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

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.