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

C-H bond activation at cationic [(η5-C5Me5)Ir(PMe2Ar')] centers is described, where PMe2Ar' are the terphenyl phosphine ligands PMe2ArXyl2 and PMe2ArDipp2. 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 PMe2ArDipp2 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.