Synthesis and characterization of five-co-ordinate alkyne complexes of platinum(II). Crystal and molecular structure of [(dmphen)MePt( m-Cl) ( m-MeC=CMe)Pt(Cl)Me].CH2Cl2, (dmphen = 2,9-dimethyI-l1,10-phenanthroline)

Alkynes with electron-withdrawing substituents add to square-planar platinum( 11) 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(CI) 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 P-methylvinyl derivative is instead observed by treating [PtMe(N-N)(MeCN)] + with MeO,CC=CCO,Me 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,/c, 2 = 4, in a unit cell of dimensions a = 15.719(4), b = 12.307(3), c = 25.048(7) A, p = 148.50(1)". The structure has been refined to R 0.054 (R'0.064) for 371 8 intensity data [/ 3 30(/)]. 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 MeCrCMe ligand transversely bridges the Pt Pt vector (3.079 A) and the dihedral angle between the two planes formed by the two Pt-p-C, units is 102.2(5)"