A Highly Efficient Dioxo(μ-oxo)molybdenum(VI) Dimer Catalyst for Olefin Epoxidation

The oxo-bridged dimer [Mo2O4(μ2-O)Cl2(pzH)4] (1; pzH = pyrazole)
exhibits unusually high activity in the liquid-phase catalytic
epoxidation of the cyclic olefins cyclooctene and (R)-(+)-limonene
under mild conditions and in the absence of additional organic
solvents, using tert-butyl hydroperoxide as the oxidant. The complex
is stable under the reaction conditions and can be used in further
catalytic runs without significant loss of performance. An X-ray
crystallographic investigation reveals that 1 has an unprecedented
and extremely rare all-cis configuration at each of the MoO2-(μ2-O)Cl(pzH)2 cores, which can be understood by considering
supramolecular contacts and geometric factors.