Nitrogen Ligands Research Articles

Oxa-TriQuinoline: A New Entry to Aza-Oxa-Crown Architectures.

A new 15-membered-macrocyclic molecular entity, oxa-TriQuinoline (o-TQ), was designed and synthesized. In o-TQ, three oxygen atoms were joined onto three quinoline units at the 2- and 8-positions in a head-to-tail fashion via three-fold SNAr reactions, giving rise to the characteristic N3O3 aza-oxa-crown architecture. o-TQ can serve as a new tridentate nitrogen ligand to capture a Cu(I) cation and adopt a bowl shape, before supramolecular complexation with corannulene and [12]CPP occurs via π-π and CH-π interactions. In the presence of the Cu(I) cation, the non-emissive o-TQ becomes a highly emissive material in the solid state, whereby the emission wavelengths depend on the ancillary ligand on the Cu(I) cation. The o-TQ/Cu(I) complex is able to promote carbene catalysis to provide a range of enamines with a gem-difluorinated terminus.

Thermal Analysis and Biocidal Studies of Copper (II) Soapgroundnut Complex Containing Urea and Thiourea as a Ligand

Background: Studies on the thermal decomposition of synthesized complexes have great importance for calculating the thermal stability and characterization of copper (II) soap complexes, and represent new investigations on the solution of environmental problems. Aim: The present research work aims to report new findings in the field of thermogravimetric analysis and biocidal studies for copper (II) groundnut complexes with urea and thiourea ligands. Objective: The objective of this study was to conduct the kinetic analysis of copper (II) soap complexes of nitrogen and sulphur-containing ligands with the help of a thermogravimetric analyser (TGA), as this technique is commonly applied for thermal analysis. Methods: In relevance of aforesaid applications, the present work deals with determining the different thermal degradation steps of newly synthesized copper (II) groundnut urea complex (CGU) and copper (II) groundnut thiourea complex (CGT) by using Coats- Redfern, Horowitz-Metzger, Broido, and Piloyan-Novikova equations for determining kinetic parameters, i.e., the energy of activation (E), rate constant, order of decomposition reaction, and pre-exponential factor (Z). Results: The results obtained from kinetic parameters were used to evaluate the thermodynamic parameters, i.e., entropy of activation (ΔS), enthalpy of activation (ΔH), and Gibbs free energy of activation (ΔG), corresponding to the activation by using previously mentioned equations. Kinetics of degradation for the synthesized complexes in solid state were studied using thermogravimetric analysis technique (TGA) in nitrogen atmosphere. Conclusion: The present study has discussed the biocidal activities of these complexes against Staphylococcus aureus and an explicit correlation between structure and biological activity has also been provided.

Europium(III) Ion-Based photoluminescence complexes of Indole-Derivative β-diketone dominated by ancillary ligands

One pot reaction of β-diketone EIFD, EuCl3·6H2O and ancillary ligand yield a sequence of five luminescence β-diketone EIFD europium complexes, including Eu(EIFD)3(H2O)·CH2Cl2 (1), Eu(EIFD)3(DMSO) (2), Eu(EIFD)3(DMF)·CH2Cl2 (3), Eu(EIFD)3(phen)·CH2Cl2 (4) and Eu(EIFD)3(bpy) (5) (EIFD: 1-(1-ethyl-1H-indol-3-yl)-4,4,4-trifluorobutane-1,3-dione, phen = 1, 10-phenanthroline, bpy = 2,2′-bipyridine,). The molecular crystals reveal five mononuclear structures with the central Eu(III) ions of seven/eight coordination configuration furnished by three EIFD ligands and ancillary ligands for complexes 1–5. All the five complexes display room-temperature strong characteristic photoluminescence emissions of Eu(III) ions. The coordination environment of Eu(III) ion is a crucial factor in the optical performance of the complex. Herein, the way to introduce of oxygen and nitrogen ancillary ligands plays an important role in characteristic photoluminescence. The luminescence lifetime and quantum yields of the complexes can vary essentially by substituting the solvent molecules with oxygen and nitrogen ligands, leading to a strong luminescence intensity, as observed experimentally.

