Bimetallic systems. Part 11. Heterobimetallic and unsymmetrical diplatinum complexes from cis-[PtR2(dppm-P)2](dppm Å Ph2PCH2PPh2; R = Me, 1 -naphthyl, or C6H4Me-o): crystal structure of [(C6H4Me-o)2Pt(µ-dppm)2PtMe2]

Abstract

Treatment of cis-[Pt(C₁₀H₇)₂(dppm-P)₂](dppm = Ph₂PCH₂PPh₂, C₁₀H₇= 1-naphthyl)(syn-anti mixture) with [Rh₂Cl₂(CO)₄] gave [(C₁₀H₇)₂Pt(µ-dppm)₂RhCl(CO)] which showed a complex ³¹P-{¹H} n.m.r. spectral behaviour with temperature. The analogue [(C₆H₄Me-o)₂Pt(µ-dppm)₂RhCl(CO)] was prepared in solution and behaved similarly. Treatment of cis-[Pt(C₆H₄Me-o)₂(dppm-P)₂] with [PtMe₂(cod)](cod = cyclo-octa-1,5-diene) gave in solution a slowly equilibrating mixture of the syn- and anti-isomers of cis,cis-[(C₆H₄Me-o)₂Pt(µ-dppm)₂PtMe₂], (4a) and (4b), respectively of which the minor (syn) isomer (4a) crystallized out and whose crystal structure has been determined. Treatment of [PtMe₂(dppm-PP′)] with dppm at –30 °C gave cis-[PtMe₂(dppm-P)₂]in situ which on treatment with [{AgI(PPh₃)}₄], [AuCl(PPh₃)], or AgPF₆gave, respectively, [Me₂Pt(µ-dppm)₂AgI], [Me₂Pt(µ-dppm)₂Au]Cl, or [Me₂Pt(µ-dppm)₂Ag] PF₆, all fully characterized. Solution ³¹P-{¹H} n.m.r. studies showed that treatment of [PtMe₂(dppm-P)₂] with [MCl(Me)(cod)] gave the donor-acceptor cations [Me₂Pt(µ-dppm)₂MMe]⁺(M = Pt or Pd) in high yield. Crystals of the title compound are monoclinic, space group P2₁/n, with a= 12.371(2), b= 21.368(5), c= 21.917(5)Å, β= 92.84(2)°, and Z= 4; the final R factor was 0.063 for 4 506 observed reflections. The structure confirms the cis square-planar co-ordination at both platinum atoms and shows the eight-membered Pt₂P₄C₂ring in a twist saddle conformation with a Pt ⋯ Pt separation of 4.91 Å. In the crystals used for data collection the o-tolyl groups adopt a syn configuration, which is shown to constitute the minor isomer in chloroform solution.