Kinetics and Mechanism of Decarbonylation

Elimination of carbon monoxide accompanied by conversion of an acyl group to the corresponding alkyl moiety has been termed decarbonylation. The process is represented by Eq. (12) with L = CO. 

The decarbonylation can be effected (1) thermally, (2) photolytically, and (3) chemically, by using a metal complex such as Rh(PPh3)3Cl. The three types of processes will be considered in turn. 

This is the most extensively, as well as intensively, studied type of the decarbonylation. Nevertheless, kinetic data are scarce. Conversion of metal acyls to their respective alkyls has been investigated for two systems RCOMn(CO), 37, 50, 51) and XCH2COIr(PPh3)2Cl2 (X = Ph or a substituted Ph group) 160). 

Given in Eq. (32) is a general mechanistic scheme for the decarbonylation ligand substitution is included for comparison  

The intermediate M(COR) is the same as that for carbon monoxide insertion. It may be a coordinatively unsaturated solvated or unsolvated a-acyl or, alternatively, a 7r-acyl. It is of interest that photolysis of MeCOMn(CO)j in an Ar matrix at 15°K produces what appears to be a trigonal bipyramidal (Cj ) MeCOMn(CO)4 209). 

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