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Twisting versus Delocalization in CAAC‐ and NHC‐Stabilized Boron‐Based Biradicals: The Roles of Sterics and Electronics
Author(s) -
Schmid Paul,
Fantuzzi Felipe,
Klopf Jonas,
Schröder Niklas B.,
Dewhurst Rian D.,
Braunschweig Holger,
Engel Volker,
Engels Bernd
Publication year - 2021
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.202004619
Subject(s) - steric effects , delocalized electron , boron , electron delocalization , psychology , chemistry , stereochemistry , organic chemistry
Twisted boron‐based biradicals featuring unsaturated C 2 R 2 (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 C 2 R 2 ‐bridged systems featuring N‐heterocyclic carbenes (NHCs) was also investigated. These results could contribute to the engineering of novel main group biradicals.