Transition metal–carbon bonds. Part 48. Allene complexes from halogeno-bridged platinum(II) complexes: crystal structures of cis-[PtCl2(PPrn3)(C3H4)] and cis-[PtCl2(PMe2Ph)(C3H4)]

Abstract

A ³¹P n.m.r. study of the system [Pt₂Cl₄(PMe₂Ph)₂]–allene shows that at low temperatures (e.g. 213 K)trans-[PtCl₂(PMe₂Ph)(C₃H₄)] forms rapidly and reversibly. At 20 °C [Pt₂Cl₄(PR₃)₂](PR₃= PPrⁿ₃, PMe₂Et, or PMe₂Ph) react with allene to give colourless complexes cis-[PtCl₂(PR₃)(C₃H₄)], the crystal structures of the PPrⁿ₃ and PMe₂Ph complexes were determined by X-ray diffraction. Crystal data are for [PtCl₂(PPrⁿ₃)(C₃H₄)]a= 15.461 (2), b= 11.437(2), c= 9.606(2)Å, space group Pna2₁, with Z= 4 and for [PtCl₂(PMe₂Ph)(C₃H₄)]a= 8.398(2), b= 10.209(3), c= 15.677(4)Å, space group P2₁2₁2₁, and Z= 4. Final R factors are R= 0.026 and 0.029 respectively. These cis complexes dissociate very slowly in solution, in contrast with cis-[PtCl₂(PPh₃)-(C₃H₄)], which was previously reported to be unstable. Treatment of cis-[PtCl₂(PMe₂Ph)(C₃H₄)] with [Pt₂Cl₄-(PMe₂Ph)₂] gives what is probably the µ-allene complex cis,cis-[(PhMe₂P)Cl₂Pt(C₃ H₄) PtCl₂(PMe₂Ph)] which was too insoluble to characterize fully. Treatment of [NBuⁿ₄]₂[Pt₂X₆](X = Cl, Br, or I) with an excess of allene gives the salts [NBuⁿ₄][PtX₃(C₃H₄)]. Treatment of [NBuⁿ₄][PtX₃(C₃H₄)] with [NBuⁿ₄]₂[Pt₂X₆](X = Cl or Br) gave the µ-allene complexes [NBuⁿ₄]₂[X₃Pt(C₃H₄)PtX₃]. The NPrⁿ₄ salt was also made. Proton, ¹³C, and ³¹P n.m.r. data and i.r. data are given and discussed.