Rhodium-Phosphine Complexes as Homogeneous Catalysts

3 Rhodium-Phosphine Complexes as Homogeneous Catalysts. Hydrogenation of Aromatic Nitro Compounds Downloaded by CALIFORNIA INST OF TECHNOLOGY on November 1, 2017 | http://pubs.acs.org Publication Date: May 5, 1979 | doi: 10.1021/ba-1979-0173.ch003

1

PÁL

KVINTOVICS,

BÁLINT

HEIL,

and

LÁSZLÓ

MARKÓ

Department of Organic Chemistry, University of C h e m i c a l Engineering, H-8200 Veszprém, H u n g a r y

Addition of triethyl amine to Rh(PPh ) Cl or to complexes 3

3

formed from [Rh(1,5-hexadiene)Cl] and phosphines under 2

hydrogen yields very active catalysts for the hydrogenation of aromatic nitro compounds to amines. The dark brown homogeneous catalyst solutions show highest activity at molar ratios of

Rh/PR /Et N 3

3

=

1:1.2:3. Turnovers above

1 mol H /mol Rh min are achieved. 2

/ ^ V n l y a f e w h o m o g e n e o u s catalysts h a v e b e e n f o u n d t o b e a c t i v e f o r the h y d r o g e n a t i o n o f the n i t r o g r o u p (2) a n d also w i t h these, o n l y l o w r e a c t i o n rates h a v e b e e n o b s e r v e d i n m o s t cases. P e r h a p s t h e best homogeneous

catalyst

described until n o w f o r the hydrogenation of

n i t r o c o m p o u n d s is R u C l ( P P h ) b u t e v e n this r e q u i r e s r a t h e r d r a s t i c 2

2

3

c o n d i t i o n s ( 3 ) . T h e r e is n o r e p o r t a b o u t t h e a p p l i c a t i o n o f t h e m o s t w i d e l y u s e d h o m o g e n e o u s h y d r o g e n a t i o n catalyst R h ( P P h ) C l f o r this 3

3

purpose. Results and Discussion T h e h y d r o g e n a t i o n o f n i t r o b e n z e n e w i t h R h ( P P h ) C l as catalyst 3

3

w a s f o u n d t o b e i m p r a c t i c a b l y s l o w w i t h t u r n o v e r s b e l o w 0.1 m i n " . T h e 1

a d d i t i o n of triethyl amine, however, considerably increased the reaction rate, i n a c c o r d a n c e w i t h o u r e a r l i e r 1

findings

a b o u t t h e f a v o r a b l e effect

This is Part 6 of a series. For Part 5 see Ref. 1. 0-8412-0429-2/79/33-173-026$05.00/0 © 1979 American Chemical Society

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

3.

KVINTOVICS E T A L .

Hydrogenation

of Homogeneous

Catalysts

27

Table I. Hydrogenation of Nitrobenzene and Its Possible Reduction Intermediates with the R h ( P P h ) C l + E t N Catalyst System 3

Substrate

Solvent

Et N/Rh

ITO(min )

1 b

3

0 1 0 1

0.02 0.08

3 1

0.41

Nitrobenzene

benzene benzene/MeOH (1:1) benzene/MeOH

Nitrobenzene

(1:1) benzene/MeOH

30 1

0.48

Nitrobenzene

(1:1) benzene/MeOH

150 1

0.77

Nitrosobenzene

(1:1) benzene/MeOH

3 1

0.02

3 1

0.05

3 1

0.57

3 1

0.35

Nitrobenzene Nitrobenzene Downloaded by CALIFORNIA INST OF TECHNOLOGY on November 1, 2017 | http://pubs.acs.org Publication Date: May 5, 1979 | doi: 10.1021/ba-1979-0173.ch003

3

a

3

(1:1) benzene/MeOH (1:1) benzene/MeOH n • •n U.ij benzene/MeOH (1:1)

iV-Phenyl hydroxyl amine Azobenzene Hydrazobenzene

° 0.025 mmol R h ( P P h ) C l , 2.5 mmol substrate, 6 m L solvent, 50°C, and 1 bar H . Initial turnover (mol H2/mol R h min). 3

3

2

6

of t r i e t h y l a m i n e o n the a c t i v i t y of r h o d i u m p h o s p h i n e c o m p l e x catalysts (I)

(Table

I).

A n i l i n e w a s f o u n d b y G L C to b e the o n l y r e a c t i o n p r o d u c t .

