Homogeneous Hydrogenation of Ketones Catalyzed by Cobalt

3 Homogeneous Hydrogenation of Ketones Catalyzed by Cobalt Carbonyl Phosphine Complexes

Downloaded by UNIV OF PITTSBURGH on May 4, 2015 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0132.ch003

L A ' S Z L O MARKÓ, B A ' L I N T H E I L and S A ' N D O R V A S T A G Veszprém University of Chemical Engineering, Veszprém, Hungary Cobalt carbonyl complexes substituted by tertiary phosphines catalyze the hydrogenation of ketones at 200°C and 150-250 atm. The catalyst is formed i n situ from Co (CO) and the phosphine(L) added separately to the starting mixture. According to IR spectra Co (CO) L , CoH(CO) L, and CoH(CO) L are the main cobalt carbonyl species present during the reaction. Trialkylphosphines were more suitable than phosphines with aryl groups. Best results were achieved with P:Co ratios of 2:1. Carbon monoxide retarded hydrogenation whereas tertiary amines like NEt had no significant effect. Consecutive hydrogenation of the secondary alcohol to the corresponding hydrocarbon was usually less than 2%. No measurable asymmetric induction was observed if PRR'R" type phosphines were used. 2

2

2

6

2

8

3

2

3

Cobalt carbonyl derivatives containing tertiary phosphines show a ^ variety of catalytic properties. These complexes are useful as catalysts for hydroformylation (1) and hydrogénation (2) of olefins

R—CH=CH +CO+H 2

150°C 2

R—CH—CH +R—CH —CH —CHO 3

50 atm

R—CH=CH

2

+ H

2

2

CHO 100°C 2

R—CH —CH 2

30 atm

hydrogénation of aldehydes (3) 27 In Homogeneous Catalysis—II; Forster, D., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

28

HOMOGENEOUS

160°C

R—CHO + H

2

30 atm

CATALYSIS

II

> R—CH OH 2

and the decomposition of formic acid (4)

HCOOH

40°C

>H + C0 . 2

2

Hydrido carbonyl phosphine complexes of the general formula C o H ( C O ) (PR ) . j are regarded as the catalysts in these reactions. The active spe cies are probably hydrido complexes with lower coordination numbers formed by the loss of carbon monoxide or phosphine from these precursors. F e w reports on the homogeneous hydrogénation of ketones (5, 6, 7, 8, 9, 10) have been published, and none have been developed into a useful general procedure. W e have found that these tertiary phosphine-substituted cobalt carbonyls are useful as catalysts for the hydrogénation of ketones too. n


3

4

7

R—C—R' + H

υ

\ R—CH—R' 200 atm |

2 ο η η

Ο

OH

The catalysts are formed in situ from C o ( C O ) , and the phosphine is added separately to the starting reaction mixture. IR spectra of samples taken from the reaction mixture show three types of complexes present (3,11): 2

Table I.

IR Bands of Reaction Products Characteristic Strong CO Bands, cmr

Complex

8

Remarks

x

CoH(CO) (PR ) CoH(CO) (PR ) 3

3

2

3

Co (CO) (PR ) 2

6

3

2

2

2050, 1970 1905

main species in samples taken from the autoclave at reaction temperature

1955

main species in the reaction product cooled under pressure to 20°C

Compared with the analogous hydrogénation of aldehydes, the reac tion requires somewhat more drastic conditions (about 200°C and 6 hrs), but the temperature is still within the stability range of the cobalt car bonyl phosphine complexes containing tertiary alkyl phosphines as ligands. If aryl phosphines are used, a more or less pronounced decomposi tion of the carbonyl complexes can be observed (as indicated by the IR

In Homogeneous Catalysis—II; Forster, D., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

3.