Complexation and Separation of Palladium with Tridentate 2,6-Bis-triazolyl-pyridine Ligands: Synthesis, Solvent Extraction, Spectroscopy, Crystallography, and DFT Calculations.

Selective extraction of palladium from high-level liquid waste (HLLW) is desirable for the sustainable development of nuclear energy and resource recovery. In this work, three tridentate 2,6-bis-triazolyl-pyridine ligands (L-I, L-II, and L-III) bearing different alkyl side chains were synthesized and systematically studied for the complexation and extraction of palladium. Altering the alkyl side chains of the ligands led to pronounced differences in extraction performance. Among the three ligands, L-II decorated with two n-octyl groups exhibited the highest Pd(II) extraction efficiency at acidity levels of 1-5 M HNO3 and outstanding selectivity over 13 coexisting competing metal ions. Results from UV-vis titration experiments and theoretical calculations suggested that the differentiated extraction abilities of the ligands could be because of their different hydrophilicity rather than electron-donating effects. Slope analyses and electrospray ionization-high resolution mass spectrometry (ESI-HRMS) experiments revealed the formation of both L/Pd 1:1 and 2:1 species during the extraction process. These stoichiometries were further confirmed by job plots and NMR titration experiments. The ligands were found to aggregate slightly, especially at higher concentrations, which could result from multiple intermolecular hydrogen bonds as illustrated by X-ray crystallography. The configurations of PdL and PdL2 were further elucidated by analysis of single crystal structure and density-functional theory (DFT) calculations, respectively, where the first coordination sphere of Pd(II) was surrounded by four nitrogen or oxygen atoms in a quadrangular manner. This study provides an alternative method to separate palladium from HLLW and brings a new understanding of the coordination and complexation behaviors of Pd(II) with tridentate nitrogen ligands.

Nickel-Catalyzed Hydrotrifluoroalkylation of Alkynes to Construct Allylic Trifluoromethyl Terminal Alkenes.

Herein, we describe a nickel-catalyzed hydrotrifluoroalkylation of terminal alkyne for the synthesis of a manifold allylic trifluoromethyl terminal alkene. The combination of nitrogen and phosphine ligands, especially electron-rich ones, plays an indispensable role in the course of the reaction, promoting the reactivity to a remarkable level, demonstrating high efficiency, broad substrate scope, and favorable functional group compatibility. The strategy provides a facile method for the synthesis of diversified allylic CF3-containing drugs and bioactive molecules.

Ruthenium(II) Tris‐Pyrazolylmethane Complexes in Transfer Hydrogenation Reactions

AbstractWhile ruthenium(II) arene complexes have been widely investigated for their potential in catalytic transfer hydrogenation, studies on homologous compounds replacing the arene ligand with the six‐electron donor tris(1‐pyrazolyl)methane (tpm) are almost absent in the literature. The reactions of [RuCl(κ3‐tpm)(PPh3)2]Cl, 1, with a series of nitrogen ligands (L) proceeded with selective PPh3 mono‐substitution, affording the novel complexes [RuCl(κ3‐tpm)(PPh3)(L)]Cl (L=NCMe, 2; NCPh, 3; imidazole, 4) in almost quantitative yields. Products 2–4 were fully characterized by IR and multinuclear NMR spectroscopy, moreover the molecular structure of 4 was ascertained by single crystal X‐ray diffraction. Compounds 2–4 were evaluated as catalytic precursors in the transfer hydrogenation of a series of ketones with isopropanol as the hydrogen source, and 2 exhibited the highest activity. Extensive NMR experiments and DFT calculations allowed to elucidate the mechanism of the transfer hydrogenation process, suggesting the crucial role played by the tpm ligand, reversibly switching from tri‐ to bidentate coordination during the catalytic cycle.

