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 (P3-) 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 P4. 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.