MARKO

Hydrogénation

E T A L .

of Ketones

29

spectra of the reaction mixture and by the formation of a precipitate) which is also reflected by the diminished yields of the hydrogénation reaction. This may be seen in Table II. Table II. Effect of Phosphine Structure on the Hydrogénation of Acetophenone a

Yield of ot-phenylethanol, %

Phosphine PEt PBu P(CeH ), PMePrPh PEt Ph PMePh(CH Ph) P(CH Ph) PPh,

87 96 67 77 62 49 36 18

3


3

n

2

2

2

3

Reaction conditions: 200°, 6 hrs, 150-250 atm p , 1 mole % Co (C0 ), P:Co = 2:1, solvent hexane. a

H2

2

8

Best results were achieved with P : C o ratios between 1:1 and 3:1, therefore a 2:1 ratio was used i n most experiments. Larger amounts of phosphine significantly inhibited the activity of the catalyst, and no hydro génation was observed without phosphines (see Table I I I ) . Carbon monoxide retarded hydrogénation even in small concentrations ( < 5 p o ) (see Table I V ) . C

Table III.

Effect of Ρ : Co Ratio on the Hydrogénation of Acetophenone" Yield of (x-Phenylethanol, %

PBu :Co (CO) s

2

8

0:1 2:1 3:1 4:1 6:1 20:1

— 90 94 96 92 36

Reaction conditions: 200°, 6 hrs, 150-250 atm pn , 1 mole % Co (CO) , solvent hexane. α

2

2

8

Tetrahydrothiophene, added i n a S : C o = 2.5:1 ratio diminished the reaction rate to about 1/6 its original value. Tertiary amines such as N E t have no significant effect and thus permit the hydrogénation of nitrogen containing ketones. Under optimum conditions, secondary alcohol yields between 6 0 99% were achieved with rather different types of ketones (see Table V ) . Subsequent hydrogénation of the secondary alcohol to the corresponding hydrocarbon was small, usually below 2 % . This compares favorably 8


30

HOMOGENEOUS

Table IV.

CATALYSIS

II

Effect of p o on the Hydrogénation of Acetophenone" C

Yield of Qt-Phenylethanol, %

Initial pco, atm

96 77 66 48

0 2 3 5

° Reaction conditions: 200°, 6 hrs, 150-250 atm pu , 1 mole % Co (CO) , 4 mole % PBu , solvent hexane. 2

2

8


3

Table V.

Hydrogénation of Different Ketones"

Ketone

Alcohol

Acetone M e t h y l ethyl ketone Acetophenone Benzophenone Cyclohexanone 4-ter£-Butylcyclohexanone

95 99 96 68 94 44 44 40 25 16 15 94 90

2-Propanol 2-Butanol a-Phenylethyl alcohol Benzhydrol Cyclohexanol m-4-ter£-Butylcyclohexanol 2rafts-4-ter£-Butylcyclohexanol Menthol Isomenthol Neomenthol Neoisomenthol Ethyl-3-hydroxybutyrate 5-Diethylamino-2-pentanol

6

Menthone

Yield, %

c

E t h y l acetoacetate 5-Diethylamino-2-pentanone

Reactions were carried out at 200° and 150-250 atm p 2 with 1 mole % Co (CO) + 4 mole % PBu in hexane as solvent. Reaction times 6 hrs. Solvent ethanol, 2 mole % Co,(CO) + 8 mole % PBu*. Mixture of 86% menthone and 14% isomenthone. Solvent toluene. a

H

2

8

3

h

8

c

with the results obtained with C o H ( C O ) as catalyst where hydrogenolysis was often the main reaction if aromatic ketones were hydrogenated (5). No detailed investigation of the reaction mechanism (kinetic mea surements, etc.) was performed. The actual catalyst is probably the coordinatively unsaturated C o H ( C O ) ( P R . 3 ) species which may be formed by the loss of one ligand from both hydrido carbonyl phosphine complexes present in the reaction mixture: 4

2

CoH(CO) (PR ) 8

8

CoH(CO) (PR ) 2

—PR

3

3

CoH(CO) (PR )2 This follows the inhibiting effect of tetrahydrothiophene, excess C O , and P R . The catalytic cycle may then proceed analogously to that sup posed i n similar reactions : 2

3

3


3.

