Revisiting the Reaction of IPr with Tritylium: An Alternative Mechanistic Pathway

Despite a recent proposal on the mechanism of a single‐electron transfer (SET) process between tritylium and 2,6‐bis(diisopropylphenyl)imidazol‐2‐ylidene (IPr) based on evidence of transient IPr radical cation intermediate ([IPr]⋅+) formation, such oxidation is still contentious because of the high...

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Bibliographic Details
Published in:Chemistry : a European journal 2023-02, Vol.29 (12), p.e202203364-n/a
Main Authors: Song, Hayoung, Lee, Eunsung
Format: Article
Language:English
Subjects:
Cations
Chemistry
Electron transfer
Oxidants
Oxidation
Oxidizing agents
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Summary:Despite a recent proposal on the mechanism of a single‐electron transfer (SET) process between tritylium and 2,6‐bis(diisopropylphenyl)imidazol‐2‐ylidene (IPr) based on evidence of transient IPr radical cation intermediate ([IPr]⋅+) formation, such oxidation is still contentious because of the high oxidation potential of N‐heterocyclic carbenes. Our experimental analysis indicates that the appearance of deep purple color, previously considered to be from transient [IPr]⋅+, originates from a zwitterionic intermediate (3 a), not a radical cation. Here, we propose an alternative mechanism for the reaction involving tritylium and IPr. This mechanism is noteworthy for explaining how [NHC−H]+ can be generated without the formation of transient [NHC]⋅+, which has been frequently proposed as an intermediate for the reaction between NHC and oxidants. These results also show that a transient strong single‐electron donor (3 a) could be generated by the alternative mechanism for oxidants using NHCs, which is a more feasible explanation for the reactivity of NHCs with oxidants. Despite the high ionization energy of imidazol‐2‐ylidene, the reactions of N‐heterocyclic carbenes (NHCs) with oxidants have been postulated to occur via a transient NHC radical cation intermediate. Herein, we propose the alternative mechanism to explain the outcome of the tritylium reaction with IPr without the intermediacy of unstable [IPr]⋅+.
ISSN:0947-6539
1521-3765
DOI:10.1002/chem.202203364