Reactivity of Terminal, Electrophilic Phosphinidene Complexes of Molybdenum and Tungsten. Nucleophilic Addition at Phosphorus and P−P Bond Forming Reactions with Phosphines and Diphosphines

Reaction of the terminal electrophilic phosphinidene complexes [Cp*M(CO)3{PN(i-Pr)2}][AlCl4] (3, M = Mo; 4, M = W) with PEt3 results in replacement of a metal carbonyl by the phosphine. The reactions occur via initial nucleophilic attack by the phosphine at the phosphinidene phosphorus, followed by carbonyl loss and migration of the phosphine to the metal. Reactions of 3 and 4 with bis(dimethylphosphino)methane (dmpm) lead to [Cp*M(CO)2{P(N(i-Pr)2)P(Me2)CH2P(Me2)-κ2 P 1,P 4}][AlCl4] (9, M = Mo; 10, M = W), in which one end of the diphosphine coordinates to phosphorus and the other end coordinates to the metal. The reactions proceed by initial nucleophilic attack by one end of the diphosphine at phosphorus, followed by carbonyl loss and coordination of the other end of the ligand to the metal. Compound 3 (M = Mo) reacts with bis(dimethylphosphino)ethane (dmpe) to give the analogous product [Cp*Mo(CO)2{P(N(i-Pr)2)P(Me2)CH2CH2P(Me2)-κ2 P 1,P 5}][AlCl4] (12), in which the two ends of the dmpe ligand coordinate to phosphorus and molybdenum, respectively. Reaction of compound 4 (M = W) with dmpe leads to two products, [Cp*W(CO)2{P(N(i-Pr)2)P(Me2)CH2CH2P(Me2)-κ2 P 1,P 5}][AlCl4] (13) and [{Cp*W(CO)2(PN(i-Pr)2)}2(μ-dmpe)][AlCl4]2 (14). Compound 13 is analogous to 12. In compound 14, the two ends of the diphosphine ligand displace carbonyl ligands from two molecules of 4, resulting in a novel bis-phosphinidene structure in which the diphosphine ligand bridges two metal centers, each of which retains a terminal phosphinidene ligand. Loss of an additional carbonyl ligand from 12, followed by migration of one end of the phosphine from phosphorus to the metal, results in re-formation of a terminal phosphinidene ligand, leading to [Cp*Mo(CO)(PN(i-Pr)2)(dmpe-κ2 P)][AlCl4] (17). The structural characterization of the phosphine adducts and carbonyl substitution products of the terminal phosphinidene complexes 3 and 4 has provided valuable insights into metal−phosphinidene bonding in these compounds.