Cationic Ir(III) Alkylidenes Are Key Intermediates in C-H Bond Activation and C-C Bond-Forming Reactions

This work describes the chemical reactivity of a cationic (eta(5)-C5Me5)Ir(III) complex that contains a bis(aryl) phosphine ligand, whose metalation determines its unusual coordination in a kappa(4)-P,C,C'C '' fashion. The complex (1(+) in this paper) undergoes very facile intramolecular C H bond activation of all benzylic sites, in all likelihood through an Ir(V) hydride intermediate. But most importantly, it transforms into a hydride phosphepine species 4(+) by means of an also facile, base-catalyzed, intramolecular dehydrogenative C C coupling reaction. Mechanistic studies demonstrate the participation as a key intermediate of an electrophilic cationic Ir(III) alkylidene, which has been characterized by low-temperature NMR spectroscopy and by isolation of its trimethylphosphonium ylide. DFT calculations provide theoretical support for these results.