Abstract
The reaction of copper(II) acetate with the 2-aminobenzothiazole (abt) heterocycle affords the new copper(II) complex of formula [Cu(abt)2(OOCCH3)2] (1) in a straightforward manner. Compound 1 served as a precatalyst for azide/alkyne cycloaddition reactions (CuAAC) in water, leading to 1,4-disubstituted-1,2,3-triazole derivatives in a regioselective manner and with excellent yields at room temperature. The main advantages of the coordination of such a heterocyclic ligand in 1 are its strong σ-donating ability (N-Cu), nontoxicity and biological properties. In addition, the click chemistry reaction conditions using 1 allow the formation of a great variety of 1,2,3-triazole-based heterocyclic compounds that make this protocol potentially relevant from biological and sustainable viewpoints. A molecular electron density theory (MEDT) study was performed by using density functional theory (DFT) calculations at the B3LYP/6-31G(d,p) (LANL2DZ for Cu) level to understand the observed regioselectivity in the CuAAC reaction. The intramolecular nature of this reaction accounts for the regioselective formation of the 1,4-regioisomeric triazole derivatives. The ionic nature of the starting copper-acetylide precludes any type of covalent interaction throughout the reaction, as supported by the electron localization function (ELF) topological analysis, reaffirming the zwitterionic-type (zw-type) mechanism of the copper(I)/aminobenzothiazole-catalysed azide-alkyne cycloaddition reactions.
Highlights
Triazole-containing heterocycles have found many applications in several disciplines, such as medicine, biology and materials science [1]
The two V(N1,N2) and V(N2,N3) disynaptic basins in the azide framework have decreased to less than e and the V(N2) monosynaptic basins integrates 3.34 e. All these results show that the ionic nature of all chemical intermediates rules out any covalent interaction involving the copper(I)-complexes, as supported by the electron localization function (ELF) topological analysis, reaffirming the zw-type mechanism of the Cu(I)-abt complex catalyzed azide-alkyne cycloaddition (AAC) reactions
The reactions were monitored by thin-layer chromatography (TLC) carried out on commercial glass-backed TLC plates
Summary
Triazole-containing heterocycles have found many applications in several disciplines, such as medicine, biology and materials science [1]. These compounds are prepared through azide-alkyne cycloaddition (AAC) reactions [2,3]. The discovery by the groups of Meldal [6] and Sharpless [7] that copper(I) is capable of accelerating the 32CA reaction of azides and alkynes with high regioselectivity, to afford the 1,4-disubstituted 1,2,3-triazole isomer under mild conditions, led to a breakthrough of such. Catalysts 2020, 10, 776 disubstituted 1,2,3-triazole isomer under mild conditions, led to a breakthrough of such a acycloaddition cycloadditionprocess. Thermodynamic instability of copper(I), as well as its oxidation to copper(II), have led led to the the thermodynamic instability of copper(I), as well as easy its easy oxidation to copper(II), have to search for suitable stabilizing ligands for Cu(I)
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