Catalytic Reductions Using Carbon Monoxide and Water in Place of

11 Catalytic Reductions Using Carbon Monoxide and Water in Place of Hydrogen R. PETTIT, K. CANN, T. COLE, C. H . MAULDIN, and W. SLEGEIR

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University of Texas at Austin, Austin, TX 78712

Carbonyl complexes of rhodium, ruthenium, osmium, iridium, and platinum, in the presence of H O and a weak base (e.g., trimethylamine), act as catalysts for the conversion of propene to a mixture of butanal and methylpropanal; with the exception of the platinum system, these catalysts are considerably more active than Fe(CO) as reported by Reppe. Under the same conditions, but in the absence of olefin, the carbonyls act as catalysts for the conversion of CO and H O to CO and H . The metal carbonyls, together with Fe(CO) , in the presence of H O, C O , and a weak base such as Me N, serve as catalysts for the conversion of nitrobenzene, dinitrobenzene, and 2,4- and 2,6-dinitrotoluene to the corresponding aminobenzene derivatives. 2

5

2

2

2

5

2

3

/ ^ a r b o n m o n o x i d e is r e a d i l y a v a i l a b l e f r o m l o w - g r a d e ^

carbonaceous

m a t e r i a l s u c h as c o a l , l i g n i t e , etc., a n d i t is r e a d i l y c o n c e i v a b l e

that

this m a t e r i a l c o u l d p l a y a n i n c r e a s i n g l y i m p o r t a n t r o l e i n t h e e n e r g y a n d " p e t r o c h e m i c a l " fields as t h e sources of p e t r o l e u m c o n t i n u e t o d i m i n i s h . I n several cases, s u c h as t h e F i s c h e r - T r o p s c h synthesis of h y d r o c a r b o n s ( I ) a n d t h e K o c h synthesis of c a r b o x y l i c acids (2), t h e p o t e n t i a l s i g n i f i c a n c e of C O is w e l l r e c o g n i z e d , a n d i t is v e r y l i k e l y t h a t other n e w uses w i l l e m e r g e f o l l o w i n g f u r t h e r research w o r k . I n this c h a p t e r w e s h a l l discuss o u r results t o date c o n c e r n i n g t h e use of C O a n d w a t e r i n p l a c e of h y d r o g e n as a r e d u c i n g m e d i u m . I n p r i n c i p l e , a n y r e d u c t i o n o f a substrate SH

2

S b y hydrogen to yield

( R e a c t i o n 1) c a n b e c o n d u c t e d w i t h C O +

H

2

0 as i n d i c a t e d i n

R e a c t i o n 2, a n d f o r e a c h h y d r o g e n m o l e c u l e i n v o l v e d t h e latter

process

is a l w a y s a p p r o x i m a t e l y 7 k c a l / m o l m o r e t h e r m o d y n a m i c a l l y f a v o r a b l e . 0-8412-0429-2/79/33-173-121$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.

122

INORGANIC

COMPOUNDS

S + H -> S H ; F = 2

2

WITH

2

PROPERTIES

- x kcal/mol

S + C O + H 0 -> S H + C 0 ; F = 2

UNUSUAL

2

II

(1)

- (x + 7) k c a l / m o l

(2)

T h e k e y p r o b l e m i n the p o t e n t i a l use of C O as i n R e a c t i o n 2 is of course the d e s i g n of catalysts w h i c h a l l o w the r e a c t i o n to p r o c e e d at a n a c c e p t a b l e rate. Just as h y d r o g e n does not r e a d i l y a d d to most substrates ( t h e a d d i t i o n of h y d r o g e n to ethylene, f o r e x a m p l e , does not o c c u r , a n d the r e a c t i o n is i n fact f o r b i d d e n b y the W o o d w a r d - H o f f m a n n r u l e s ) , a n d Downloaded by UNIV OF ARIZONA on November 9, 2012 | http://pubs.acs.org Publication Date: May 5, 1979 | doi: 10.1021/ba-1979-0173.ch011

i n most cases r e q u i r e s i n t e r v e n t i o n of a catalyst, s u c h w i l l also b e t r u e w h e n C O -f- H 0 is u s e d . 2

Reppe Modification

of the

Hydroformylation

Reaction

O u r i n i t i a l efforts i n the area of r e d u c t i o n s w i t h C O + H 0 i n v o l v e d 2

a s t u d y of the m e c h a n i s m of w h a t w e s h a l l t e r m the R e p p e m o d i f i c a t i o n of 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 ( 3 ) .

