R.G.,Ford, P.C.,J.Am. Chem. Soc. (1977) 99, 252. 8. Eady, C. R., Johnson, B. F. G., Lewis, J., J. Chem.Soc.,Dalton Trans. (1977) 838. 9. Koepke, J. W., Johnson, J. R., Knox, S. A. R., Kaesz, H. D.,J.Am. Chem. Soc. (1975)97,3947. 10. "Encyclopedia of Chemical Technology," 2nd ed., Vol. 10, p. 101, Wiley, New York, 1972. 11. Iwata, M., Nagaoka Kogyo Tanki Daigaku Koto Semmon Gakko Kenkyu Kiyo (1968) 4, 307; Chem. Abstr. (1969) 70, 76989. 12. Walker, H., unpublished results. 13. Meutteries, E. L., Inorg. Chem. (1965) 4, 1841. 14. Darensbourg, D. J., Froelich, J. A., J. Am. Chem. Soc. (1977) 99, 5940. 15. Deeming, A. J., Shaw, B. L., J. Chem. Soc. A (1969) 443. 16. Clark, H. C., Dixon, K. R., Jacobs, W. J., J. Am. Chem. Soc. (1969) 91, 1346. 17. Mays, M. J., Simpson, R. N. F., Stefanini, F. P., J. Chem. Soc. A (1970) 300. 18. Cheng, C. H., Hendriksen, D. E., Eisenberg, R., J. Am. Chem. Soc. (1977) 99, 2791. 19. Edgell, W. F., Yang, M. T., Bulkin, B. J., Bayer, R., Korzumi, N.,J.Am. Chem. Soc. (1965)87,3080. 20. Casey, C. P., Neumann, S. M., J. Am. Chem. Soc. (1976) 98, 5395. 21. Coffey, R. S.,J.Chem.Soc.,Chem. Commun. (1967) 923. 22. Laine, R. M., unpublished data. 23. Knox, S. A. R., Koepke, J.W., Andrews, M. A., Kaesz, H. D.,J.Am. Chem. Soc. (1975)97,3942. 24. Hieber, W., Vetter, H., Z. Anorg. Allg. Chem. (1933) 212, 145. 25. Imyanitov, N. S., Kuvaev, B. E . , Rudkovskii, D. M., Zh. Prikl. Khim. (Leningrad) (1967) 40, 2821. 26. Fenton, D. M., U.S. Patents 3,490,872 and 3,539,298 (1970). 27. Kang, H., Mauldin, C. H., Cole, T., Slegeir, W., Cann, K., Pettit, R., J. Am. Chem. Soc. (1977) 99, 8323. RECEIVED February 22, 1978.


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