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 stable 3D Co(II)-based coordination framework with mixed ligands was synthesized via hydrothermal and microwave-assisted methods, and employed to catalyze solvent-free ring-opening polymerization of L-lactide. [Display omitted] •A novel 3D Co(II) coordination polymer by microwave-assisted synthesis is presented.•Good tolerance to both acidic and basic aqueous solutions is demonstrated.•Highly efficient catalytic ROP of L-lactide by a Co(II)-organic framework is illustrated. 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-OMe-1,2-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.