A highly efficient immobilization strategy for chiral ferrocene P, P-ligands with enhanced performance in asymmetric catalysis

The immobilization of chiral catalyst enables a cost-effective reuse and simplifies product separation. However, the classical covalent bonding immobilization strategies often require additional steps to modify the ligands or supports. Herein, an immobilization of two typical chiral ferrocene ligands and three corresponding metal complexes onto commercially available styrene-based polymers has been achieved via a one-step Friedel-Crafts reaction. Our method enables facile immobilization without the need for premodification of ligands or supports, and represents as a straightforward strategy for the rapid access of aryl-containing heterogeneous ligands or ligand/metal complexes. The resulting heterogeneous catalysts, Taniaphos/Cu(Ι) and Zhaophos/Rh(Ι), displayed excellent activity in asymmetric alkylation and hydrogenation reactions, achieving up to 99 % yield and 98 % enantiomeric excess (e.e.) respectively. Notably, the Zhaophos/Ir(Ι) heterogeneous catalyst exhibited more than double the performance in the asymmetric hydrogenation of benzoxazinones compared to its homogeneous counterpart. Moreover, all of the products could be obtained without chromatography purification with over 95 % NMR purity. Recycling tests and continuous flow experiments demonstrated that the heterogeneous catalyst could be reused for at least five times without any decrease in activity, or operated continuously for 100 h without loss of activity, achieving turnover numbers exceeding 1875 and reducing the reaction from 24 h to 4.7 min.