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

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 Cy₂NH·BH₃ (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.