We found a match
Your institution may have access to this item. Find your institution then sign in to continue.
- Title
Triazolium Salt Organocatalysis: Mechanistic Evaluation of Unusual Ortho -Substituent Effects on Deprotonation.
- Authors
Quinn, Peter; Smith, Matthew S.; Zhu, Jiayun; Hodgson, David R. W.; O'Donoghue, AnnMarie C.
- Abstract
Organocatalysis by N-heterocyclic carbenes is normally initiated by the deprotonation of precursor azolium ions to form active nucleophilic species. Substituent effects on deprotonation have an impact on catalytic efficiency and provide insight into general catalytic mechanisms by commonly used azolium systems. Using an NMR kinetic method for the analysis of C(3)-H/D exchange, we determined log kex–pD profiles for three ortho-substituted N-aryl triazolium salts, which enables a detailed analysis of ortho-substituent effects on deprotonation. This includes N-5-methoxypyrid-2-yl triazolium salt 7 and di-ortho-methoxy and di-ortho-isopropoxyphenyl triazolium salts 8 and 9, and we acquired additional kinetic data to supplement our previously published analysis of N-pyrid-2-yl triazolium salt 6. For 2-pyridyl triazoliums 6 and 7, novel acid catalysis of C(3)-H/D exchange is observed under acidic conditions. These kinetic data were supplemented by DFT analyses of the conformational preferences of 6 upon N-protonation. A C(3) deprotonation mechanism involving intramolecular general base deprotonation by the pyridyl nitrogen of the N(1)-deuterated dicationic triazolium salt is most consistent with the data. We also report kDO values (protofugalities) for deuteroxide-catalyzed exchange for 6–9. The protofugalities for 8 and 9 are the lowest values to date in the N-aryl triazolium series.
- Subjects
PROTON transfer reactions; ORGANOCATALYSIS; SALT; SALTS; CATALYSIS
- Publication
Catalysts (2073-4344), 2021, Vol 11, Issue 9, p1055
- ISSN
2073-4344
- Publication type
Article
- DOI
10.3390/catal11091055