PREPARATION AND CHARACTERIZATION OF PALLADIUM(I) AND PLATINUM(I) DINUCLEAR COMPLEXES BRIDGED BY 2-(DIMETHYLPHOSPHINO)PYRIDINE

A series of dinuclear complexes containing Me2Ppy (= 2-(dimethylphosphino)pyridine) as a bridging ligand, [MM'X2(mu-Me2Ppy)2] (M, M' = Pd(I), Pt(I); X = Cl, Br, and I), have been prepared by reactions between [MX2(Me2Ppy-P)2] and [M'2(dba)3] (dba = 1,5-diphenyl-1,4-pentadien-3-one). In these reactions it has been found by P-31{H-1} NMR studies that a dimeric head-to-head isomer was formed in the first place and then isomerized to a head-to-tail isomer. The reactions for analogous Ph2Ppy (= 2-(diphenylphosphino)pyridine) complexes have been also examined in the same manner. The monomeric Pd(II) complexes reacted more rapidly than did the corresponding Pt(II) complexes in these dimerization and isomerization reactions. For each halogeno series of the Me2Ppy and Ph2Ppy complexes, it seems that the dimerization occurs faster in the order of Cl < Br < I, while the order is reversed in the isomerization, Cl > Br > I. The Me2Ppy complexes isomerized to a head-to-tail isomer more rapidly than did the Ph2Ppy complexes, indicating a larger trans effect of Me2Ppy than Ph2Ppy.