A Paddle-Wheel Binuclear Copper(II)-Based MOF for Cyclization of Propargylic Amines with Flue Gas CO ₂ 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(1<i>H</i>-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.