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

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 PdCl2(6,6′-Me2bpy) (6,6′-Me2bpy: 6,6′-dimethyl–2,2′-bipyridyl)/Mn(TMHD)3 (TMHD: 2,2,6,6-tetramethyl–3,5-heptandionate)/(Ph3P)2NBr [bis(triphenylphosphoranylidene)ammonium bromide] system where TOF reached 13.17 (mol-DPC/mol-Pd h). The efficiency of our PdCl2(6,6′-Me2bpy)/Mn(TMHD)3/(Ph3P)2NBr system was higher than that of conventional PdBr2/Ce(Trop)4 (Trop: tropolonate)/(Ph3P)2NBr system.