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Trans-N-alkylation Covalent Exchanges on 1,3,4-
Trisubstituted 1,2,3-Triazolium Iodides
Rania Akacha,[a, b] Imen Abdelhedi-Miladi,[b] Damien Montarnal,[c] Hatem Ben Romdhane,*[b]
and Eric Drockenmuller*[a]
1,3,4-Trisubstituted 1,2,3-triazolium salts having either aliphatic
or benzylic substituents at the N-1 and N-3 positions were
synthesized in two steps involving: i) copper(I) catalyzed azide-
alkyne 1,3-dipolar cycloaddition (CuAAC), and ii) N-alkylation of
the 1,2,3-triazole intermediates. Trans-N-alkylation reactions in
bulk and in the presence of excess methyl iodide were
monitored by 1H NMR spectroscopy for each 1,2,3-triazolium
molecular model. By assigning the different formed species and
their respective evolution with time, it was possible to conclude
that trans-N-alkylation exchange reactions are significantly
faster for benzylic substituents than for aliphatic ones. Further-
more, the exchange reactions are noticeably faster at the N-3
position than at the N-1 position most likely due to the steric
hindrance induced by the neighboring C-4 substituent. The
kinetics of trans-N-alkylation reactions are thus influenced by
both the chemical nature of the N-1 and N-3 substituents and
the regiochemistry of the 1,2,3-triazolium group. This provides
important structural design rules to improve the properties of
thermosetting covalent adaptable networks involving trans-N-
alkylation of 1,2,3-triazolium salts.
Introduction
Ever since its introduction in 2001 the concept of click
chemistry that gathers robust, efficient and orthogonal (REO)
chemical transformations has revolutionized the fields of
synthetic chemistry, biology, materials science, and beyond.[1]
The copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) that
yields 1,4-disubstituted 1,2,3-triazoles,[2,3] is the most wide-
spread illustration of the click chemistry concept and has been
widely applied to the field of macromolecular engineering for
the synthesis and functionalization of (co)polymers with diverse
functionality and architecture.[4–10] However, the exploitation of
the inherent properties of 1,2,3-triazoles beyond the concept of
REO ligation has only been scarcely addressed. Most relevant
examples include the use of 1,2,3-triazoles in metal chelating
systems[11] or metallopolymers.[12] Meanwhile, the synthesis of
1,3,4-trisubstituted 1,2,3-triazolium salts by N-alkylation of the
N-3 position of 1,4-disubstituted 1,2,3-triazoles has provided a
broad library of task-specific 1,2,3-triazolium ionic liquids (TILs)
with highly tunable chemical and physical properties.[13–15] TILs
have been valuably applied as ligands of metal complexes,[16]
chemosensors for anion recognition,[17,18] organocatalysts,[19,20]
electrolytes for dye sensitized solar cells,[21] or therapeutics.[22,23]
The combination of CuAAC and quantitative N-alkylation of
1,2,3-triazole groups with diverse polymerization or post-
polymerization chemical modification approaches has paved
the way for the development of 1,2,3-triazolium-based
poly(ionic liquid)s, as a recent class of polymer electrolytes with
enhanced ion conducting properties.[24–27] Moreover, polymer
networks including 1,2,3-triazolium cross-links featuring all
attributes of covalent adaptable networks (CANs) were
reported.[28] CANs are usually divided into two categories:
i) associative CANs where an intermediate state with higher
connectivity provides constant cross-link density during flow
through network rearrangement at high temperature and,
ii) dissociative CANs where a decrease in cross-link density with
increasing temperature is observed.[29–34] 1,2,3-Triazolium-based
CANs (TCANs) undergo network topology reshuffling through a
two-step dissociative trans-N-alkylation covalent exchange:
i) cleavage of a 1,2,3-triazolium cross-link by de-N-alkylation
reaction involving a nucleophilic attack of the counter-anion on
the N-1 or N-3 methylene group and, ii) reformation of a 1,2,3-
triazolium cross-link by re-N-alkylation reaction between a 1,2,3-
triazole group and a dangling chain bearing an alkylating group
(e.g. halide, mesyl).[35,36] Although relying on a dissociative trans-
N-alkylation mechanism,[36] TCANs display a temperature de-
pendence of the cross-link density typical of associative CANs
(a.k.a. vitrimers).[37] As a consequence, TCANs exhibit weldability,
reprocessability and recyclability features.
TCANs based on aliphatic,[36] benzylic,[38] polyether,[39] or
perfluoroether,[40] segments have been obtained by catalyst-
and solvent-free azide-alkyne cycloaddition step growth poly-
merization and concomitant cross-linking of the resulting non-
regioisomeric poly(1,2,3-triazole) chains by N-alkylation using
[a] R. Akacha, Prof. E. Drockenmuller
Université Claude Bernard Lyon 1
Ingénierie des Matériaux Polymères, UMR CNRS 5223
F-69622, Villeurbanne (France)
E-mail: eric.drockenmuller@univ-lyon1.fr
[b] R. Akacha, Dr. I. Abdelhedi-Miladi, Prof. H. Ben Romdhane
Laboratoire de Chimie (Bio)Organique Structurale et de Polymères: Synthèse
et Études Physicochimiques (LR99ES14)
Université de Tunis El Manar, Faculté des Sciences de Tunis
2092, El Manar (Tunisie)
E-mail: hatem.benromdhane@fst.utm.tn
[c] Dr. D. Montarnal
Université Claude Bernard Lyon 1
Catalyse, Polymérisation, Procédés et Matériaux, UMR CNRS 5128
F-69622, Villeurbanne (France)
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/ejoc.202300587
Wiley VCH Montag, 13.11.2023
2343 / 324091 [S. 51/57] 1
Eur. J. Org. Chem. 2023,26, e202300587 (1 of 7) © 2023 Wiley-VCH GmbH
www.eurjoc.org
Research Article
doi.org/10.1002/ejoc.202300587
