Performance of a tetracarbonylmolybdenum(0) pyrazolylpyridine (pre)catalyst in olefin epoxidation and epoxide alcoholysis

Abstract

Tetracarbonylmolybdenum(0) complexes of the type cis-[Mo(CO)4(L)] are attractive synthetic precursors of high oxidation state oxomolybdenum catalysts since the byproducts (CO/CO2) readily separate from the reaction mixture, facilitating separation/purification procedures (e.g. avoiding contamination/acidification of the medium for halide (X)-containing precursors such as [Mo(η3-C3H5)Cl(CO)2(L)]). In this work, the conversion of the tetracarbonyl complex cis-[Mo(CO)4(ppp)] (ppp = 2-(1-pentyl-3-pyrazolyl)pyridine) to oxomolybdenum compounds has been studied. The molybdenum compounds prepared were explored for liquid phase oxidation and acid catalysis, specifically the epoxidation of cis-cyclooctene with hydroperoxide oxidants, and the alcoholysis of styrene oxide. The routes for the conversion of the cis-[Mo(CO)4(ppp)] precursor to oxomolybdenum compounds, during either the synthesis (ex situ) or catalytic (in situ) processes (involving isolation/characterisation of metal species after the catalytic runs), were studied for the different catalytic systems, which helped establish relationships between the type of metal species formed and the catalytic performance. Catalyst recyclability was investigated using a homogeneous catalytic ionic liquid-standing approach.