Tetracosanuclear nickel complexes as effective catalysts for cycloaddition of carbon dioxide with epoxides

Abstract

A series of well-defined tetracosanuclear nickel complexes 3–7 facilely produced by one-pot synthesis were active catalysts for cycloaddition of CO₂ and cyclohexene oxide (CHO). These nickel complexes were doughnut-like supramolecular coordination complexes involving eight repeating units, and each of them contains one Schiff base ligand and three nickel(II) ions. Notably, the 24-nuclear nickel cluster complex 3 in combination with nucleophilic additives was the most efficient catalyst to mediate CO₂ coupling with CHO to generate CO₂-based cis-cyclohexene carbonates. In addition to CO₂/CHO cycloaddition, complex 3 was also found to effectively couple CO₂ with other alicyclic epoxides, generating the corresponding cyclic carbonates. Additionally, kinetic investigations for CO₂ cycloaddition of CHO using 3 were reported.