Self-assembly of tetranuclear 3d-4f helicates as highly efficient catalysts for CO2 cycloaddition reactions under mild conditions
A series of novel asymmetry 3d-4f helicates Zn3LnL4 (H2L = N-(2-((3,5-di-tert-butyl-2-hydroxybenzylidene)amino)ethyl)-2-hydroxybenzamide, Ln = Dy(1), Gd(2), Er(3)) were successfully constructed via selective incorporation of groups with different coordination capabilities. These helicates with the well-defined conformation demonstrate high catalytic efficiency in converting CO2 to cyclic carbonates under mild conditions. Particularly, Zn3ErL4 showed superior catalytic performance with high catalytic activity (TOF up to 38000 h-1) and extraordinary selectivity (up to 99%) across the wide substrate scope. Meanwhile, these 3d-4f helicates showed stable catalytic performance without being influenced by the moisture and air. The results presented herein highlight an important consideration for constructing heterometallic and asymmetric complexes for catalyzing CO2 conversion.