Kinetic Studies on the Oxidation of η5-Cyclopentadienyl Methyl Tricarbonyl Molybdenum(II) and the Use of Its Oxidation Products as Olefin Epoxidation Catalysts

Abstract

The oxidation of η5-cyclopentadienyl(methyl)(tricarbonyl)molybdenum(II) (1) with excess tert-butylhydroperoxide (TBHP) initially yields η5-cyclopentadienyl(methyl)(dioxo)molybdenum(VI) (2), which further reacts with TBHP, forming η5-cyclopentadienyl(methyl)(oxo)(peroxo)molybdenum(VI) (3). The solid-state structure of 3 has been determined by single-crystal X-ray crystallography. Detailed kinetic studies have been carried out on the oxidation of 1 with TBHP as an oxidizing agent and on the catalytic activities of the resulting oxidation products, 2 and 3, in olefin epoxidation. In the absence of oxidant, neither of the molybdenum species is able to transfer an O-atom to an olefin. However, both Mo(VI) species act as catalysts for the epoxidation of olefins with TBHP through the formation of active intermediates. It has been found that compound 3 reacts with excess TBHP to give an active intermediate, which exists in equilibrium with the catalyst precursor 3 with a Keq close to 1. This intermediate is slowl...