Nickel Complexes Research Articles

Direct, Stereodivergent, and Catalytic Michael Additions of Thioimides to α,β‐Unsaturated Aldehydes – Total Synthesis of Tapentadol

AbstractDirect and stereodivergent Michael additions of N‐acyl 1,3‐thiazinane‐2‐thiones to α,β‐unsaturated aldehydes catalyzed by chiral nickel(II) complexes are reported. The reactions proceed with a remarkable regio‐, diastereo‐, and enantioselectivity, so access to any of the four potential Michael stereoisomers is granted through the appropriate choice of the chiral ligand of the nickel(II) complex. Simple removal of the heterocyclic scaffold furnishes a wide array of either syn or anti enantiomerically pure derivatives, which can be exploited for the asymmetric synthesis of biologically active compounds, as demonstrated in a new approach to tapentadol. In turn, a mechanism, based on theoretical calculations, is proposed to account for the stereochemical outcome of these transformations.

Controlling the Activation at NiII-CO2 2- Moieties through Lewis Acid Interactions in the Second Coordination Sphere.

Nickel complexes with a two-electron reduced CO2 ligand (CO2 2-, "carbonite") are investigated with regard to the influence alkali metal (AM) ions have as Lewis acids on the activation of the CO2 entity. For this purpose complexes with NiII(CO2)AM (AM=Li, Na, K) moieties were accessed via deprotonation of nickel-formate compounds with (AM)N(iPr)2. It was found that not only the nature of the AM ions in vicinity to CO2 affect the activation, but also the number and the ligation of a given AM. To this end the effects of added (AM)N(R)2, THF, open and closed polyethers as well as cryptands were systematically studied. In 14 cases the products were characterized by X-ray diffraction and correlations with the situation in solution were made. The more the AM ions get detached from the carbonite ligand, the lower is the degree of aggregation. At the same time the extent of CO2 activation is decreased as indicated by the structural and spectroscopic analysis and reactivity studies. Accompanying DFT studies showed that the coordinating AM Lewis acidic fragment withdraws only a small amount of charge from the carbonite moiety, but it also affects the internal charge equilibration between the LtBuNi and carbonite moieties.

Synthesis, spectral, DFT, and antibacterial studies of Nickel(II) and Cobalt(II) complexes with aminoantipyrine based Schiff base ligands

Schiff base complexes are a class of molecules that have sparked a great deal of attention due to their interesting chemical and physical properties, as well as their diverse applicability in a variety of scientific fields. Schiff bases and aminoantipyrine derivatives are continuously being investigated, despite their widespread use as medicines and bioactive compounds. In this study, we present the synthesis of new Ni(II) and Co(II) Schiff base complexes [M(L1-5)2Cl2] using the following ligands: 1,5-dimethyl-2-phenyl-4-((3,4,5-trimethoxy-benzylidene)amino)-1H-pyrazol-3(2H)-one (L1), 4-((4-methoxybenzylidene)amino)-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one (L2), 4-((3,4-dimethoxy-benzyli-dene)amino)-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one (L3), 4-((1-([1,1′-biphenyl]-4-yl)ethyli-dene)amino)-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one (L4), 4-((4-hydroxy-3-methoxy-benzylidene)amino)-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one (L5), derived from aminoantipyrine. Various approaches, including UV, IR, NMR (1H, 13C), DFT analyses, and molar conductance measurement, have been employed to characterise freshly synthesised compounds. The antimicrobial screening results indicate that the anti-bacterial activities of the metal complexes are more active than the free ligands. All the synthesized compounds were found to be active against both Gram positive and Gram negative bacteria. Compound [Ni(L4)2Cl2] was found to show best activity. According to the reactivity parameter factors, compound Co(L2)2Cl2 has a higher value of hardness (η = 1.677 eV) and a lower value of softness (σ = 0.596 eV), It suggests that compound [Co(L2)2Cl2] is less reactive and more stable.

A mixed-anion complex of nickel(II) with monoethanolamine

A mixed-anion complex of nickel(II) with monoethanolamine

Nickel Pincer Complexes Catalyzed Sustainable Synthesis of 3,4-Dihydro-2H-1,2,4-benzothiadiazine-1,1-dioxides via Acceptorless Dehydrogenative Coupling of Primary Alcohols.

