Providing Support in Favor of the Existence of a Pd II /Pd IV 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 Pd IV complexes (OC‐6‐54)‐ and (OC‐6‐26)‐[Pd( O , N , C ‐L)( O , C ‐C 6 H 4 CO 2 ‐2)I] (1.5:1 molar ratio, at −55 °C). These complexes and the Pd II species [Pd( O , N , C ‐L)(OX)] and [Pd( O , N , C ‐L′)(NCMe)]ClO 4 , (X=MeC(O) or ClO 3 , L′=another monoanionic pincer ligand derived from 2,6‐diacetylpyridine), are precatalysts for the arylation of CH 2 CHR (RCO 2 Me, CO 2 Et, Ph) using IC 6 H 4 CO 2 H‐2 and AgClO 4 . These catalytic reactions have been studied and a tentative mechanism is proposed. The presence of two Pd IV complexes was detected by ESI(+)‐MS during the catalytic process. All the data obtained strongly support a Pd II /Pd IV catalytic cycle.