Heptacoordinate dithiophosphate Mo(II) and W(II) complexes: molecular structures of mono and binuclear phosphine complexes

The complex [M(CO)3{S2P(OEt)2}2] (M=Mo, W) can be obtained in situ from the reaction of [MI2(CO)3(NCMe)2] with ammoniumdiethyldithiophosphate, in dichloromethane. One or two carbonyl groups can be replaced by mono and bidentate phosphines, such as Ph2PCH2PPh2 (dppm), Ph2P(CH2)2PPh2 (dppe), or PPh3, to afford heptacoordinate complexes [M(CO)2(PPh3){S2P(OEt)2}2] (M=Mo, 2a; W, 2b), [M(CO)2{S2P(OEt)2}2]2(μ-dppe) (M=Mo, 3a; W, 3b), [M(CO)(dppm){S2P(OEt)2}2] (M=Mo, 4a; W, 4b), [Mo(CO)(dppe){S2P(OEt)2}2] (5a), [W(CO)2(dppe){S2P(OEt)2}2] (6b), and [Mo(O)(I)(dppe){S2P(OEt)2}] (7a). All these complexes, with the exception of 4b, were structurally characterized by single crystal X-ray diffraction. The capped octahedral geometry was observed in all biscarbonyl species, the CO being the capping ligand. Complex 4a exhibits a pentagonal bipyramidal arrangement, with the carbonyl occupying one axial position, while 7a is an octahedral complex. These complexes were studied by cyclic voltammetry, showing essentially irreversible processes, involving orbitals with a strong d character.