N-donor Ligands Research Articles

Copper(I) complexes bearing pyrrole-bridged S,N and N-donor ligands as catalysts for tandem hydroamination-alkynylation: effect of anions on product formation.

In this study, the reaction between 2-(3,5-dimethylpyrazolylmethyl)-5-(dimethylaminomethyl)pyrrole and thiophenol under heating conditions afforded the new ligand 2-(3,5-dimethylpyrazolylmethyl)-5-(phenylthiomethyl)pyrrole 2. The reaction of 2 with meta-chloroperbenzoic acid provided sulfoxide 3 and sulfone 4 group-containing ligands. The reaction of 2 with copper(I) halides provided the binuclear complexes [Cu(μ-X){μ-C4H3N-2-(CH2Me2pz)-5-(CH2SPh)-κ2-S,N}]2 (X = Cl, Br and I, 5-7) in high yields. Conversely, the analogous reaction of 4 with copper(I) halides yielded two types of complexes, three coordinate bi- and mononuclear of the type [Cu(μ-Cl){C4H3N-2-(CH2Me2pz)-5-(CH2SO2Ph)-κ1-N}]28 and [CuX{C4H3N-2-(CH2Me2pz)-5-(CH2SO2Ph)-κ1-N}2], X = Br, 9 and I, 10. When the reaction was carried out in the presence of KPF6, the two-coordinate complex [Cu{C4H3N-2-(CH2Me2pz)-5-(CH2SO2Ph)-κ1-N}2]PF6-11a was isolated, whereas its BF4- analogue 11b was synthesized by the reaction of 8 with AgBF4. The structures of these complexes were determined using single-crystal X-ray crystallography. These copper complexes catalyzed the hydroamination-alkynylation reaction between several secondary amines and alkyl and aryl terminal alkynes. Using 1 mol% of complexes 5-10 as catalysts, both tri- and tetra-substituted propargylamines were isolated. Alternatively, phenylacetylene and different secondary amines afforded the corresponding trisubstituted propargylamines as the major products and alkyl terminal alkynes gave the tetrasubstituted products in excellent yields. In addition, the role of counter anions such as TfO-, PF6-, BF4-, PO43- and Ph4B- on the product selectivity was studied. When fluorinated anions such as TfO-, PF6-, and BF4- were present with the copper complexes, the hydroamination-hydrovinylation product 1-aminodiene 23 was observed, which was not formed with PO43-, Ph4B- or halide ions. Specifically, TfO- and PF6- favored the formation of 23, while BF4- favored the tetrasubstituted product as the major product. This was further supported by the isolated copper(I) complexes containing PF6- and BF4- and by other specific reactions. The peaks for enamines and [LCu]+ species in the HRMS spectra of the reaction mixtures and the isolation of the morpholinium copper(I) salt support the proposed mechanism.

A homoleptic AgIII complex stabilized by succinimidate ligands.

Herein, the first example of a homoleptic AgIII complex stabilized by a monodentate N-donor ligand is presented. Na2[S2O8] oxidizes the linear AgI complex, Na[Ag(succ)2] (1Na), to form a square planar argentate(iii) ion, [Ag(succ)4]-, which crystallizes with a polymeric chain-structure, M[Ag(succ)4] (2M), when treated with alkali metal sulfate M2SO4 (M = K, Rb, Cs). A mixed-valent Robin-Day class I system, [(H2O)Ag][Ag(succ)4] (2Ag), forms in the absence of K+/Rb+/Cs+ ion. Diamagnetic 2Cs displays a succinimide C[double bond, length as m-dash]O stretching frequency at higher energy than does the isoelectronic PdII complex, [(H2O)Na]2[Pd(succ)4] (3Na). Moreover, 2Cs displays UV-vis absorptions that are more intense and occur at lower energy than those in 3Na. The electron-deficient nature of 2Cs is further evident from its ability to oxidize water to O2. From 109Ag magic-angle spinning NMR studies, a highly deshielded AgIII environment in 2Cs (2080 ppm) relative to the AgI starting material 1Na (492 ppm) is observed.

