N‐Heterocyclic Imine‐Supported Bimetallic Cu(II) Catalyst for Azide‐Alkyne Cycloaddition: Solvent‐free, Reductant‐free, ppm‐level Catalysis to Access 1,4‐Disubstituted Triazoles

Abstract

In this article, we present a unique bimetallic paddle wheel copper(II) complex with the molecular formula [Cu 2 C 42 H 54 N 6 O 8 ]. Several characterization tools have been employed to analyze this complex including single-crystal Xray diffraction, HRMS, FTIR, and UV-vis spectroscopy. This copper(II) complex excels admirably as a catalytic system in parts-per-million level (ppm) loading for the azide-alkyne 'click' reaction under solvent-free conditions, allowing for the quantitative conversion of numerous 1,4-disubstituted 1,2,3triazole. The specially designed coordinated ligand (perimidin-2-imine) in the Cu(II) complex accelerates the reaction rate significantly during the oxidative homocoupling reaction (OHC) and acts as a base for Cu-coordinated alkyne deprotonation. It has been demonstrated that the catalyst loading of 2.5 ppm is adequate to catalyze the cycloaddition of benzyl azide to phenylacetylene, leading to the extremely high turnover number of 120000 and a turnover frequency of 5000 h À 1 . Synergistic evidence from stoichiometric reactions and experimental results provides insights into the plausible mechanism for the reaction. Each copper atom contributes to the outcome of the proposed reaction, one by bonding to the acetylide and the other by activating the azide as part of a bimetallic synergistic pathway.

Application of Functionalized Zn-Based Metal–Organic Frameworks (Zn-MOFs) with CuO in Heterocycle Synthesis via Azide–Alkyne Cycloaddition

“…Despite extensive research and the development of various strategies, only a few sustainable and economical approaches have been reported for synthesizing complex chemical structures. Click chemistry, particularly the copper-catalyzed alkyne–azide cycloaddition (CuAAC) reaction, has emerged as a suitable method for the architecture and synthesis of pharmaceutical and biological compounds. − The term “click” refers to the facile joining of molecular building blocks through rapid reactions that provide high product yields, are versatile, simple to use, and easy to purify. − This reaction has found wide applications in diverse scientific disciplines, including pharmaceuticals, polymer chemistry, and materials science. − The CuAAC click reaction is an effective and attractive tool for the 1,3-dipolar cycloaddition of azides and terminal alkynes, leading to the formation of macro-1,4-disubstituted-1,2,3-triazole derivatives in the presence of copper-containing catalysts. − …”

Structural Characterization, DFT Analysis and Catalysis by Highly Active Cationic Fe(II)‐Cu(I) Complexes in the Green Synthesis of Triazoles in Water

“…Since first report of Copper(I)‐catalyzed Azide‐Alkyne Cycloaddition (CuAAC) by Meldal and Sharpless in 2002, variety of copper(I) complexes have been introduced [38,39] . Bimetallic complexes have been reported as excellent homogeneous or heterogeneous catalysts in the azide‐alkyne cycloaddition reactions [40–47] . However, a quick literature survey about Cu(I) complexes reported so far reveals that well defined heteroleptic complexes of Fe(II)‐Cu(I) in an S2P2 environment are rare.…”

N-Heterocyclic imino-catalyzed 1,4-regioselective azide–alkyne cycloaddition (AAC): a metal-free approach

“…The perimidin-2-imine coordinated apically to Cu( ii ), serves as a base when needed, thereby expediting the oxidative homo coupling (OHC) step in triazole synthesis. 12 The perimidin-2-imine, a preeminent clan of N-heterocyclic imine/imino (NHI), is an N-heterocyclic carbene (NHC) adduct of nitrogen, featuring an array of NHC-nitrogen derivatives [(NHC)NR]. These derivatives constitute cyclic guanidine derivatives, HN(NH 2 ) 2 , and may be explicitly (!)…”