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

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'-Me(2)bpy) (6,6'-Me(2)bpy: 6,6'-dimethyl-2,2'-bipyridyl)/Mn(TMHD)(3) (TMHD: 2,2,6,6-tetramethyl-3,5-heptandionate)/(Ph3P=)(2)NBr [bis(triphenylphosphoranylidene)ammonium bromide] system where TOF reached 13.17 (mol-DPC/mol-Pdh). The efficiency of our PdCl2(6,6'-Me(2)bpy)/Mn(TMHD)(3)/(Ph3P=)(2)NBr system was higher than that of conventional PdBr2/Ce(Trop)(4)(Trop: tropolonate)/(Ph3P=)(2)NBr system. (C) 2000 Elsevier Science B.V. All rights reserved.