Oxidative addition cobalt halide catalysts

A quite different process, called Reppe carbonylation, has been used to convert acetylene to acrylic acid esters. The catalysts are carbonyls of iron, cobalt or nickel and the hydrogen source is a hydrogen halide, HX. The process is thought to involve oxidative addition of HX to the metal carbonyl, followed by coordination and insertion of alkyne into the M—H bond and insertion of CO into the M—C bond. The resulting acyl complex is cleaved by alcohol to produce the ester and the metal hydride catalyst. De Angelis et al. have reported a theoretical analysis of the Ni(CO)4 system. 

Carbonylation and decarbonylation reactions of alkyl complexes in catalytic cycles have been reviewed . A full account of the carbonylation and homologation of formic and other carboxylic acid esters catalysed by Ru/CO/I systems at 200 C and 150-200 atm CO/H2 has appeared. In a novel reaction, cyclobutanones are converted to disiloxycyclopentenes with hydrosilane and CO in the presence of cobalt carbonyl (reaction 4) . The oxidative addition of Mel to [Rh(CO)2l2] in aprotic solvents (MeOH, CHCI3, THF, MeOAc), the rate determining step in carbonylation of methyl acetate and methyl halides, is promoted by iodides, such as Bu jN+I", and bases (eg 1-methylimidazole) . A further kinetic study of rhodium catalysed methanol carbonylation has appeared . The carbonylation of methanol by catalysts prepared by deposition of Rh complexes on silica alumina or zeolites is comparable with the homogeneous analogue . 

Homogeneous catalyst systems include transition metals, for example, Schiff base complexes with cobalt [59]. Unfortunately, there is no protocol known to recover and recycle the expensive Schiff base. Many copper complexes have been employed for the oxidation of phenols to 1,4-benzoquinones [60]. Copper salts such as CUCI2 and CuBr2 are widely used for the oxidation of trimethylphenol with molecular oxygen at larger scale [61]. In addition, applications of the halides of Cr, Mn, Fe, Ni, and Zn as catalysts have been described [58]. Copper halides have also been combined with earth metal halides, for example, MgCl2 [62] or LiCl, in the presence of a phase transfer catalyst [63]. 

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