Design of Stereogenic-at-Iron Catalysts with a (3+2+1)-Ligand Sphere

A stereogenic-at-iron(II) catalyst scaffold is introduced which contains one coordinated meridional tridentate imidazolidin-2-ylidene-functionalized 2,2′-bipyridine, one bidentate pyrazolylpyridine, and one monodentate acetonitrile ligand. This (3+2+1)-coordination sphere implements a stereogenic iron center. A carbon stereocenter in the N-heterocyclic carbene moiety controls the absolute metal-centered configuration. The bench-stable diamagnetic iron(II) complexes can be synthesized in a highly diastereoselective fashion from iron dibromide in an efficient one-pot coordination reaction. The obtained enantiopure complexes were applied as chiral catalysts in the ring contraction of an isoxazole to a chiral 2H-azirine (quantitative yields, up to 90 : 10 er).