Chemistry and Catalytic Performance of Pyridyl-Benzimidazole Oxidomolybdenum(VI) Compounds in (Bio)Olefin Epoxidation

The chemistry and catalytic performance of the dichlorido complex [MoO2Cl2(pbim)] (1) [pbim = 2-(2-pyridyl)benzimidazole] in the epoxidation of olefins is reported. Complex 1 acts as a precatalyst and is more effective with tert-butyl-hydroperoxide (TBHP) as the oxidant than with aq. hydrogen peroxide: the cis-cyclooctene (Cy) reaction with TBHP gave 98 % epoxide yield at 70 degrees C/24 h. Catalyst characterization showed that 1 is transformed in situ to the oxidodiperoxido complex [MoO(O-2)(2)(pbim)] (2), with H2O2 and a hybrid molybdenum(VI) oxide solid formulated as [MoO3(pbim)] (3) with TBHP. The hybrid material 3 was prepared on a larger scale and explored for the epoxidation of the biorenewable olefins methyl oleate, methyl linoleate, and (R)-(+)-limonene. With TBHP as the oxidant, 3 acts as a source of soluble active species of the type 2. A practical method for recycling oxidodiperoxidomolybdenum(VI) catalysts for the Cy/TBHP reaction is demonstrated by using an ionic liquid as the solvent for the molecular catalyst 2.