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Reaction of [MI2(CO)3(NCMe)2] [M = Mo, W] with 2 or 3 equiv of PH2Fc or PH2CH2Fc [Fc = Fe(η5-C5H5)(η5-C5H4)] in CH2Cl2 or THF at various temperatures gave [MI2(CO)3L2] [M = Mo:  L = PH2Fc (1a), PH2CH2Fc (2a), PH(CH2Fc)2 (5a); M = W:  L = PH2Fc (1b), PH2CH2Fc (2b), PH(CH2Fc)2 (5b)] and [MI2(CO)2L3] [M = Mo:  L = PH2Fc (3a), PH2CH2Fc (4a); M = W:  L = PH2Fc (3b), PH2CH2Fc (4b)] in high yields. 2b and 4a were the first primary ferrocenylphosphine complexes of molybdenum(II) and tungsten(II) to be crystallographically characterized. Reaction of [WI2(CO)3(NCMe)2] with 1 equiv of PH(CH2Fc)2 in CH2Cl2 gave [WI2(CO)3(NCMe){PH(CH2Fc)2}] (6), the first structurally characterized tungsten(II) monophosphine complex with an acetonitrile ligand. All complexes show the structural motif of a capped octahedron. The formation of the bis-phosphine-substituted products is preferred when the reaction is carried out in a noncoordinating solvent at low temperatures, and with tungsten as the central atom, whereas coordinating solvents, higher temperatures, and molybdenum give rise to the formation of tris-phosphine-substituted products. VT 31P NMR studies of 1−5 show fluxional behavior in solution. Density functional theory (DFT) calculations give insight into the reasons for the structural characteristics and the dynamic behavior of the complexes. Complexes 1−4 show only very low activity in the polymerization of norbornadiene.

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