I n the n o r m a l h y d r o f o r m y l a t i o n

process, the elements of h y d r o g e n a n d C O are a d d e d to a n olefin t o generate a n a l d e h y d e ( R e a c t i o n 3 ) .

I n the R e p p e m o d i f i c a t i o n of t h i s

process, the same r e a c t i o n is a c h i e v e d u s i n g C O -f- H 0 i n p l a c e of h y d r o 2

gen (Reaction 4). R R -

I n the n o r m a l process, the catalyst u s e d is u s u a l l y a

C H =

C H + CO + 2

H -» 2

RCH CH CH0 2

(3)

2

C H — C H + 2C0 + H 0 -» R C H C H C H 0 + C 0 2

2

2

2

2

(4)

c a r b o n y l d e r i v a t i v e of c o b a l t or r h o d i u m , w h e r e a s i n the R e p p e m o d i f i c a t i o 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 L e w i s or B r o n s t e d base is u s e d . A c o m p a r i s o n of the t w o processes reveals s e v e r a l i n t r i g u i n g p o i n t s of interest.

T h u s , i n the n o r m a l process w i t h c o b a l t c a r b o n y l as

the

catalyst, temperatures of 150 ° C or h i g h e r a n d pressures of 3000 p s i are u s e d , w h e r e a s i n the R e p p e m o d i f i c a t i o n the c o n d i t i o n s are m u c h less severe;

100 ° C t e m p e r a t u r e a n d 500 p s i of C O pressure are sufficient.

Furthermore, when F e ( C O )

5

is u s e d as a catalyst i n the n o r m a l process

w i t h h y d r o g e n , it p e r f o r m s v e r y p o o r l y ( 4 ) ; l i k e w i s e , w e find that w h e n c o b a l t c a r b o n y l is u s e d u n d e r R e p p e ' s c o n d i t i o n s i t too p e r f o r m s v e r y poorly (zero activity). T o u n d e r s t a n d the m a n n e r i n w h i c h the F e ( C O )

5

p l u s base catalyst

system uses C O -f- H 0 i n p l a c e of h y d r o g e n , s p e c u l a t i n g that s u c h a n 2

u n d e r s t a n d i n g w o u l d b e of v a l u e to the d e s i g n of other catalysts c a p a b l e of effecting r e d u c t i o n s w i t h C O + H 0 , w e i n v e s t i g a t e d the m e c h a n i s m 2

of the R e p p e r e a c t i o n . T h e p e r t i n e n t results are s u m m a r i z e d b e l o w . W e f o u n d that

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 s t r o n g l y

o n t h e p H of the m e d i u m i n t h e reactor ( 5 ) .

depended

W h e n an autoclave was

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

11.

PETTIT ET AL.

Catalytic

Reductions

Using CO and

c h a r g e d w i t h ethylene, w a t e r , F e ( C O ) , a n d N a C 0 5

C O , the F e ( C O )

2

d i s s o l v e d to f o r m N a H F e ( C O )

5

4

2

u n d e r 500 p s i of

3

a c c o r d i n g to

t i o n 5. T h e f o r m a t i o n of the H F e ( C O ) " a n i o n f r o m F e ( C O ) 4

Na C0 2

+ Fe(CO)

3

5

+ H 0 -> N a H F e ( C O ) + C 0 2

123

H0

4

2

Reac-

a n d base

5

+ NaHC0

(5)

3

is the o l d a n d w e l l - e s t a b l i s h e d r e a c t i o n , a n d the a n i o n is a w e l l - c h a r a c t e r i z e d species (6,7).

U p o n c o m p l e t e d i s s o l u t i o n of the F e ( C O )

in

5

this m a n n e r , the p H of the m e d i u m is a r o u n d 12.0, b u t o n l y w h e n the Downloaded by UNIV OF ARIZONA on November 9, 2012 | http://pubs.acs.org Publication Date: May 5, 1979 | doi: 10.1021/ba-1979-0173.ch011

p H d r o p s to the v i c i n i t y of 10.7 ( a t t r i b u t a b l e to the r e a c t i o n of C O O H " -> H C O O " ) does the f o r m a t i o n of p r o p a n o l b e g i n to o c c u r .

