Enhanced oxygen transfer over bifunctional Mo-based oxametallacycle catalyst for epoxidation of propylene

Activation of inert propylene to produce propylene oxide (PO) is critical, but still faces some challenges in realizing higher PO selectivity and productivity. Herein, a temperature-controlled phase transfer catalyst (MoOO.DMF) is prepared for the liquid-phase epoxidation of propylene with tert-butyl hydroperoxide (TBHP) as oxidant, which exhibit the selectivity of 90.6% and the productivity of 1286.42.h(-1) for PO (catalyst/propylene = 0.77 mol parts per thousand). Some experimental factors (solvent types, reaction temperature, contact time, the dosage of catalyst, TBHP and substrate) were investigated, and the reaction kinetics and thermodynamics are discussed. MoOO.DMF has the characteristic of both homogeneous and heterogeneous catalysts, which can be dissolved in the solvent at higher temperatures and separated from the solvent after reaction by lowering the temperature. Importantly, MoOO.DMF has a wonderful epoxidation performance for many olefins (e.g., light olefins, linear alpha-olefins, cyclic olefins and others). The mechanisms are proved by in-situ FT-IR, ESR and HRMS spectrum to be the selective oxygen transfer from tertbutyl peroxide radical and the Mo-O-O bridge in MoOO.DMF to propylene. Density functional theory (DFT) calculations show that the Mo-O-O bridge in catalyst is the key role for the activation of both the O-H bond in TBHP and the C=C bond in propylene, thus enhanced the epoxidation of propylene. (C) 2021 Published by Elsevier Inc.

Automated summary

Activation of inert propylene to produce propylene oxide (PO) is crucial, and a temperature-controlled phase transfer catalyst MoOO.DMF has been prepared for efficient epoxidation. The catalyst exhibits high selectivity and productivity for PO, and can be dissolved in solvent at higher temperatures and separated after reaction. The mechanisms have been proved by in-situ FT-IR, ESR and HRMS spectrum, showing the selective oxygen transfer from tertbutyl peroxide radical and Mo-O-O bridge in MoOO.DMF.