Pyrazine-bridged molybdenum(0) carbonyl and molybdenum(VI) oxide network solids as catalysts for epoxidation and sulfoxidation

Abstract

The horizons of epoxidation and sulfoxidation processes may be expanded by developing new, efficient, and versatile catalysts. In the present work, three pyrazine-bridged molybdenum(0/VI)-based coordination network solids have been investigated for the epoxidation of olefins and the oxidation of sulfides. The materials studied were the Mo0-based metal-organic framework (MOF) fac-Mo(CO)3(pyz)3/2·1/2pyz (1) with a structure consisting of stacked fac-Mo(CO)3(pyz)3/2 coordination layers, the cubic phase fac-Mo(CO)3(pyz)3/2 (2) with a dense framework consisting of two interpenetrating coordination networks, and the molybdenum oxide-pyrazine hybrid material [Mo2O6(pyz)] (3) with a structure consisting of perovskite-like MoO3 layers pillared by pyz molecules. In the model reaction of cis-cyclooctene with tert-butyl hydroperoxide (TBHP) at 70 °C, quantitative yields of the epoxide were obtained within 2 h for 1, 4 h for 2, and 24 h for 3. Catalysts 1-3 were further examined for the epoxidation of other olefins, including the bio-olefins dl-limonene, methyl oleate and methyl linoleate, and the reaction scope was expanded to include the oxidation of sulfides. In the reactions of the bio-olefins, 3 was highly selective, giving only diepoxide and/or monoepoxide products. While the tricarbonyl-pyrazine-molybdenum(0) compounds displayed higher activity, by-products were obtained in the reactions of dl-limonene and methyl linoleate, namely limonene-1,2-diol and hydroxytetrahydrofuran cyclization products, respectively. Catalysts 1-3 displayed high activity for the selective oxidation of sulfides (methyl phenyl sulfide and diphenyl sulfide) to sulfones under mild conditions (35 °C).