Oxidative carbonylation of phenol to diphenyl carbonate catalyzed by Pd complex with 2,2′-bipyridyl ligands

Abstract

Pd–2,2′-bipyridyl complexes were investigated as novel Pd catalysts for direct synthesis of diphenyl carbonate (DPC) by oxidative carbonylation of phenol using carbon monoxide (CO) and air. Pd–2,2′-bipyridyl complexes which possess a pair of substituents at 6,6′-position of 2,2′-bipyridyl moiety were found to be more effective than Pd–2,2′-bipyridyl complexes without any substituents at the 6,6′-position. The best efficiency was obtained by using PdCl 2(6,6′-Me 2bpy) (6,6′-Me 2bpy: 6,6′-dimethyl–2,2′-bipyridyl)/Mn(TMHD) 3 (TMHD: 2,2,6,6-tetramethyl–3,5-heptandionate)/(Ph 3P) 2NBr [bis(triphenylphosphoranylidene)ammonium bromide] system where TOF reached 13.17 (mol-DPC/mol-Pd h). The efficiency of our PdCl 2(6,6′-Me 2bpy)/Mn(TMHD) 3/(Ph 3P) 2NBr system was higher than that of conventional PdBr 2/Ce(Trop) 4 (Trop: tropolonate)/(Ph 3P) 2NBr system.