Neutral Boryl Radicals in Mixed-Valent B(III) Br-B(II) Adducts

Tong-Tong Liu; Jiaxin Chen; Xin-Lei Chen; Li Ma; Bing-Tao Guan; Zhenyang Lin; Zhang-Jie Shi

doi:10.1002/chem.202202634

Neutral Boryl Radicals in Mixed-Valent B^(III) Br-B^(II) Adducts

Chemistry. 2023 Jan 2;29(1):e202202634. doi: 10.1002/chem.202202634. Epub 2022 Nov 14.

Authors

Tong-Tong Liu¹, Jiaxin Chen², Xin-Lei Chen¹, Li Ma¹, Bing-Tao Guan¹, Zhenyang Lin², Zhang-Jie Shi¹

Affiliations

¹ Department of Chemistry, Fudan University, Shanghai, 200438, P. R. China.
² Department of Chemistry, The Hong Kong University of Science and Technology Clear Water Bay, Kowloon, Hong Kong, P. R. China.

PMID: 36217568
DOI: 10.1002/chem.202202634

Abstract

The general strategies to stabilize a boryl radical involve single electron delocalization by π-system and the steric hinderance from bulky groups. Herein, a new class of boryl radicals is reported, with intramolecular mixed-valent B^(III) Br-B^(II) adducts ligated by a cyclic (alkyl)(amino)carbene (CAAC). The radicals feature a large spin density on the boron center, which is ascertained by EPR spectroscopy and DFT calculations. Structural and computational analyses revealed that the stability of radical species was assisted by the CAAC ligand and a weak but significant B(III)Br-B(II) interaction, suggesting a cooperative avenue for stabilization of boryl radicals. Two-electron reduction of these new boryl radicals provides C-H insertion products via a borylene intermediate.

Keywords: C−H activation; large spin density; neutral boryl radical; stabilizing factors; σ interaction.