A Brief Overview of the General Characteristics and Reactivity Towards Dioxygen of the Ferrous Tris (2-Pyridylmethyl Amine) Series Complexes is Presented

This paper examines the coordination chemistry of iron to TPA-like nitrogenous tripod ligands, focusing on how the spin state of the metal is affected by the presence of steric constraints and the coordination of acetonitrile ligands which can be displaced easily. Additionally, the reactivity of the derivatives with molecular oxygen, the conservation of geometry between the solid state and the solution and the various coordination geometries, electronic properties, and redox properties of ferrous tris(2-pyridylmethyl amine) series complexes are discussed. Furthermore, the molecular mechanisms of reactivity of these complexes are evaluated, providing an outlook for future research

Design of C1-symmetric tridentate ligands for enantioselective dearomative [3 + 2] annulation of indoles with aminocyclopropanes

Chiral polycyclic indolines are widely present in natural products and have become the focus of extensive synthetic efforts. Here, we show the catalytic asymmetric dearomative [3 + 2] annulation of indoles with donor-acceptor aminocyclopropanes to construct tricyclic indolines. Key to the success of the reaction is the rational design of C1-symmetric bifunctional tridentate imidazoline-pyrroloimidazolone pyridine ligand. Under 5 mol% of Ni(OTf)2-ligand complex, diverse tricyclic indolines containing cyclopentamine moieties are obtained in good chemoselectivities, high diastereoselectivities, and excellent enantioselectivities. An unusual cis-configuration ligand is superior to the trans-configuration ligand and the corresponding C2-symmetric tridentate nitrogen ligands in the annulation reaction. Mechanistic studies by control experiments and density functional theory calculations reveal a dual activation manner, where Ni(II) complex activates the aminocyclopropane via coordination with the geminal diester, and imidazolidine NH forms a H-bond with the succinimide moiety.

Complexes of 2-Amino-3-methylpyridine and 2-Amino-4-methylbenzothiazole with Ag(I) and Cu(II): Structure and Biological Applications

Coordination complexes (1–4) of 2-amino-4-methylbenzothiazole and 2-amino-3-methylpyridine with Cu(CH3COO)2 and AgNO3 were prepared and characterized by UV/Vis and FT-IR spectroscopy. The molecular structure for single crystals of silver complexes (2 and 4) were determined by X-ray diffraction. The coordination complex (2) is monoclinic with space group P21/c, wherein two ligands are coordinated to a metal ion, affording distorted trigonal geometry around the central Ag metal ion. The efficient nucleophilic center, i.e., the endocyclic nitrogen of the organic ligand, binds to the silver metal. Ligands are coordinated to adopt cis arrangement, predominantly due to steric reasons. The O(2) and O(3) atoms of the NO3− group further play an important role in such type of ligand arrangement by hydrogen bonding with the NH2 group of ligands. Complex (4) is orthorhombic, P212121, comprising two molecules of 2-amino-3-methylpyridine as ligand coordinated with the metal ion, affording a polymeric structure. The coordination behavior of the ligand is identical to that in complex 2, wherein ring nitrogen is coordinated to the metal center and bridged to another metal ion through an NH2 group. The resulting product is polymeric in nature with the Ag metal in the backbone and ligand as the bridge. Compounds (2–4) were found to be luminescent, while 1 did not show such activity. All compounds were screened for their preliminary biological activities such as antibacterial, antioxidant and enzyme inhibition. Compounds exhibited moderate activity in these tests.

