Base-Promoted, Remote C-H Activation at a Cationic (η5-C5Me5)Ir(III) Center Involving Reversible C-C Bond Formation of Bound C5Me5

Abstract

C-H bond activation at cationic [(η⁵-C₅Me₅)Ir(PMe₂Ar')] centers is described, where PMe₂Ar' are the terphenyl phosphine ligands PMe₂Ar^Xyl₂ and PMe₂Ar^Dipp₂. Different pathways are defined for the conversion of the five-coordinate complexes [(η⁵-C₅Me₅)IrCl(PMe₂Ar')]⁺, 2(Xyl)⁺ and 2(Dipp)⁺, into the corresponding pseudoallyls 3(Xyl)⁺ and 3(Dipp)⁺. In the absence of an external Brønsted base, electrophilic, remote ζ C-H activation takes place, for which the participation of dicationic species, [(η⁵-C₅Me₅)Ir(PMe₂Ar')]²⁺, is proposed. When NEt₃ is present, the PMe₂Ar^Dipp₂ system is shown to proceed via 4(Dipp)⁺ as an intermediate en route to the thermodynamic, isomeric product 3(Dipp)⁺. This complex interconversion involves a non-innocent C₅Me₅ ligand, which participates in C-H and C-C bond formation and cleavage. Remarkably, the conversion of 4(Dipp)⁺ to 3(Dipp)⁺ also proceeds in the solid state.