A redox-active diborane platform performs C(sp 3 )-H activation and nucleophilic substitution reactions

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 reactio...

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Bibliographic Details
Published in:Chemical science (Cambridge) 2018, Vol.9 (15), p.3881-3891
Main Authors: Kaese, Thomas, Trageser, Timo, Budy, Hendrik, Bolte, Michael, Lerner, Hans-Wolfram, Wagner, Matthias
Format: Article
Language:English
Subjects:
Boron
Chemical attack
Chemical bonds
Deuterium
Diborane
Polarity
Quantum chemistry
Reagents
Substitution reactions
Substrates
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Summary: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) H and its B[double bond, length as m-dash]B-bonded formal deprotonation product Li [ ] can activate the particularly inert C(sp )-H bonds of added H CLi and H CCl, respectively. The first case involves the attack of [H C] 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 H CCl. 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, H CLi/ H and H CCl/Li [ ], ultimately funnel into the same reaction pathway, which likely proceeds past a borylene-type intermediate and requires the cooperative interaction of both boron atoms.
ISSN:2041-6520
2041-6539
DOI:10.1039/c8sc00743h