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Updated: Feb 14, 2026

Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
Published on: April 19, 2019
Crystalline Radicals Derived from Classical N-Heterocyclic Carbenes
Dennis Rottschäfer1, Beate Neumann1, Hans-Georg Stammler1
1Anorganische Molekülchemie und Katalyse, Lehrstuhl für Anorganische Chemie und Strukturchemie, Centrum für Molekulare Materialien, Fakultät für Chemie, Universität Bielefeld, Universitätsstrasse 25, 33615, Bielefeld, Germany.
Abstract:
One-electron reduction of C2-arylated 1,3-imidazoli(ni)um salts (IPrAr )Br (Ar=Ph, 3 a; 4-DMP, 3 b; 4-DMP=4-Me2 NC6 H4 ) and (SIPrAr )I (Ar=Ph, 4 a; 4-Tol, 4 b) derived from classical NHCs (IPr=:C{N(2,6-iPr2 C6 H3 )}2 CHCH, 1; SIPr=:C{N(2,6-iPr2 C6 H3 )}2 CH2 CH2 , 2) gave radicals [(IPrAr )]. (Ar=Ph, 5 a; 4-DMP, 5 b) and [(SIPrAr )]. (Ar=Ph, 6 a; 4-Tol, 6 b). Each of 5 a,b and 6 a,b exhibited a doublet EPR signal, a characteristic of monoradical species. The first solid-state characterization of NHC-derived carbon-centered radicals 6 a,b by single-crystal X-ray diffraction is reported. DFT calculations indicate that the unpaired electron is mainly located at the original carbene carbon atom and stabilized by partial delocalization over the adjacent aryl group.
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