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Issue 15, 2018
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A redox-active diborane platform performs C(sp3)–H activation and nucleophilic substitution reactions

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Abstract

Organoboranes are among the most versatile and widely used reagents in synthetic chemistry. A significant further expansion of their application spectrum would be achievable if boron-containing reactive intermediates capable of inserting into C–H bonds or performing nucleophilic substitution reactions were readily available. However, current progress in the field is still hampered by a lack of universal design concepts and mechanistic understanding. Herein we report that the doubly arylene-bridged diborane(6) 1H2 and its B[double bond, length as m-dash]B-bonded formal deprotonation product Li2[1] can activate the particularly inert C(sp3)–H bonds of added H3CLi and H3CCl, respectively. The first case involves the attack of [H3C] on a Lewis-acidic boron center, whereas the second case follows a polarity-inverted pathway with nucleophilic attack of the B[double bond, length as m-dash]B double bond on H3CCl. Mechanistic details were elucidated by means of deuterium-labeled reagents, a radical clock, α,ω-dihaloalkane substrates, the experimental identification of key intermediates, and quantum-chemical calculations. It turned out that both systems, H3CLi/1H2 and H3CCl/Li2[1], ultimately funnel into the same reaction pathway, which likely proceeds past a borylene-type intermediate and requires the cooperative interaction of both boron atoms.

Graphical abstract: A redox-active diborane platform performs C(sp3)–H activation and nucleophilic substitution reactions

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Publication details

The article was received on 13 Feb 2018, accepted on 19 Mar 2018 and first published on 19 Mar 2018


Article type: Edge Article
DOI: 10.1039/C8SC00743H
Citation: Chem. Sci., 2018,9, 3881-3891
  • Open access: Creative Commons BY license
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    A redox-active diborane platform performs C(sp3)–H activation and nucleophilic substitution reactions

    T. Kaese, T. Trageser, H. Budy, M. Bolte, H. Lerner and M. Wagner, Chem. Sci., 2018, 9, 3881
    DOI: 10.1039/C8SC00743H

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