Microwave-assisted synthesis of a stable cobalt(II)-organic framework as highly efficient heterogeneous catalyst for solvent-free ring-opening polymerization of L-lactide

A new Co(II)-based coordination polymer, [Co(Fbtx)1.5(1,2-BDC-OMe)]n (denoted as Co -CP) was constructed from the mixed-ligand system of 1,4-bis(1,2,4-triazole-1-ylmethyl)-2,3,5,6-tetrafluorobenzene (Fbtx) and 4-OMe1,2-benzenedicarboxylic acid (1,2-H2BDC-OMe) under both hydrothermal and microwave-assisted reaction conditions. Single-crystal X-ray diffraction analysis revealed that Co -CP features a three-dimensional (3D) CdSO4-like framework in which helical [Co(1,2-BDC-OMe)]n chains are interlinked by anti- and gauche-Fbtx ligands. The crystalline Co -CP material with considerable thermal and chemical stability was demonstrated to be an efficient heterogeneous catalyst for the solvent-free ring-openining polymerization of L-lactide without any co-catalyst or initiator, which yields a L-lactide conversion of 99 % and a polymer molecular weight of 44.6 kDa. Moreover, the Co -CP catalyst could be recycled up to eight times with the retention of both catalytic activity and crystal structure.