Synthesis of cyclic carbonate by CO2 fixation to epoxides using interpenetrated MOF-5/n-Bu4NBr

Phase-pure interpenetrated MOF-5 ([Zn-4(O)(BDC)(3)]) was synthesized by pH* control in a reaction medium, and its stability in the presence of epoxides was confirmed by powder X-ray diffraction analysis. Interpenetrated MOF-5/tetra-n-butylammonium bromide (int-MOF-5/n-Bu4NBr) showed a high catalytic activity toward CO2 fixation to epoxide to synthesize cyclic carbonates. The conversions of propylene oxide (PO) and styrene oxide (SO) by int-MOF-5/n-Bu4NBr were almost two times higher than those by MOF-5/n-Bu4NBr under the same conditions. From a kinetics point of view, the coupling reaction rate of PO and CO2 was much higher than that of SO and CO2, which may be due to steric effects. The optimized geometries by the density functional theory calculation revealed that Lewis acidic Zn(II) sites of tetranuclear {Zn4O} clusters can work as the catalytic center to bind epoxides to open the rings by a nucleophilic attack. This co-catalyst system may be useful for the synthesis of cyclic carbonate by CO2 fixation.