Triazole Ligands Research Articles

ChemInform Abstract: Palladium(II) Complexes Featuring Bidentate Pyridine—Triazole Ligands: Synthesis, Structures, and Catalytic Activities for Suzuki—Miyaura Coupling Reactions.

AbstractThree new palladium catalysts bearing a triazole and a pyridine moiety are synthesized and characterized.

Syntheses, Structures, and Photoluminescence of Two Three‐dimensional Cadmium Coordination Polymers with Benzene­dicarboxylate Ligands

AbstractTwo cadmium(II) coordination polymers, namely, [Cd3(m‐phth)2(atz)2]n (1) (m‐phth = m‐phthalate and atz = 3‐amino‐1,2,4‐triazolate) and [Cd(atphth)(H2O)]n (2) (atphth = 2‐aminoterephthalate), were synthesized and structurally characterized. Compound 1 features a three‐dimensional (3D) pillared framework based on two‐dimensional (2D) cadmium‐benzenedicarboxylate ladders pillared by the triazolate ligands. Compound 2 has a 3D framework constructed from 2D cadmium‐benzenedicarboxylate layers, which are further linked by Cd–N bonds between the cadmium ions and amino groups of the atphth2– ligands of the adjacent layers to form the final 3D structure. Compounds 1 and 2 exhibit solid‐state photoluminescence with emission maxima at 448 and 470 nm, respectively.

Substituent position-induced diverse architectures of polyoxovanadate-based hybrid materials constructed from a linear trinuclear transition metal complex and a hexanuclear [V6O18]6−cluster

Four new hexavanadate cluster-based hybrid materials [Ni(3-atrz)2V2O6]·2H2O (1) and [M3(4-atrz)6V6O18]·4H2O [atrz = amino-1,2,4-triazole; M = Ni (2), Co (3) and Zn (4)] have been synthesized under hydrothermal conditions by the reaction of transition metal salts, amino-triazole ligands and sodium metavanadate. Single crystal X-ray diffraction analyses reveal that compound 1 shows a one-dimensional (1D) chain formed by the alternative arrangement of linear trinuclear complexes [Ni3(3-atrz)6]6+ and hexanuclear [V6O18]6− clusters. Compounds 2–4 are isostructural three-dimensional (3D) frameworks, which are constructed from the linear trinuclear transition metal complexes and 2D inorganic layers derived from transition metal ions and hexanuclear [V6O18]6− clusters. The distinct amino positions in the two types of triazole ligands play the key role in determining the final dimensionality and structures of the title compounds. The thermal stability, photocatalytic activity and magnetic properties of 1–4 have been investigated.

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.

The synthesis and characterization of a silver complex of the tripodal triazole ligand, tris(benzyltriazolylmethyl)amine (TBTA, L(1)), that is used as promoter to enhance Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reactions is reported. X-ray analysis of the silver(I) complex with L(1) reveals a dinuclear cation, [Ag2(L(1))2](2+), that is essentially isostructural to the copper(I) analogue. While the [Ag2(L(1))2](BF4)2 complex provides catalysis for the azide-alkyne cycloaddition process, evidence is presented that this arises from trace copper contamination. The synthesis of silver(I), copper(II), and copper(I) complexes of a second tripodal ligand, tris(2-benzimidazolymethyl)amine (L(2)), which is used to enhance the rate of CuAAC reactions, is also reported. X-ray crystallography of the Cu(I) complex [Cu(I)3(L(2))2(CH3CN)2](BF4)3 offers structural insight into previous mechanistic speculation about the role of this ligand in the CuAAC reaction.

"Click" synthesis of nona-PEG-branched triazole dendrimers and stabilization of gold nanoparticles that efficiently catalyze p-nitrophenol reduction.

