Dinuclear MoV Complexes with Thiophenolate‐oxazoline Ligands: Synthesis, Characterization, and Exceptional Activity in Catalytic Olefin Epoxidation

Abstract

The synthesis, characterization, and epoxidation catalysis of two neutral, dinuclear molybdenum(V) complexes [{MoO(Lx)(µ‐O)}2] (x = 1: 1; x = 2: 2) bearing S,N‐bidentate thiophenolate‐oxazoline ligands (L1, L2) are described. Both complexes are formed under reduction of the metal with formation of disulfides (L1)2 and (L2)2. Each Mo center is coordinated by one bidentate thiophenolate‐oxazoline ligand and one terminal and two bridging oxido ligands. The solid‐state structures of NaL2 and complex 1 were confirmed by single‐crystal X‐ray diffraction. The five‐coordinate nature of the molybdenum atoms in 1 and 2 leads to exceptionally high catalytic activities in the epoxidation of cyclooctene. The catalyst loading can be reduced to 0.001 mol‐% (10 ppm), with a turnover number (TON) of 85000 and a maximum turnover frequency (TOF) of 62000 h–1 for 1, and a TON of 87400 and a TOF of 107400 h–1 for 2. For cyclooctene, the catalyst solutions can be recycled multiple times without significant loss of activity; however, other substrates (styrene, 1‐octene, and limonene) showed conversions with lower selectivity. The fate of catalyst 1 was examined by stoichiometric addition experiments with tert‐butyl hydroperoxide, which resulted in the formation of benzenesulfonate‐oxazoline derivative HL3 and polyoxomolybdates.