Formation and isomerisation of cis-bis(phenylethynyl)bis(tertiary phosphine)platinum complexes

Abstract

cis-[Pt(CCPh)₂L₂](L = PPh₃ or PMePh₂) have been isolated from the reactions of PhCCH and cis-[PtCl₂L₂] with Na(OEt), from ligand displacement by L from [Pt(CCPh)₂(cod)](cod = cyclo-octa-1,5-diene){itself made from [PtCl₂(cod)], PhCCH, and Na(OEt)}, and from CO displacement by L from cis-[Pt(CCPh)₂(CO)L]. Failures were encountered with some other ethynyls and phosphines, and none of these routes may be generally applicable to the preparation of cis bis-ethynyls. The cis complexes formed, though not affected by the usual nucleophilic Isomerisation catalysts, were readily converted to the trans isomers by traces of HgCl₂, HgBr₂, Hg I₂, HgCl(CCPh), HgClPh, CuI, [CuCl(PPh₃)], or SnCl₂. The mechanism proposed to account for these observations involves reversible ethynyl transfers between platinum and mercury, copper, or tin, and ready Isomerisation of the intermediates cis-[PtX(CCPh)L₂](X = Cl, Br, or I).