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Issue 9, 2019
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Heterolytic bond activation at gold: evidence for gold(III) H–B, H–Si complexes, H–H and H–C cleavage

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Abstract

The coordinatively unsaturated gold(III) chelate complex [(C^N–CH)Au(C6F5)]+ (1+) reacts with main group hydrides H–BPin and H–SiEt3 in dichloromethane solution at −70 °C to form the corresponding σ-complexes, which were spectroscopically characterized (C^N–CH = 2-(C6H3But)-6-(C6H4But)pyridine anion; Pin = OCMe2CMe2O). In the presence of an external base such as diethyl ether, heterolytic cleavage of the silane H–Si bond leads to the gold hydrides [{(C^N–CH)AuC6F5}2(μ-H)]+ (2+) and (C^N–CH)AuH(C6F5) (5), together with spectroscopically detected [Et3Si–OEt2]+. The activation of dihydrogen also involves heterolytic H–H bond cleavage but requires a higher temperature (−20 °C). H2 activation proceeds in two mechanistically distinct steps: the first leading to 2 plus [H(OEt2)2]+, the second to protonation of one of the C^N pyridine ligands and reductive elimination of C6F5H. By comparison, formation of gold hydrides by cleavage of suitably activated C–H bonds is very much more facile; e.g. the reaction of 1·OEt2 with Hantzsch ester is essentially instantaneous and quantitative at −30 °C. This is the first experimental observation of species involved in the initial steps of gold catalyzed hydroboration, hydrosilylation and hydrogenation and the first demonstration of the ability of organic C–H bonds to act as hydride donors towards gold.

Graphical abstract: Heterolytic bond activation at gold: evidence for gold(iii) H–B, H–Si complexes, H–H and H–C cleavage

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Publication details

The article was received on 23 Nov 2018, accepted on 15 Jan 2019 and first published on 16 Jan 2019


Article type: Edge Article
DOI: 10.1039/C8SC05229H
Citation: Chem. Sci., 2019,10, 2633-2642
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    Heterolytic bond activation at gold: evidence for gold(III) H–B, H–Si complexes, H–H and H–C cleavage

    L. Rocchigiani, P. H. M. Budzelaar and M. Bochmann, Chem. Sci., 2019, 10, 2633
    DOI: 10.1039/C8SC05229H

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