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Issue 7, 2013
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Electronic effects of triarylphosphines in metal-free hydrogen activation: a kinetic and computational study

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Abstract

The frustrated Lewis pair-mediated reversible hydrogen activation is studied as a function of the electron-donor quality of a series of phosphines. The increasing acidity of the generated phosphonium species leads to a stepwise lowering of the temperature for the highly reversible H2-activation and permits concrete classification for the first time. The influence of the acid strength on the metal-free hydrogenation of selected olefins is investigated by kinetic experiments and quantum chemical calculations. Detailed information for the rate-determining steps fully support our mechanistic model of a protonation step prior to hydride transfer. The rate of hydrogenation is strongly dependent on the electronic nature of the phosphine and of the acidity of the corresponding phosphonium cation. A careful balance of these two factors provides highly efficient metal-free hydrogenation catalysts. The provided findings are used to revise the reactivity of Lewis bases in the hydrogenation of imines, one of the most recognized applications of FLPs.

Graphical abstract: Electronic effects of triarylphosphines in metal-free hydrogen activation: a kinetic and computational study

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Publication details

The article was received on 06 Feb 2013, accepted on 29 Apr 2013 and first published on 30 Apr 2013


Article type: Edge Article
DOI: 10.1039/C3SC50347J
Citation: Chem. Sci., 2013,4, 2788-2796
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    Electronic effects of triarylphosphines in metal-free hydrogen activation: a kinetic and computational study

    L. Greb, S. Tussing, B. Schirmer, P. Oña-Burgos, K. Kaupmees, M. Lõkov, I. Leito, S. Grimme and J. Paradies, Chem. Sci., 2013, 4, 2788
    DOI: 10.1039/C3SC50347J

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