The

w e l l - k n o w n possible intermediates nitrosobenzene, N - p h e n y l h y d r o x y l amine, azobenzene, a n d hydrazobenzene c o u l d a l l be hydrogenated b y the same catalyst c o m b i n a t i o n to a n i l i n e . C o m p a r i n g the rates of h y d r o genations ( T a b l e I ) , the o n l y c o n c l u s i o n one c a n r e a c h a b o u t the m e c h a n i s m of n i t r o b e n z e n e h y d r o g e n a t i o n is that n i t r o s o b e n z e n e a n d I V - p h e n y l h y d r o x y l a m i n e ( a n d thus p r o b a b l y also a z o b e n z e n e a n d h y d r a z o b e n z e n e ) are n o t i n t e r m e d i a t e s of the r e a c t i o n . E v e n m o r e a c t i v e w a s the I n s i t u " catalyst p r e p a r e d f r o m [ R h ( l , 5 hexadiene)Cl] and P P h 2

3

w i t h a l o w r a t i o of P / R h =

1.2, a n d the use of

a p - x y l e n e / m e t h a n o l solvent i n s t e a d of b e n z e n e / m e t h a n o l r e s u l t e d i n a f u r t h e r increase of a c t i v i t y ( T a b l e I I ) . o b s e r v e d (1,4)

B o t h effects a l r e a d y h a v e b e e n

w h i c h shows that these m a y b e c h a r a c t e r i s t i c f o r s u c h

r h o d i u m , p h o s p h i n e , a n d a m i n e catalyst c o m b i n a t i o n s . T h e h o m o g e n e o u s c h a r a c t e r of the catalyst w a s c h e c k e d i n s e v e r a l w a y s : n o p r e c i p i t a t e or d e p o s i t i o n c o u l d b e o b s e r v e d v i s u a l l y ; w h e n f i l t r a t i n g a c a t a l y t i c a l l y a c t i v e s o l u t i o n , n o r e s i d u e r e m a i n e d o n the if n o P P h

3

filter;

was a d d e d , a visually w e l l observable, grey precipitate ap-

p e a r e d ( p r o b a b l y r h o d i u m m e t a l ) w h i c h p r o v e d to b e m u c h less a c t i v e


28

INORGANIC COMPOUNDS W I T H UNUSUAL PROPERTIES

Table II.

Hydrogenation of Nitrobenzene with in situ R h -|-

No.

Downloaded by CALIFORNIA INST OF TECHNOLOGY on November 1, 2017 | http://pubs.acs.org Publication Date: May 5, 1979 | doi: 10.1021/ba-1979-0173.ch003

II

Phosphine

1 2 3 4 5 6 7 8 9 10 11 12 13 14

PPh PPh PPh PPh PPh PPh

Amine

Rh/P/N 1.2:3 1.2:3 1.2:3 1.2:3 2.2:3 3.2:3 0:3 1.2:3 1.2:3 1.2:3 1.2:3 1.2:3 1.2:3 1.2:3

Et N Et N Et N Et N Et N Et N Et N Et N Et NH pyridine pyperidine Et N Et N EtqN 3

3

3

3

3

3

3

3 3

3

3

3

3

PPh PPh PPh PPh PBu Ph PCH CH PPh P(OMe)

3

3

3

2

3 3

3

2

2

2

3 3

2

3

° 0.0125 mmol [Rh(l,5-hexadiene)Cl] , 2.5 mmol nitrobenzene, 6 m L solvent, 50°C, and 1 bar H . Initial turnover (mol H / m o l R h min). * Time necessary for the consumption of 3.75 mmol H (50% conversion or turnover number 150). 2

2

b

2

2

as a h y d r o g e n a t i o n catalyst t h a n the h o m o g e n e o u s e x p e r i m e n t s 2 a n d 7 of T a b l e

system

(compare

II).

S o m e a d d i t i o n a l i n f o r m a t i o n o n t h e n a t u r e of the a c t i v e w a s f u r n i s h e d b y the experiments at different r h o d i u m ( T a b l e II, N o . 2, 3, a n d 4).

catalyst

concentrations

A s c a n b e seen, the r e a c t i o n rate s h o w e d a

s m a l l f r a c t i o n a l o r d e r w i t h respect to catalyst c o n c e n t r a t i o n w i t h i n t h e r a n g e i n v e s t i g a t e d . T h i s suggests t h a t m o s t of t h e r h o d i u m is present i n the f o r m of a m e t a l cluster c o m p l e x a n d the a c t i v e catalyst is a m o n o n u c l e a r species present i n s m a l l c o n c e n t r a t i o n a n d i n e q u i l i b r i u m w i t h

Table III. Substrate

Hydrogenation of Some

ITO (min ) 1

UJmin)

b

0

Nitrobenzene 1-Nitro naphthalene o - N i t r o phenol p - N i t r o chloro benzene

3.4 0.80 0.90 1.4

60 450 250 230

m - D i n i t r o benzene

1.5

410

° 0.0125 mmol [Rh(l,5-hexadiene)Cl] , 0.03 mmol P P h , 0.075 mmol E t N , 2.5 mmol substrate, 3 m L benzene, 4 m L methanol, 50°C, and 1 bar H . I n i t i a l turnover (mol H / m o l R h min). Time necessary for the consumption of 3.75 mmol H (50% conversion of one nitro group or turnover number 150). 2

3

3

2

6

0

2

2


3.

