An effective Ni/Zn catalyst system for the chemical fixation of carbon dioxide with epoxides

A new catalyst system Ni(PPh3)2(Naphthyl)Cl/PPh3/n-Bu4NBr/Zn was developed and the system showed high activity and selectivity for the coupling reaction of carbon dioxide (CO2) and epoxides. The effects of reaction temperature, CO2 pressure and different component of catalyst system have been investigated systematically. It was found that a 92.6% conversion of propylene oxide (PO), high selectivity (>99%) and turnover frequency (TOF) value (661 h−1) could be achieved within 5 h in the presence of Ni(PPh3)2(Naphthyl)Cl/PPh3/n-Bu4NBr/Zn/PO (molar ratio = 1:2:4:20:3600) at a low pressure of CO2 (3.0 MPa) and temperature (130 °C) without any organic solvents. Moreover, the conversion yield for epichlorohydrin and styrene oxide were alomost 100% with 100% selectivity at the same conditions. The catalyst was also proved to be applicable to other terminal epoxides. Besides, the influence of water on the catalytic activity within the range of H2O/PO (0-15 molar ratio) was elucidated, and a reaction mechanism focusing on the active Ni(0) center has been proposed, which plausibly explained the reaction result.