Non‐covalent Immobilization of Chiral Rhodium Catalysts on Carbon Nanotubes for Asymmetric Hydrogenation

Abstract

Supported chiral catalysts were prepared by ionic anchoring of two cationic rhodium complexes (A and B) onto functionalized carbon nanotubes (CNTs). The immobilization of the Rh complexes was done by applying two ionic anchoring strategies: i) electrostatic interaction with the negatively charged surface of carboxylate‐functionalized CNTs (CNT‐COO‐); ii) electrostatic interaction through a heteropoly acid (HPA) spacer previously grafted at the CNTs surface (CNT‐HPA). The characterization of the obtained CNT‐COO‐@complex A, CNT‐COO‐@complex B, CNT‐HPA@complex A, and CNT‐HPA@complex B materials by ICP, TEM and XPS showed the successful anchoring of the Rh complexes onto the supports. The HPA spacer was found to increase the catalyst’s stability and to limit the effect of the CNT surface on the catalytic performances of the immobilized Rh complexes. CNT‐HPA@complexes performed the hydrogenation of dimethyl itaconate into methyl succinate with high conversions (83‐100%) and good enantioselectivities (58‐63%). The recyclability tests showed the catalysts were less active but still enantioselective after recycling.