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Article Dans Une Revue Chemistry - A European Journal Année : 2020

Hydroboration of Alkenes Catalysed by a Nickel N‐Heterocyclic Carbene Complex: Reaction and Mechanistic Aspects

Résumé

The pentamethylcyclopentadienyl N-heterocyclic carbene nickel complex [Ni(η5-C5Me5)Cl(IMes)] (IMes = 1,3-dimesitylimidazol-2-ylidene) efficiently catalyses the anti-Markovnikov hydroboration of alkenes with catecholborane in the presence of a catalytic amount of potassium tert-butoxide, and joins the very exclusive club of nickel catalysts for this important transformation. Interestingly, the regioselectivity can be reversed in some cases by using pinacolborane instead of catecholborane. Mechanistic investigations involving control experiments, 1H and 11B NMR spectroscopy, cyclic voltammetry, piezometric measurements and DFT calculations suggest an initial reduction of the Ni(II) precursor to a Ni(I) active species with the concomitant release of H2. The crucial role of the alkoxo-catecholato-borohydride species resulting from the reaction of potassium tert-butoxide with catecholborane in the formation of an intermediate nickel-hydride species that would then be reduced a Ni(I) active species, is highlighted.
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Dates et versions

hal-02921998 , version 1 (04-01-2021)

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Franck Ulm, Yann Cornaton, Jean-Pierre Djukic, Michael Chetcuti, Vincent Ritleng. Hydroboration of Alkenes Catalysed by a Nickel N‐Heterocyclic Carbene Complex: Reaction and Mechanistic Aspects. Chemistry - A European Journal, 2020, 26 (41), pp.8916-8925. ⟨10.1002/chem.202000289⟩. ⟨hal-02921998⟩
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