+

(Propa-

n a l is the i n i t i a l p r o d u c t , b u t u n d e r the c o n d i t i o n s u s e d i t is r e a d i l y r e d u c e d to p r o p a n o l ) . I n a s i m i l a r e x p e r i m e n t i n w h i c h 1,5-cyclooctadiene

is u s e d i n p l a c e

of ethylene, a g a i n , o n l y w h e n the p H d r o p s to a b o u t 10.7 is there o b s e r v e d i s o m e r i z a t i o n of 1,5- to 1,3-cyclooctadiene.

W h e n the same e x p e r i m e n t is

r u n w i t h o u t a n y olefin present, t h e n h y d r o g e n begins to a p p e a r i n the reactor w h e n the p H a g a i n reaches a p p r o x i m a t e l y 10.7. I n a s i m i l a r e x p e r i m e n t to that d e s c r i b e d w i t h ethylene, b u t w i t h a d d i t i o n of a c e t a l d e h y d e , i t is f o u n d that the a c e t a l d e h y d e is i m m e d i a t e l y r e d u c e d to e t h a n o l at a p H of 12.0, b u t a g a i n o n l y w h e n the p H is l o w e r e d to 10.7 does the h y d r o f o r m y l a t i o n of e t h y l e n e b e g i n to take p l a c e . A p l a u s i b l e e x p l a n a t i o n of this p H d e p e n d e n c e is that a significant c o n c e n t r a t i o n of H F e ( C O ) 2

4

begins to f o r m at a p H of a b o u t 10.7 a n d

t h a t this is the species w h i c h initiates 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 . H Fe(CO) 2

4

is k n o w n to b e a p o w e r f u l catalyst f o r the i s o m e r i z a t i o n of

olefins ( 8 ) , a n d i t also w o u l d b e a sensible c a n d i d a t e f o r the f o r m a t i o n of molecular hydrogen through simple thermal decomposition

(9).

The

H F e ( C O ) " a n i o n is not the catalyst f o r these three reactions; h o w e v e r , 4

it is c a p a b l e of r e d u c i n g a l d e h y d e s to a l c o h o l s . W e c o n s i d e r t h e n that the m e c h a n i s m of the R e p p e m o d i f i c a t i o n of 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 l o s e l y p a r a l l e l s that of the n o r m a l process as d e s c r i b e d b y H e c k a n d B r e s l o w (10).

T h e p r i n c i p a l steps are g i v e n

i n the f o l l o w i n g s c h e m e : H CH =CH 2

H Fe(CO) 2

2

CO

4

*CH CH 3

-Fe(CO)

2

4

HFe(CO)"4 CH CH CH OH 3

2

2


124

INORGANIC

COMPOUNDS

WITH

UNUSUAL

PROPERTIES

II

T h e n o r m a l h y d r o f o r m y l a t i o n r e a c t i o n a n d the R e p p e m o d i f i c a t i o n are m e c h a n i s t i c a l l y c l o s e l y r e l a t e d ; the k e y p o i n t w h i c h emerges is t h a t i n the latter process it is easier to f o r m the species H F e ( C O ) 2

r e a c t i o n of F e ( C O )

f r o m the

4

5

a n d a q u e o u s base t h a n it is f r o m F e ( C O )

molecular hydrogen.

F o r this reason, the c o m b i n a t i o n of C O +

5

and H 0 2

p r o v i d e s a s u p e r i o r r e d u c i n g system f o r the r e d u c t i v e a d d i t i o n of C O t o a n olefin t h a n does m o l e c u l a r h y d r o g e n .


Other Catalysts for

the Hydroformylation

T h e f o r m a t i o n of the H F e ( C O ) 2

4

Reaction with CO

+

H0 2

catalyst d e s c r i b e d a b o v e p r e s u m -

a b l y occurs v i a n u c l e o p h i l i c attack of h y d r o x y l i o n o n a C O l i g a n d of Fe(CO)

5

w i t h g e n e r a t i o n of the a n i o n i c m e t a l l o c a r b o x y l i c a c i d f o l l o w e d

b y decarboxylation and protonation (Reaction 6).

