Related Experiment Video
Updated: Jun 20, 2025

Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
Published on: April 19, 2019
Crystalline Radical Anion of a Diboratriazole and Its Conversion to a Neutral Radical Driven by a Carbene
Lizhao Zhu1, Zhongtao Feng1, Rei Kinjo1
1School of Chemistry, Chemical Engineering and Biotechnology, Nanyang Technological University, Singapore 637371, Singapore.
Abstract:
One-electron reduction of diboratriazole 1 with potassium graphite (KC8) generates the radical anion 1•K, which undergoes a salt (KCl) elimination reaction upon addition of an N-heterocyclic carbene (NHC) to afford the neutral diboratriazole radical 3. An X-ray diffraction analysis, electron paramagnetic resonance spectroscopy, and computational studies revealed that an unpaired electron in radical species 1•K and 3 is delocalized over the π-system of the B2N3 and carbene rings. Reversible oxidation of 3 gives rise to a diboratriazole cation 4 featuring a 6π aromatic character. Moreover, treating 1•K with a half equivalent of a bis(NHC) produces a biradical species 5, in which there is little interaction between two radical moieties separated by the bis(NHC) linker, suggesting the dis-biradical property. 5 undergoes stepwise and reversible two-electron oxidation, establishing three formal oxidation states.
Related Concept Videos
Radical Substitution: Hydrogenolysis of Alkyl Halides with Tributyltin Hydride
The bonds formed in this reaction are stronger than the bonds broken, making it energetically favorable. The reaction follows a radical chain mechanism similar to radical halogenation...
Radicals: Electronic Structure and Geometry
Accordingly, the structure of a trivalent radical lies between the geometries of carbocations and carbanions. An sp2-hybridized carbocation is trigonal planar, while an sp3-hybridized carbanion is trigonal pyramidal. Here, the difference in geometry is...
Hydroboration-Oxidation of Alkenes
Benzene to 1,4-Cyclohexadiene: Birch Reduction Mechanism
Radical Substitution: Allylic Bromination
Halogenation of Alkenes
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.

