Water reduction and dihydrogen addition in aqueous conditions with <em>ansa</em>-phosphinoborane
Sorochkina, Kristina; Chernichenko, Konstantin; Zhivonitko, Vladimir V.; Nieger, Martin; Repo, Timo (2022-11-02)
K. Sorochkina, K. Chernichenko, V. V. Zhivonitko, M. Nieger, T. Repo, Chem. Eur. J. 2022, 28, e202201927, https://doi.org/10.1002/chem.202201927
© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
https://creativecommons.org/licenses/by/4.0/
https://urn.fi/URN:NBN:fi-fe2023062759462
Tiivistelmä
Abstract
Ortho-phenylene-bridged phosphinoborane (2,6-Cl₂Ph)₂B-C₆H₄-PCy₂ 1 was synthesized in three steps from commercially available starting materials. 1 reacts with H2 or H2O under mild conditions to form corresponding zwitterionic phosphonium borates 1-H₂ or 1-H₂O. NMR studies revealed both reactions to be remarkably reversible. Thus, when exposed to H₂, 1-H₂O partially converts to 1-H₂ even in the presence of multiple equivalents of water in the solution. The addition of parahydrogen to 1 leads to nuclear spin hyperpolarization both in dry and hydrous solvents, confirming the dissociation of 1-H₂O to free 1. These observations were supported by computational studies indicating that the formation of 1-H₂ and 1-H₂O from 1 are thermodynamically favored. Unexpectedly, 1-H₂O can release molecular hydrogen to form phosphine oxide 1-O. Kinetic, mechanistic, and computational (DFT) studies were used to elucidate the unique “umpolung” water reduction mechanism.
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