Reactivity of co-ordinated ligands. Part XXIV. Cyclopentadienyl cyclo-enyl complexes of platinum(II)

Abstract

The preparation of the complex [(C₇H₈)Pt(σ-C₅H₅)₂] is reported. The ¹H n.m.r. spectrum of this complex indicates that the Cyclopentadienyl rings are σ-bonded to platinum and that they display fluxional behaviour in solution but with an activation energy too low to permit ‘freezing-out’ at accessible temperatures. In solution the complex rearranges with time to form a σ–π complex, having a π-cyclopentadienyl ring co-ordinated to platinum and a Cyclopentadienyl attached to the dienyl ligand. Both endo- and exo-isomers may possibly be formed in this rearrangement, for which a concerted mechanism with a cyclic transition state is proposed. Other similar complexes of cyclo-octatetraene, cyclo-octa-1,5-diene, and dicyclopentadiene have also been prepared but have not been subjected to detailed study.