Chemical fixation of atmospheric CO2 in tricopper(II)-carbonato complexes with tetradentate N-donor ligands: reactive intermediates, probable mechanisms, and catalytic and magneto-structural studies.

In the present era, the fixation of atmospheric CO2 is of significant importance and plays a crucial role in maintaining the balance of carbon and energy flow within ecosystems. Generally, CO2 fixation is carried out by autotrophic organisms; however, the scientific community has paid substantial attention to execute this process in laboratory. In this report, we synthesized two carbonato-bridged trinuclear copper(II) complexes, [Cu3(L1)3(μ3-CO3)](ClO4)3 (1) and [Cu3(L2)3(μ3-CO3)](ClO4)3 (2) via atmospheric fixation of CO2 starting with Cu(ClO4)2·6H2O and easily accessible pyridine/pyrazine-based N4 donor Schiff base ligands L1 and L2, respectively. Under very similar reaction conditions, the ligand framework embedded with the phenolate moiety (HL3) fails to do so because of the reduction of the Lewis acidity of the metal center, inhibiting the formation of a reactive hydroxide bound copper(II) species, which is required for the fixation of atmospheric CO2. X-ray crystal structures display that carbonate-oxygen atoms bridge three copper(II) centers in μ3syn-anti disposition in 1 and 2, whereas [Cu(HL3)(ClO4)] (3) is a mononuclear complex. Interestingly, we also isolated an important intermediate of atmospheric CO2 fixation and structurally characterized it as an anti-anti μ2 carbonato-bridged dinuclear copper(II) complex, [Cu2(L2)2(μ2-CO3)](ClO4)2·MeOH (2-I), providing an in-depth understanding of CO2 fixation in these systems. Variable temperature magnetic susceptibility measurement suggests ferromagnetic interactions between the metal centers in both 1 and 2, and the results have been further supported by DFT calculations. The catalytic efficiency of our synthesized complexes 1-3 was checked by means of catechol oxidase and phenoxazinone synthase-like activities. While complexes 1 and 2 showed oxidase-like activity for aerobic oxidation of o-aminophenol and 3,5-di-tert-butylcatechol, complex 3 was found to be feebly active. ESI mass spectrometry revealed that the oxidation reaction proceeds through the formation of complex-substrate intermediations and was further substantiated by DFT calculations. Moreover, active catalysts 1 and 2 were effectively utilized for the base-free oxidation of benzylic alcohols in the presence of air as a green and sustainable oxidant and catalytic amount of TEMPO in acetonitrile. Various substituted benzylic alcohols smoothly converted to their corresponding aldehydes under very mild conditions and ambient temperature. The present catalytic protocol showcases its environmental sustainability by producing minimal waste.

Multinuclear beryllium amide and imide complexes: structure, properties and bonding.

The beryllium amide and imide complexes [Be(HNMes)2]3, [(py)2Be(HNMes)2], [Be(HNDipp)2]2, [Be(NPh2)(μ2-HNDipp)]2 and [Be(NCPh2)2]3 have been prepared and characterised with NMR and IR spectroscopy as well as single crystal X-ray diffraction. Analysis of the localised molecular orbitals (LMOs) and intrinsic atomic orbital (IAO) atomic charges in the framework of the intrinsic bond orbital (IBO) localization method revealed a covalent bonding network consisting of 2-electron-2-centre and 2-electron-3-centre σ bonds, in which one electron pair of the anionic N-donor ligands is involved. The electron deficiency at the beryllium atoms is partially compensated through additional electron donation from the lone pair at the nitrogen atoms.

A homochiral tartrate-bridged dinuclear chromium(III) complex anion with a resonance-assisted hydrogen bond for proton conduction.