Synthesis and characterization of heterobinuclear Schiff base nickel(II) complexes involving nitrogen and oxygen donor ligand

This study reports the synthesis of five novel Schiff base heterobinuclear nickel(II) and tin(II) complexes. The heterobinuclear complexes were synthesized by the interaction of N,N′-ethylenebis(2-hydroxyacetophenoniminato) nickel(II) with tin(II) salts of 2,4,6-trinitrophenol, 1-nitroso-2-naphthol, o-nitrophenol, 8-hydroxyquinoline and 2,4-dinitrophenol. Characterization of these complexes was carried by physico-chemical techniques such as elemental analyses, conductivity measurements, magnetic measurements, infrared spectra and electronic spectral studies. The molar conductance data reveals that the complexes are non-electrolytic in nature. The magnetic susceptibility data and the spectral studies propose square planar geometry of the complexes around nickel(II) and coordination to the metal centre via azomethine nitrogen and deprotonated phenolic oxygen atoms.

Nitrogen ligand influence on the CO-assisted ruthenium-catalyzed reductive amination

A representative set of amines and N-heterocycles was applied as additives in the CO-assisted Ru-catalyzed reductive amination of p-anisaldehyde with p-anisidine. Among the tested ligands, pyridine caused a strong activation for low active aliphatic substrates while bidentate heterocyclic ligands possess significant inhibition of catalyst for the majority of substrates.

Highly Reactive Hydrocarbon Soluble Alkylsodium Reagents for Benzylic Aroylation of Toluenes using Weinreb Amides

AbstractDeaggregating the alkyl sodium NaCH2SiMe3 with polydentate nitrogen ligands enables the preparation and characterisation of new, hydrocarbon soluble chelated alkylsodium reagents. Equipped with significantly enhanced metalating power over their organolithium counterparts, these systems can promote controlled sodiation of weakly acidic benzylic C−H bonds from a series of toluene derivatives under mild stoichiometric conditions. This has been demonstrated through the benzylic aroylation of toluenes with Weinreb amides, that delivers a wide range of 2‐arylacetophenones in good to excellent yields. Success in isolating and determining the structures of key organometallic intermediates has provided useful mechanistic insight into these new sodium‐mediated transformations.

Highly Reactive Hydrocarbon Soluble Alkylsodium Reagents for Benzylic Aroylation of Toluenes using Weinreb Amides.

Deaggregating the alkyl sodium NaCH2 SiMe3 with polydentate nitrogen ligands enables the preparation and characterisation of new, hydrocarbon soluble chelated alkylsodium reagents. Equipped with significantly enhanced metalating power over their organolithium counterparts, these systems can promote controlled sodiation of weakly acidic benzylic C-H bonds from a series of toluene derivatives under mild stoichiometric conditions. This has been demonstrated through the benzylic aroylation of toluenes with Weinreb amides, that delivers a wide range of 2-arylacetophenones in good to excellent yields. Success in isolating and determining the structures of key organometallic intermediates has provided useful mechanistic insight into these new sodium-mediated transformations.

Coordination Compounds of Cu, Zn, and Ni with Dicarboxylic Acids and N Donor Ligands, and Their Biological Activity: A Review.

Complexes of carboxylic acids are very often studied due to their interesting structural, spectral, and magnetic properties. This review is focused on complexes of four dicarboxylic acids, namely, 2,2'-thiodioacetic, 3,3'-thiodipropionic, 3,3'-dithiodipropionic, and fumaric acid. Many of the complexes were characterized by single crystal X-ray analyses. Without the analyses, it is very difficult to predict the coordination mode of carboxylate groups or nitrogen ligands on central atoms. Thus, structural properties are also discussed, as well as potential applications.

Aromatic 1,2-Azaborinin-1-yls as Electron-Withdrawing Anionic Nitrogen Ligands for Main Group Elements.

