Oxidative carbonylation is a class of reactions that use carbon monoxide in combination with an oxidant to generate esters and carbonate esters. These transformations utilize transition metal complexes as homogeneous catalysts.[1] Many of these reactions employ palladium catalysts. Mechanistically, these reactions resemble the Wacker process.
Oxidative carbonylation, using palladium-based catalysts, allows certain alkenes to be converted into homologated esters:
2 RCH=CH2 + 2 CO + O2 + 2 MeOH → 2 RCH=CHCO2Me + 2 H2OSuch reactions are assumed to proceed by the insertion of the alkene into the Pd(II)-CO2Me bond of a metallacarboxylic ester followed by beta-hydride elimination (Me = CH3).
Arylboronic acids react with Pd(II) compounds to give Pd(II)-aryl species, which undergo carbonylation to give Pd(II)-C(O)aryl. These benzyl-Pd intermediates are intercepted by alkenes, which insert. Subsequent beta-hydride elimination gives the arylketone.[1]
The conversion of methanol to dimethylcarbonate by oxidative carbonylation is economically competitive with phosgenation. This reaction is practiced commercially using Cu(I) catalysts:
2 CO + O2 + 4 MeOH → 2 (MeO)2CO + 2 H2O
The preparation of dimethyl oxalate by oxidative carbonylation has also attracted commercial interest. It requires only C1 precursors:[2]
4 CO + O2 + 4 MeOH → 2 (MeO2C)2 + 2 H2O