A series of structurally well-defined dinickel carboxylate complexes based on the ^RBiIBTP derivatives [^RBiIBTP = bis(benzotriazole iminophenolate), where R = 3C for the propyl-bridged backbone and 5C for the 2,2-dimethyl-1,3-propyl-bridged backbone] were synthesized and developed for copolymerization of CO₂ and epoxides. The one-pot reactions of nickel perchlorate with the ^RBiIBTP-H₂ proligands and an appropriate amount of carboxylic acid derivatives (CF₃COOH or 4-X-C₆H₄CO₂H; X = H, CF₃, OMe) upon the addition of triethylamine in refluxing methanol (MeOH) afforded dinuclear nickel dicarboxylate complexes, which could be formulated as either [(^RBiIBTP)Ni₂(O₂CCF₃)₂] (1 and 2) or [(^RBiIBTP)Ni₂(O₂CC₆H₄-4-X)₂] (3-7). The dinickel monobenzoate complexes [(^RBiIBTP)Ni₂(O₂CPh)(ClO₄)(H₂O)] [R = 3C (8) and 5C (9)] were prepared by using a similar synthetic route in tetrahydrofuran under reflux with a ligand precursor to metal salt to benzoic acid ratio of 1:2:1 in the presence of NEt₃. Recrystallization of neutral nickel perchlorate complex 8 in a saturated MeOH or ethanol (EtOH) solution gave ionic and alcohol-solvated monobenzoate bimetallic analogues [(^3CBiIBTP)Ni₂(O₂CPh)(S)₂]ClO₄, where S = MeOH (10) and EtOH (11). Single-crystal X-ray crystallography of dinickel analogues 1-11 indicates that the BiIBTP scaffold performs as a N,O,N,N,O,N-hexadentate ligand to chelate two Ni atoms, and the ancillary carboxylate group adopts a bridging bidentate bonding mode. Catalysis for copolymerization of carbon dioxide (CO₂) with cyclohexene oxide (CHO) by complexes 1-9 was systematically investigated, and the influence of carboxylate ligands on the catalytic behavior was also studied. Trifluoroacetate-ligated dinickel complex 1 efficiently catalyzed CO₂ and CHO with a high turnover frequency (>430 h^-1) in a controlled fashion, generating perfectly alternating poly(cyclohexenecarbonate) with large molecular weight (M_n > 50000 g/mol). In addition to CO₂/CHO copolymerization, bimetallic complex 1 was found to effectively copolymerize CO₂ with 4-vinyl-1,2-cyclohexene oxide (VCHO) or cyclopentene oxide, producing the high carbonate contents of poly(VCHC-co-VCHO)s and highly alternating poly(cyclopentene carbonate)s, respectively. This study also enabled us to compare the catalytic efficiency of using cyclic epoxides with different ring strains or functional groups as comonomers by the dinickel catalyst 1.

	Year	Citations

About