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
King; Inorganic Compounds with Unusual Properties—II Advances in Chemistry; American Chemical Society: Washington, DC, 1979.
28
INORGANIC COMPOUNDS W I T H UNUSUAL PROPERTIES
Table II.
Hydrogenation of Nitrobenzene with in situ R h -|-
No.
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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
King; Inorganic Compounds with Unusual Properties—II Advances in Chemistry; American Chemical Society: Washington, DC, 1979.
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
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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
King; Inorganic Compounds with Unusual Properties—II Advances in Chemistry; American Chemical Society: Washington, DC, 1979.
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.
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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.
King; Inorganic Compounds with Unusual Properties—II Advances in Chemistry; American Chemical Society: Washington, DC, 1979.