The synthesis of a homochiral building block based on L-tartrate-chromium(III) complex anions is reported. The dinuclear complex anion, which contains two bridging L-tartrate ligands and one aromatic N-donor ligand coordinated to chromium(III) ions, exhibits a boat conformation in which intramolecular resonance-assisted hydrogen bonding is present. The sodium L-tartrate-chromium(III) compound with the formula Na[Cr2(bpy)2(L-tart)2H]·9H2O (1) crystallizes from a methanol-water solution as a high water content material in the monoclinic space group P2. The as-synthesized compound is only stable at high relative humidity and undergoes structural transformations during drying, which are accompanied by water loss. However, these transformations are reversible and upon wetting, the material returns to its high water content structure. Based on a combination of experimental techniques (PXRD, in situ ATR-FTIR and EPR spectroscopy), the structure of the complex anions appears to be insensitive to the humidity variable processes (wetting and drying). Due to the presence of several hydrogen acceptor and donor groups in the L-tartrate-chromium(III) complex anion, we investigated the proton transport properties of a sodium L-tartrate-chromium(III) compound by impedance spectroscopy under dry and wet conditions at different temperatures. Since the relative humidity affects the structural transformations in this system, it also has a large influence on the proton conductivity, which varies by up to four orders of magnitude depending on the degree of hydration. These results confirm that the proton conductivity can be tuned in flexible structures in which non-covalent interactions determine the crystal packing.

Al-alkyl borate salt cocatalysts for olefin polymerization: exploration of N-donor ligand variations

The stability and reactivity of {[iBu2(L)Al]2(μ-H)}+[B(C6F5)4]− (AlHAl), recently identified as a promising cocatalyst for olefin polymerization, can be modulated by varying the structure of the neutral N-donor (L).

Retraction of “Two mixed-ligand coordination polymers based on 2,5-thiophenedicarboxylic acid and flexible N-donor ligands: The protective effect on periodontitis via reducing the release of IL-1β and TNF-α”

Retraction of “Two mixed-ligand coordination polymers based on 2,5-thiophenedicarboxylic acid and flexible N-donor ligands: The protective effect on periodontitis via reducing the release of IL-1β and TNF-α”

Structural consequences in differently substituted haloarylcarboxylates and non-covalent interactions on crystal packing and biological efficacy of copper(II) complexes with N,N,N′,N′-tetramethylethylenediamine N-donor ligand

In this work, we reported four new copper(II) halo-benzoate complexes (2-chloro-4-nitrobenzoate (2-Cl-4-NO2-BZ), 3,5-DICBZ, 2-chloro-5-nitrobenzoate (2-Cl-5-NO2-BZ), 3,5-difluoro benzoate (3,5-DIFBZ), and 3,5-dichlorobenzene (3,5-DICBZ) respectively in complexes 1–4) with N,N,N’,N’- tetramethylethylene diamine (temed) N-donor ligand in order to study the interesting coordination features and biological evaluation of such complexes under ambient reaction conditions. All the complexes 1–4 were characterized by elemental analyses, and spectroscopic techniques, including FT-IR, UV–vis, and EPR etc. Single crystal X-ray structure determination (SCXRD) of complexes revealed the distorted octahedral geometry in all complexes. Notably, the halobenzoate ligands exhibited a bidentate chelation mode in complexes 1 and 2, while they showed a monodentate mode in complex 3. In complex 4, the carboxylate ligand exhibited both monodentate as well as bidentate coordination. Furthermore, detailed packing analyses of complexes 1–4 highlighted the significance of halogen bonding in lattice stabilization besides hydrogen bonding and π∙∙∙π interactions as evidenced by Hirshfeld surface analyses and crystal analysis. Moreover, packing analyses displayed that complex 1 exhibited a layered or wave-like arrangement, while complex 2 featured a helical arrangement supported by a supramolecular halogen-bonded network guided by Cl∙∙∙O interactions. Complex 3 displayed a zig-zag layered arrangement with a stacking topology, and Complex 4 showcased a ribbon-like arrangement stabilized by F∙∙∙F and Cl∙∙∙Cl halogen bonding interactions. Furthermore, sigma hole on halogen atoms has also been examined (which play an important role in halogen bonding) by electrostatic-potential isosurfaces. In order to exploit the biological efficacy of complexes 1–4 owing to the inherent biological activity of copper metal, molecular docking analyses against gram +ve bacteria i.e. S. epidermidis (PDB ID; 8DO6), B. subtilis (1QD9), as well as two gram -ve bacteria, namely, P. aeruginosa (5WZE) and S. dysenteriae (1DM0), have also been carried out. Interestingly, values of docking scores and inhibition constant of all complexes 1–4 (with a maximum binding score (inhibition constant) of -9.8 kcal/mol (0.063 µMol) in 1 against 8DO6 and 1DM0) revealed higher biological efficacy than that of standard drugs.

