Oxidant-Dependent Switch of a Molybdenum(VI) Tetrazolate Complex from a Homogeneous to a Self-Separating Catalyst for Olefin Epoxidation.

Although several decades have passed since the introduction of homogeneous molybdenum catalysts for the bulk industrial production of epoxides from light olefins, the development of recyclable catalytic systems to produce more complex epoxides remains a challenge. In this work, we present a strategy for preparing a self-separating catalyst by exploiting reaction-induced precipitation, starting from the molybdenum-(VI) tetrazolate complex [MoO-(O2)-(pto)2] (Hpto = 5-(2-pyridyl-1-oxide)-tetrazole), which was synthesized via a one-pot approach and crystallographically characterized. High epoxide selectivities (96-100%) were achieved at high conversions (88-100%) under mild conditions (70 °C) in all the studied reactions, from that of the model substrate cis-cyclooctene to the epoxidation of biobased dl-limonene and fatty acid methyl esters. The catalytic reaction is homogeneous using tert-butyl hydroperoxide as the oxidant, whereas with hydrogen peroxide, a transformation to a self-separating catalyst takes place, which combines the high catalytic activity of a homogeneous catalyst with the easy recovery and reuse of a heterogeneous catalyst.