SYNTHESIS AND CHARACTERIZATION OF 5-CO-ORDINATE ALKYNE COMPLEXES OF PLATINUM(II) - CRYSTAL AND MOLECULAR-STRUCTURE OF [(DMPHEN)MEPT(MU-CL)(MU-MECCME)PT(CL)ME].CH2CL2 (DMPHEN = 2,9-DIMETHYL-1,10-PHENANTHROLINE)

Alkynes with electron-withdrawing substituents add to square-planar platinum(II) complexes of general formula [Pt(Cl)R(N-N)] (R = Me or C6H4OMe-4, N-N = bidentate nitrogen ligand) affording the corresponding five-co-ordinate trigonal-bipyramidal (TBPY) compounds [Pt(Cl)R(alkyne)(N-N)]. The related five-co-ordinate cationic species [PtMe(alkyne) (N-N) (MeCN)] + have also been characterized in the presence of excess MeCN. Methyl insertion and formation of a beta-methylvinyl derivative is instead observed by treating [PtMe(N-N)(MeCN)]+ with MeO2CC=CCO2Me in the absence of free MeCN. Using a 1:2 alkyne:[Pt(Cl) Me(dmphen)] ratio (dmphen = 2,9-dimethyl-1,10-phenanthroline), binuclear species [Pt2Cl2Me2(alkyne)(dmphen)] are isolated. An X-ray crystallographic study was carried out on the but-2-yne derivative. Crystals are monoclinic, space group P2(1)/c, Z = 4, in a unit cell of dimensions a = 15.719(4), b = 12.307(3), c = 25.048(7) angstrom, beta = 148.50(1)-degrees. The structure has been refined to R 0.054 (R' 0.064) for 3718 intensity data [I greater-than-or-equal-to 3 sigma(I)]. The two platinum atoms display different co-ordination numbers [a five- (TBPY) and a four-co-ordinate square-planar arrangement of the ligands] and are held together by the but-2-yne and one chlorine bridge. The MeC=CMe ligand transversely bridges the Pt ... Pt vector (3.079 angstrom) and the dihedral angle between the two planes formed by the two Pt-mu-C2 units is 102.2(5)-degrees.