Decarbonylation reactions, catalysis

Carbon monoxide insertion and decarbonylation reactions of rhodium complexes have been studied mainly in the context of investigations concerned with catalysis. 

The product described here, 4-(4-chlorophenyl)butan-2-one, was previously prepared in the following ways a) by reduction of the corresponding benzalacetone, b) by catalyzed decarbonylation of 4-chlorophenylacetaldehyde by HFeiCO) in the presence of 2,4-pentanedione, - c) by reaction of 4-chlorobenzyl chloride with 2,4-pentanedione under basic catalysis (K2CO3 in EtOH), d) by reaction of 4-chlorobenzyl chloride with ethyl 3-oxobutanoate under basic catalysis (LiOH), - and e) by reaction of 3-(4-chlorophenyl )-propanoic acid with methyl lithium. - ... 

This section concerns catalytic processes that transform chemicals from renewables by C-C bond breaking. Among these are thermochemical processes, such as pyrolysis and also gasification, catalytic reactions, such as catalytic cracking and different reforming reactions, and decarbonylation and decarboxylation reactions. Many of these reactions occur simultaneously, particularly in the thermochemical processes. Another technically important class of C-C bond breaking reactions is the fermentation processes, however, they will not be considered in this section since they do not involve heterogeneous catalysis. 

Carbonylation-Decarbonylation. These reactions constitute a large and important segment of the homogeneous catalytic literature. Catalysis by most of the group VIII noble metals has been found, and a variety of substrates have been converted. For example, olefins react with CO and PdCl2 or (< 3P)2PdCl2 to yield -chloroacyl chlorides (58) and unsaturated acyl chlorides (59), respectively, a, w-Dienes, such as... 

The cychzation of pent-4-enals and related compounds to cyclopentanones is catalyzed by [RhCl(PPh3)3] in a reaction that involves oxidative addition of the -CHO group to the rhodium(I) catalyst. This reaction has much in common with the decarbonylation that most aldehydes undergo in the presence of this catalyst (see Decarbonylation Catalysis). 

Substitution reactions. Benzylation of phenols by benzyl methyl carbonates with Pd catalysis proceeds via transesterification and decarbonylation. Triarylmethanes are obtained from a reaction of benzhydryl carbonates with arylboronic acids. ... 

Tanaka and co-workers have found that the irradiation of Rh(PR3)2(CO)Cl in hydrocarbon solvents under 1 atm of CO can yield aldehyde and alcohol derivatives of the hydrocarbon in a photoassisted catalytic reaction. They attribute the reaction to photochemical dissociation of CO followed by C—H activation and then CO insertion. The observation that the catalysis is improved if the irradiation wavelength is below the absorbance maximum of Rh(PR3)2(CO)Cl indicates that photochemistry may be involved in other steps in addition to the decarbonylation. This system has been the subject of a theoretical study. ... 

A related approach involves the direct decarbonylation of stable ketones. DauguUs and Brookhart demonstrated that the rhodium-catalyzed decarbonylation of diaryl ketones was feasible [11]. Efficient extrusion of CO from alkyl aryl ketones to form alkylarenes was easily achieved by rhodium(I) catalysis directed by apyridyl ortho to the RCO group (Scheme 22.6) [12]. (CO)2Rh(acac) was found to be the optimal catalyst and the methodology had a broad substrate scope. This method offers an alternative way to synthesize alkyl benzenes through an ARCIS reaction, complementary to the known Friedel-Crafts alkylation reaction of arenes. 

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