OH-

(CO) Fe(CO) 4

0 O || -C0 O > (CO) Fe—C—OH > (CO) FeH 2

4

4

1

H H Fe(CO) 2

(6)

+

4

W h e n aqueous amines are u s e d as the base i n s t e a d of N a C 0 , p r e 2

3

s u m a b l y the a m i n e rather t h a n h y d r o x y l i o n acts as the a t t a c k i n g n u c l e o p h i l e ; h y d r o l y s i s of the r e s u l t i n g m e t a l l o c a r b o x y a m i d e d e r i v a t i v e t h e n affords the m e t a l l o c a r b o x y l i c a c i d 1

(II).

T h e s e considerations n o w p r o v i d e a g u i d e l i n e f o r the

development

of other p o t e n t i a l catalysts f o r the use of C O -f- H 0 i n the h y d r o f o r m y l a 2

t i o n of olefins. I f the catalyst is to f u n c t i o n i n the same m a n n e r as just d e s c r i b e d f o r F e ( C O ) , t h e n a m i n i m u m r e q u i r e m e n t is that the system 5

f o r m a m e t a l c a r b o n y l w h i c h w i l l b e r e a d i l y a t t a c k e d b y a w e a k base to f o r m a n a n i o n analogous to 1. A w e a k base is essential b e c a u s e C 0 a n i n e v i t a b l e b y - p r o d u c t , a n d o n l y the carbonate regenerate the base a n d C 0

2

2

is

salts of w e a k bases

u p o n h e a t i n g . T h u s , i f the system is to b e

c a t a l y t i c i n base as w e l l , t h e n c l e a r l y o n l y a w e a k base c a n b e u s e d . T h i s w o u l d a p p e a r to b e the c r i t i c a l r e q u i r e m e n t , f o r the l i t e r a t u r e i n d i c a t e s t h a t m e t a l l o c a r b o x y l i c acids r e a d i l y d e c a r b o x y l a t e

(12),

a n d the

final

step i n R e a c t i o n 6, the p r o t o n a t i o n of a h y d r i d o m e t a l c a r b o n y l a n i o n , w o u l d seem to offer n o p r o b l e m p r o v i d e d the catalyst system w a s n o t i n a h i g h l y basic m e d i u m . O f the s i m p l e m o n o n u c l e a r m e t a l c a r b o n y l s , o n l y F e ( C O ) to b e r e a d i l y a t t a c k e d b y a w e a k base w i t h s u b s e q u e n t metal hydride bonds.

5

appears

f o r m a t i o n of

W e r e a s o n e d that i f the m e t a l c a r b o n y l system


11.

PETTIT

ET

AL.

Catalytic

Reductions

Using CO and

125

H0 2

c o n t a i n e d the s t r u c t u r a l feature s h o w n i n f o r m u l a 2, i.e., a m e t a l - m e t a l b o n d system c o n t a i n i n g a b r i d g i n g c a r b o n y l g r o u p a n d a t e r m i n a l carb o n y l l i g a n d , t h e n n u c l e o p h i l i c attack of O H " m i g h t b e f a c i l i t a t e d . T h i s w o u l d b e a t t r i b u t a b l e to the p o s s i b l e d e r e a l i z a t i o n of n e g a t i v e

charge

f r o m the m e t a l a t o m to a n o x y g e n a t o m t h r o u g h the resonance i n t e r a c t i o n i n d i c a t e d i n 3.


M

M = C = 0

OH"

~ M—COOH
M

\/

v

c

»M

\/

c

II

M—COOH

c

II

0

II

0

0 -

T h e s e c o n s i d e r a t i o n s thus p o i n t e d to a l a r g e n u m b e r of m e t a l c l u s t e r c a r b o n y l c o m p o u n d s w h i c h h a v e the s t r u c t u r a l features i n d i c a t e d i n 2. A s m e n t i o n e d earlier, the d e c a r b o x y l a t i o n of c o m p o u n d s of t y p e 3 to g i v e m e t a l h y d r i d e s w a s e x p e c t e d to p r o c e e d easily. S e v e r a l m e t a l cluster systems h a v e n o w b e e n t r i e d 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 of p r o p y l e n e a n d C O +

