Cyclohexene hydroformylation, rhodium

In addition to rhodium(III) oxide, cobalt(II) acetylacetonate or dicobalt octacarbonyl has been used by the submitters as catalyst precursors for the hydroformylation of cyclohexene. The results are given in Table I. 

The formation of multinuclear clusters is much more favorable for rhodium than for cobalt. Additional evidence was obtained in comparative hydroformylation rate studies of 1-heptene and of cyclohexene at 75°C and 150 atm 1/1 H2/CO (19). For the acyclic olefin the kinetics followed the kinetic expression (except at low olefin) ... 

In 2004 Caporali investigated the hydroformylation of 1-hexene and cyclohexene using HRh(CO)(PPh3)3 [61]. The collected data indicated that the rate-determining step in the hydroformylation cycle depends upon the structure of the olefin. With an alpha-olefin like 1-hexene, the slowest step seems to be the hydrogenolysis of the acyl rhodium complex. In the presence of cyclohexene as a model for an internal olefin, the rate-determining step is the reaction of the olefin with the rhodium hydride complex (intermediate II in Fig. 6). 

The hydroformylation of alkenes generally has been considered to be an industrial reaction unavailable to a laboratory scale process. Usually bench chemists are neither willing nor able to carry out such a reaction, particularly at the high pressures (200 bar) necessary for the hydrocarbonylation reactions utilizing a cobalt catalyst. (Most of the previous literature reports pressures in atmospheres or pounds per square inch. All pressures in this chapter are reported in bars (SI) the relationship is 14.696 p.s.i. = 1 atm = 101 325 Pa = 1.013 25 bar.) However, hydroformylation reactions with rhodium require much lower pressures and related carbonylation reactions can be carried out at 1-10 bar. Furthermore, pressure equipment is available from a variety of suppliers and costs less than a routine IR instrument. Provided a suitable pressure room is available, even the high pressure reactions can be carried out safely and easily. The hydroformylation of cyclohexene to cyclohexanecarbaldehyde using a rhodium catalyst is an Organic Syntheses preparation (see Section 4.5.2.5). 

Hydr/formyUttion. Swiss chemists recommend rhodium(lII) oxide as catalyst for hydroformylation of olefins. Thus they have prepared cyclohexanecarboxaldchyde (2) in 95% yield from cyclohexene (1). Lower yields were obtained using cobalt catalysts. 

Using phosphite-modified rhodium catalysts, otherwise unreactive alkenes, such as 2-methyl-l-hexene, limonene and cyclohexene, are hydroformylated under mild conditions. " 2-Methyl-1-hexene, for example, yields almost exclusively 3-methylheptaldehyde, which is in contrast to the result of cobalt catalysis where a compound with a quaternary carbon is formed (Scheme 12). 

Yildiz-Unveren, H.H. and Schomacker, R. (2005) Hydroformylation with rhodium phosphine-modified catalyst in a microemulsion comparison of organic and aqueous systems for styrene, cyclohexene and l,4-diacetoxy-2-butene. Catal. Lett., 102, 83. 

In Os3(CO)ii(jU-CH2), two moles of CO react with the cluster via nucleophilic attack at both a metal atom and at the methylene, affording Os3(CO)i2-(//- / -CH2C0). This process is clearly of catalytic significance even though it is not catalytic in itself. Several reactions are, however, catalyzed by molecular clusters which are believed to involve reversible polyhedral rearrangements. For example, in the hydroformylation reaction of cyclohexene the tetrahedral rhodium... 

Grubbs and coworkers (35) while examining Rh and Co catalysts derived from 14 reported the loss of infrared CO stretches and visual darkening of the catalysts after use for hydrogenation of olefins, aldehydes or ketones, cyclohexene disproportionation to benzene and cyclohexane or the cyclotrimerization of a wide variety of acetylenes. Stille (36) using a rhodium catalyst prepared from 14 observed activity for the hydrogenation of benzene that increased with reuse, a phenomenon usually associated with metal crystallite formation. Rhodium catalysts of 15 and 16 used to hydroformylate octene-1 revealed a loss of carbonyl adsorptions and a loss in catalytic activity upon reuse (37). 

A similar in situ spectroscopic strategy was undertaken to determine if a Heck and Breslow binuclear elimination mechanism might be present in the unmodified rhodium-catalysed hydroformylation of alkenes. In one study alone, over 15 substrates were investigated where the acyl species RCORh(CO)4 was always observed, but under the conditions used, only the linear term was statistically supported [49], However, hydroformylation of two substrates, namely, cyclohexene and cyclooctene, exhibited outlier behaviour. With these two substrates, full conversion of the catalyst precursor Rh4(CO)i2 was never observed. Further detailed study of cyclohexene could not verify a statistically supported quadratic contribution [50, 51], The in situ study of cyclooctene at much lower CO partial pressure was more fruitful, as RCORh(CO>4, HRh(CO>4 and Rh2(CO)g were all observed simultaneously [52]. At the mean reaction conditions used in this study, 40% of product formation arose from the quadratic term k2[Rh]. Therefore, it appears that... 

Feng J, Garland M (1999) The unmodified homogeneous rhodium-catalyzed hydroformylation of cyclohexene and the search for monometallic catalytic binuclear elimination. Organometallics 18(8) 1542-1546... 

Bulky monophosphite hgands proved to be very useful for the functionalization of very unreactive substrates. Already in their first study van Leeuwen and Roobeek obtained relatively high rates for the hydroformylation of substrates such as cyclohexene and limonene. [8]. Van Rooy performed a systematic study to the rhodium catalyzed hydroformylation of substituted alkenes and compared the reaction rates with the triphenylphosphine system [42]. The bulky monophosphite derived catalyst was up to two orders of magnitude faster and gave acceptable rates using substrates for which the Wilkinson hydrofomylation catalyst gave hardly any activity. 

Noteworthy, the hydroformylation with cobalt catalysts can draw benefit from the addition of ruthenium [9]. For example, the initial rate of the reaction with cyclohexene was 19 times faster with Co2(CO)g/Ru3(CO)j2 in comparison to the monometallic Co system [10]. By combining the superior hydroformylation properties of a rhodium catalyst with the excellent hydrogenation activity of... 

The water-soluble rhodium complex [Rh(p.-pz)(CO)(TPPTS)]2 (pz = pyrazolate) was used as catalyst precursor during the two-phase catalytic hydroformylation of different olefins at 100 °C, 50 bar (CO H2 = 1 1), 600 rpm, and substrate catalyst ratio of 100 1. A reaction order- 1-hexene > styrene > allylbenzene > 2,3-dimethyl-1-butene > cyclohexene-was found. The experiments also showed that the binuclear catalyst precursor was resistant to possible sulfur poisons [108]. 

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