Lanthanide Coordination Polymers through Design for Exceptional Catalytic Performances in CO2 Cycloaddition Reactions

New lanthanide coordination polymers, (I) [Ln(III)(Habtc)(H2O)center dot 2H(2)O (Ln = Sm-III, Eu-III, Gd-III, Tb-III, Dy-III, Ho-III, Er-III, and Tm-III), (II) [Ln(III)(Habtc)(H2O)(4)]center dot 3H(2)O (Lo(III) = Eu-III, Gd-III, Tb-III, Dy-III, Ho-III, and Yb-III), and (III) [Eu-2(III)(Habtc)(2) (H2O)(6)]center dot 2.75H(2)O (H(4)abtc = 3,3',5,5'-azobenzene-tetracarboxylic acid), were designed and synthesized for use as catalysts. The framework structures, phase formation, and purity were characterized. The catalytic performances of [Eu-III(Habtc)-(H2O)(2)]center dot 2H(2)O (Ib) and [Eu-III(Habtc)-(H2O)(4)]center dot 3H(2)O (IIb) were evaluated based on CO2 cycloaddition with epichlorohydrin under ambient CO2 pressure and solvent-free conditions. Discussion has been made with respect to the multiple Lewis and Bronsted acidic and Lewis basic sites coresiding in the frameworks, which were revealed by single-crystal X-ray diffraction and measurements of acidity and basicity. Depending on the reaction conditions, excellent turnover numbers and turnover frequencies (2778 and 694 h(-1) for Ib and 2870 and 718 h(-1) for IIb) with >= 99% conversion and >= 87% selectivity could be achieved. The robustness of lb and lib over 10 cycles of catalysis and the makeup process was disclosed. The potential of Ib and IIb as promising catalysts for other epoxides was also examined.

Automated summary

New lanthanide coordination polymers were designed and synthesized for use as catalysts, with excellent catalytic performance in CO2 cycloaddition reactions. The frameworks exhibited multiple Lewis and Bronsted acidic and Lewis basic sites, leading to promising turnover numbers and frequencies with high conversion and selectivity. Ib and IIb also demonstrated robustness over multiple cycles of catalysis, showing potential as catalysts for other epoxides.