Copper and Silver Complexes of Tris(triazole)amine and Tris(benzimidazole)amine Ligands: Evidence that Catalysis of an Azide–Alkyne Cycloaddition (“Click”) Reaction by a Silver Tris(triazole)amine Complex Arises from Copper Impurities

Design, Synthesis, and Characterization of Novel Coordination Compounds of Benzimidazole Derivatives with Cadmium

Four complexes of Cd(II) with benzimidazole derivatives were synthesized and named C1, C2, C3, and C4. All coordination compounds were characterized through elemental analysis (EA), flame atomic absorption spectrometry (FAAS), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis coupled with mass spectrometry) (TG-MS), a cytotoxicity assay (MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide)), and computational chemical analysis for absorption, distribution, metabolism, and excretion (ADME). All of the obtained results are compatible and are consistent with the respective structures of the obtained compounds and their properties. The various techniques used allowed the determination of the composition, proposed structure of the compounds, their thermal stability and thermal properties, and the method of coordination between the metal (II) ion and the ligand. The ADME technique was also used to estimate the physicochemical and biological properties. The antitumor activity of the compounds was determined with an MTT assay on the glioblastoma (T98G), neuroblastoma (SK-N-AS), and lung adenocarcinoma (A549) cell lines, as well as normal human skin fibroblasts (CCD-1059Sk). Compound C2 was found to have potential antitumor properties and to be effective in inhibiting the growth of neuroblastoma cells. The antimicrobial activity of Cd complexes, free ligands, and reference drugs was tested against six strains of Gram-positive bacteria, five strains of Gram-negative rods, and three strains of yeasts. Compound C3 significantly increased activity against Gram-positive bacteria in comparison to the ligand.

Alkynylated and Dendronized 5-Aza-7-deazaguanine Nucleosides: Cross-Coupling with Tripropargylamine and Linear Alkynes, Click Functionalization, and Fluorescence of Pyrene Adducts†

The change of the recognition face of 5-aza-7-deazaguanine bridgehead nucleosides with respect to purine nucleosides permits the construction of new purine-purine or purine-pyrimidine base pairs in DNA and RNA. Clickable derivatives of 5-aza-7-deazaguanine were synthesized by introducing ethynyl, 1,7-octadiynyl, and tripropargylamino side chains in the 7-position of the 5-aza-7-deazapurine moiety by Sonogashira cross-coupling. Click reactions were performed with 1-azidomethylpyrene by the copper-catalyzed azide-alkyne cycloaddition. The copper(I)-catalyzed click reaction on the tripropargylamino nucleoside was significantly faster and higher yielding than that for nucleosides carrying linear alkynyl chains. Also, this reaction could be performed with copper(II) as the catalyst. An autocatalyzed cycle was suggested in which the click product acts as a catalyst. Pyrene click adducts of linear alkynylated nucleosides showed pyrene monomer emission, while tripropargylamino adducts showed monomer and excimer fluorescence. The fluorescence intensities of the 5-aza-7-deazaguanine nucleosides were higher than those of their 7-deazaguanine counterparts. The reported clickable nucleosides can be utilized to functionalize or to cross-link monomeric nucleosides or DNA for diagnostic or imaging purposes and other applications in nucleic acid chemistry and biotechnology.

Crystallization Induced Enhanced Emission in Two New Zn(II) and Cd(II) Supramolecular Coordination Complexes with the 1-(3,4-Dimethylphenyl)-5-Methyl-1H-1,2,3-Triazole-4-Carboxylate Ligand

Two new d¹⁰ metal supramolecular metal-organic frameworks (SMOFs) with general formula [ML₂(H₂O)₂]_n (M = Zn, Cd) have been synthetized using the sodium salt of the anionic 1-(3,4-dimethylphenyl)-5-methyl-1H-1,2,3-triazole-4-carboxylate ligand (Na⁺L^-). Both SMOFs have been structurally characterized by single-crystal X-ray diffraction analysis and IR spectroscopy. The compounds are isostructural and form supramolecular aggregates via hydrogen bonds with the presence of less common dihydrogen bonds. Interestingly, they show ionic conductivity and porosity. The luminescent properties have been also studied by means of the excitation and emission spectra. Periodic DFT and molecular TD-DFT calculations have been used to unravel the emergence of luminescence in the otherwise non-emitting 1-(3,4-dimethylphenyl)-5-methyl-1H-1,2,3-triazole-4-carboxylate ligand once incorporated in the SMOFs. Our results also illustrate the importance of considering the dielectric environment in the crystal when performing excited state calculations for isolated fragments to capture the correct electronic character of the low-lying states, a practice which is not commonly adopted in the community.

