Zakharov Danila O, Chernichenko Konstantin, Sorochkina Kristina, Repo Timo, Zhivonitko Vladimir V
NMR Research Unit, Faculty of Science, University of Oulu, P.O. Box 3000, Oulu, 90014, Finland.
Department of Chemistry, University of Helsinki, A. I. Virtasen Aukio 1, 00014 Helsinki, Finland.
Dalton Trans. 2022 Sep 20;51(36):13606-13611. doi: 10.1039/d2dt02178a.
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 -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-H 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.
仲氢诱导极化是一种核自旋超极化技术，它可以为催化氢化反应产物和中间体提供显著增强的核磁共振信号。除此之外，该技术可用于研究相应化学转化的机理。通常，贵金属配合物用于与仲氢的反应。在此，我们展示了由氨基硼烷催化剂QCAT催化的无金属亚胺氢化反应的PHIP研究。我们通过展示初始氢活化步骤的成对性质来讨论反应机理，该步骤导致在QCAT-H中间体中形成N-H氢的负净核自旋极化，从而使仲氢来源的质子进一步转移到亚胺底物上，并积累超极化的胺产物。仲氢诱导极化还证明了催化循环的可逆性。