Two new water-soluble 1,2,3-triazole-containing nona-PEG-branched dendrimers are obtained with nine intradendritic 1,2,3-triazoles (trz). Addition of HAuCl4 in water to these dendrimers quantitatively leads to the intradendritic formation of AuCl3(trz) moieties subsequent to complete Cl(-) substitution by trz on Au(III), whereas the analogous complexation reaction of AuCl3 with a linear PEG trz ligand forms only an equilibrium between trz-coordinated Au(III) and Au(III) that is not coordinated to trz. Reduction of the dendrimer-Au(III) complexes to Au(0) by NaBH4 then leads to stabilization of gold nanoparticles (AuNPs) in water. The sizes of the AuNPs stabilized by the dendritic macromolecules are further controlled between 1.8 and 12 nm upon selecting the stoichiometry of Au(III) addition per dendritic trz followed by NaBH4 reduction. With a 1:1 Au/trz stoichiometry, the AuNP size depends on the length of the PEG tether of the dendrimer; small dendrimer-encapsulated AuNPs are formed with PEG2000, whereas large AuNPs are formed with PEG550. With Au/trz stoichiometries larger than unity, Au(III) is reduced outside the macromolecule, resulting in the formation of large interdendritically stabilized AuNPs. The formation of very small and only mildly stabilized AuNPs by neutral hydrophilic triazole ligands offers an opportunity for very efficient p-nitrophenol reduction by NaBH4 in water at the AuNP surface.

Two cobalt and nickel coordination polymers constructed from 1,4-bis(1,2,4-triazol-1-ylmethyl)benzene: Crystal structure and magnetic properties

Two new transition metal coordination polymers with 1,4-bis(1,2,4-triazol-1-ylmethyl)-benzene(btx), [Ni(btx)(ip)(H2O)] (1) and [Co(btx)(ox)]·2H2O (2) (H2ip=isophthalic acid; ox=oxalate) have been synthesized and characterized. Single crystal X-ray diffraction analyses reveal compounds 1 and 2 are two-dimensional structure in which the flexible bis(triazole) ligands act as bridging ligands. The variable-temperature magnetic susceptibility data show that two compounds exhibit weak antiferromagnetic interactions. The magnetic behaviors are explained in connection with the crystal structure.

Metallodendrimers in three oxidation states with electronically interacting metals and stabilization of size-selected gold nanoparticles

Metallodendrimers containing redox-robust centres may have applications in molecular redox recognition, sensing, biosensing and catalysis. So far, however, no metallodendrimer is known in several oxidation states. Here we report metallodendrimers with two electronically communicating iron centres that are stable and isolated in both the Fe(II) and Fe(III) oxidation states, and in addition as class-II mixed-valent Fe(II)Fe(III) complexes. These dendrons are branched to arene-centred dendrimer cores either by Sonogashira coupling or 'click' reactions. The latter reaction involves the introduction of intradendritic 1,2,3-triazolyl ligands, which allows investigation of the selective role of these ligands in intradendritic Au(III) coordination and Au(0) nanoparticle stabilization. As a result, and using the various metallodendrimers with different oxidation states, small Au(0) nanoparticles are intradendritically stabilized by the triazole ligands, whereas with the related non-'click' dendrimers large Au(0) nanoparticles are formed outside the dendrimers and stabilized by a group of dendrimers.

Structural Characterization, Solution Dynamics, and Reactivity of Palladium Complexes with Benzimidazolin‐ 2‐ylidene N‐Heterocyclic Carbene Ligands

AbstractMononuclear and halide‐bridged dinuclear palladium(II) complexes with symmetrically (1 and 3) and nonsymmetrically (2, 4–6) substituted benzimidazolin‐2‐ylidene N‐heterocyclic carbene ligands were synthesized and characterized by 1H and 13C NMR spectroscopy, elemental analysis, and X‐ray crystallography. The mononuclear complexes exist as a mixture of cis and trans isomers, and the identity of these was ascertained by NMR spectroscopy and structural characterization. The dinuclear complexes 4–6 with nonsymmetrically substituted benzimidazolin‐2‐ylidene ligands form rotamers (cis/anti, cis/syn, trans/anti, and trans/syn) at room temperature, which can be transformed to a single rotamer at higher temperatures as evidenced by 1H NMR spectroscopy. Crystal structure analyses of representative examples show that the PdII centers are bound in a distorted square‐planar environment by halides and carbene C ligands, and the carbene ligands are perpendicular to the Pd–halide plane. All of the complexes were tested for their efficiency as (pre)catalysts in the Suzuki–Miyaura cross‐coupling reaction, as well as in hydrodehalogenation reactions, and they show good activity. The Suzuki–Miyaura coupling reactions can be performed under air and in water as an environmentally benign solvent. The most active catalyst for the Suzuki–Miyaura coupling was also used in a sequence together with a “click reaction” to synthesize valuable sterically demanding tripodal triazole ligands.

