Two novel tetranuclear Yb(iii)-based compounds for highly efficient conversion of CO2 to cyclic carbonates

Abstract

Two new tetranuclear Ln(III)-based compounds were formulated, namely, [Yb₄(μ₃-O)₂(dbm)₄(L1)₆]·2CH₂Cl₂·6CH₃CN (1) and [Yb₄(μ₃-O)₂(dbm)₄(L2)₆] (2) (Hdbm = dibenzoylmethane, HL1 = (E)-5-((4-methoxybenzylidene)amino)quinolin-8-ol, and HL2 = (E)-5-(benzylideneamino)quinolin-8-ol), using two 8-hydroxyquinoline Schiff bases (HL1 and HL2) under solvothermal conditions. The single-crystal structures and catalytic properties of the two Yb₄ compounds (1 and 2) were comprehensively studied. Single-crystal X-ray diffraction analysis showed that both Yb₄ compounds (1 and 2) possessed a rhombic Yb₄ core and showed butterfly-shaped structures. Both tetranuclear Yb(III)-based compounds displayed typical near-infrared luminescence of Yb³⁺ ions at room temperature. Catalytic study indicates that the two Yb₄ compounds are heterogeneous catalysts that can catalyze the cycloaddition of CO₂ with epoxides and offer high yield under mild conditions (TBAB as the co-catalyst, T = 70 °C, P = 0.1 MPa and solvent-free).