Stereogenic-at-Iron Catalysts with a Chiral Tripodal Pentadentate Ligand

Abstract

A class of stereogenic-at-iron catalysts is introduced and applied to asymmetric 3d-transition metal catalysis. The pentadentate coordination of a tripodal ligand creates a stereogenic iron center, while an isopropyl group in the ligand backbone serves as a chiral lever to thermodynamically favor one diastereomer (>20:1 dr) of the obtained iron complexes. The coordination sphere is completed with a labile acetonitrile ligand. Ligand coordination and dynamics were studied by NMR spectroscopy. A modular design of the tripodal ligand enables the convenient implementation of different modifications, which have been incorporated and investigated in this work. The catalytic performance of the obtained complexes was evaluated in the ring contraction of isoxazoles to chiral 2H-azirines in up to 99% yield and with up to 93% ee and features a remarkably high catalytic activity with up to 10,000 turnover numbers (TON).