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 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.
ASJC Scopus subject areas
- Colloid and Surface Chemistry