Mechanism of white phosphorus activation by three-coordinate molybdenum(III) complexes: A thermochemical, kinetic, and quantum chemical investigation

White phosphorus (P₄) reacts with three-coordinate molybdenum(III) trisamides or molybdaziridine hydride complexes to produce either bridging or terminal phosphide (P^3-) species, depending upon the ancillary ligand steric demands. Thermochemical measurements have been made that place the Mo=P triple bond dissociation enthalpy at 92.2 kcal·mol^-1. Thermochemical measurements together with computational analysis rule out simple P-atom abstraction from P₄ as a step in the phosphorus activation mechanism. Kinetic measurements made by the stopped-flow method show that the reaction between the monomeric molybdenum complexes and P₄ is first-order both in metal complex and in P ₄. cyclo-P₃ complexes can be obtained when ancillary ligand steric demands are small, but kinetic measurements rule them out as monometallic intermediates in the P₄ activation mechanism. Also studied by calorimetric, kinetic, and in one case variable-temperature NMR methods is the process of μ-phosphide bridge formation. Post-rate-determining steps of the P₄ activation process were examined in a search for minima on the reaction's potential energy surface, leading to the proposal of two plausible, parallel, bimetallic reaction channels.