Carbon-hydrogen oxidative addition and reductive elimination reactions in a dinuclear iridium complex

Abstract

Thermolysis of the hydridoallyliridium complex ({eta}{sup 5}-C{sub 5}Me{sub 5})({eta}{sup 3}-C{sub 3}H{sub 5})(H)Ir at relatively high concentrations of starting material in benzene leads to the dinuclear benzene C-H oxidative addition product ({eta}{sup 5}-C{sub 5}Me{sub 5})(C{sub 6}H{sub 5})Ir({eta}{sup 1},{eta}{sup 3}-C{sub 3}H{sub 4})({mu}-H)-Ir({eta}{sup 5}-C{sub 5}Me{sub 5}) (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 than an intermediate is formed in the reductive elimination; this species is proposed to be the coordinatively unsaturated dinuclear complex ({eta}{sup 5}-C{sub 5}Me{sub 5})Ir({eta}{sup 1},{eta}{sup 3}-C{sub 3}H{sub 4})Ir({eta}{sup 5}-C{sub 5}Me{sub 5}) (13). Transient intermediate 13 reacts with dative ligands such as phosphines, ethylene, and tert-butyl isocyanide to give direct trapping products ({eta}{sup 5}-C{sub 5}Me{sub 5})(L)Ir({eta}{sup 1},{eta}{sup 3}-C{sub 3}H{sub 4})Ir({eta}{sup 5}-C{sub 5}Me{sub 5}) (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-d{sub 6}, H{sub 2}, 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 reactionmore » of 13 with benzene, an additional {eta}{sup 2}-arene intermediate is not required to explain the results. Thermolysis of 2 and 4, the PMe{sub 3{sup {minus}}} and ethylene-trapped products of 13, leads to three new dinuclear complexes (7, 8, and 9). These materials are formed by intramolecular insertion into the dative ligand C-H bonds, followed by rearrangement. 30 refs., 6 figs., 2 tabs.« less