A redox-active diborane platform performs C(sp3)–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 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.

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Author:Thomas Kaese, Timo TrageserGND, Hendrik Budy, Michael BolteORCiD, Hans-Wolfram LernerGND, Matthias Wagner
Pubmed Id:https://pubmed.ncbi.nlm.nih.gov/29780520
Parent Title (English):Chemical science
Place of publication:Cambridge
Document Type:Article
Year of Completion:2018
Date of first Publication:2018/03/19
Publishing Institution:Universitätsbibliothek Johann Christian Senckenberg
Release Date:2018/05/29
Page Number:11
First Page:3881
Last Page:3891
This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.
Institutes:Biochemie, Chemie und Pharmazie / Biochemie und Chemie
Dewey Decimal Classification:5 Naturwissenschaften und Mathematik / 54 Chemie / 540 Chemie und zugeordnete Wissenschaften
Licence (German):License LogoCreative Commons - Namensnennung 3.0