Facile Access to Cationic Methylstannylenes and Silylenes Stabilized by E-Pt Bonding and their Methyl Group Transfer Reactivity.

We describe a family of cationic methylstannylene and chloro- and azidosilylene organoplatinum(II) complexes supported by a neutral, binucleating ligand. Methylstannylenes MeSn:+ are stabilized by coordination to PtII and are formed by facile Me group transfer from dimethyl or monomethyl PtII complexes, in the latter case triggered by concomitant B-H, Si-H, and H2 bond activation that involves hydride transfer from Sn to Pt. A cationic chlorosilylene complex was obtained by formal HCl elimination and Cl- removal from HSiCl3 under ambient conditions. The computational studies show that stabilization of cationic methylstannylenes and cationic silylenes is achieved through weak coordination to a neutral N-donor ligand binding pocket. The analysis of the electronic potentials, as well as the Laplacian of electron density, also reveals the differences in the character of Pt-Si vs. Pt-Sn bonding. We demonstrate the importance of a ligand-supported binuclear Pt/tetrel core and weak coordination to facilitate access to tetrylium-ylidene Pt complexes, and a transmetalation approach to the synthesis of MeSnII :+ derivatives.

Substitution of apical iodide ligands in octahedral molybdenum cluster complexes by N-donor molecules: Synthesis and investigation of [{Mo6I8}(L)I5]– and cis-[{Mo6I8}(L)2I4] (L = CH3CN or 1,2,4-triazole)

In this work, reactivity of the [{Mo6I8}I6]2– cluster anion toward some N-donor ligands was investigated. Heating of the solution of Cs2[{Mo6I8}I6] salt in acetonitrile leads to the partial substitution of apical iodide ligands by CH3CN molecules forming crystalline solid Cs0.1[{Mo6I8}(CH3CN)I5]0.1·cis-[{Mo6I8}(CH3CN)2I4]0.9·0.9CH3CN (1). The solid includes anionic [{Mo6I8}(CH3CN)I5]– and neutral cis-[{Mo6I8}(CH3CN)2I4] cluster units at a ratio of 1:9. In the crystal structure of 1, these clusters occupy common crystallographic sites, which allows us to consider this compound as a solid solution. When 1,2,4-triazole (tz) was added to the reaction mixture, a solid solution of mono- and disubstituted products was also formed and crystallized in a ratio of approximately 1:3, yielding the compound Cs0.27[{Mo6I8}(tz)I5]0.27·cis-[{Mo6I8}(tz)2I4]0.73 (2). It was assumed that compound 2 was formed as a product of direct substitution of the apical iodide ligands by tz molecules. Structural features and luminescence properties of the new compounds 1 and 2 were studied.

Coordination Polymer or Cluster: Zinc Bis(3,5-di-tert-octyl-semiquinolate) with Pyrazine

New zinc bis-o-semiquinolate complexes based on 3,5-di-tert-octyl-o-benzoquinone bearing the N-donor ligand (pyrazine) coordinated to the metal are synthesized. Two different products can be obtained depending on the synthesis method: coordination polymer (direct oxidation of metallic zinc with o-quinone (CIF file CCDC no. 2250574 (I)) or polynuclear cluster (exchange reaction (CIF file CCDC no. 2250575 (II)). The coordination polymer is linear and free of intermolecular π,π interactions between the aromatic fragments of the adjacent molecules. The magnetochemical study of complexes I and II shows that intramolecular antiferromagnetic exchange interactions between spins of the o-semiquinolate radical centers dominate.

