Hydroformylation of Some Optically Active Olefins

19 Hydroformylation of Some Optically Active Olefins F. P I A C E N T I , M . B I A N C H I , and P. F R E D I A N I

Downloaded by CORNELL UNIV on September 7, 2016 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0132.ch019

Università di Firenze, Via Gino Capponi 9, Florence, I T A L Y The hydroformylation of several olefins in the presence of Co (CO) under high carbon monoxide pressure is reported. (S)-5-Methylheptanal (75%) and (S)-3-ethylhexanal (4.8%) were products from (+)(S)-4-methyl-2-hexene with optical yields of 94 and 72%, respectively. The main products from (+)(S)-2,2,5-trimethyl-3-heptene were (S)-3-ethyl-6,6-dimethylheptanal (56.6%) and (R)-4,7,7-trimethyloctanal (41.2%) obtained with optical yields of 74 and 62%, respectively. (R)(S)-3-Ethyl-6,6-dimethylheptanal (3.5%) and (R)(S)-4,7,7-trimethyloctanal (93.5%) were formed from (R)(S)-3,6,6-trimethyl-1-heptene. (+)(S)-1-Phenyl-3-methyl1-pentene, under oxo conditions, was almost completely hydrogenated to (+)(S)-1-phenyl-3-methylpentane with 100% optical yield. 3-(Methyl-d )-1-butene-4-d gave 4(methyl-d )pentanal-5-d (92%), 2-methyl-3-(methyl-d )butanal-4-d (3.7%), 3-(methyl-d )pentanal-2-d ,3-d (4.3%) with practically 100% retention of deuterium. The reaction mechanism is discussed on the basis of these results. 2

8

3

3

3

3

3

3

3

2

1

'Hphe mechanism for forming isomeric aldehydes by hydroformylation of olefins has recently been given considerable attention. Different techniques have been used to gain more and better information ( J , 2, 3, 4, 5, 6, 7, 8). The present investigation concerns the formation of alde hydes as a result of introducing a formyl group on a chain carbon atom other than at the double bond of the starting olefin when the reaction is carried out under a relatively high carbon monoxide pressure which suppresses olefin isomerization (4). The formation of the straight-chain and the α-methyl substituted aldehydes by hydroformylation of a linear α-olefin has been explained by Breslow and Heck (9), but the mechanism cannot be extended to the other isomers. 283 Forster and Roth; Homogeneous Catalysis—II Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

284

HOMOGENEOUS CATALYSIS

Table I.

Hydroformylation of Some Olefins: Isomeric

Olefin


II

(+) 0S)-3-Methyl-l-pentene (+) 0S)-3-Methyl-l-hexene ( - ) (S)-4-Methyl-l-hexene (+) (S)-4-Methyl-2-hexene (+) (S)-5-Methyl-l-heptene (+XS)-2,2,5/rrimethyl-34ieptene (fi)(S)-3,6,6-Trimethyl-l-heptene ([+) (S)-l-Phenyl-3-methyl-l-pentene

c

T,

fco,

°C

atm

atm

100 110 100 110 100 110 110 150

102 100 80 80 80 95 95 115

80 100 80 80 80 95 95 145

° The following numbering has been adopted: C = C—C—C—C—C—C ; C—C—C—C—C—C—C.

I 1

2

3

4

C

I 6

7

1

2

C

I 4

5

C

7

M M The isomerization of the olefin prior to its hydroformylation has been the explanation of this question (3) and the formation of isomeric alde hydes was related to the presence of isomeric free olefins during the hy droformylation. This explanation, however, is being questioned in the literature. The formation of (-f ) ( S )-4-methylhexanal with an optical yield of more than 98% by hydroformylation of ( + )(S)-3-methyl-lpentene (2, 6) is inconsistent with the olefin isomerization explanation. Another inconsistency has been the constance of the hydroformylation product composition and the contemporary absence of isomeric olefins throughout the whole reaction in hydroformylation experiments carried out with 4-methyl-l-pentene and 1-pentene under high carbon monoxide partial pressure. The data reported in Ref. 4 on the isomeric composition of the hydroformylation products of 1-pentene under high carbon monox ide pressure at different olefin conversions have recently been checked. The ratio of n-hexanal:2-methylpentanal:2-ethylbutanal was constant throughout the reaction and equal to 82:15.5:2.5 at 100°C and 90 atm carbon monoxide. The hydroformylation of ( + ) ( S )-3-methyl- 1-hexene giving [besides (S)-4-methylheptnal] (R)-3-ethylhexanal with an optical yield of 70% gives further support to the argument that the olefin isomerizes only a small extent under oxo conditions (Table I ) . Different hypotheses have been made on the possible mechanism of formation of ( R ) -3-ethylhexanal from the original substrate without racemization. It was suggested by Piacenti et al. (5) that (R)-3-ethylhexanal could be formed with a high Forster and Roth; Homogeneous Catalysis—II Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