We report the atom-economic and sustainable synthesis of biologically important 3,4-dihydro-2H-1,2,4-benzothiadiazine-1,1-dioxide (DHBD) derivatives from readily available aromatic primary alcohols and 2-aminobenzenesulfonamide catalyzed by nickel(II)-N∧N∧S pincer-type complexes. The synthesized nickel complexes have been well-studied by elemental and spectroscopic (FT-IR, NMR, and HRMS) analyses. The solid-state molecular structure of complex 2 has been authenticated by a single-crystal X-ray diffraction study. Furthermore, a series of 3,4-dihydro-2H-1,2,4-benzothiadiazine-1,1-dioxide derivatives have been synthesized (24 examples) utilizing a 3 mol % Ni(II) catalyst through acceptorless dehydrogenative coupling of benzyl alcohols with benzenesulfonamide. Gratifyingly, the catalytic protocol is highly selective with the yield up to 93% and produces eco-friendly water/hydrogen gas as byproducts. The control experiments and plausible mechanistic investigations indicate that the coupling of the in situ generated aldehyde with benzenesulfonamide leads to the desired product. In addition, a large-scale synthesis of one of the thiadiazine derivatives unveils the synthetic usefulness of the current methodology.

Spectroscopic, density functional theory and molecular docking studies of zinc (II) and nickel (II) complexes of Nˈ-(Furan-2-ylmethylene) furan-2-carbohydrazide as potential antibacterial drug

A furoic acid hydrazide derivative C10H8N2O3 (L), its nickel (II) and zinc (II) complexes (Ni(L)2 and Zn(L)2 respectively have been synthesized. The prepared ligand and its metal(II) complexes were characterized by melting point determination, elemental analysis, conductivity, and magnetic susceptibilities measurements, infrared, UV–visible, and 1H NMR spectroscopic techniques. In addition, the crystal structure of the ligand was determined by single-crystal X-ray diffraction techniques. DFT calculations were used in the determination of quantum chemical parameters. Based on the experimental and computational results, distorted tetrahedral geometries have been proposed for the zinc (II) and nickel (II) complexes. The antibacterial activity of the ligand and its Ni (II) and Zn (II) complexes were evaluated against three Gram-positive bacteria Methicillin-resistant Staphylococcus aureus, Staphylococcus epidermidis, and Staphylococcus aureus. The nickel (II) complex showed promising results as an antibacterial agent for Methicillin-resistant Staphylococcus aureus with MIC value of 3.12± 0.13 µg/mL as compared to the standard drug with MIC value of 2.0 ± 0.34 µg/mL. Furthermore, molecular docking analysis was performed and the average binding energy of Ni(L)2 with MRSA strain was extremely favourable (-8.4 kcal/mol), followed by the Zn(L)2 complex with average binding energy of -8.3 kcal/mol when docked against 1SAX. The nickel and zinc complexes had average binding energies -7.0 kcal/mol and -6.7 kcal/mol respectively against 2D45, as compared to that of the vancomycin drug (-4.2 kcal/mol). These results revealed that, the complexes are potential candidates for the development of new MRSA drug.

Synthesis, characterization, antimicrobial and antitubercular evaluation of nickel (II) complexes of ON donor quinoline-hydrazide core

Synthesis, characterization, antimicrobial and antitubercular evaluation of nickel (II) complexes of ON donor quinoline-hydrazide core

Effect of perfluorination at the 3-ethyl group in chlorophyll-a derivatives on physical properties in solution

Methyl 3-perfluoroethyl-pyropheophorbide-a exhibited a redmost visible (Qy) absorption maximum in solution at a longer wavelength than that of the non-fluorinated counterpart, while the former Qy band was sharper and more intense than the latter. In addition, the other visible bands of the fluorinated compound were red-shifted from those of the non-fluorinated. The perfluoroethylated molecule was more fluorescent at a longer wavelength with a longer lifetime, comparing with the ethylated analog. Similar results as in the above free bases were obtained for the corresponding nickel, copper, and zinc complexes. Additionally, the nickel and copper complexes exhibited similar absorption behaviors. This observation was due to the electron-withdrawing perfluoroethyl group bonding directly to the core chlorin π-system.

