Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 27, Issue 21, Pages 6557-6568Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.202100105
Keywords
carbene– selenium adducts; cyclic voltammetry; mesoionic carbenes; radicals; spectroelectrochemistry
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Funding
- ZEDAT (Freie Universitat Berlin)
- DFG
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Extensive electrochemical investigations on 1,2,3-triazolylidene selenium adducts revealed a correlation between their reduction potentials and molecular structures. Unexpected quasi-reversibility was discovered in the reduction of two triazoline selones. Through spectroelectrochemical studies and calculations, the radical anion was successfully assigned to be triazoline centered, providing design principles for stabilizing radicals based on MICs.
Carbene-based radicals are important for both fundamental and applied chemical research. Herein, extensive electrochemical investigations of nine different 1,2,3-triazolylidene selenium adducts are reported. It is found that the half-wave potentials of the first reduction of the selones correlate with their calculated LUMO levels and the LUMO levels of the corresponding triazolylidene-based mesoionic carbenes (MICs). Furthermore, unexpected quasi-reversibility of the reduction of two triazoline selones, exhibiting comparable reduction potentials, was discovered. Through UV/Vis/NIR and EPR spectroelectrochemical investigations supported by DFT calculations, the radical anion was unambiguously assigned to be triazoline centered. This electrochemical behavior was transferred to a triazolylidene-type MIC-gold phenyl complex resulting in a MIC-radical coordinated Au-I species. Apart from UV-Vis-NIR and EPR spectroelectrochemical investigations of the reduction, the reduced gold-coordinated MIC radical complex was also formed in situ in the bulk through chemical reduction. This is the first report of a monodentate triazolylidene-based MIC ligand that can be reduced to its anion radical in a metal complex. The results presented here provide design principles for stabilizing radicals based on MICs.
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