Persistent Borafluorene Radicals.

Authors :: Yang W
Krantz KE
Freeman LA
Dickie DA
Molino A
Frenking G
Pan S
Wilson DJD
Gilliard RJ Jr
Source :: Angewandte Chemie (International ed. in English) [Angew Chem Int Ed Engl] 2020 Mar 02; Vol. 59 (10), pp. 3850-3854. Date of Electronic Publication: 2020 Feb 03.
Publication Year :: 2020
Abstract: N-Heterocyclic carbene (NHC)- and cyclic (alkyl)(amino)carbene (CAAC)-stabilized borafluorene radicals have been isolated and characterized by elemental analysis, single-crystal X-ray diffraction, UV/Vis absorption, cyclic voltammetry (CV), electron paramagnetic resonance (EPR) spectroscopy, and theoretical studies. Both the CAAC-borafluorene radical (2) and the NHC-borafluorene radical (4) have a considerable amount of spin density localized on the boron atoms (0.322 for 2 and 0.369 for 4). In compound 2, the unpaired electron is also partly delocalized over the CAAC ligand <superscript>carbene</superscript> C and N atoms. However, the unpaired electron in compound 4 mainly resides throughout the borafluorene π-system, with significantly less delocalization over the NHC ligand. These results highlight the Lewis base dependent electrostructural tuning of materials-relevant radicals. Notably, this is the first report of crystalline borafluorene radicals, and these species exhibit remarkable solid-state and solution stability.<br /> (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)