Kinetics and Composition of Gaseous Products of Pyrolysis of Organometallic Complexes of Nickel, Iron, and Copper with Inorganic Anions

Kinetics and Composition of Gaseous Products of Pyrolysis of Organometallic Complexes of Nickel, Iron, and Copper with Inorganic Anions

Catalytic Synthesis of Butene-1 and Hexene-1 in the Homogeneous Oligomerization of Ethylene in the Presence of Nickel Complexes Based on N-Heteroaryl-Substituted α-Diphenylphosphinoglycines

Catalytic Synthesis of Butene-1 and Hexene-1 in the Homogeneous Oligomerization of Ethylene in the Presence of Nickel Complexes Based on N-Heteroaryl-Substituted α-Diphenylphosphinoglycines

A Tris-Chelate Nickel Complex of Formylhydrazine: Synthesis and Crystal Structure

A Tris-Chelate Nickel Complex of Formylhydrazine: Synthesis and Crystal Structure

Ligand- and metal-exchange reactions of robust nickel complexes with pentagonal bipyramidal structures.

The coordination chemistries of transition metal complexes with pentagonal bipyramidal geometries were investigated, and the highly stable nature of a cyclic pentapyridyl ligand was disclosed. A NiCl2 complex with the pentapyridyl ligand was found to be stable toward water and acidic conditions. The stable complex underwent ligand-exchange reactions with nucleophilic reagents, and a series of pentagonal bipyramidal complexes with different apical ligands was prepared. Crystallographic analyses with the aid of theoretical calculations revealed that the complexes were constructed by electrostatic threading of a divalent linear nickel complex into the ring of the neutral, cyclic pentapyridyl, which resulted in robust water- and acid-resistant complexes with unique pentagonal bipyramidal structures. A reductive metal exchange reaction was then discovered, which enabled "linear divalent metal + electrostatic ring" formulations with different metal atoms.

Structural versatility in nickel (II) complexes of a hydrazone ligand based on alloxan: Preparation, spectroscopic, DFT, anticancer, and molecular docking studies

New binary and mixed‐ligand nickel (II) chelates of a hyrdazone ligand (HYQX) carrying alloxan and quinoline moieties were synthesized. Spectroscopic and analytical techniques were effectively used for identifying the composition and structure of the prepared nickel (II) HYQX chelates. The neutral nature of Ni‐HYQX complexes was demonstrated by molar conductivity studies, and magnetic moment values revealed octahedral geometry. The results demonstrated that HYQX behaves as a monoanionic di‐/tridentate chelating agent in all complexes, except nitrato C2 and acetato C4 complexes, which are bi‐ and tri‐nuclear complexes, respectively, with a unique mode of coordination. The thermal decomposition patterns of Ni‐HYQX complexes were investigated in relation to structure, and thermodynamic parameters were successfully calculated. The molecular structural features of HYQX and its Ni (II) chelates were investigated based on density functional theory (DFT) level at B3LYP/6‐311G(d,p) and LanL2dz level. Ni‐HYQX complexes were found to have anticancer action against Ehrlich Ascites Carcinoma. A molecular docking investigation was conducted to determine in what way the title compounds connect to the CDK‐5 inhibitor‐crystal structure of the inhibitor EFP with CDK‐2 (PDB ID: 3IG7) in order to verify their biological activity.

Computational Methods Enable the Prediction of Improved Catalysts for Nickel-Catalyzed Cross-Electrophile Coupling.

Cross-electrophile coupling has emerged as an attractive and efficient method for the synthesis of C(sp2)-C(sp3) bonds. These reactions are most often catalyzed by nickel complexes of nitrogenous ligands, especially 2,2'-bipyridines. Precise prediction, selection, and design of optimal ligands remains challenging, despite significant increases in reaction scope and mechanistic understanding. Molecular parameterization and statistical modeling provide a path to the development of improved bipyridine ligands that will enhance the selectivity of existing reactions and broaden the scope of electrophiles that can be coupled. Herein, we describe the generation of a computational ligand library, correlation of observed reaction outcomes with features of the ligands, and the in silico design of improved bipyridine ligands for Ni-catalyzed cross-electrophile coupling. The new nitrogen-substituted ligands display a 5-fold increase in selectivity for product formation versus homodimerization when compared to the current state of the art. This increase in selectivity and yield was general for several cross-electrophile couplings, including the challenging coupling of an aryl chloride with an N-alkylpyridinium salt.

