Fluxional behavior in platinum(II) complexes of the tridentate ligand 1,1,1-tris(diphenylphosphinomethyl) ethane. Evidence for the importance of cis effects in an associative mechanism

Fluxional behavior is observed in complexes of the type [PtX(2)(triphos)] (triphos=1,1,1-tris(diphenylphosphinomethyl)ethane) where X=CN and NCS, but not Cl, Br, I, CH3 or C6H5. The existence of intramolecular exchange in the former two complexes is attributed to the smaller steric requirements of the anions. An associate mechanism which involves a five-coordinate intermediate is proposed for the exchange. Extended Huckel Molecular Orbital Calculations (EHMO) suggest that the rates of exchange are not thermodynamically controlled. The electronic structures of some of the intermediates are addressed by EHMO.