COORDINATION CHEMISTRY OF PERHALOGENATED CYCLOPENTADIENES AND ALKYNES .17. REACTION OF DICHLOROETHYNE WITH PLATINUM(0) PHOSPHINE COMPLEXES - FORMATION OF A PI-COMPLEX, ISOMERIZATION TO BETA-CHLOROETHYNYL COMPLEXES, AND SYNTHESES OF DIPLATINIOETHYNE DERIVATIVES - MOLECULAR-STRUCTURES OF (PH3P)2PT(ETA-2-CLC-EQUIVALENT-TO-CCL) AND CL(PH3P)2PT-C-EQUIVALENT-TO-C-PT(PPH3)2CL

Dichloroethyne ClC=CCl reacts with Pt(PPh3)2(C2H4) or Pt(PPh3)4 to give the pi-complex Pt(PPh3)2(eta2-ClC=CCl) (1), which can be isomerized by prolonged refluxing in toluene to trans-(Ph3P)2ClPt-C=CCl (2). 2 easily undergoes exchange reactions with alkylphosphines and with halide anions to yield trans-(R3P)2ClPt-C=CCl (R = Et (3), Bu (4)) and trans-(Ph3P)2-(X)Pt-C=CCl (X = F (5a), Br (5b), I (5c)), respectively. The alkylphosphine complexes 3 and 4 can also be obtained by reaction of Pt(PR3)4 (R = Et, (n)Bu) with ClC=CCl or from 1 and the corresponding phosphine. When Pt(PPh3)2(C2H4) is added to a solution of 3, a dinuclear complex 6 is formed, in which the C=C-Cl group acts as a sigma, pi-bridging ligand. Upon standing, oxidative addition of the remaining C-Cl bond occurs and the mu-ethynediyl complex trans-Cl(R3P)2Pt-C=C-Pt(PPh3)2Cl-CiS (R = Et (7a)) can be obtained. The corresponding mu-ethynediyl complex 7b (R = Ph) is formed directly from 2 and Pt(PPh3)2(C2H4). 7b isomerizes upon heating in toluene to the symmetrical all-trans isomer 8. The molecular structures of 1 and 8 were determined by X-ray diffraction (1: C38H30Cl2P2Pt.CH2Cl2, a = 10.311(3) angstrom, b = 10.392(4) angstrom, c = 33.675(16) angstrom, beta = 90.17(3)-degrees, monoclinic, P2(1)/n, Z = 4. 8: C74H60Cl2P4Pt2, a = 12.938(2) angstrom, b = 19.964(3) angstrom, c = 24.844(3) angstrom, beta = 96.t4(1)-degrees, monoclinic, C2/c, Z = 4).