Abstract
A combined experimental study and molecular electron density theory (MEDT) analysis was carried out to investigate the click of 1,2,3-triazole derivatives by Ag(I)-catalyzed azide-alkyne cycloaddition (AgAAC) reaction as well as its corresponding mechanistic pathway. Such a synthetic protocol leads to the regioselective formation of 1,4-disubstituted-1,2,3-triazoles in the presence of AgCl as catalyst and water as reaction solvent at room temperature and pressure. The MEDT was performed by applying Density Functional Theory (DFT) calculations at both B3LYP/6-31G(d,p) (LANL2DZ for Ag) and ωB97XD/6-311G(d,p) (LANL2DZ for Ag) levels with a view to decipher the observed regioselectivity in AgAAC reactions, and so to set out the number of silver(I) species and their roles in the formation of 1,4-disubstituted-1,2,3-triazoles. The comparison of the values of the energy barriers for the mono- and dinuclear Ag(I)-acetylide in the AgAAC reaction paths shows that the calculated energy barriers of dinuclear processes are smaller than those of the mononuclear one. The type of intramolecular interactions in the investigated AgAAC click chemistry reaction accounts for the regioselective formation of the 1,4-regiosisomeric triazole isomer. The ionic character of the starting compounds, namely Ag-acetylide, is revealed for the first time. This finding rules out any type of covalent interaction, involving the silver(I) complexes, along the reaction pathway. Electron localization function (ELF) topological analysis of the electronic structure of the stationary points reaffirmed the zw-type (zwitterionic-type) mechanism of the AgAAC reactions.
Highlights
Dedicated by one of us S.-E.S. to his beloved mom Aicha Lakani, who passed away on 24 October 2019
The reaction of benzyl azide (1a) and phenylacetylene (2a) was initially chosen as a reaction of our study (Scheme 1). The result for this 32CA reaction proved that the 1,4-isomer model of our study (Scheme 1). The result for this 32CA reaction proved that the 1,41,2,3-triazole (3a) was formed in high yield (92%) within 24 h with 10 mol% of the AgCl catalyst in the isomer 1,2,3-triazole (3a) was formed in high yield (92%) within 24 h with 10 mol% of the AgCl dark under ambient conditions, using water as solvent
The present Ag(I)-catalyzed azide-alkyne cycloaddition (AgAAC) protocol involves a fast click of 1,4-disubstituted-1,2,3-triazoles by using AgCl in water and working at room temperature. 1,4-disubstituted-1,2,3-triazoles are obtained in good yields and are isolated from the reaction mixture without the need for further purification methods
Summary
Dedicated by one of us S.-E.S. to his beloved mom Aicha Lakani, who passed away on 24 October 2019. A combined experimental study and molecular electron density theory (MEDT) analysis was carried out to investigate the click of 1,2,3-triazole derivatives by Ag(I)-catalyzed azide-alkyne cycloaddition (AgAAC) reaction as well as its corresponding mechanistic pathway. Such a synthetic protocol leads to the regioselective formation of 1,4-disubstituted-1,2,3-triazoles in the presence of. The type of intramolecular interactions in the investigated AgAAC click chemistry reaction accounts for the regioselective formation of the 1,4-regiosisomeric triazole isomer. The ionic character of the starting compounds, namely Ag-acetylide, is revealed for the first time This finding rules out any type of covalent interaction, involving the silver(I) complexes, along the reaction pathway. Electron localization function (ELF) topological analysis of the electronic structure of the stationary points reaffirmed the zw-type (zwitterionic-type) mechanism of the AgAAC reactions
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