The 2-aryl-3,4,5,6-tetraphenyl-1,2-azaborinines 1-EMe3 and 2-EMe3 (E=Si, Sn; aryl=Ph (1), Mes (=2,4,6-trimethylphenyl, 2)) were synthesized by ring-expansion of borole precursors with N3 EMe3 -derived nitrenes. Desilylative hydrolysis of 1- and 2-SiMe3 yielded the corresponding N-protonated azaborinines, which were deprotonated with nBuLi or MN(SiMe3 )2 (M=Na, K) to the corresponding group 1 salts, 1-M and 2-M. While the lithium salts crystallized as monomeric Lewis base adducts, the potassium salts formed coordination polymers or oligomers via intramolecular K⋅⋅⋅aryl π interactions. The reaction of 1-M or 2-M with CO2 yielded N-carboxylate salts, which were derivatized by salt metathesis to methyl and silyl esters. Salt metathesis of 1-M or 2-M with methyl triflate, [Cp*BeCl] (Cp*=C5 Me5 ), BBr2 Ar (Ar=Ph, Mes, 2-thienyl), ECl3 (E=B, Al, Ga) and PX3 (X=Cl, Br) afforded the respective group 2, 13 and 15 1,2-azaborinin-2-yl complexes. Salt metathesis of 1-K with BBr3 resulted not only in N-borylation but also Ph-Br exchange between the endocyclic and exocyclic boron atoms. Solution 11 B NMR data suggest that the 1,2-azaborinin-2-yl ligand is similarly electron-withdrawing to a bromide. In the solid state the endocyclic bond length alternation and the twisting of the C4 BN ring increase with the sterics of the substituents at the boron and nitrogen atoms, respectively. Regression analyses revealed that the downfield shift of the endocyclic 11 B NMR resonances is linearly correlated to both the degree of twisting of the C4 BN ring and the tilt angle of the N-substituent. Calculations indicate that the 1,2-azaborinin-1-yl ligand has no sizeable π-donor ability and that the aromaticity of the ring can be subtly tuned by the electronics of the N-substituent.

Synthesis, characterization and antimicrobial activity of novel silver nanoparticles functionalized with nitrogenous ligands

As-synthesized nanoparticles AgNPsAA prepared using ascorbic acid (AA) were post-functionalized with ligands, viz., 4-hydroxybenzhydrazide (BH) and with 4-hydroxybenzaldehyde thiosemicarbazone (BTSC) to produce new silver nanoparticles, AgNPsAA-BH and AgNPsAA-BTSC. The nanoparticles were characterized by using UV–visible spectroscopy, FT-IR spectroscopy, P-XRD, SEM with EDX, and TEM techniques. The PXRD patterns of AgNPsAA, AgNPsAA-BH, and AgNPsAA-BTSC revealed diffraction peaks which correspond to (1 1 1), (2 0 0), (2 2 0), and (3 1 1) planes of face-cantered cubic (FCC) crystalline structure. The TEM images revealed spherical and agglomerated rod-like morphologies of as-synthesized and post-functionalized, respectively. The average particle sizes of AgNPsAA AgNPs@BH, and AgNPs@BTSC are found to be 28.4, 46.6, and 135.6 nm, respectively. The nanoparticles exhibited significant activity against bacteria, viz., Staphylococcus aureus, Escherichia coli and fungal species, viz., Candida albicans. The post-functionalized silver nanoparticles (AgNPsAA-BH and AgNPsAA-BTSC) showed higher antimicrobial activity than as-synthesized AgNPsAA metal nanoparticles.

Mixing nitrogenous ligands in osmium(VI)ligand-polysaccharide complexes. Voltammetric sensing

• Electroinactive dextran was modified with complexes of Os(VI) and nitrogenous ligands. • Os(VI)ligand modified dextran is electroactive and yields several redox peaks. • Nitrogenous ligand type significantly influences interfacial properties of modified dextrans. • Ligand combination can improve dextran analysis comparing to one-ligand modification. Simple chemical modification of carbohydrates with complexes of sixvalent osmium and nitrogenous ligands (Os(VI)L) changes electro inactive carbohydrates to electroactive species. In this work we show that the type of the nitrogenous ligand (L) significantly influences adsorption of Os(VI)L-modified dextrans at a charged surface. Modification by mixture containing two ligands can improve electrochemical analysis in comparison to simple modification only with one ligand. For instance, modification with complexes of Os(VI) and mixture of N,N,Ń,Ń-tetramethylethylenediamine (temed) with 2,2́-bipyridine (bipy) allows to (i) determine the concentration of Os(VI)L modified dextran in one order higher range as in case of dextran modified only with Os(VI)temed and (ii) discriminate between various polysaccharides differing in building units and structures.

