Nature of the metal-alkene bond in platinum complexes of strained olefins

Density functional theory and high-level ab initio molecular orbital methods have been used to investigate complexes of platinum with highly pyramidalized olefins: Pt(PH₃)₂(R) with R = C₁₁H₁₆, C₁₀H₁₄, C⁹H₁₂, and C₈H₁₀. Geometries and binding energies are reported and compared to experimental values where available. Charge decomposition analyses have been carried out for all complexes, and they show a beautiful increase in olefin←Pt back-donation as the olefin becomes more pyramidal. Natural bond orbital analyses show a corresponding increase in the platinum 6s and carbon 2s character in the Pt-C bond orbital, in agreement with previous NMR studies. We also find that the binding energies of all the complexes correlate well with the olefin strain energies calculated for the free olefins.