Hybrid nanomaterials for asymmetric purposes: green enantioselective C–C bond formation by chiralization and multi-functionalization approaches

Abstract

A chiral MOF with synergic Lewis basicity for asymmetric purpose was developed by chiralization and multi-functionalization strategies. A secondary nanomaterial (L-proline@Fe₃O₄) was used as a chiral agent to achieve a chiral hybrid nanomaterial with a metal–organic framework (MOF). Using a chiral secondary agent is a simple method for the chiralization of an achiral MOF-structure that cannot be chiralized directly. So, the (L-proline@Fe₃O₄)@TMU-5 (LPF@5) composite was developed by stabilization of chiral L-proline on the Fe₃O₄ magnetic surface, followed by encapsulation of the (L-proline@Fe₃O₄) nanoparticles (LPF NPs) by TMU-5 in an in situ ultrasonication synthesis. Since the right selection of functionalities in the construction of hybrid nanomaterials is essential observation of the synergic effects between functional groups, L-proline was applied as the chiral ligand because it contains a Lewis basic amine group, which can work alongside the Lewis basicity of the azine groups of TMU-5 to allow synergic effects in the Lewis basicity of the LPF@5 nanocomposite. To evaluate this, we applied LPF@5 in the asymmetric C–C bond formation in nitroaldol condensation. The results showed that LPF@5 had a higher selectivity toward β-nitroalcohol over the pristine TMU-5 and enantioselectivity than the LPF NPs in a mild and green asymmetric nitroaldol condensation. Although, LPF@5 was constructed based on a facile synthesis, it showed remarkable results in asymmetric nitroaldol condensation.