A Theoretical Study on the Oxidative Addition of a Si–H σ-Bond to [MCl(CO)(PH3)2] (M = Rh or Ir). Similarities to and Differences from [M′(PH3)2] (M′ = Pd or Pt) and [RhCl(PH3)2

Abstract

Abstract The Si–H Oxidative Addition to [MCl(CO) (PH3)2] (M = Rh or Ir) was theoretically investigated with ab initio MO/MP2—MP4, SD-CI, and CCD (coupled cluster with double substitutions) methods. This reaction proceeds with a somewhat high activation energy (Ea) and a moderate exothermicity (Eexo); when the oxidative addition occurs in the Cl–M–CO plane, Ea = 19 kcal mol−1 for Rh and 13 kcal mol−1 for Ir, and Eexo = 0.4 kcal mol−1 for Rh and 17.4 kcal mol−1 for M = Ir. This result is in significant contrast to [M′(PH3)2] (M′ = Pd or Pt) and [RhCl (PH3)2] : the Si–H oxidative addition occurs with a very small barrier for [M′(PH3)2], but a zero barrier and significantly high exothermicity for [RhCl(PH3)2]. The low reactivity of [MCl(CO)(PH3)2] is interpreted in terms of the low energy level of the d orbital, a considerable weakening of the M–Cl and M–CO bonds, and an exchange repulsion between SiH4 and the M d orbital in [MCl(CO)(PH3)2]. The above results indicate that Vaska-type complexes are less favorable for an oxidative addition reaction than [M′(PH3)2] and [RhCl(PH3)2], and that they cannot be used for a catalytic reaction including an oxidative addition which requires a high activation energy.