Syntheses, Structures, and Characterization of a Series of Novel Cobalt(II) Complexes with Bi- and Mono- Triazole Ligands

Using the bi- and mono-triazole ligand, a series of novel cobalt(II) complexes [Co(L1)2(NCS)2(H2O)2] (1), [Co2(NCS)4(H2O)6]·3L2 (2) and [Co(L3)2(NCS)2(H2O)2] (L1 = 4–3-pyridine-1,2,4-triazole, L2 = 1,4-bis(4H-1,2,4-triazol-4-yl)benzene, and L3 = 2,6-di(1,2,4- triazol-4-yl)pyridine) have been synthesized. The crystal structures of 1–3 have been determined by single-crystal X-ray diffraction analysis. 1 and 3 has the mononuclear fundamental structure unit while 2 form the dinuclear structure unit. 1–3 were furthermore assembled into three-dimensional (3D) supramolecular complex via the intermolecular hydrogen bonds and aromatic π–π stacking interactions. The complexes 1–3 also have been characterized by elemental analysis, FT-IR, and TGA analysis. Variable temperature magnetic susceptibility measurement (2–300 K) also reveals weak anti-ferromagnetic interactions in 2.

Impeller-like dodecameric water clusters in metal–organic nanotubes

A triazole ligand, 3-amino-1,2,4-triazole-5-carboxylic acid (H2atc), bearing carboxylate and amino groups, has been incorporated into a nanotubular copper(ii)–organic framework that displays an nbo-type topology in which the impeller-like (H2O)12 water clusters were trapped in the nanotubes that can be encapsulated reversibly and precisely.

Fluorinated metal–organic frameworks of 1,4-bis(1,2,4-triazol-1-ylmethyl)-2,3,5,6-tetrafluorobenzene: synergistic interactions of ligand isomerism and counteranions

A fluorinated bis(triazole) ligand, 1,4-bis(1,2,4-triazol-1-ylmethyl)-2,3,5,6-tetrafluorobenzene (Fbtz), was applied to coordinate with a series of Mn(II), Co(II), Fe(II), and Cu(II) ions, respectively. In comparison with its nonfluorinated analogue 1,4-bis(1,2,4-triazol-1-ylmethyl)benzene (btx), Fbtz is able to build six novel metal-organic frameworks by acting as a versatile bridge combining with the terminal chlorides (1-5) or acetates (6) ligands. The solid-state crystal structures of 1-6 are studied by single-crystal X-ray crystallography to form the following structures: 3D polymers [M(Fbtz)2Cl2]n (1: M = Mn, 2: M = Co), 1D double chain polymers {[M(Fbtz)2Cl2]·CH2Cl2·xH2O}n (3: M = Co, x = 1; 4: M = Fe, x = 2), {[Cu(Fbtz)2Cl2]·4H2O}n (5), and a 1D double-stranded helical polymer {[Cu2(Fbtz)(OAc)2]·2H2O}n (6). Conformations of Fbtz in 1-6 can be tuned as a result of varying the anions or solvent system, which ultimately form a series of novel coordination frameworks with different supramolecular architectures. The antibacterial activities of all complexes are investigated. Complexes 4 and 5 show a wide range of bactericidal activities to Gram positive (B. subtilis and S. aureus) and negative (E. coli and P. fluorescence) bacterial strains. The synergistic interactions of ligand isomerism and counteranions have profound effects on the supramolecular networks and properties.

A series of interdigitated Cd(ii) coordination polymers based on 4,6-dibenzoylisophthalic acid and flexible triazole ligands

Different bridging ligands with various flexibilities and lengths were utilized to assemble interdigitated coordination polymers with Cd(ii) cations. The length and flexibility of the ligands could significantly influence the interdigitation level of the crystal structure.

ChemInform Abstract: Crystal Engineering of FeII Spin Crossover Coordination Polymers Derived from Triazole or Tetrazole Ligands

AbstractReview: 109 refs.

