REACTIONS OF ACETYLENES WITH NOBLE-METAL CARBONYL HALIDES .11. SYNTHESIS OF [PT(CME=C(H)COOME)(CO)CL] VIA POLYNUCLEAR PLATINUM CARBONYLS - X-RAY CRYSTAL-STRUCTURE DETERMINATION OF THE SIGMA-ALKENYL PLATINUM COMPLEX [N(PPH3)2][PT(CME=C(H)CO2ME)(CO)CL2]

The polynuclear derivative [{Pt(CO)2}n] reacts, in chloroform solution, with H[Pt(CO)Cl3] and MeC=CCO2Me to give [Cl(CO)Pt-CMe=C(COOMe)-C(=O-Pt(CO)Cl] (2) and [Pt{CMe=C(H)COOMe}(CO)Cl] (3). Compound (3) reacts with PPh3 to give [Pt{CMe=C(H)CO2Me}(PPh3)2Cl] (7a), while with chloride ions it is transformed into the anionic complex [Pt{CMe=C(H)CO2Me}(CO)Cl2]- (4). A multinuclear n.m.r. study on a series of derivatives is reported. The crystal and molecular structure of [N(PPh3)2][Pt{CMe=C(H)CO2Me}(CO)Cl2] (4a) has been determined from three-dimensional X-ray data. The complex crystallizes in the monoclinic space group Pc, with two formula units in a unit cell of dimensions a = 9.378(2), b = 14.362(3), c = 14.760(4) Å, and β = 100.10(5)°. The structure was determined by Patterson and Fourier methods and refined by least-squares methods to R = 0.0268 from 3 212 independent reflections with I > 3σ(I). The platinum atom has the expected square-planar co-ordination; relevant bond lengths are Pt-C(sp2) 2.016(7), Pt-C(sp) 1.836(9), Pt-Cl (trans to the alkene) 2.404(2), and Pt-Cl (trans to CO) 2.313(2), while the C=C bond distance is 1.32(1) Å. The plane of the olefinic moiety is rotated by 65.6(2)° with respect to the co-ordination plane of the metal atom giving a short intramolecular separation of 3.163(7) Å between Pt and the oxygen of the carboxylate carbonyl group.