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Non-Kekulé meta-Quinodimethane Singlet Diradicals Based on Classical N-Heterocyclic Carbenes.
- Source :
-
Chemistry (Weinheim an der Bergstrasse, Germany) [Chemistry] 2024 Aug 14, pp. e202403029. Date of Electronic Publication: 2024 Aug 14. - Publication Year :
- 2024
- Publisher :
- Ahead of Print
-
Abstract
- Diradicals based on a meta-quinodimethane (m-QDM) scaffold generally have a triplet ground state and are rather scarce. Herein, m-QDM-based non-Kekulé diradicals [3,3'-(NHC) <subscript>2</subscript> BP] (3-NHC) (NHC = SIPr = C{N(Dipp)CH <subscript>2</subscript> } <subscript>2</subscript> ; IPr = C{N(Dipp)CH} <subscript>2</subscript> , Me-IPr = C{N(Dipp)CMe} <subscript>2</subscript> ; Dipp = 2,6-iPr <subscript>2</subscript> C <subscript>6</subscript> H <subscript>3</subscript> ; BP = 1,1'-C <subscript>6</subscript> H <subscript>4</subscript> C <subscript>6</subscript> H <subscript>4</subscript> ) featuring N-heterocyclic carbene (NHC) pendants are reported as crystalline solids. The EPR spectra of 3-NHC show both allowed (Δm <subscript>s</subscript> = 1) and forbidden (Δm <subscript>s</subscript> = 2; 'half-field') transitions characteristic for triplet diradicals. Variable temperature EPR studies however reveal a singlet ground state for 3-SIPr. Consistent with the EPR spectra, calculations predict a remarkably small singlet-triplet energy gap (ΔE <subscript>ST</subscript> ≤ 0.26 kcal/mol) for the 3-NHC compounds. The calculated singlet diradical character for the ground states of the 3-NHC compounds amounts to ~99 %.<br /> (© 2024 The Author(s). Chemistry - A European Journal published by Wiley-VCH GmbH.)
Details
- Language :
- English
- ISSN :
- 1521-3765
- Database :
- MEDLINE
- Journal :
- Chemistry (Weinheim an der Bergstrasse, Germany)
- Publication Type :
- Academic Journal
- Accession number :
- 39140842
- Full Text :
- https://doi.org/10.1002/chem.202403029