Synthesis and characterization of a novel 3D porous luminescent Ag(I) framework with a multidentate triazole ligand

By using a multidentate N-(4-(4H-1,2,4-triazol-4-yl)phenyl)formamide (L) ligand and AgClO4, a novel three-dimensional(3D) porous luminescent silver(I) complex {[Ag2(μ3-L)2]·(ClO4)2}n (1) has been isolated and characterized by single crystal diffraction analysis. The result reveals that 1 contains two kinds of distinct 1D channels with different sizes and shapes, in which free perchlorate anions are located in these 1D channels. Anion exchange experiment of 1 with NaNO3 was monitored by FT-IR, PXRD, elemental analysis and photoluminescence characterization, indicating that the porous framework of 1 can remain intact throughout the anion exchange process. 1 has green luminescence emission and can behave anion-responsive tunable photoluminescence properties. The result also reveals that the multidentate L ligand can be used for the preparation of novel functional coordination materials.

Palladium(II) complexes featuring bidentate pyridine–triazole ligands: Synthesis, structures, and catalytic activities for Suzuki–Miyaura coupling reactions

Preparation of the Pd(II) complexes containing 2-(4-R-1,2,3-triazol-1-yl)pyridine [R = C6H5 (1), NC5H4 (2), n-C6H13 (3)] were described. Crystal structures of 1 and 2 revealed a square planar geometry with bidentate ligand coordination to Pd using different N donor of the triazole ring. Catalytic studies indicated that 1–3 exhibited moderate to high activity for Suzuki–Miyaura coupling between aryl bromides and phenylboronic acid under mild and aerobic conditions.

Syntheses, spectral and structural characterization of Ni(II) complexes of 4-amino-5-phenyl/3-pyridyl/thiophen-2H-1,2,4-triazole-3-thione

New mixed ligand complexes [Ni(aptt)2(en)2] (1), [Ni(apytt)2(en)2]⋅CHCl3 (2) and [Ni(athtt)2(en)2] (3) with 4-amino-5-phenyl-2H-1,2,4-triazole-3-thione (Haptt), 4-amino-5-(pyridin-3-yl)-4,5-dihydro-3H-1,2,4-triazole-3-thione (Hapytt) and 4-amino-5-thiophen-2H-1,2,4-triazole-3-thione (Hathtt) have been prepared containing en as the secondary ligand. The metal complexes have been characterized with the aid of elemental analyses, IR, magnetic susceptibility and single crystal X-ray data. All the complexes are bonded through two nitrogen atoms of two triazole ligands and four nitrogens of two ethylenediamine and the resulting complexes have distorted octahedral geometry. The triazole ligands behave as uninegative monodentate, bonding through triazole nitrogen due to the hard character of the nickel(II). The complexes contain extended hydrogen bonding providing supramolecular framework. The course of the thermal degradation of complex 2 has been investigated by TG–DTA which suggest the loss of CHCl3 molecule around 200°C and finally a residue of NiS is left behind.

Synthesis and characterization of transition metal complexes of 4-Amino-5-pyridyl-4H-1,2,4-triazole-3-thiol

Series of coordination complexes of Ni(II), Cu(II), Zn(II), Cd(II) and Sn(II) metal with 4-amino-5-(pyridyl)-4H-1,2,4-triazole-3-thiol, as a ligand has been successfully prepared in alcoholic medium. The prepared complexes were characterized quantitatively and qualitatively by using: microelemental analysis, FTIR spectroscopy, UV-visible spectroscopy, 1H and 13C NMR, magnetic susceptibility and conductivity measurements. This triazole ligand act as bidentate that coordination to the metal ions through sulphur and amine group. According to the spectral data of the complexes a tetrahedral geometry was suggested for these complexes except Cu (II) complexes which exhibit a square structure.

Synthesis, Crystal Structure, and Spectral Properties of Two Manganese(II) and Zinc(II) Complexes with 3,4-Dimethyl-5-(2-pyridyl)-1,2,4-triazole

Two complexes, cis-[MnL2(NCS)2] (1) and cis-[ZnL2(NCS)2] (2) with asymmetrical substituted triazole ligands [L = 3,4-dimethyl-5-(2-pyridyl)-1,2,4-triazole], were synthesized and characterized by elemental analysis, UV/Vis and FT-IR spectroscopy as well as thermogravimetric analyses (TGA), powder XRD, and single-crystal X-ray diffraction. In the complexes, each L molecule adopts a chelating bidentate mode by the nitrogen atoms of pyridyl and triazole. Both complexes have a similar distorted octahedral [MN6] core (M = Mn2+ and Zn2+) with two NCS– ions in the cis position.

