Molecular-orbital studies on carbametallaboranes. Part 1. Icosahedral carbaplatinaborane polyhedra

Abstract

Extended-Hückel molecular-orbital calculations are reported for the icosahedrel platinaboranes and carbaboranes [B₁₁{Pt(PH₃)₂}H₁₁]^2–, [B₁₀C{Pt(PH₃)₂}H₁₁]^–, and B₉C₂[Pt(PH₃)₂]H₁₁. The failure of the polyhedral skeletal electron-counting rules when applied to carbaplatinaboranes is discussed, and attributed to the unequal bonding capabilities of the platinum 5d_xz and 5d_yz orbitals in the Pt(PH₃)₂ fragment. The conformations of icosahedral carbaplatinaboranes are rationalised on the basis of the symmetry characteristics of the lowest-unoccupied orbital of thecarbaboraneand the highest-occupied orbital ofthe metal-phosphine moiety. Analogous d⁸ metal compounds are predicted to be stable and expected to have conformations which are complementary to those observed for d¹⁰ metal compounds.