C-H Oxidative Addition and Reductive Elimination Reactions in a Dinuclear Iridium Complex

Article abstract of DOI:10.1021/ja00233a020

Thermolysis of the hydridoallyliridinium complex (η⁵-C5Me5)(η³-C3H5)-(H)Ir at relatively high concentrations of starting material in benzene leads to the dinuclear benzene C-H oxidative addition product (η⁵-C5Me5)(C6H5)Ir(η¹,η³-C3H4)(μ-H)Ir(η⁵-C5Me5) (1).Heating this material causes reductive elimination of benzene from the dinuclear complex 1 in a clean first-order process.The lack of dependence of the rate of this process on the concentration of entering ligand demonstrates that an intermediate is formed in the reductive elimination; this species is proposed to be the coordinatively unsaturated dinuclear complex (η⁵-C5Me5)Ir(η¹,η³-C3H4)Ir(η⁵-C5Me5) (13).Transient intermediate 13 reacts with dative ligands such as phosphines, ethylene, and tert-butyl isocyanide to give direct trapping products (η⁵-C5Me5)(L)Ir(η¹,η³-C3H4)Ir(η⁵-C5Me5) (2-6), formed by coordination of the ligand to one of the iridium centers.Reaction of 13 with reagents having activated X-H bonds, such as benzene-d₆, H2, and acetonitrile, leads to intermolecular oxidative addition products having structures analogous to that of 1.Comparative inter- and intramolecular kinetic isotope effect studies have provided evidence that in the reversible reaction of 13 with benzene, an additional η²-arene intermediate is not required to explain the results.Thermolysis of 2 and 4, the PMe3- and ethylene-trapped products of 13, leads to three new dinuclear complexes (7, 8, and 9).These materials are formed by intermolecular insertion into the dative ligand C-H bonds, followed by rearrangement.The structures of the intermolecular benzene C-H insertion product 1, PMe3-trapped product 2, and intramolecular C-H activation product 7 have been determined by X-ray diffraction.