Efficient Molybdenum Hydrazonato Epoxidation Catalysts Operating under Green Chemistry Conditions: Water vs. Decane Competition

Abstract

Molybdenum compounds containing benzaldehyde-based hydrazones were obtained. The reaction in MeOH resulted with monomeric Mo complexes, [MoO2(L)(MeOH)], while the reaction in dichloromethane (DCM) provided oligomeric complexes, [MoO2(L)]n. The solid-state structures of the obtained compounds were investigated through Infrared Spectroscopy - Attenuated Total Reflection (IR-ATR), Thermogravimetric analysis (TGA), and via X-ray diffraction. The prepared molybdenum species were employed as cyclooctene epoxidation catalysts. TBHP (tert-butylhydroperoxide) in water and TBHP in decane were employed and compared as oxidants, with 0.25 mol% [Mo]. The catalyst activity and selectivity towards epoxide is >90% for all the reactions. The results have been linked to theoretical calculations, showing the importance of the first step, i.e., the transformation of [MoO2(L)(MeOH)] into the pentacoordinate [MoO2(L)].