Kinetics and mechanism of nitrite reduction by trichloro-oxobis(triphenylphosphine oxide)molybdenum(V)

Abstract

In the presence of excess of nitrite ion the complex [MoOCl₃(OPPh₃)₂] is completely oxidised to Mo^VI in CH₂Cl₂. The reaction proceeds by three observable stages. Data for the first stage correspond to co-ordination of nitrite at molybdenum(V), via a limiting S_N1 mechanism, involving loss of a triphenylphosphine oxide molecule. At 25 °C, k₁= 51·8 ± 2·1 s^–1, ΔH₁^‡= 12·6 ± 0·3 kcal moh^–1, and ΔS₁^‡=–8·2 ± 1·0 cal K^–1 mol^–1. The data for the second stage of reaction are taken to indicate chelation and/or isomerisation of co-ordinated nitrito-ligand into a position cis to the oxo-group, followed by rapid non-rate-determining electron transfer. The third and final stage of reaction appears to involve co-ordination of the available nitrite to the primary molybdenum(VI) product, and subsequent rearrangement of these molybdenum(VI) products.