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Iridicycle-catalysed imine reduction: an experimental and computational study of the mechanism

Chen, Hsin-Yi Tiffany, Wang, Chao, Wu, Xiaofeng and Catlow, Charles Richard ORCID: https://orcid.org/0000-0002-1341-1541 2015. Iridicycle-catalysed imine reduction: an experimental and computational study of the mechanism. Chemistry: A European Journal 21 (46) , pp. 16564-16577. 10.1002/chem.201501074

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Abstract

The mechanism of imine reduction by formic acid with a single-site iridicycle catalyst has been investigated by density functional theory (DFT), NMR spectroscopy, and kinetic measurements. The NMR and kinetic studies suggest that the transfer hydrogenation is turnover-limited by the hydride formation step. The calculations reveal that, amongst a number of possibilities, hydride formation from the iridicycle and formate probably proceeds by an ion-pair mechanism, whereas the hydride transfer to the imino bond occurs in an outer-sphere manner. In the gas phase, in the most favourable pathway, the activation energies in the hydride formation and transfer steps are 26–28 and 7–8 kcal mol−1, respectively. Introducing one explicit methanol molecule into the modelling alters the energy barrier significantly, reducing the energies to around 18 and 2 kcal mol−1 for the two steps, respectively. The DFT investigation further shows that methanol participates in the transition state of the turnover-limiting hydride formation step by hydrogen-bonding to the formate anion and thereby stabilising the ion pair.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Chemistry
Subjects: Q Science > QD Chemistry
Publisher: Wiley-Blackwell
Last Modified: 31 Oct 2022 10:09
URI: https://orca.cardiff.ac.uk/id/eprint/83841

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