Mass spectrometric analysis of transition metal complexes formed through contact of artificial sweat with circulating Euro coins

AbstractIt is well‐known that some metals/alloys sensitize the skin of susceptible individuals. Trace amounts of metals and chemical compounds containing metal ions can affect human health, i. e., cause allergy or inflammation. However, the details of this metal‐induced allergic reaction are not well understood. Complexes of nickel, copper, and zinc are known to be easily formed through contact of metal alloys with ubiquitously available organic compounds such as triacylglycerols, amino acids, urea, and fatty acids found in skin secretions or skin care products. Thus, an analytical technique is required to characterize and identify metal complexes formed on metallic everyday products, ideally offering a chemically specific, laterally resolved view of allergy‐causing processes. Here we present a mass‐spectrometry‐based analytical workflow to characterize metal‐containing compounds formed on the surface of 1‐euro coins when in contact with artificial sweat. This study identified different metal complexes by using tandem mass spectrometry (MS/MS). Surface imaging of 1‐Euro coins employing laser‐based mass spectrometry revealed the lateral distribution of Zn, Cu, and Ni complexes with low‐micrometer resolution.

Mono(Lewis Base)-Stabilized Gallium Iodide: An Unexplored Class of Promising Ligands.

Quantum-chemical (DFT) calculations on hitherto unknown base(carbene)-stabilized gallium monoiodides (LB→GaI) suggest that these systems feature one lone pair of electrons and a formally vacant p-orbital - both centered at the central gallium atom - and exhibit metallomimetic behavior. The calculated reaction free energies as well as bond dissociation energies suggest that these LB→GaI systems are capable of forming stable donor-acceptor complexes with group 13 trichlorides. Examination of the ligand exchange reactions with iron and nickel complexes indicates their potential use as ligands in transition metal chemistry. In addition, it is found that the title compounds are also able to activate various enthalpically robust bonds. Further, a detailed mechanistic investigation of these small molecule activation processes reveals the non-innocent behavior of the carbene (base) moiety attached to the GaI fragment, thereby indicating the cooperative nature of these bond activation processes. The energy decomposition analysis (EDA) and activation strain model (ASM) of reactivity were also employed to quantitatively understand and rationalize the different activation processes.

Nickel(II) Cyanoborates and Cyanoborate-Ligated Nickel(II) Complexes.

Nickel(II) cyanoborates Ni[BH2(CN)2]2·H2O (1b·H2O), Ni[BH(CN)3]2·0.5H2O (1c·0.5H2O), and Ni[B(CN)4]2·0.5H2O (1d·0.5H2O) were synthesized, and their reactivity with respect to dppeO2 (=1,2-bis-(diphenylphosphinoethane dioxide)), pyNO (=pyridine-N-oxide), dppe (=1,2-bis-(diphenylphosphinoethane), and DMSO (=dimethyl sulfoxide) was examined. Using these ligands, either cyanoborate (CB) complex salts of [Ni(dppe)2]2+ (2b-d) and [Ni(pyNO)6]2+ (3c-d) were isolated or complexes [Ni(DMSO)4{NC-B(CN)3}2] (1dDMSO) and [Ni(dppeO2)2{NC-B(CN)3}2] (1ddppeO2) were formed. Salt metathesis of [Ni(dppe)Cl2] with alkali metal cyanoborates resulted in mono- and disubstituted coordination compounds [Ni(dppe){NC-BH(CN)2}Cl] (5c) and [Ni(dppe){NC-BH2CN)2}] (4b), which decomposed to salts 2b-d. The synthetical pathways explored offer convenient routes to nickel(II) cyanoborates, nickel(II) complexes ligated with cyanoborates, and nickel(II) complex salts of cyanoborates. Further, our studies demonstrate the diverse character of cyanoborates in coordination chemistry as noncoordinating counteranions and also as medium coordinating anions forming novel transition-metal complexes and salts.