MARKO

Hydrogénation

E T A L .

CoH(CO) (PR ) + R — C — R ' 2

3

* R—CH—R' Ο—Co(CO) (PR )

Ο R—CH—R'

+ H

O—Co(CO) (PR )


2

3

2

31

of Ketones

2

3

R — C H — R ' + CoH(CO) (PR ) 2

3

OH

Using chiral phosphines as catalyst components, asymmetric induc tion may be expected if R R'. This assumption was tested with acetophenone as substrate ( R = P h , R ' = M e ) and two different optically active tertiary phosphines as ligands: (S)-( + )-PMePrPh and (S)-( — )P M e P h ( C H P h ) . Only insignificant optical activity of the product was achieved i n both cases (optical yields below 1% ). H i g h reaction tem perature and/or the low coordination number of the intermediate com plexes ( lack of steric factors ) may be the cause of this negative result. 2

Experimental Experiments were performed in a 125 m l stainless steel rocking auto clave. C o ( C O ) (12), (S)-( + )-PMePrPh (13, 14) and ( S ) - ( - ) P M e P h ( C H P h ) (13, 14) were prepared according to published meth ods, all other reagents were laboratory grade chemicals. One-tenth mole ketone, 0.001 mole C o ( C O ) , 0.004 mole phosphine, and the quantity of hexane necessary to bring the reaction mixture to 40 grams total weight were measured into the autoclave which was then flushed and pressured to 170 atm with dihydrogen. Pressure rose during heating to 240-270 atm and dropped according to the reaction rate; repressuring was only necessary if larger quantities of substrates were used. In some experiments samples were taken from the autoclave during the reaction. The cobalt carbonyl phosphine complexes dissolved i n the samples, and the products were detected by IR. Ketones, alcohols, and other organic components were determined after distillation (to eliminate cobalt) by G L C . 2

8

2

2

8

Literature Cited 1. Slaugh, L. H., Mullineaux, R. D., J. Organometal. Chem. (1968) 13, 469. 2. Ferrari, G. F., Andreetta, Α., Pregaglia, G. F., Ugo, R., J. Organometal. Chem. (1972) 43, 213. 3. Pregaglia, G. F., Andreetta, Α., Ferrari, G. F., Ugo, R.,J.Organometal Chem. (1971) 30, 387. 4. Marangoni, Α., Andreetta, Α., Ferrari, G. F., Pregaglia, G. F., Chim. Ind. Milano (1970) 52, 862. 5. Wender, I. et al., J. Amer. Chem. Soc. (1951) 73, 2656. 6. Bressan, C., Broggi, R., Chim. Ind. Milan (1968) 50, 1194. 7. Pregaglia, G., Castelli, R., French Patent 1,509,863 (1968). 8. Schrock, R. R., Osborn, J. Α., Chem. Commun. (1970) 567. In Homogeneous Catalysis—II; Forster, D., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

32

HOMOGENEOUS

CATALYSIS

II

9. Markó, L., Szabó, P., Laky, J., Hungarian Patent 157,605 (1971). 10. Bonvicini, P., Levi, Α., Modena, G., Scorrano, G., Chem. Commun. (1972) 1188. 11. Piacenti, E., Bianchi, M . , Benedetti, E., Chim. Ind. Milan (1967) 49, 245. 12. Szabó, P., Markó, L., Bor, G., Chem. Tech. Leipzig (1961) 13, 549. 13. Korpium, O., Lewis, R. Α., Chickos, J., Mislow, K., J. Amer. Chem. Soc. (1968) 90, 4842. 14. Naumann, K., Zon, G., Mislow, K., J. Amer. Chem. Soc. (1969) 91, 7012.


RECEIVED August 20, 1973.


Homogeneous Hydrogenation of Ketones Catalyzed by Cobalt

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