Synthesis and dynamic behaviour of bis(ethylene)(tertiary phosphine)-platinum complexes

Abstract

Reactions of ethylene-saturated solutions of bis(cyclo-octa-1,5-diene)platinum in light petroleum with tertiary phosphines or triphenylarsine afford white crystalline bis(ethylene)platinum complexes [Pt(C2H4)2L][L = PMe3, PMe2, Ph, PMePh2, PPh3, P(C6H11)3 or AsPh3]. Bis(ethylene)(tricyclohexyIphosphine)platinum reacts with tetrafluoroethylene to give the mixed-olefin complex [Pt(C2H4)(C2F4){P(C6H11)3}]. These 16-electron platinum(o) complexes show dynamic behaviour in solution with rotation of the ethylene ligands. N.m.r. studies (1H and 13C) at various temperatures establish an apparent equivalence of methylene-group sites at ambient temperatures, but at low temperatures there are two CH2, group signals in agreement with a molecular structure in which the ligand atom L, the platinum atom, and the carbon atoms of the ethylene molecules are coplanar. Activation energies for ethylene rotation in the complexes [Pt(C2H4)2L] fall in the range (10.2–13.0)± 0.4 kcal mol–1, Substitution in [Pt(C2H4)2{P(C6H11)3] of C2H4 by C2F4 results in a 3 kcal mol–1 lowering of the barrier to rotation of the remaining ethylene molecule.