Reactivities of Photoredox Generated Nickel‐Nucleophilic Reactive Organometallic Species

AbstractDual photoredox catalysis has revolutionized the field of cross‐coupling reactions, enabling the discovery of numerous highly efficient reactions. This breakthrough is attributed to the exceptional combination of nickel catalysis with photoredox catalysis. Nickel exhibits both oxidative addition and reductive elimination processes, and a wide range of oxidation states (ranging from I to IV) accessible within a single catalytic cycle. Furthermore, nickel complexes are capable of catalyzing various processes through radical mechanisms. The latest feature has proven to be incredibly potent in facilitating the formation of new C−C and C−X bonds (X=H, O, S, N). The powerful combination of photoredox and nickel catalysis reveals an expansive domain of unexplored possibilities. It offers unparalleled opportunities for improving reactions and exploring innovative pathways. Under photoredox conditions, it is possible to form nucleophilic reactive organometallic intermediates, useful in reaction with electrophiles. We have devoted a research program towards the rediscovery and use of organometallic reagents, introduced by Corey, Hegedus, and Semmelack many years ago. The results unveiled the extraordinary capabilities of photoredox catalysis, enabling the creation and efficient utilization of potent nucleophilic organometallic reagents under mild conditions, free from the need for strong bases or stoichiometric metal reductants.

Effects of Temperature, Axial Ligand, and Photoexcitation on the Structure and Spin-State of Nickel(II) Complexes with Water-Soluble 5,10,15,20-Tetrakis(1-methylpyridinium-4-yl)porphyrin.

Water-soluble metalloporphyrins, depending on the metal center, possess special spectral, coordination, and photochemical features. In nickel(II) porphyrins, the Ni(II) center can occur with low-spin or high-spin electronic configuration. In aqueous solution, the cationic nickel(II) complex (Ni(II)TMPyP4+, where H2TMPyP4+ = 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin), exists in both forms in equilibrium. In this study, an equilibrium system involving the low-spin and high-spin forms of Ni(II)TMPyP4+ was investigated via application of irradiation, temperature change, and various potential axial ligands. Soret band excitation of this aqueous system, in the absence of additional axial ligands, resulted in a shift in the equilibrium toward the low-spin species due to the removal of axial solvent ligands. The kinetics and the thermodynamics of the processes were also studied via determination of the rate and equilibrium constants, as well as the ΔS, ΔH, and ΔG values. Temperature increase had a similar effect. The equilibrium of the spin isomers was also shifted by decreasing the solvent polarity (using n-propanol) as well as by the addition of a stronger coordinating axial ligand (such as ammonia). Since triethanolamine is an efficient electron donor in Ni(II)TMPyP4+-based photocatalytic systems, its interaction with this metalloporphyin was also studied. The results promote the development of efficient photocatalytic systems based on this complex.

Synthesis, Characterization, Fluorescence and Antibacterial Activities Studies of Transition Metals Complexes with a Macro Acyclic Schiff Base Ligand

The reactions of the Schiff base 2,2’-[(2-hydroxypropane-1,3-diyl) bis-(imino-methane diyl)] bis-(4-bromophenol) (H3L), with metal transition ions (Mn(II), Ni(II), Cu(II), Zn(II), and Cd(II),) afforded one type of complex formulated as [M(HL)(H2O)2].nH2O. These compounds have been characterized by elemental analysis, UV–Vis, FTIR, 1H and 13C NMR spectroscopies, molar conductivity and room temperature magnetic measurements. The structure of nickel (II) complex has been determined by X-ray crystallography. The complex crystallizes in the orthorhombic space group Pnma with a = 7.7702(4) Å, b = 23.1921(15) Å, c = 10.6853(5) Å, V = 1925.57(15) Å3, Z = 8, R1 = 0.043 and wR2 = 0.107, Dcalc = 1.893 Mg m−3. The ligand acts in tetradentate fashion in its di-deprotonated form. Two coordinated water molecules complete the coordination sphere. The environment around the Ni(II) center is best described as an octahedral geometry. In the crystal structure of the Schiff base ligand, the existence of a strong intramolecular O-H•••O hydrogen bonding [O2W-H2W 0.80(3) Å, H2W •••O1 1.915(3) Å, O2W••• O1 2.6258(19) Å, O2W-H2W•••O1 148(3)°] and [O1W-H1W 0.73(3), H1W•••O1 2.15(4) Å, O1W•••O1 2.836(2)Å, O1W-H1W•••O1 156(4)°] are observed. Antibacterial activity study shows that the cadmium (II) complex is more active than the free ligand on.