A Ni(salen)‐Based Metal–Organic Framework: Synthesis, Structure, and Catalytic Performance for CO2 Cycloaddition with Epoxides

Abstract

A three‐dimensional (3D) chiral metal–organic framework [Cd2{Ni(salen)}(DMF)3]·4DMF·7H2O (1) based on a new enantiopure tetracarboxyl‐functionalized metallosalen Ni(H4salen) {where H6salen is (R,R)‐N,N′‐bis[3‐tert‐butyl‐5‐(3,5‐dicarboxybenzyl)salicylidene]‐1,2‐diphenylethylenediame} was synthesized and characterized by infrared spectroscopy, thermogravimetric analysis, nitrogen and carbon dioxide adsorption, and powder and single‐crystal X‐ray diffractions. In 1, the dinuclear Cd2 cluster [Cd2(COO)4(DMF)3] as a node is cross‐linked by four isophthalate groups on the salen ligands, forming a 2D lamellar structure, which are further linked by Ni(salen) into the 3D network with a 1D open channel (ca. 7.0 × 8.0 Å2) along the a axis. On account of its porosity, Lewis acid sites, and moderate uptake for CO2, 1 can be used as an efficient heterogeneous catalyst for the CO2 cycloaddition with epoxides under relatively mild conditions. Moreover, the bulky epoxide shows a decrease in activity with an increase in the alkyl chain length of the substrate as a result of the confinement effect of 1, showing size‐dependent selectivity.