Efficient additive-free formic acid dehydrogenation with a NNN-ruthenium complex.

A new ruthenium complex containing a pyridylidene amine-based NNN ligand was developed as a catalyst precursor for formic acid dehydrogenation, which, as a rare example, does not require basic additives to display high activity (TOF ∼10 000 h-1). Conveniently, the complex is air-stable, but sensitive to light. Mechanistic investigations using UV-vis and NMR spectroscopic monitoring correlated with gas evolution profiles indicate rapid and reversible protonation of the central nitrogen of the NNN ligand as key step of catalyst activation, followed by an associative step for formic acid dehydrogenation.

Coinage metal complexes of BN analogues of m-terphenyl ligands.

We report the synthesis of a series of group 11 metal complexes with sterically demanding anionic nitrogen ligands based on the 1,2-azaborinine motif. The ligands, which share structural similarities with m-terphenyls, have been used to stabilize two-coordinate phosphine complexes and dimeric complexes with close contacts between the metal centers. Spectroscopic, crystallographic, and theoretical investigations reveal close parallels to the related m-terphenyl complexes, including metallophilic interactions in the dimers.

Measurement and thermodynamic analysis of the solubility of iodine-containing organoaluminum supported by nitrogenous ligands in pure solvents

In this work, the solubility of L1H (1) (L1 = HC(CMeNAr)2, Ar = 2,4,6-Me3C6H2, molecular weight 334.5) in five pure solvents and the solubility of L1AlI2(2) (molecular weight 614.29) and L2AlI2(3) (L2 = HC(CMeNAr)2, Ar = 2,6-Et2C6H3, molecular weight 642.34) in four pure solvents ranging from 268.15 K to 303.15 K were determined by static analysis method.The experimental results showed that the solubility of the three compounds increased with the increase of temperature. At 303.15 K, the order of solubility (102x) of L1H (1) was toluene (37.160) > tetrahydrofuran (34.590) > n-hexane (25.527) > ethanol (0.849) > methanol (0.275). The order of solubility (102x) of L1AlI2(2) is dichloromethane (10.475) > toluene (2.383) > tetrahydrofuran (2.200) > n-hexane (0.352). The order of solubility (102x) of L2AlI2(3) is dichloromethane (5.836) > toluene (3.607) > tetrahydrofuran (0.829) > n-hexane (0.289). Seven common thermodynamic models are used to correlate experimental solubility data: Apelblat model, Yaws model, polynomial empirical equation, λh model, Wilson model, NRTL model, and UNIQUAC model. Most models fit well, with an average absolute relative deviation (ARD) less than 5 % and an average root mean square deviation (RMSD) less than 0.2 %. Among them, the Apelblat model has a wide range of applicability in terms of empirical models with an average ARD less than 3.5 %. The Wilson model has the best fitting effect in terms of activity coefficient models with an average ARD of 0.538 %. Hirshfeld surface analysis of L1AlI2(2) and L2AlI2(3) showed that H···H contact had the highest contact rate between the two compounds. accounting for 65.0 % and 66.0 %, respectively. In addition, Hansen solubility parameters were calculated to account for differences in solubility of L1H (1) in different solvents. Finally, the calculation results of the apparent thermodynamic function show that the dissolution process of the three compounds is an entropy-enhancing and endothermic process. The solubility data determined in this paper, the activity coefficient calculated by fitting, and the melting enthalpy can be used as basic chemical data for the synthesis and recrystallization of organoaluminum compounds.