Bimetallic systems. Part 2. Synthesis and interconversion of monodentate- and bridging-bis(diphenylphosphino)methane platinum, diplatinum, and mercury–platinum acetylides

Abstract

Treatment of [PtCl₂(dppm-PP′)][dppm = bis(diphenylphosphino)methane] with LiCCR gives good yields of the diplatinum ‘face-to-face’ complexes trans,trans-[Pt₂(CCR)₄(µ-dppm)₂](2a), (2b), (2d), or (2e), with R = C₆H₄Me-p, Ph, CH₂CH₂Ph, or C(Me)CH₂ respectively. These diplatinum complexes react with more dppm to give the mononuclear fluxional complexes trans-[Pt(CCR)₂(dppm-P)₂](3a), (3b), (3d), or (3e). A more convenient method of making the mononuclear complexes (3a)–(3e) is to treat [PtCl₂(dppm-PP′)] with LiCCR in the presence of dppm. Treatment of [Pt(dppm-PP′)₂]Cl₂ with LiCCPh gives (3b) but deprotonation to give [Pt(Ph₂PCHPPh₂)₂] also occurs. Treatment of [PtCl₂(dppm-PP′)] with an excess of LiCCPh gives (3b) and [Pt(CCPh)₄]^2–, isolated as its [NBuⁿ₄]⁺ salt. Treatment of [Pt(dppm-PP′)₂]Cl₂ with Hg(CCR)₂ rapidly gives the platinum–mercury complexes [(RCC)₂Pt(µ-dppm)₂HgCl₂](4a)–(4d) in very high yields, with R = C₆H₄Me-p, Ph, Me, or Prⁿ respectively. Treatment of the platinum–mercury complexes (4a)–(4c) with Na₂S·9H₂O gives HgS and high yields of the mononuclear complexes trans-[Pt(CCR)₂(dppm-P)₂](3a)–(3c), with R = C₆H₄Me-p, Ph, or Me respectively. More conveniently, when [Pt(dppm-PP′)₂]Cl₂ is treated with Hg(O₂CMe)₂+ RCCH the platinum–mercury complexes (4a)–(4c) are formed in excellent yields. Preliminary work shows that [(HOCH₂CH₂CC)₂Pt(µ-dppm)₂HgCl₂](4e) is formed from [Pt(dppm-PP′)₂]Cl₂+ Hg(O₂CMe)₂+ HOCH₂CH₂CCH. Treatment of the complex trans-[Pt(CCPh)₂(dppm-P)₂](3b) with HgCl₂ gives [(PhCC)₂Pt(µ-dppm)₂HgCl₂](4b). The fluxional monodentate-dppm complexes trans-[Pt(CCR)₂(Ph₂PCH₂PPh₂)₂](3a)–(3c), R = C₆H₄Me-p, Ph, or Me respectively, are oxidised by hydrogen peroxide to give the non-fluxional phosphine oxide complexes trans-[Pt(CCR)₂{Ph₂PCH₂P(O)Ph₂}₂](5a)–(5c) or quaternised by methyl iodide to give trans-[Pt(CCR)₂(Ph₂PCH₂PMePh₂)₂]l₂(6a)–(6c). Complex (6b; R = Ph) is deprotonated by lithium propan-2-oxide probably to give the di-ylide trans-[Pt(CCPh)₂(Ph₂PCHPMePh₂)₂](7) which hydrolyses to trans-[Pt(CCPh)₂(PMePh₂)₂]. l.r., and ¹H, ³¹P, and ¹⁹⁵Pt n.m.r. data are given.