Bulk gold (non-nanogold) catalysis of aerobic oxidations of amines, isocyanides, carbon monoxide, and carbene precursors

Abstract

Oxidative reactions that are catalysed by bulk gold consisting of ∼50 000 nm gold powder particles or gold (∼50 nm) supported on Al₂O₃ are reviewed. Using O₂ as the oxidizing agent, bulk gold catalyzes the following types of reactions in organic solvents at 45–90 °C: (1) the conversion of amines to imines [(RCH₂)₂NH → RCH₂NCHR], (2) the oxidation of benzyl alcohol to benzaldehyde, (3) the reaction of isocyanides with primary amines to give carbodiimides [CN–R + H₂N–R′ → R′–NCN–R] and with secondary amines to give ureas , (4) the reactions of CO with primary amines to give ureas [CO + H₂N–R → OC(NHR)₂], and (5) the reactions of diazoalkanes with amines to give enamines . In some of these reactions, amine oxides (e.g., Me₃N–O) may be used in place of O₂. Mechanisms of these and related reactions are examined. These studies show that bulk, non-nanogold is capable of catalysing a variety of different reactions.