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Copper(II)-Bis-Cyclen Intercalated Graphene Oxide as an Efficient Two-Dimensional Nanocomposite Material for Copper-Catalyzed Azide-Alkyne Cycloaddition Reaction.

ABSTRACT: We report stable and heterogeneous graphene oxide (GO)-intercalated copper as an efficient catalyst for the organic transformations in green solvents. The GO-intercalated copper(II) complex of bis(1,4,7,10-tetraazacyclododecane) [Cu(II)-bis-cyclen] was prepared by a facile synthetic approach with a high dilution technique. The as-prepared GO-Cu(II)-bis-cyclen nanocomposite was used as a click catalyst for the 1,3 dipolar Huisgen cycloaddition reaction of terminal alkyne and azide substrates. On directing a great deal of attention toward the feasibility of the rapid electron transfer rate of the catalyst in proliferating the yield of 1,2,3-triazole products, the click catalyst GO-Cu(II)-bis-cyclen nanocomposite was designed and synthesized via non-covalent functionalization. The presence of a higher coordination site in an efficient 2D nanocomposite promotes the stabilization of Cu(I) L-acetylide intermediate during the catalytic cycle initiated by the addition of reductants. From the XRD analysis, the enhancement in the d-interlayer spacing of 1.04 nm was observed due to the intercalation of the Cu(II)-bis-cyclen complex in between the GO basal planes. It was also characterized by XPS, FT-IR, RAMAN, UV, SEM, AFM, and TGA techniques. The recyclability of the heterogeneous catalyst [GO-Cu(II)-cyclen] with the solvent effect has also been studied. This class of GO-Cu(II)-bis-cyclen nanocomposite paves the way for bioconjugation of macromolecules through the click chemistry approach.

SUBMITTER: Samuel AG

PROVIDER: S-EPMC8782203 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:We described in a previous communication a variant of the popular Cu(I)-catalyzed azide-alkyne cycloaddition (AAC) process where 5 mol % of Cu(OAc)(2) in the absence of any added reducing agent is sufficient to enable the reaction. 2-Picolylazide (1) and 2-azidomethylquinoline (2) were found to be by far the most reactive carbon azide substrates that convert to 1,2,3-triazoles in as short as a few minutes under the discovered conditions. We hypothesized that the abilities of 1 and 2 to chelate Cu(II) contribute significantly to the observed high reaction rates. The current work examines the effect of auxiliary ligands near the azido group other than pyridyl for Cu(II) on the efficiency of the Cu(OAc)(2)-accelerated AAC reaction. The carbon azides capable of binding to the catalytic copper center at the alkylated azido nitrogen in a chelatable fashion were indeed shown to be superior substrates under the reported conditions. The chelation between carbon azide 11 and Cu(II) was demonstrated in an X-ray single-crystal structure. In a limited set of examples, the ligand tris(benzyltriazolylmethyl)amine (TBTA), developed by Fokin et al. for assisting the original Cu(I)-catalyzed AAC reactions, also dramatically enhances the Cu(OAc)(2)-accelerated AAC reactions involving nonchelating azides. This observation leads to the hypothesis of an additional effect of chelating azides on the efficiencies of Cu(OAc)(2)-accelerated AAC reactions, which is to facilitate the rapid reduction of Cu(II) to highly catalytic Cu(I) species. Mechanistic studies on the AAC reactions with particular emphasis on the role of carbon azide/copper interactions will be conducted based on the observations reported in this work. Finally, the immediate utility of the product 1,2,3-triazole molecules derived from chelating azides as multidentate metal coordination ligands is demonstrated. The resulting triazolyl-containing ligands are expected to bind with transition metal ions via the N(2) nitrogen of the 1,2,3-triazolyl group to form nonplanar coordination rings. The Cu(II) complexes of bidentate T1 and tetradentate T6 and the Zn(II) complex of T6 were characterized by X-ray crystallography. The structure of [Cu(T1)(2)(H(2)O)(2)](ClO(4))(2) reveals the interesting synergistic effect of hydrogen bonding, π-π stacking interactions, and metal coordination in forming a one-dimensional supramolecular construct in the solid state. The tetradentate coordination mode of T6 may be incorporated into designs of new molecule sensors and organometallic catalysts.

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Copper(II)-Bis-Cyclen Intercalated Graphene Oxide as an Efficient Two-Dimensional Nanocomposite Material for Copper-Catalyzed Azide-Alkyne Cycloaddition Reaction.

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