Phenyl 1,2,3-triazole-thymidine ligands stabilize G-quadruplex DNA, inhibit DNA synthesis and potentially reduce tumor cell proliferation over 3'-azido deoxythymidine.

Triazoles are known for their non-toxicity, higher stability and therapeutic activity. Few nucleoside (L1, L2 and L3) and non-nucleoside 1,2,3-triazoles (L4–L14) were synthesised using click chemistry and they were screened for tumor cell cytotoxicity and proliferation. Among these triazole ligands studied, nucleoside ligands exhibited higher potential than non-nucleoside ligands. The nucleoside triazole analogues, 3′-Phenyl-1,2,3- triazole-thymidine (L2) and 3′-4-Chlorophenyl-1,2,3-triazole-thymidine (L3), demonstrated higher cytotoxicity in tumor cells than in normal cells. The IC50 value for L3 was lowest (50 µM) among the ligands studied. L3 terminated cell cycle at S, G2/M phases and enhanced sub-G1 populations, manifesting induction of apoptosis in tumor cells. Confocal studies indicated that nucleoside triazole ligands (L2/L3) cause higher DNA fragmentation than other ligands. Preclinical experiments with tumor-induced mice showed greater reduction in tumor size with L3. In vitro DNA synthesis reaction with L3 exhibited higher DNA synthesis inhibition with quadruplex forming DNA (QF DNA) than non quadruplex forming DNA (NQF DNA). Tm of quadruplex DNA increased in the presence of L3, indicating its ability to enhance stability of quadruplex DNA at elevated temperature and the results indicate that it had higher affinity towards quadruplex DNA than the other forms of DNA (like dsDNA and ssDNA). From western blot experiment, it was noticed that telomerase expression levels in the tissues of tumor-induced mice were found to be reduced on L3 treatment. Microcalorimetry results emphasise that two nucleoside triazole ligands (L2/L3) interact with quadruplex DNA with significantly higher affinity (Kd≈10−7 M). Interestingly the addition of an electronegative moiety to the phenyl group of L2 enhanced its anti-proliferative activity. Though IC50 values are not significantly low with L3, the studies on series of synthetic 1,2,3-triazole ligands are useful for improving and building potential pro-apoptotic ligands.

Heterobimetallic Cu–dppf (dppf = 1,1′-Bis(diphenylphosphino)ferrocene) Complexes with “Click” Derived Ligands: A Combined Structural, Electrochemical, Spectroelectrochemical, and Theoretical Study

Heterodinuclear complexes of the form [(dppf)Cu(L)](BF4) (dppf = 1,1′-bis(diphenylphosphino)ferrocene), where L are the chelating, substituted 4,4′-bis(1,2,3-triazole) or 4-pyridyl(1,2,3-triazole) ligands, were synthesized by reacting [Cu(dppf)(CH3CN)2](BF4) with the corresponding “click” derived ligands. Structural characterization of representative complexes revealed a distorted-tetrahedral coordination geometry around the Cu(I) centers, with the donor atoms being the P donors of dppf and the N donors of the substituted triazole ligands. The “local-pseudo” symmetry around the iron center in all the investigated complexes of dppf is between that of the idealized D5h and D5d. Furthermore, for the complex with the mixed pyridine and triazole donors, the Cu–N bond distances were found to be shorter for the triazole N donors in comparison to those for the pyridine N donors. Electrochemical studies on the complexes revealed the presence of one oxidation and one reduction step for each. These studies were combined with UV–vis–near-IR and EPR spectroelectrochemical studies to deduce the locus of the oxidation process (Cu vs Fe) and to see the influence of changing the chelating “click” derived ligand on both the oxidation and reduction processes and their spectroscopic signatures. Structure-based DFT studies were performed to get insights into the experimental spectroscopic results. The results obtained here are compared with those of the complex [(dppf)Cu(bpy)](BF4) (bpy = 2,2′-bipyridine). A comparison is made among bpy, pyridyl-triazole, and bis-triazole ligands, and the effect of systematically replacing these ligands on the electrochemical and spectroscopic properties of the corresponding heterodinuclear complexes is investigated.