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Dialkyl Ether Formation at High-Valent Nickel

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Le Vaillant,  Franck
Research Group Cornellà, Max-Planck-Institut für Kohlenforschung, Max Planck Society;

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Leutzsch,  Markus
Service Department Farès (NMR), Max-Planck-Institut für Kohlenforschung, Max Planck Society;

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Cornella,  Josep
Research Group Cornellà, Max-Planck-Institut für Kohlenforschung, Max Planck Society;

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Citation

Le Vaillant, F., Reijerse, E. J., Leutzsch, M., & Cornella, J. (2020). Dialkyl Ether Formation at High-Valent Nickel. Journal of the American Chemical Society, 142(46), 19540-19550. doi:10.1021/jacs.0c07381.


Cite as: http://hdl.handle.net/21.11116/0000-0007-9B14-4
Abstract
In this article, we investigated the I2-promoted cyclic dialkyl ether formation from 6-membered oxanickelacycles originally reported by Hillhouse. A detailed mechanistic investigation based on spectroscopic and crystallographic analysis revealed that a putative reductive elimination to forge C(sp3)–OC(sp3) using I2 might not be operative. We isolated a paramagnetic bimetallic NiIII intermediate featuring a unique Ni2(OR)2 (OR = alkoxide) diamond-like core complemented by a μ-iodo bridge between the two Ni centers, which remains stable at low temperatures, thus permitting its characterization by NMR, EPR, X-ray, and HRMS. At higher temperatures (>−10 °C), such bimetallic intermediate thermally decomposes to afford large amounts of elimination products together with iodoalkanols. Observation of the latter suggests that a C(sp3)–I bond reductive elimination occurs preferentially to any other challenging C–O bond reductive elimination. Formation of cyclized THF rings is then believed to occur through cyclization of an alcohol/alkoxide to the recently forged C(sp3)–I bond. The results of this article indicate that the use of F+ oxidants permits the challenging C(sp3)–OC(sp3) bond formation at a high-valent nickel center to proceed in good yields while minimizing deleterious elimination reactions. Preliminary investigations suggest the involvement of a high-valent bimetallic NiIII intermediate which rapidly extrudes the C–O bond product at remarkably low temperatures. The new set of conditions permitted the elusive synthesis of diethyl ether through reductive elimination, a remarkable feature currently beyond the scope of Ni.