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

The complex [Pd( O, N, C-L)(OAc)], in which L is a monoanionic pincer ligand derived from 2,6-diacetylpyridine, reacts with 2-iodobenzoic acid 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, C-C6H4CO2-2)I] (1.5:1 molar ratio, at −55 °C). 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 was detected by ESI(+)-MS during the catalytic process. All the data obtained strongly support a PdII/PdIV catalytic cycle. [ABSTRACT FROM AUTHOR]