Multifunctional Magnetic\nChiral HKUST MOF Decorated\nby Triazine, Fe<sub>3</sub>O<sub>4</sub>, and Cu(l‑Proline)<sub>2</sub> Complex for Green and Mild Asymmetric Catalysis

A multifunctional magnetic chiral metal–organic\nframework\n(MOF) was developed for asymmetric applications by utilizing strategies\nof chiralization and multifunctionalization. Cu(l-proline)<sub>2</sub>-Triazine/Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub>–NH<sub>2</sub> was employed as a chiral secondary agent to synthesize a\nchiral hybrid nanocomposite within a MOF. The use of a chiral secondary\nagent efficiently induces chirality in an achiral MOF structure that\ncannot be directly chiralized. The HKUST-1@Cu(l-proline)<sub>2</sub>-Triazine/Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub>–NH<sub>2</sub> nanocomposite was afforded by first anchoring chiral Cu(l-proline)<sub>2</sub> on the Triazine/Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub>–NH<sub>2</sub> surface and then encapsulating\nthe Cu(l-proline)<sub>2</sub>-Triazine/Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub>–NH<sub>2</sub> nanoparticles with\nHKUST-1 via in situ ultrasonication synthesis. In the synthesis of\nthe HKUST-1@Cu(l-proline)<sub>2</sub>-Triazine/Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub>–NH<sub>2</sub> nanocomposite,\nCu(l-proline)<sub>2</sub> was used as a chiral complex due\nto its Lewis acidic/basic hydroxyl groups, carboxylate carbonyl functional\ngroups acting as Lewis bases, an active Cu site functioning as a Lewis\nacid center, and azine groups of TCT acting as Lewis bases, all synergistically\ninteracting with the Lewis acidity of the Cu centers in HKUST-1. To\nassess these synergic effects, HKUST-1@Cu(l-proline)<sub>2</sub>-Triazine/Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub>–NH<sub>2</sub> was used in the formation of an asymmetric C–C bond\nin nitroaldol condensation and asymmetric cycloaddition of CO<sub>2</sub> to epoxides. The findings demonstrated that under mild and\ngreen conditions, in both the asymmetric nitroalcohol condensation\nand the asymmetric cycloaddition of CO<sub>2</sub>, HKUST-1@Cu(l-proline)<sub>2</sub>-Triazine/Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub>–NH<sub>2</sub> had better enantioselectivity than\nthe Cu(l-proline)<sub>2</sub>-Triazine/Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub>–NH<sub>2</sub> nanoparticles and a\nhigher selectivity toward β-nitroalcohol and cyclic carbonate\nover the pure HKUST-1. Despite its simple and easy synthesis, HKUST-1@Cu(l-proline)<sub>2</sub>-Triazine/Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub>–NH<sub>2</sub> exhibited exceptional performance in\nthe asymmetric nitroaldol condensation and asymmetric cycloaddition\nof CO<sub>2</sub> to epoxides. Additionally, the mechanism of the\nreactions was depicted with reference to the total energy of the reactants,\nintermediates, and products.