Hui-Ju Chuang

Synthesis, characterization and catalytic activity of magnesium and zinc aminophenoxide complexes: Catalysts for ring-opening polymerization of L-lactide

A series of novel magnesium and zinc aminophenoxide complexes were successfully synthesized and one zinc complex was characterized by X-ray crystallography. They were also investigated as initiators for the ring opening polymerization of L-lactide. The complexes are effective in forming polylactides with good conversions. The nature and steric bulk of the ligands coordinated to the central metal ions enormously influenced the polymer properties. Among all the complexes, the zinc aminophenoxide complexes as initiators produced polymers with good molecular weight control and relatively narrow PDIs.

Bimetallic Nickel Complexes that Bear Diamine‐Bis(Benzotriazole Phenolate) Derivatives as Efficient Catalysts for the Copolymerization of Carbon Dioxide with Epoxides

We report the facile synthesis and structural characterization of efficient bimetallic nickel catalysts that bear diamine‐bis(benzotriazole phenolate) derivatives for the copolymerization of CO2 and epoxides. Thermally robust di‐nickel 2 is an effective catalyst for the alternating copolymerization of cyclohexene oxide (CHO) with CO2 to give turnover numbers of up to >4000 and turnover frequencies of up to >400 h−1. Ni catalyst 2 leads to not only controlled CO2/CHO coupling, but it has also been applied to catalyze the copolymerization of 4‐vinyl‐1,2‐cyclohexene oxide (VCHO) and CO2 to obtain the corresponding polycarbonate with the vinyl functionality on the side chains. This is the first example of a dinuclear Ni complex that is efficient for both CO2/VCHO copolymerization and the formation of a high‐molecular‐weight copolymer with a large amount of carbonate linkages.

Copolymerization of Carbon Dioxide with Epoxides Catalyzed by Structurally Well-Characterized Dinickel Bis(benzotriazole iminophenolate) Complexes: Influence of Carboxylate Ligands on the Catalytic Performance

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 (Mn > 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.