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

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 &#176;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)A, space group Pna21, with Z= 4 and for [PtCl2(PMe2Ph)(C3H4)]a= 8.398(2), b= 10.209(3), c= 15.677(4)A, 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 &#181;-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 &#181;-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.