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).