Construction of multifunctionally integrated catalyst via a self-assembly strategy for efficient CO2 cycloaddition

A series of novel imidazolium-based cationic metal complexes ([EIMBr-COO] n M, n = 1, 2, 3, 4 and M = Mg 2+ , Al 3+ , Ca 2+ , Ti 4+ , V 2+ , Cr 3+ , Mn 2+ , Fe 2+ , Co 2+ , Ni 2+ , Cu 2+ , Zr 4+ , Ag 1+ , Sb 3+ , Pb 2+ , La 3+ and Ce 3+ ) were successfully constructed through coordination-driven self-assembly by an efficient one-step grinding strategy. This self-assembly process occurs when hydroxyl oxygen atoms from [ECOOHIM]Br ligand donate electron pairs to empty orbitals in the metal ions, resulting in the formation of stable complexes. Notably, the prepared [EIMBr-COO] 2 Zn catalyst displayed excellent catalytic activity in the cycloaddition reaction of propylene oxide (PO) and CO 2 , and the propylene carbonate (PC) yield reached 83.55% with a TOF of 1461 h −1 within only 10 min. The synergistic effects of Zn 2+ centers (Lewis acid), imidazolinium groups (Lewis base) and Br - ions (nucleophilic site) in [EIMBr-COO] 2 Zn contributed the excellent catalytic performance. Meanwhile, the formation of a chemical bond (Zn-O) through the coordination-driven self-assembly strategy guarantees its stability. Moreover, a rational dual-activation mechanism of Lewis acid and Br - centers was proposed based on density functional theory calculations (DFT) to explain the acceleration mechanism of the rate-determining step. Besides, [EIMBr-COO] 2 Zn showed a wide range of catalytic universality in cycloaddition reactions and satisfactory stability. Therefore, this study is expected to present theoretical and practical support for the design and synthesis methodology of multifunction catalysts for CO 2 cycloaddition.