Stereospecific transfer of ethynyl groups between platinum(II) and mercury(II)

Abstract

Reactions between cis-[PtCl₂(CO)L](L = PMePh₂) and Hg(CCR)₂(R = Me or Ph) lead first to [PtCl(CCR)(CO)L][isomer (I); L trans to CCR] and Hg(CCR)Cl, then to cis-[Pt(CCR)₂(CO)L] and HgCl₂, and finally to [PtCl(CCR)(CO)L][isomer (II); L trans to Cl] and Hg(CCR)Cl. The reactions of (II) with Hg(CCR)₂ quantitatively form cis-[Pt(CCR)₂(CO)L], and (II) with Hg(CR′)₂(R′= Me or Ph; R ≠ R′) produce single isomers of [Pt(CCR)(CCR′)(CO)L]. Treatment of these bis(ethynyl)platinum complexes with HgCl₂ specifically removes the ethynyl trans to L, reforming (II) and the ethynylmercury(II) chloride. Reactions of the bis(ethynyl)mercurials can be advantageously carried out in the presence of [NEt₄]Cl, which symmetrises the Hg(CCR)Cl by-product to Hg(CCR)₂(thus making both ethynyls available for transfer to platinum) and [NEt₄]₂[Hg₂Cl₆](which, being insoluble in organic solvents, is easily separated from the desired product).