Parahydrogen-induced polarization study of imine hydrogenations mediated by a metal-free catalyst
Zakharov, Danila O.; Chernichenko, Konstantin; Sorochkina, Kristina; Repo, Timo; Zhivonitko, Vladimir V. (2022-08-29)
Zakharov, D. O., Chernichenko, K., Sorochkina, K., Repo, T., & Zhivonitko, V. V. (2022). Parahydrogen-induced polarization study of imine hydrogenations mediated by a metal-free catalyst. Dalton Transactions, 51(36), 13606–13611. https://doi.org/10.1039/D2DT02178A
© The Royal Society of Chemistry 2022. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence
https://creativecommons.org/licenses/by/3.0/
https://urn.fi/URN:NBN:fi-fe2022102563234
Tiivistelmä
Abstract
Parahydrogen-induced polarization is a nuclear spin hyperpolarization technique that can provide strongly enhanced NMR signals for catalytic hydrogenation reaction products and intermediates. Among other matters, this can be employed to study the mechanisms of the corresponding chemical transformations. Commonly, noble metal complexes are used for reactions with parahydrogen. Herein, we present a PHIP study of metal-free imine hydrogenations catalyzed by the ansa-aminoborane catalyst QCAT. We discuss the reaction mechanism by showing the pairwise nature of the initial hydrogen activation step that leads to the formation of the negative net nuclear spin polarization of N–H hydrogen in the QCAT-H₂ intermediate, enabling the further transfer of parahydrogen-originating protons to the imine substrate with the accumulation of hyperpolarized amine products. Parahydrogen-induced polarization also demonstrates the reversibility of the catalytic cycle.
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