H 0 ( 1 3 ) , a n d as is seen 2

f r o m the d a t a i n T a b l e I, some of t h e m are f o u n d to b e m u c h s u p e r i o r to Fe(CO)

5

as catalysts. T h i s is e s p e c i a l l y t r u e of R h ( C O ) i a n d I r ( C O ) i . 6

6

4

2

S i n c e each of these catalyst systems w a s e x p e c t e d to p r o c e e d v i a i n t e r m e d i a t e f o r m a t i o n of a m e t a l h y d r i d e a n i o n ( f r o m 3 ) a n d p r o t o n a t i o n to a n e u t r a l d i h y d r o g e n m e t a l species, t h e n i n the absence of a n y olefin, e a c h c o u l d b e e x p e c t e d to p r o d u c e m o l e c u l a r h y d r o g e n u p o n therm a l d e c o m p o s i t i o n . T h a t is, e a c h also s h o u l d b e a catalyst f o r the w a t e r gas s h i f t r e a c t i o n ( R e a c t i o n 7 ) .

S u c h w a s f o u n d to b e t h e case; i n t h e

C O + H 0 -> C O + H 2

2

(7)

last c o l u m n of T a b l e I there is l i s t e d the moles of h y d r o g e n p r o d u c e d p e r m o l e of catalyst u s e d u n d e r i d e n t i c a l r e a c t i o n c o n d i t i o n s as w i t h 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 except f o r the o m i s s i o n of olefin. It is seen t h a t e a c h of the catalyst systems u s e d are catalysts f o r the f o r m a t i o n of hydrogen from C O and H 0 . 2

It m u s t be p o i n t e d o u t that the exact n a t u r e of the c a t a l y t i c species has n o t b e e n e s t a b l i s h e d i n the case of the m e t a l cluster c o m p o u n d s l i s t e d i n T a b l e I.

Rearrangement

of the a d d e d cluster c o m p o u n d s to

some other cluster species u n d e r the r e a c t i o n c o n d i t i o n s is r e a d i l y c o n c e i v a b l e , a n d i n s e v e r a l cases, v e r y p r o b a b l e .


126

INORGANIC

COMPOUNDS

Table 1.

WITH

UNUSUAL

PROPERTIES

Hydroformylation of Propane

Experiment"


II

T(°C)

1 2 3 4 5 6 7 8 9

110 125 100 100 180 180 180 125 125

Fe(CO) Rh (CO) Ru (CO) H Ru (CO) Os (CO) H Os (CO) H Os (CO)i Ir (CO) (Bu N) [Pt (CO) ]5 5

6

1 6

3

1 2

4

4

1 2

3

1 2

2

3

4

4

1 0 2

4

a 2

4

2

3

6

° A l l experiments run for 10 hr in a 300 m L stirred autoclave containing 0.05 mmol of catalyst, 22 m L of 25% aqueous trimethylamine, 78 m L of T H F , 350 psi of C O , and 150 psi of propylene. Small amounts of propane were formed in experiments 2, 5, 6, 7, and 8. Reduction In

of Aromatic

Nitro

Compounds

1925, i n a G e r m a n p a t e n t

solutions of F e ( C O )

5

(14),

to

Amines

it was revealed that alkaline

w o u l d reduce aromatic nitro compounds to amines

in a stoichiometric manner.

M o r e recently, L a d e n s b e r g a n d co-workers

( 1 5 ) h a v e s h o w n t h a t salts of t h e t r i n u c l e a r a n i o n H F e ( C O ) u " 3

also effect t h e r e d u c t i o n , a n d W a t a n a b e

a n d co-workers

will

(16)

have

o b t a i n e d s i m i l a r results w i t h t h e m o n o n u c l e a r a n i o n H F e ( C O ) ~ .

Each

4

of these species c o u l d h a v e b e e n f o r m e d u n d e r t h e c o n d i t i o n s u s e d i n the first r e p o r t , a n d p r e s u m a b l y o n e or b o t h w o u l d b e t h e r e a c t i v e r e d u c i n g species.

