Immobilization of a chiral dirhodium catalyst on SBA-15 via click-chemistry: Application in the asymmetric cyclopropanation of 3-diazooxindole with aryl alkenes

Abstract

A novel immobilized chiral dirhodium catalyst, Rh2(S-PTTL)3(S-PTTL-linker)∼SBA-15 (8), has been prepared via click reaction of azide-groups on functionalized SBA-15 with the dirhodium complex Rh2(S-PTTL)3(S-PTTL-alkyne) (6) containing an alkyne moiety. During the synthesis of this complex, one chiral ligand of the parent Rh2(S-PTTL)4 catalyst is exchanged with an analogous chiral ligand system containing an alkyne moiety, which to a great extent maintains the intrinsic catalytic performance of the catalyst. The heterogeneous dirhodium catalyst is characterized by FT-IR and 13C solid-state NMR to validate the successful immobilization. The catalytic performance of the heterogeneous catalyst 8 is investigated in the asymmetric cyclopropanation of 3-diazooxindole with different aryl alkenes that form spiro-cyclopropyloxindoles which serve as precursors for pharmaceuticals. The resulting heterogeneous catalyst shows high catalytic activity and significant enantioselectivity. Importantly, it can be readily recovered and reused at least four times without significant loss of its catalytic performance.