Preparation and characterisation of seven-co-ordinate trifluoroacetate and oxalate complexes of molybdenum(II) and tungsten(II)
Abstract
The 1 : 1 reaction of sodium trifluoroacetate with either [MBr2(NCMe)(CO)2(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(µ-C2O4)]. The tungsten species [{WBr(CO)2(PMe2Ph)2}2(µ-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.
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