( H . A l p e r has r e c e n t l y s h o w n t h a t F e ( C O ) > i n t h e p r e s e n c e 5

of N a O D / D 0 , w i l l c o n v e r t n i t r o b e n z e n e i n t o ND ; h o w e v e r , t h e n a t u r e 2

2

of t h e r e d u c i n g species has n o t b e e n e s t a b l i s h e d

(17).)

W i t h H F e ( C O ) " as t h e r e d u c i n g agent, W a t a n a b e a n d c o - w o r k e r s 4

report that the reaction remains stoichiometric rather t h a n catalytic w h e n c o n d u c t e d u n d e r a pressure of C O . T h e s t o i c h i o m e t r y , h o w e v e r , is m o s t r e m a r k a b l e i n t h a t 1 m o l of H F e ( C O ) ~ salt w i l l r e d u c e 1.8 m o l of n i t r o 4

b e n z e n e t o a n i l i n e . Since, i n terms o f e l e c t r o n - t r a n s f e r r e d u c t i o n , t h e c o n v e r s i o n o f n i t r o b e n z e n e t o a n i l i n e i n v o l v e s six electrons p e r m o l e c u l e , then the H F e ( C O )

4

salt is a c t i n g as a n 11 ( 1 0 . 8 ) e l e c t r o n - t r a n s f e r agent.

I r r e s p e c t i v e o f t h e exact m e c h a n i s m of t h e electron-transfer

process,

c l e a r l y m o s t of these electrons m u s t b e p r o v i d e d b y t h e C O l i g a n d s , w h i c h i n turn become oxidized to C 0 . 2

A r a t i o n a l e x p l a n a t i o n o f t h e process w o u l d b e a succession of t w o electron-transfer steps as i n d i c a t e d i n R e a c t i o n s 8 a n d 9. W i t h c o m p l e t e d e p l e t i o n of t h e C O l i g a n d s a n d final o x i d a t i o n of F e ° to F e

+ +

(Reaction

1 0 ) , t h e n a t o t a l of 12 electrons c o u l d b e p r o v i d e d b y F e ( C O ) . 5


11.

PETTIT ET

AL.

Catalytic

Reductions

and Water Gas Shift with C O + Moles of C Aldehyde/Moles of Catalyst

Using CO and


2

H 0 2

C Aldehyde/ C Alcohol

Water Gas Shift Reaction (Moles of H /Moles of Catalyst)

4.5 40 43 37 6.6 - 300 -300 - 300 —

5 1700 3300 3400 270 270 400 300 700

h

n-/Isoaldehyde Ratio

5.2 300 47 79 13 6 9 250 0.5

127

H0

h

2

6

h

1.0 1.4 11.5 11.0 1.9 1.2 1.4 1.8 1.9

Identical conditions as in (a) expect that the propylene is omitted; a temperature of 150°C was used for experiments 2 and 8. Optimum conditions for each catalyst system have not been determined. 6

S i m p l e i n s p e c t i o n of R e a c t i o n s 8, 9, a n d 10 leads t o t h e c o n c l u s i o n that t h e r e a c t i o n s h o u l d b e m a d e to b e c a t a l y t i c i n F e ( C O )

i f it w e r e

5

c o n d u c t e d u n d e r a C O pressure i n the presence of excess base. Fe(CO)

4

g e n e r a t e d as i n R e a c t i o n 8 s h o u l d r e v e r t to F e ( C O )

treatment

with

C O , a n d p r o v i d e d i n e v i t a b l e loss

of

Fe°

5

to F e

The upon + +

is

a v o i d e d ( C O does n o t r e d u c e t h e ferrous i o n u n d e r m i l d c o n d i t i o n s ) , t h e n o n l y c a t a l y t i c q u a n t i t i e s of F e ( C O ) T h i s p r e d i c t i o n has b e e n

realized.

5

w o u l d be required. Various aromatic nitro com-

p o u n d s h a v e b e e n r e d u c e d to t h e c o r r e s p o n d i n g amines b y t r e a t m e n t at 25 ° C i n a q u e o u s s o l u t i o n of g l y m e c o n t a i n i n g c a t a l y t i c q u a n t i t i e s Fe(CO)

5

a n d l a r g e a m o u n t s of t r i e t h y l a m i n e u n d e r a pressure of

p s i of C O (18).

of

1700

T o observe catalysis, h o w e v e r , i t w a s necessary to

m a i n t a i n the c o n c e n t r a t i o n of the o x i d a n t , i.e., the n i t r o b e n z e n e , l o w at all times.

