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>Bimetallic bis(benzotriazole iminophenolate) cobalt, nickel and zinc complexes as versatile catalysts for coupling of carbon dioxide with epoxides and copolymerization of phthalic anhydride with cyclohexene oxide
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Bimetallic bis(benzotriazole iminophenolate) cobalt, nickel and zinc complexes as versatile catalysts for coupling of carbon dioxide with epoxides and copolymerization of phthalic anhydride with cyclohexene oxide
A family of cobalt, nickel and zinc complexes containing the (BiIBTP)-Bi-5C or (BiIBTP)-Bi-2C derivative (BiIBTP = bis(benzotriazole iminophenolate)) were synthesized and structurally characterized. The reactions of (BiIBTP)-Bi-5C-H-2 pro-ligand with 2.0 molar equivalents of M-t(OAc)(2)center dot 4H(2)O (M-t = Co or Ni) or Zn(OAc)(2) furnished di-nuclear cobalt, nickel and zinc complexes (1: [((BiIBTP)-Bi-5C)Co-2(OAc)(2)], 2: [((BiIBTP)-Bi-5C)Ni-2(OAc)(2)], and 3: [((BiIBTP)-Bi-5C)Zn-2(OAc)(2)]), but treatment of (BiIBTP)-Bi-2C-H-2 as the ligand precursor under a similar synthetic method gave the acetate-free species [((BiIBTP)-Bi-2C)Ni] (5) or [((BiIBTP)-Bi-2C)Zn(H2O)] (6). Interestingly, (BiIBTP)-Bi-2C-H-2 reacted with 2.0 molar equiv. of cobalt(II) acetate tetrahydrate to generate a water-solvated di-cobalt complex, [((BiIBTP)-Bi-2C) Co-2(OAc)(2)(H2O)] (4). The solid-state structure of 1-4 displays a bimetallic metal(II) acetate (metal = Co, Ni, Zn) with a hexadentate BiIBTP ligand chelating two metal atoms, whereas complexes 5 and 6 reveal a monomeric feature with a tetra- or penta-coordinated metal centre chelated by one ONNO-tetradentate (BiIBTP)-Bi-2C ligand. Versatile catalysis towards coupling of CO2 with epoxides and ring-opening copolymerization of phthalic anhydride (PA) with cyclohexene oxide (CHO) by these bimetallic cobalt and nickel acetate complexes was systematically examined. BiIBTP-featuring di-nickel 2 was found to efficiently copolymerize CO2 and CHO with a high TOF (> 200 h(-1)) in a controlled character, giving a highly alternating poly(cyclohexene carbonate) with high molecular weight (M-n > 30000 g mol(-1)). Di-cobalt catalyst 1 in combination with n-Bu4NBr co-catalysts was able to catalyse CO2/CHO coupling to produce > 99% cis-selectivity cyclohexene carbonate with good activity under optimal conditions. Not only was the efficient catalytic performance of di-Co complex 1 for CO2/epoxides coupling enabled, but 1 was also able to catalyse the copolymerization of PA and CHO to afford the molecular weight controllable poly(PA-alt-CHO)s with high ester linkage content. This is the first example of utilizing versatile BiIBTP-ligated cobalt(II) acetate catalysts for the production of cyclic carbonate, biodegradable polycarbonate or polyester.
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