Iron‐Catalyzed Tunable Double Bond Migration and Geometrical Isomerization in Olefins via a Spin‐Accelerated Alkyl Mechanism

Despite the central relevance of metal‐catalyzed alkene isomerization in academia and industry and the overarching role of iron in sustainable catalysis, highly efficient iron‐catalyzed positional and geometrical isomerizations of alkenes remain long‐sought‐after goals. Herein, we disclose the development of an easily accessible, well‐defined anilido‐aldimine iron(II) alkyl catalyst that efficiently and selectively performs, for the first time, tunable olefin migration over one and multiple carbon–carbon bonds and configurational alkene isomerization. This singular catalyst behavior also unraveled the implementation of productive regiodivergent and regio‐ and stereoconvergent olefin isomerization processes. Notably, with only 1 equiv. of Cy 2 NH·BH 3 (relative to Fe) under mild conditions, these reactions exhibited a broad substrate scope, including (hetero)aryl‐substituted and aliphatic alkenes of different substitution patterns and with diverse functionalities. They also displayed high regio‐ and stereoselectivities. Using experimental and computational approaches, a detailed mechanistic study of the positional isomerization regime suggested a redox‐neutral alkyl‐type mechanism via an isolable iron(II)‐hydride species. This study indicated the stereo‐ and rate‐determining β‐hydride elimination step occurs through a two‐state reactivity resulting in spin acceleration and a stereoselectivity correlated to these spin state changes. This work also elucidated the peculiar and critical role of the anilido‐aldimine skeleton on the reactivity.