Providing Support in Favor of the Existence of a PdII/PdIV Catalytic Cycle in a Heck-Type Reaction

Abstract

The complex [Pd(O,N,C-L)(OAc)], where L is a monoanionic pincer ligand derived from 2,6-diacetylpyridine, reacts with IBzOH at room temperature to afford the very stable pair of PdIV complexes (OC-6-54)- and (OC-6-26)-[Pd(O,N,C-L)(O,CC6H4CO2-2)I] (1.5:1 molar ratio, at –55 ºC). These complexes and the PdII species [Pd(O,N,C-L)(OX)] and [Pd(O,N,C-L’)(NCMe)]ClO4, (X = MeC(O) or ClO3, L’ = another monoanionic pincer ligand derived from 2,6-diacetylpyridine), are precatalysts for the arylation of CH2=CHR (R = CO2Me, CO2Et, Ph) using IC6H4CO2H-2 and AgClO4. These catalytic reactions have been studied and a tentative mechanism is proposed. The presence of two PdIV complexes is detected by ESI(+)-MS during the catalytic process. All data obtained strongly support a PdII/PdIV catalytic cycle.