Heptacoordinate dithiophosphate W(II) and Mo(II) complexes of diphosphines and iodide

New complexes [MI(CO)2(dppe){S2P(OEt)2}] (M=W, 1a; M=Mo, 1b), [MI(CO)2(dppm){S2P(OEt)2}] (M=W, 2a; M=Mo, 2b) and [W(CO)(dppe){S2P(OEt)2}2][O2dppe] (3a), were synthesised from [MI2(CO)3(NCMe)2] (M=Mo, W), after treatment with ammonium diethyldithiophosphate and phosphine under different conditions. The structure of the tungsten complexes was determined by single crystal X-ray diffraction. During the synthesis of 3a, oxidation of the phosphine took place and a molecule of oxidised phosphine occupies channels in the crystal. DFT/B3LYP calculations on models of 1a and 2a showed the capped octahedron structure, observed in most dicarbonyl complexes of this family, to be preferred by 1.4 and 2.6 kcalmol−1 for the dppm and the dppe complexes, respectively. Strong steric repulsions can reverse this trend, as happens with the rigid dppm ligand. Complex 1a adopts a pentagonal bipyramidal geometry, which is often found in related monocarbonyl complexes.