I f this w e r e n o t d o n e , t h e n r a p i d loss of t h e C O l i g a n d s

o c c u r r e d ( R e a c t i o n 9 ) a n d i r r e v e r s i b l e f o r m a t i o n of i r o n oxides ( R e a c t i o n 10)

resulted.

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

i n s i d e the reactor vessel s i m p l y b y p u m p i n g i n the n i t r o b e n z e n e o v e r a

Fe(CO)

Fe(CO)

m ( M

HFe(CO) "-» Fe(CO) 4

4

+ H

+ OH> H F e ( C O ) - . ! -> F e ( C O ) . i + M

F e ° -> F e

+ +

m

+

+

+ 2e

H

+

+

2e"


(8)

2e

(9)

(10)

128

INORGANIC

Table II.

COMPOUNDS

WITH

UNUSUAL

PROPERTIES

Catalytic Reductions w i t h F e ( C O ) s

II

0

% Compound

Product

N i t r o b e n z e n e (11.0 m-Dinitrobenzene 2,4-Dinitrotoluene 2,6-Dinitrotoluene


% Nitroarene Reduced

g) (8.2 g) (16.8 g) (9.3 g)

aniline m-phenylene diamine 2,4-diaminotoluene 2,6-diaminotoluene

Fe(CO), Remaining b

100 100 100 100

95 12 32 56

"Reaction conditions: the nitro compound dissolved in 50 m L of glyme was pumped over a 10-12 hr period into a stirred 300 m L reaction vessel containing 120 m L of glyme, 6g H 0 , 30 g of E t N , and 1 g Fe(CO)s. The reaction was run at room temperature under 1700 psi of C O . Determined by I R absorption intensities. 2

3

6

r e l a t i v e l y l o n g p e r i o d of t i m e ( a p p r o x i m a t e l y 12 h r ) . the F e ( C O )

5

E v e n so, s o m e of

w a s d e s t r o y e d a n d a p p e a r e d as oxides of i r o n . T h e p e r t i -

n e n t d a t a are s h o w n i n T a b l e I I . I n a separate, n o n c a t a l y t i c t y p e of e x p e r i m e n t , w e d e m o n s t r a t e d t h a t n i t r o b e n z e n e c o u l d b e r a p i d l y r e d u c e d t o a n i l i n e i n a l k a l i n e s o l u t i o n s of K H F e ( C O ) m a i n t a i n e d at a p H of 12.0; this i n d i c a t e d t h a t the H F e ( C O ) 4

anion rather than H F e ( C O ) 2

4

is c a p a b l e of e f f e c t i n g the r e d u c t i o n .

o u r e a r l i e r studies d e a l i n g w i t h h y d r o f o r m y l a t i o n ( 1 3 ) ,

4

In

w e have shown

t h a t s e v e r a l m e t a l c l u s t e r species r e a d i l y generate m e t a l h y d r i d e a n i o n s u p o n t r e a t m e n t w i t h m i l d bases, a n d these w e r e also tested as c a n d i d a t e s f o r t h e c a t a l y t i c r e d u c t i o n of n i t r o b e n z e n e t o a n i l i n e w i t h C O -f- H 0 as 2

t h e r e d u c i n g agent. T h e results o b t a i n e d are s u m m a r i z e d i n T a b l e

Table III.

Reduction of Nitrobenzene with C O +

Catalyst Rh (CO) Ru (CO) H Ru (CO)i2 Os (CO) H Os (CO) H Os (CO) Ir (CO)i2 [Bu N] [Pt3(CO) ] Re (CO) e

1 6

3

1 2

4

4

3

1 2

2

3

1 0

4

3

1 2

4

4

2

2

6

1 0

5

T

Time (hr)

125 100 100 180 180 180 150 125 180

1 2 2 1 1 1 10 10 2

III.

H 0 2

Reduction (%)

(%)

100 71 73 100 100 100 47 42 10

2-6 52 56

Catalytic Reductions Using Carbon Monoxide and Water in Place of

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