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Updated: Nov 29, 2025
Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
Published on: April 19, 2019
Twisting versus Delocalization in CAAC- and NHC-Stabilized Boron-Based Biradicals: The Roles of Sterics and
Paul Schmid1, Felipe Fantuzzi1,2,3, Jonas Klopf1
1Institute for Physical and Theoretical Chemistry, Julius-Maximilians-Universität Würzburg, Emil-Fischer-Strasse 42, 97074, Würzburg, Germany.
Abstract:
Twisted boron-based biradicals featuring unsaturated C2 R2 (R=Et, Me) bridges and stabilization by cyclic (alkyl)(amino)carbenes (CAACs) were recently prepared. These species show remarkable geometrical and electronic differences with respect to their unbridged counterparts. Herein, a thorough computational investigation on the origin of their distinct electrostructural properties is performed. It is shown that steric effects are mostly responsible for the preference for twisted over planar structures. The ground-state multiplicity of the twisted structure is modulated by the σ framework of the bridge, and different R groups lead to distinct multiplicities. In line with the experimental data, a planar structure driven by delocalization effects is observed as global minimum for R=H. The synthetic elusiveness of C2 R2 -bridged systems featuring N-heterocyclic carbenes (NHCs) was also investigated. These results could contribute to the engineering of novel main group biradicals.
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