19.

piACENTi

ET AL.

Optically Active Olefins

285

Composition of Products and Optical Yields Formyl Group Insertion on Carbon Atom of the Olefin" 1 Prod ., b


%

92.0 93.0 88.0 75.3 77.0 41.2 93.5

2

8

ΟΥ.,»

%

98 n.d. 95 94 94 62 —

4

5

6

M O.Y.,

%

Prod., % 3.3 3.1 10.2 16.6 18.9 1.8 2.4

— 2.4 — —

— — 0.43 0.6

b

— — — —

3.2 — — —

4.5 3.1 1.7 4.8 1.3 56.6 3.5

70 72 72 77 74 —

Ref. 6 5 12 —

12 — —

>Prod.: Product; O.Y.: Optical yield = optical purity of product optical purity ol starting material. This olefin is almost completely hydrogenated with 100% optical yield. c

optical yield by hydroformylation of ( + ) (S)-3-methyl-l-hexene through an oxidative addition of a C — H bond of the methyl group on the cobalt atom of the catalytically active species. This does not involve the asym metric carbon atom and therefore does not affect its optical purity. Casey and C y r {7,8) have repeated the experiment using 3-methyl-lhexene-3-di as substrate, and the results agreed with a 1,2 hydrogen shift in the complexed olefin. The expression, "olefin isomerization accompany ing the hydroformylation," that Casey and C y r used (8) to indicate the isomerization of the complex containing the olefin is misleading because, even according to them, free, isomerized olefins are not formed during the hydroformylation. The formation of isomeric aldehydes has been attrib uted to the presence of isomerized olefins in the substrate to react (3). To determine if the presence of a hydrogen atom on the asymmetric carbon atom of the olefins mentioned above is essential to obtain the formylation of the methyl group, α-olefins containing a quaternary carbon atom were subjected to hydroformylation (10). 3,3-Dimethyl-l-butene, 2,3,3-trimethyl-l-butene, 3,3-dimethyl-l-hexene, and 4,4-dimethyl-1-hex ene (Table II) all yielded more than 96% (and i n one case nearly 100% ) of the aldehyde deriving from the formylation of the carbon atom i n position 1 while the remaining product was derived from formylation of the carbon atom in position 2. N o product was detected from formylation of any of the carbon atoms belonging to the saturated alkyl substituents of the quaternary one. This implies strongly that at least one hydrogen atom must be present on each carbon atom of the olefinic chain to have Forster and Roth; Homogeneous Catalysis—II Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

286

HOMOGENEOUS

CATALYSIS

II

Table II. Composition of the Hydroformylation Products of Olefins Containing a Quaternary Carbon Atom" Formyl Group Addition on Carbon Atoms of the Olefin Olefin

1,

2,


% 3,3-Dimethyl-l-butene 2,3,3-Trimethyl-l-butene 3.3- Dimethyl-l-hexene 4.4- Dimethyl-l-hexene a

%

99.2 99.2 100 96.6

0.8 0.8 trace 3.4

Catalyst: Co (CO) ; solvent: benzene; Τ : 110°C; p : 80 atm; p \ 80 atm. 2

s

H2

co

the formylation of carbon atoms different from the originally unsaturated ones. These data have been confirmed further by the results of the investi gation of the hydroformylation of 3-(methyl-d )-l-butene-4-iZ (I) under a high carbon monoxide partial pressure (125 atm) (11) (Scheme 1). 4-(Methyl-

Hydroformylation of Some Optically Active Olefins

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