Ligand effects in the copper catalyzed aerobic oxidative carbonylation of methanol to dimethyl carbonate (DMC)

The influence of the type and amount of added N-donor ligand, of the anion and the oxidation state on the copper catalyzed aerobic oxidative carbonyla tion of methanol to dimethyl carbonate (DMC) is systematically studied. A s urprising increase in activity and selectivity compared to the plain copper halides CuXn (X = Cl, Br, I; n = 1, 2) is found for catalyst complexes wit h three or four N-methylimidazole (NMI) ligands at Cu+/2+, a ligand regime reminiscent of the oxygen activating copper enzymes in nature. However, a l arge excess of NMI inhibits the catalysis. The NMI complexes turned out to be more active and selective as redox catalysts and less active in the comp eting undesired hydrolytic cleavage of DMC into methanol and carbon dioxide by the unavoidable byproduct water. Furthermore, corrosion of stainless st eel autoclaves is efficiently inhibited in the presence of >2 eq. of NMI pe r copper halide. (C) 2001 Elsevier Science B.V. All rights reserved.