Molecular orbital description of the bonding and reactivity of the platinum eta(3)-propargyl complex [(eta(3)-CH2CCPh)Pt(PPh3)(2)](+)

The recently prepared eta(3)-propargyl complex [(eta(3)-CH2CCPh)Pt(PPh3)(2) ](+) (1) exhibits unusual regioselectivity in reactions involving nucleophi lic addition to the propargyl ligand. Fenske-Hall approximate molecular orb ital calculations and density functional calculations have been carried out to study the structure, bonding, and reactivity of 1. The calculations sug gest that the principal bonding interaction between Pt and the propargyl li gand occurs through the terminal carbon atoms of the ligand, despite the ob served short Pt-central carbon distance. Optimized geometries for model com plexes calculated by density functional methods agree well with the reporte d crystal structure of 1. The observed nucleophilic addition to the central carbon of the propargyl ligand is suggested to occur through a charge-cont rolled mechanism, assisted by the presentation of a low-lying acceptor orbi tal on the central carbon along the reaction path.