Redox-Active Bipyridine-Iron Half-Sandwich Complexes for Catalytic Carbene Transfer

Redox-active ligands are well established for enabling open-shell reactivity in first-row transition-metal catalysis. Despite the privileged role of 2,2'-bipyridine (bpy) ligands in homogeneous catalysis, bpy-supported half-sandwich organoiron complexes have remained essentially unexplored. Here we report the synthesis and characterization of a previously elusive family of half-sandwich iron complexes, (η5-C5Me5)Fe(bpy)(X) (X = Cl, Br), and their application in catalytic carbene transfer. Single-electron reduction affords a low-valent 17-electron complex best described as having a predominantly Fe(II)/bpy•- electronic structure. In contrast to classical (η5-C5H5)Fe(CO)2 (Fp)-type iron systems that mainly engage in two-electron reactivity, the redox-active bpy-(η5-C5Me5)Fe platform undergoes homolytic bond activation, including halogen-atom transfer from benzylic gem-dihalides. Leveraging this open-shell reactivity, catalytic cyclopropanation of styrenes and related alkenes was achieved using gem-dihalides as carbene precursors and manganese as terminal reductant. These findings establish bpy-supported half-sandwich iron complexes as a structurally tunable, non-heme platform for catalytic carbene transfer reactivity.