The Mechanism of Silicon−Hydrogen and Carbon−Hydrogen Bond Activation by Iridium(III):  Production of a Silylene Complex and the First Direct Observation of Ir(III)/Ir(V) C−H Bond Oxidative Addition and Reductive Elimination

The complexes Cp*(PMe{sub 3})Ir(Me)OTf (Me = CH{sub 3}, OTf = OSO{sub 2}CF{sub 3}) (1) and Cp*(PMe{sub 3})Ir(Me)(CH{sub 2}Cl{sub 2})[BAr{sub f}] (BAr{sub f}{sup {minus}} = [(3,5-(CF{sub 3}){sub 2}C{sub 6}H{sub 3}){sub 4}B]{sup {minus}}) (2), which contain iridium in oxidation state +3, were recently shown to undergo C-H activation reactions with alkanes under mild thermal conditions. The authors report a series of observations, including the first conversion of Ir(III) precursors to an isolable, structurally characterized Ir(V) aryl-hydride and a spectroscopically observable Ir(V) alkyl-hydride, that lends convincing experimental support to the Ir(III) {r{underscore}arrow} Ir(V) {r{underscore}arrow} Ir(III) mechanism. The complex Cp*(PMe{sub 3})Ir(Me)OTf (1) reacts rapidly with alkanes (H-CR{sub 3}) to produce 1 equiv of methane (CH{sub 4}) and rearranged products derived from Cp*(PMe{sub 3})Ir(CR{sub 3})OTf, which form as a consequence of the {beta}-hydride elimination pathway. When 1 is added to silanes (H-SiR{sub 3}, R = Me, Ph), products of a structural rearrangement type unobserved in C-H activation reactions are isolated along with 1 equiv of methane. These products, Cp*(PMe{sub 3})Ir(SiR{sub 2}OTf)(R), are presumably derived from a 1,2-migration in Cp*(PMe{sub 3})Ir(SiR{sub 3})OTf, wherein one of the groups initially bound to silicon migrates to iridium (eq 1).