A Paddle-Wheel Binuclear Copper(II)-Based MOF for Cyclization of Propargylic Amines with Flue Gas CO2 at Ambient Conditions.

Metal-organic frameworks (MOFs) exhibit attractive catalytic performance, particularly for carbon dioxide (CO2) fixation. We here developed a new MOF {Cu2(Bibt)(Apta)2}n, namely CuBA, under the solvothermal process {Bibt = (4,7-bis(1H-imidazol-1-yl)benzo-[2,1,3]thiadiazole, Apta = deprotonation of 2-aminophthalic acid}. CuBA forms a paddle-wheel binuclear copper(II) Cu2(COO)4N2 unit, which is further extended to a 6-connected three-dimensional (3D) {412•63} topology. In particular, CuBA shows a high CO2/N2 selectivity at 298 K, which encourages us to apply it to catalyze CO2 fixation. The experiments demonstrate that CuBA can catalyze the carboxylative cyclization of various propargylic amines with CO2 at ambient conditions (1 atm, 25 °C) with high TON. Moreover, CuBA maintains good catalytic activities for 5 cycles, showing good recyclability. Significantly, the gram-scale reaction is performed with a good yield. Furthermore, the low-concentration CO2 (30 vol %) experiments under CuBA afford the products in moderate to good yields (25 °C, 24 h). 1H NMR studies indicate that CuBA and DBU work together to activate the propargylic amine substrate, facilitating the reaction. It is anticipated that this work will inspire the rational design of non-noble-metal-containing MOFs for efficient CO2 utilization under mild conditions.