Molecular Orbital Description of the Bonding and Reactivity of the Platinum η³-Propargyl Complex [(η³-CH₂CCPh)Pt(PPh₃)₂]

The recently prepared η3-propargyl complex [(η³-CH₂CCPh)Pt(PPh₃)₂] ⁺ (1) exhibits unusual regioselectivity in reactions involving nucleophilic addition to the propargyl ligand. Fenske-Hall approximate molecular orbital calculations and density functional calculations have been carried out to study the structure, bonding, and reactivity of 1. The calculations suggest that the principal bonding interaction between Pt and the propargyl ligand occurs through the terminal carbon atoms of the ligand, despite the observed short Pt-central carbon distance. Optimized geometries for model complexes calculated by density functional methods agree well with the reported crystal structure of 1. The observed nucleophilic addition to the central carbon of the propargyl ligand is suggested to occur through a charge-controlled mechanism, assisted by the presentation of a low-lying acceptor orbital on the central carbon along the reaction path.