Towards molecular electronic devices based on 'all-carbon' wires

Nascent molecular electronic devices based on linear 'all-carbon' wires attached to gold electrodes through robust and reliable C-Au contacts are prepared via efficient in situ sequential cleavage of trimethylsilyl end groups from an oligoyne, Me₃Si-(C[triple bond, length as m-dash]C)₄-SiMe₃ (1). In the first stage of the fabrication process, removal of one trimethylsilyl (TMS) group in the presence of a gold substrate, which ultimately serves as the bottom electrode, using a stoichiometric fluoride-driven process gives a highly-ordered monolayer, Au|C[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CSiMe₃ (Au|C₈SiMe₃). In the second stage, treatment of Au|C₈SiMe₃ with excess fluoride results in removal of the remaining TMS protecting group to give a modified monolayer Au|C[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CC[triple bond, length as m-dash]CH (Au|C₈H). The reactive terminal C[triple bond, length as m-dash]C-H moiety in Au|C₈H can be modified by 'click' reactions with (azidomethyl)ferrocene (N₃CH₂Fc) to introduce a redox probe, to give Au|C₆C₂N₃HCH₂Fc. Alternatively, incubation of the modified gold substrate supported monolayer Au|C₈H in a solution of gold nanoparticles (GNPs), results in covalent attachment of GNPs on top of the film via a second alkynyl carbon-Au σ-bond, to give structures Au|C₈|GNP in which the monolayer of linear, 'all-carbon' C₈ chains is sandwiched between two macroscopic gold contacts. The covalent carbon-surface bond as well as the covalent attachment of the metal particles to the monolayer by cleavage of the alkyne C-H bond is confirmed by surface-enhanced Raman scattering (SERS). The integrity of the carbon chain in both Au|C₆C₂N₃HCH₂Fc systems and after formation of the gold top-contact electrode in Au|C₈|GNP is demonstrated through electrochemical methods. The electrical properties of these nascent metal-monolayer-metal devices Au|C₈|GNP featuring 'all-carbon' molecular wires were characterised by sigmoidal I-V curves, indicative of well-behaved junctions free of short circuits.

A mineralogically-inspired silver–bismuth hybrid material: an efficient heterogeneous catalyst for the direct synthesis of nitriles from terminal alkynes

A silver-containing hybrid material is reported as an effective heterogeneous catalyst for the direct synthesis of organic nitriles from terminal alkynes.

Silver-catalysed azide-alkyne cycloaddition (AgAAC): assessing the mechanism by density functional theory calculations

'Click reactions' are the copper catalysed dipolar cycloaddition reaction of azides and alkynes to incorporate nitrogens into a cyclic hydrocarbon scaffold forming a triazole ring. Owing to its efficiency and versatility, this reaction and the products, triazole-containing heterocycles, have immense importance in medicinal chemistry. Copper is the only known catalyst to carry out this reaction, the mechanism of which remains unclear. We report here that the 'click reactions' can also be catalysed by silver halides in non-aqueous medium. It constitutes an alternative to the well-known CuAAC click reaction. The yield of the reaction varies on the type of counter ion present in the silver salt. This reaction exhibits significant features, such as high regioselectivity, mild reaction conditions, easy availability of substrates and reasonably good yields. In this communication, the findings of a new catalyst along with the effect of solvent and counter ions will help to decipher the still obscure mechanism of this important reaction.

Ag-catalyzed azide alkyne cycloaddition: a DFT approach

In this study, the mechanism of AgAAC reaction has been studied by quantum mechanical calculations to gain insights into this promising reaction and the first successful application of a Ag catalyst alone in AAC.

Structural snapshots in the copper(ii) induced azide–nitrile cycloaddition: effects of peripheral ligand substituents on the formation of unsupported μ1,1-azido vs. μ1,4-tetrazolato bridged complexes

Peripheral substituents on click-derived tripodal ligands dictate the reactivity of their copper(ii) azido complexes.

Exploring potential cooperative effects in dicopper(i)-di-mesoionic carbene complexes: applications in click catalysis

Dicopper(i) dimesoionic carbene complexes are active catalysts for the azide–alkyne cycloaddition reaction and are more active than their mononuclear counterparts.

The ligand field of the azido ligand: insights into bonding parameters and magnetic anisotropy in a Co(II)-azido complex

The azido ligand is one of the most investigated ligands in magnetochemistry. Despite its importance, not much is known about the ligand field of the azido ligand and its influence on magnetic anisotropy. Here we present the electronic structure of a novel five-coordinate Co(II)-azido complex (1), which has been characterized experimentally (magnetically and by electronic d-d absorption spectroscopy) and theoretically (by means of multireference electronic structure methods). Static and dynamic magnetic data on 1 have been collected, and the latter demonstrate slow relaxation of the magnetization in an applied external magnetic field of H = 3000 Oe. The zero-field splitting parameters deduced from static susceptibility and magnetizations (D = -10.7 cm(-1), E/D = 0.22) are in excellent agreement with the value of D inferred from an Arrhenius plot of the magnetic relaxation time versus the temperature. Application of the so-called N-electron valence second-order perturbation theory (NEVPT2) resulted in excellent agreement between experimental and computed energies of low-lying d-d transitions. Calculations were performed on 1 and a related four-coordinate Co(II)-azido complex lacking a fifth axial ligand (2). On the basis of these results and contrary to previous suggestions, the N3(-) ligand is shown to behave as a strong σ and π donor. Magnetostructural correlations show a strong increase in the negative D with increasing Lewis basicity (shortening of the Co-N bond distances) of the axial ligand on the N3(-) site. The effect on the change in sign of D in going from four-coordinate Co(II) (positive D) to five-coordinate Co(II) (negative D) is discussed in the light of the bonding scheme derived from ligand field analysis of the ab initio results.