Homogeneous oxidative transformations mediated by copper catalyst systems

Abstract

• State of the art copper-catalysed oxidative transformations is described. • Oxidation and oxygenation, peroxidation and hydroxylation reactions are reviewed. • Key differences in the mechanistic pathways are discussed. Oxidative transformations involve the conversion of organic substrates, through various processes to obtain oxygenates such as alcohols, phenolic and carbonyl compounds which can be used in the pharmaceutical and chemistry industries. Inspired by nature, particularly copper-based enzymes, these reactions include, but are not exclusive to, the radical co-catalyst free oxidation of activated alcohols inspired by copper-based oxidases, the hydroxylation of monophenols which is inspired by tyrosinase, the hydroxylation of benzene, peroxidation of hydrocarbons and oxidative cleavage of polysaccharide model substrates, which draws inspiration from oxygenases. Copper, as an environmentally benign metal pre-catalyst, has received considerable attention during the development of various catalyst systems to generate oxygenates. The mechanistic pathways by which these Cu-based catalyst systems operate has been investigated extensively and the major differences involve the initial oxidation state of copper, the redox lability of these oxidation states and the nature of the Cu-based active species. Herein we provide critical review of developments in copper-catalysed oxidative transformations.