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

Phase-pure interpenetrated MOF-5 ([Zn₄(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.