Copper(ii)-benzotriazole coordination compounds in click chemistry: a diagnostic reactivity study

Abstract

This diagnostic study aims to shed light on the catalytic activity of a library of Cu(ii) based coordination compounds with benzotriazole-based ligands. We report herein the synthesis and characterization of five new coordination compounds formulated as [Cu(L)(MeCN)(CFSO)] (1), [Cu(L)(CFSO)] (2), [Cu(L)(MeCN)(CFSO)]·(CFSO) (3), [Cu(L)(HO)(CFSO)]·(CFSO)·2(MeCO) (4), and [Cu(L)(L)(CFSO)]·4(CFSO)·8(MeCO) (5), derived from similar nitrogen-based ligands. The homogeneous catalytic activity of these compounds along with our previously reported coordination compounds (6-13), derived from similar ligands, is tested against the well-known Cu(i)-catalysed azide-alkyne cycloaddition reaction. The optimal catalyst [Cu(L)(CFSO)] (10) activates the reaction to afford 1,4-disubstituted 1,2,3-triazoles with yields up to 98% and without requiring a reducing agent. Various control experiments are performed to optimize the method and examine parameters such as ligand variation, metal coordination geometry and environment, in order to elucidate the behaviour of the catalytic system.

Facile Synthesis of 1,4‐Disubstituted 1,2,3‐Triazoles Using Tetraaza‐coordinated Copper(II) Complexes as Efficient Catalysts

“…Kostakis et. al., have proved the semi‐rigid ligand framework of benzotriazole complex with Cu(II) ions used for CuAAC reaction and isolated yield of 98 %. The Cu(I) complexes of triazoles and imidazoles were also performed for 1,3‐dipolar cycloaddition (Cu I AAC) reactions by Fukuzawa et al .…”

Recent advances in the coordination chemistry of benzotriazole-based ligands

“…Furthermore, the azidealkyne cycloaddition reaction was activated by 178 through a protocol which employs either organic halides or phenylboronic acid as starting materials, along with sodium azide to generate the organic azides in situ and avoid the isolation of potentially unstable intermediates (Scheme 10, reaction D). Up to 99% yields of the resulting triazoles were afforded when the reaction mixture was stirred in EtOH for 24 hrs, under reflux and 5 mol% of catalyst; importantly, the presence of a reducing agent was not required under these conditions [155]. It is also worth noting that 178 exhibited superior catalytic activity and efficiency compared to Cu II salts in all of the above reactions.…”

“…A diagnostic copper hydride signal was also observed in solid-state infrared spectroscopy studies, further supporting these findings. In a subsequent article, the authors reported [125] the synthesis of an analogous 0D complex based on gold sources, formulated as [Au I (pbta)(PPh3)]•(CF3SO3) (155). In a similar fashion, 155 was found to be an ideal catalytic precursor in borrowing hydrogen and dehydrogenation reactions of alcohols and amines, resulting in the selective synthesis of substituted amines and ketones as detailed in Scheme 7.…”

“…In particular, our studies were focused on already known organic transformations of significant importance, in which the proposed mechanism involved intermediates related to the suggested catalytic function of our system. Our selected reactions for these purposes, as shown in a number of subsequent reports [153][154][155], were (i) the multicomponent reaction (MCR) known as A 3 coupling of an aldehyde, an amine and an alkyne: this reaction yields propargylamines, which are important synthetic blocks towards N-containing biologically active compounds; (ii) the multicomponent synthesis of poly-substituted pyrroles from aldehydes, amines, and βnitroalkenes, (iii) the azide-alkyne cycloaddition ("click" reaction), which affords 1,4disubstituted 1,2,3-triazoles and requires the generation of Cu I species in the reaction medium.…”

Discrete Benzotriazole‐Copper(II) Complexes in Chelated and Non‐Chelated Coordination Modes: Structural Analysis and Catalytic Application in Click and A3 Coupling Reactions

“…[1] The N-donor ligands possessing modular electronic and steric properties are particularly suitable in stabilizing such variable oxidation states of Cu, thus justifying their immense significance in efficient operation of the relevant catalytic cycles. Among several N-donor heterocyclic ligands, benzotriazole-based motifs, [2,3,4,5] owing to some excellent attributes such as inexpensive, simple, stable, and ready accessibility, have been well-explored as suitable auxiliary ligands in various Cu-catalyzed organic syntheses. In addition to exhibiting very good σ-donor property, these nitrogen-enriched benzotriazole ligands also act as excellent π-acceptors, and thus they are able to stabilize low-valent Cu(I) intermediates which are key to several catalytic reactions.…”