Is a Transition State Planar or Nonplanar in Oxidative Additions of C−H, Si−H, C−C, and Si−C σ-Bonds to Pt(PH3)2? A Theoretical Study

Abstract

A theoretical study of oxidative additions of H−CH3, CH3−CH3, H−SiR3, and SiR3−CH3 (RH, Cl, or Me) to Pt(PH3)2 was carried out with ab initio MO/MP2-MP4SDQ, CCD, and CCSD methods. The oxidative addition reactions of C−H and Si−H σ-bonds occur through a planar transition state (TS) structure, in accordance with the expectation from an orbital interaction diagram. However, the oxidative addition reactions of CH3−CH3 and SiH3−CH3 take place through a nonplanar TS structure, unexpectedly; the dihedral angle δ between PtP2 and PtXC planes (X = C or Si) is about 70° for X = Si and about 80° for X = C. Intrinsic reaction coordinate calculation of the SiH3−CH3 oxidative addition clearly indicated that this nonplanar TS is smoothly connected to the planar product on the singlet surface. The dihedral angle δ at the TS is larger in the SiMe3−CH3 and SiCl3−CH3 oxidative additions than that in the SiH3−CH3 oxidative addition. Electron distribution in the TS and effects of bulky substituent on the dihedral angle sugges...