Cation-cation interaction in Np(V) o-chlorobenzoate complexes with 1,10-phenanthroline and 2,2′-bipyridine

Two new Np(V) o-Cl-benzoates of composition [(NpO2)(phen)(C7H4ClO2)]3 (1) and [(NpO2)(bipy)(C7H4ClO2)]4·2H2O (2) with N-donor ligands phenantroline (phen) and bipyridine (bipy) have been synthesized and structurally characterized. In these complexes, NpO2+ cations are linked by cation-cation bonds, acting as monodentate ligands with respect to each other. As a result, a trimeric complex is formed in 1, and a tetrameric complex is formed in 2. The Np atoms in both compounds have a pentagonal-bipyramidal environment with “yl” oxygen atoms in apical positions. The equatorial planes of the bipyramids are formed by two nitrogen atoms of phen (1) or bipy (2), one oxygen atom of another NpO2+ cation, and two oxygen atoms from two C7H4ClO2– anions. Electronic absorption spectra of crystalline compounds were measured in the near IR-visible range.

Copper(II) Catecholate Complexes with Polypyridyl Ligands

Copper(II) catecholate complexes based on 3,6-di-tert-butyl-o-benzoquinone with N-donor ligands of the phenanthroline series have been synthesized: (3,6-Cat)Cu(Phen) (I), (3,6-Cat)Cu(DPQ) (II), and (3,6-Cat)Cu(DPPZ) (III), where 3,6-Cat is the 3,6-di-tert-butyl-o-benzoquinone dianion, Phen is phenanthroline, DPQ is dipyrido[3,2-d:2',3'-f]quinoxaline, and DPPZ is dipyrido[3,2-a:2',3'-c]phenazine. The synthesized copper(II) complexes demonstrate intramolecular ligand-to-ligand charge transfer responsible for their intense violet color. The electronic structure of the synthesized chromophores was studied by electronic spectroscopy, cyclic voltammetry, and quantum-chemical calculations. The molecular and crystal structures of the synthesized compounds were determined by X-ray diffraction analysis (CIF files CCDC 2 250 975 (I⋅THF), 2 250 976 ([(II⋅THF)(II)]⋅3THF), 2250977 (II)).

Why non-heme Mn complexes of amino 2-quinolylmethyl ligands are inactive in oxidation catalysis? An insight from X-ray data

In the last decade, manganese complexes with bis-amino-bis-pyridylmethyl and structurally related N4 donor ligands have emerged as efficient catalysts of selective epoxidations and C–H oxidations of organic substrates with H2O2. Although a plethora of various ligand structures have been designed, (quinolin-2-yl)methyl moieties have not been involved in constructing such catalysts. Herewith we report crystal structures of several Mn complexes with (quinolin-2-yl)methyl and discuss possible reasons of their inactivity in oxidation catalysis.

Tetranuclear Heterometallic Iron(II)–Lithium Carboxylates Stabilized by N-Donor Ligands: Synthesis and Structure

Tetranuclear Heterometallic Iron(II)–Lithium Carboxylates Stabilized by N-Donor Ligands: Synthesis and Structure

Tetranuclear Heterometallic Iron(II)–Lithium Carboxylates Stabilized by N-Donor Ligands: Synthesis and Structure

The multicomponent chemical reactions of Fe(SO4)∙7H2O, Li(Рiv), K(Рiv) (Рiv is pivalate anion), and heterocyclic N-donor ligands (pyridine (Рy), 1,10-phenanthroline (Рhen)) in anhydrous acetonitrile under an inert atmosphere afford new heterometallic tetranuclear complexes [FeII2Li2(Рiv)6(Рy)4] (I) and [FeII2Li2(Рiv)6(Рhen)2] (II) in which all carboxylate anions act as bridging ligands. The molecular and crystal structures of the compounds are determined by X-ray diffraction (XRD) (CIF files CCDC nos. 2220576 (I) and 2220577 (II·2CH3CN). In the studied complexes, the iron(II) atoms exist in the distorted octahedral ligand environment.

