Catalytic activities and properties of Au(III)/Schiff-base complexes in methanol oxidative carbonylation

Several Au(III)/Schiff-base complexes were studied and proven to be effective catalysts for oxidative carbonylation of methanol to generate dimethyl carbonate (DMC). Effects of Schiff-base ligands, promoters, and promoter mole ratio to Au(III)/Schiff-base complexes on catalytic activity were studied. When the reaction was carried out at a methanol/Au(III) molar ratio of 5060:1, an [AuCl2(phen)]Cl/KI (phen = 1,10-phenanthroline) ratio of 1:4, a CO/O2 pressure of 2:1, and a temperature of 120 °C for 3 h, the conversion, selectivity, and TOF value of the model reaction were 10.8%, 98%, and 138.9 h−1, respectively. The catalyst was characterized by FTIR, UV–vis, 1H NMR, and cyclic voltammetry. The oxidation state of gold during the reaction and the role of KI were discussed using data on electrochemical experiments and ESI-MS. [AuI2(phen)]+ was considered an intermediate in the reaction. A plausible Au(III)/Au(I) catalytic cycle mechanism was proposed.

Au(III)/Schiff base complexes were used and proven, for the first time, to be effective catalysts for the oxidative carbonylation of methanol to generate dimethyl carbonate (DMC).Figure optionsDownload high-quality image (85 K)Download as PowerPoint slideHighlights
► Oxidative carbonylation is an efficient method for synthesizing dimethyl carbonate.
► [AuCl2(phen)]Cl/KI was successfully employed in the reaction for the first time.
► I− and phen complexes used in the reaction show synergistic effect on the activity.
► The oxidation state of gold during the reaction and the role of KI were discussed.