Oxidative carbonylation

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.

Illustrative oxidative carbonylations

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 H₂O

Such 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]

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:^[3]

4 CO + O₂ + 4 MeOH → 2 (MeO₂C)₂ + 2 H₂O