Aminopolycarboxylate zinc(II) complexes with 1,10-phenanthroline and 2,2′-bipyridyl: kinetic studies in the surfactants solutions systems

Aminopolycarboxylate zinc(II) complexes with 1,10-phenanthroline and 2,2′-bipyridyl {[Zn(IDA)(H2O)2], [Zn(IDA)(bipy)(H2O)]·2H2O and [Zn(IDA)(phen)(H2O)]·2H2O} were synthesized. In order to confirm the composition and purity of the synthesized complex compounds, elemental analysis was used. Next, the kinetics of the substitution reaction of two water molecules in the zinc(II) iminodiacetate complex for 1,10-phenanthroline and 2,2′-bipyridyl in two surfactant solvents: CTAB and Triton X-100 were investigated. The kinetic studies were carried out using the stopped flow method. The kinetic research were carried out at 3 different temperatures: 288.15, 293.15 and 298.15 K and at different molar concentrations of the complex compound [Zn(IDA)(H2O)2]: 1 mM; 0.75 mM, 0.5 mM and 0.25 mM and at a constant molar concentration of ligands: i.e. 1,10-phenanthroline and 2,2′-bipyridyl, were 0.05 mM. Changes in absorbance during the kinetic run of the tested reactions were measured at a wavelength of 260 nm. Thanks to the conducted kinetic studies, the order of the reaction was determined, and the observable rate constants of the reaction rates of the substitution of two aqua molecules into the N-donor ligand were determined by the stopped—flow method using the Glint program. In the next step the thermodynamic parameters of complexes: {[Zn(IDA)(H2O)2], [Zn(IDA)(bipy)(H2O)]·2H2O and [Zn(IDA)(phen)(H2O)]·2H2O} in aqueous solutions by use potentiometric titrations were determined. The Hyperquad2018 program was used for determining of stability constants. In addition, the stoichiometry of complexes of zinc(II) with N-heterocyclic ligands in aqueous solutions was determined using the conductometric titrations.

Synthesis, structural characterization, fluorescence properties and antimicrobial activities of dinuclear zinc(II) methacrylate complexes with N-donor ligands

Two new dinuclear Zn(II) methacrylate complexes, [Zn2(µ-maa)3(2-IPim)2]·NO3 (1), [Zn2(µ-maa)4(2-vpy)2] (2) [maaH = methacrylic acid, 2-IPim = 2-Isopropylimidazole and 2-vpy = 2-vinylpyridine] have been synthesized and characterized by FT-IR, 1H NMR and 13C NMR spectroscopy, elemental analysis, thermal analysis (TG/DTG, DTA) and single-crystal X-ray diffraction. In complex 1 each Zn(II) atom has a distorted tetrahedral coordination geometry, while in complex 2 each Zn(II) atom is in a distorted square pyramid geometry. The X-ray crystallographic studies of both complexes revealed that the Zn(II) ions are μ-bridged by the maa ligands to generate dinuclear structures. Quantum chemical calculations were carried out to ascertain the ground state optimization of both complexes and the calculated bond lengths and bond angles of the complexes were presented. To study in more detail the properties of these complexes, we also investigated their antibacterial and antifungal activity by in vitro agar diffusion method against Staphylococcus aureus, Escherichia coli, Bacillus cereus and Candida, respectively. Additionally, the fluorescence properties of the complexes are discussed herein.

Heteroleptic Zinc Catecholate Complexes with N-Donor Ligands

New heteroleptic zinc catecholate complexes based on 3,6-di-tert-butyl-o-benzoquinone and containing metal-coordinated N-donor ligands (2,2'-bipyridine and phenanthroline) were prepared by ligand exchange. According to X-ray diffraction data, both complexes were dimers with multiple intermolecular π–π interactions between the aromatic moieties of neighboring molecules (CCDC nos. 2222704 (I), 2222705 (II)). The electronic transmission spectra of crystalline samples of I and II and their solutions show broad absorption bands in the visible region with a maximum at about 500 nm.

Heteroleptic Zinc Catecholate Complexes with N-Donor Ligands

Heteroleptic Zinc Catecholate Complexes with N-Donor Ligands