Nickel N-Heterocyclic Carbene Catalysts for Ester Carbonylation

Abstract

Millions of tons of “acetyls” such as acetic acid and acetic anhydride are produced each year. These basic building blocks of chemical industry are elaborated into esters, amides, and eventually polymer materials, pharmaceuticals, and other consumer products. The vast majority of acetyls are produced industrially using homogeneous catalysis, but exclusively using scarce and expensive precious metal catalysts (principally rhodium and iridium complexes). We report here that nickel catalysts supported by N-heterocyclic carbene ligands mediate the carbonylation of methyl esters, selectively producing anhydrides with high activity at low catalyst loading. Carbene supporting ligands with aryl substituents, which can be added as air-stable imidazolium salts, dramatically improve carbonylation performance relative to prior nickel catalysts supported by tertiary phosphine ligands, raising hopes for industrial application of base metal carbonylation catalysts.