Enhanced catalysis of CO2 cycloaddition at ambient pressure through rational design of interpenetrating ZnII/LnIII heterometallic coordination polymers

Abstract

The major obstacle in using CO2 in the cycloaddition reactions with epoxides can be subdued through the use of high performance catalysts particularly those efficient at or near ambient temperature and pressure. Performances of heterogeneous catalysts are, however, subpar compared to the homogeneous counterparts although being preferable from practical viewpoint. Heterometallic 3d-4f coordination polymers have offered the best opportunity to date and their best possible performances is not yet achieved. Through rational use of 2,2′-bipyridine-4,4′-dicarboxylic acid (H2bipydc), new series of interpenetrating coordination polymers, i.e. [ZnIILnIII(bipydc)2(HCOO)(H2O)3]∙2H2O where LnIII = PrIII (I), NdIII (II), SmIII (III) and EuIII (IV), were synthesized and characterized. Their single crystal structures were elucidated, and potential functioning sites were identified. Their performances in catalyzing the reactions of allyl glycidyl ether were evaluated. The aid of tetrabutylammonium bromide was notably necessary. The unparallel performances were disclosed. The percentage yields of over 80 %, percentage conversion of 85–90 %, turn-over number of 2088 - 2260, and turn-over frequencies of 522 - 565 h−1 could be achieved from the reactions conducted at 90 °C for 4 h at ambient pressure. Synergistic contribution from various structural features is postulated. Viability of IV in catalyzing the reactions of other monosubstituted epoxides was also studied. Taking advantage of the single crystal structure, the preferential and influential interactions of selected epoxides at different metal sites and the prime motivation of their interactions were investigated using computational calculations.

Keywords

• Coordination polymer
• Heterometallic
• Interpenetration
• Catalyst
• CO2 cycloaddition
• Epoxides