PREPARATION AND CHARACTERIZATION OF 7-CO-ORDINATE TRIFLUOROACETATE AND OXALATE COMPLEXES OF MOLYBDENUM(II) AND TUNGSTEN(II)

The 1:1 reaction of sodium trifluoroacetate with either [MBr2(NCMe)(CO),(PR3)2] (M = Mo or W, PR3 = PMe2Ph or PMePh2) or [MBr2(CO)2(PPh3)2] (M = Mo or W) formed the mononuclear complexes [MBr(O2CCF3)(CO)2(PR3)2] containing a bidentate carboxylate ligand. Addition of a second equivalent of the carboxylate salt generated [M(O2CCF3)2(CO)2(PR3)2] in which the oxygen-donor ligands adopt one bidentate and one monodentate bonding mode. Single-crystal X-ray diffraction studies of [MoBr(O2CCF3)(CO)2(PPh3)2] confirm a 4:3 polytopal form. The treatment of [MBr2(NCMe)(CO)2(PR3)2] (M = Mo, PR3 = PMePh2; M = W, PR3 = PMe2Ph or PMePh2) or [MBr2(CO)2(PPh3)2] (M = Mo or W) with a suspension of sodium oxalate in acetone yielded the complexes [{MBr(CO)2(PR3)2}2(mu-C2O4)]. The tungsten species [{WBr(CO)2(PMe2Ph)2}2(mu-C2O4)] crystallises in two forms both of which contain a planar oxalate bridge linking two seven-co-ordinate metal centres, but have different 4: 3 geometries. The triangular face of the polygon in each of the three structures is occupied by a bromine atom and two oxygens of a carboxylate group, and the quadrilateral face by pairs of carbonyl and phosphine ligands.