KVINTOVICS E T A L .

Phosphine +

Hydrogenation

Amine Catalysts.

1 h

benzene benzene/MeOH(l:l) benzene/MeOH(l:l) benzene/MeOH(l:l) benzene/MeOH(l:l) benzene/MeOH(l:l) benzene/MeOH(l:l) p-xylene/MeOH(l:l) benzene/MeOH(l:l) benzene/MeOH(l:l) benzene/MeOH(l:l) benzene/MeOH(l:l) benzene/MeOH(l:l) benzene/MeOH(l:l)

29

Catalysts

Effect of Reaction Parameters ITO(min' )

Solvent


of Homogeneous

0

to.s(min)' 80 70 60 40

1.6 3.4 3.8" 4.5' 0.57 0.38 0.35' 6.7 3.1 0.70 2.7 0.16 1.5 4.1

— — —

30 70 310 70

—

120 50

°Rh/PhNO = l:50. R h / P h N 0 = l:33. Rhodium metal precipitated from the solution. 2

e

2

f

the p o l y n u c l e a r c o m p l e x .

S u c h a system w o u l d at the same t i m e also

e x p l a i n the d a r k c o l o r of the r e a c t i o n m i x t u r e . T r i e t h y l a m i n e p e r f o r m e d as the best a m i n e c o m p o n e n t , a n d P B u and P h P C H C H P P h 2

2

2

2

( d i p h o s ) w e r e less u s e f u l t h a n P P h . 3

p h o s p h i t e gave, h o w e v e r , a rather active c a t a l y s t — a n n o t w i t h o u t precedent

3

Trimethyl

observation

also

(1).

T h e dark b r o w n " i n s i t u " catalyst s o l u t i o n was successfully a p p l i e d f o r the h y d r o g e n a t i o n of other a r o m a t i c n i t r o c o m p o u n d s too III).

(Table

T h e f o r m a t i o n of a n i l i n e as the m a i n p r o d u c t f r o m p - c h l o r o n i t r o -

Aromatic N i t r o Compounds" H Consumed, mol/mol Substrate

Product

Yield (%)

aniline 1-amino-naphthalene o - a m i n o phenol p - c h l o r o aniline aniline ra-nitro a n i l i n e m-phenylene diamine

90 52 55 9 48 57 1

2

3.0 1.9* 1.8* 2.2° 1.8"

Based on total amount of substrate. * Experiment stopped before complete conversion.

d


d

30 benzene

INORGANIC

deserves

COMPOUNDS WITH

m e n t i o n i n g : t h e H C 1 acceptor

UNUSUAL PROPERTIES

II

necessary f o r h y d r o -

d e h a l o g e n a t i o n (4) is a p p a r e n t l y t h e a r o m a t i c a m i n e f u r n i s h e d b y t h e r e d u c t i o n o f t h e n i t r o g r o u p , thus

enabling the combination of t w o

f u n c t i o n s of t h e s a m e catalyst.


Experimental F i v e a n d o n e h a l f m g (0.0125 m m o l ) [ R h ( l , 5 - h e x a d i e n e ) C l ] , 7.9 m g ( 0 . 0 3 m m o l ) P P h , a n d 10.6 /JL (0.075 m m o l ) E t N w e r e d i s s o l v e d a t 5 0 ° C i n 3.0 m L m e t h a n o l u n d e r H i n a t h e r m o s t a t e d r e a c t i o n flask c o n n e c t e d t o a t h e r m o s t a t e d gas b u r e t t e a n d e q u i p p e d w i t h a m a g n e t i c stirrer a n d a s i l i c o n e r u b b e r c a p . T h i s c a t a l y s t s o l u t i o n w a s p r e h y d r o g e n a t e d f o r 3 0 m i n u t e s . F o l l o w i n g this t h e substrate ( 2 . 5 m m o l ) w a s a d d e d w i t h a syringe a n d the reaction was f o l l p w e d b y measuring h y d r o gen consumption. T h e reaction product was analyzed b y G L C . 2

3

3

2

Literature Cited 1. Nagy-Magos, Z., Vastag, S., Heil, B., Markó, L . , Transition Met. Chem. (1978) 3, 123. 2. James, B. R., "Homogeneous Hydrogenation," Wiley, New York, 1973. 3. Knifton, J. F.,J.Org. Chem. (1976) 41, 1200. 4. Kvintovics, P., Heil, B., Palágyi, J., Markó, L . ,J.Organomet. Chem. (1978) 148, 311. RECEIVED February 22, 1978.


Rhodium-Phosphine Complexes as Homogeneous Catalysts

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