Mononuclear Copper Complexes Research Articles

Homogeneous oxidation of alcohols in water catalyzed with Cu(II)-triphenyl acetate/bipyridyl complex

A water-soluble mononuclear copper(II) complex, [Cu(OOCC(C6H5)3)(C10H8N2)(H2O)](ClO4)(CH3OH) (triphenylacetic acid=HOOCC(C6H5)3, 2-2′-bipyridyl (bipy)=C10H8N2) was synthesized and used as a catalyst precursor in the oxidation of primary (cinnamyl alcohol, benzyl alcohol, cyclohexanol, and 1-heptanol) and secondary alcohols (1-phenylethanol, 3-pentanol, and 2-octanol) to corresponding aldehydes, ketones, and acids. The complex exhibited high catalytic activity toward benzyl alcohol to benzaldehyde as one product (97% conversion in 6h) and cinnamyl alcohol to benzaldehyde (91.5%) and cinnamaldehyde (6.6%), in 6h reaction time with less catalyst loading (1mol%) at a moderate temperature (70°C). Water was used as a solvent and H2O2 as an oxidant for alcohol oxidation. Thus, the Cu(II)/H2O/H2O2 catalytic system could serve as an environmentally benign “green chemistry” alternative to oxidation methods in traditional organic solvents.

Mononuclear copper(II) and binuclear cobalt(II) complexes with halides and tetradentate nitrogen coordinate ligand: Synthesis, structures and bioactivities

In this work, we present the synthesis of four mononuclear copper(II) complexes [Cu(bdpab)X]Y and two binuclear cobalt(II) complexes [Co(bdpab)Cl]2Y2 (X=Cl−, Br−; Y=PF6−, BF4−) with tripodal N4-coordinate N-benzyl-N′,N′-bis(3,5-dimethyl-1H- pyrazol-1-yl)-2-methy]-1,2-ethylenediamine (bdpab) and the complexes were characterized by elemental analyses, IR spectral data, molar conductivity measurement, EPR and crystal structure determination. Single crystal X-ray diffraction studies indicate that the copper centers in the complexes [Cu(bdpab)Cl]PF6 and [Cu(bdpab)Br]PF6 have distorted square pyramidal geometry and complex [Co(bdpab)Cl]2(PF6)2 has octahedral geometry and two [Co(bdpab)Cl]+ units are linked by two (µ-Cl) bridges. Copper(II) complexes form 1D supramolecular chain along c-axis through C-H-π interaction whereas cobalt(II) complex form 1D supramolecular chain along a-axis through π-π interaction. The antimicrobial activity of complexes [Cu(bdpab)Cl]PF6, [Cu(bdpab)Br]PF6 and [Co(bdpab)Cl]2(PF6)2 were investigated against gram positive (Bacillus subtilus, Streptococcus aureus) and gram negative (Escherichia coli, Pseudomonas aeruginosa) bacterial strains by agar well dilution method and have demonstrated significant antimicrobial activity of the compounds. [Co(bdpab)Cl]2(PF6)2 exhibited the best antibacterial activity among all the synthesized complexes. The studies on the interaction of complexes and DNA by agarose gel electrophoresis method revealed that the complexes can effectively cleave the circular plasmid DNA at very low concentrations. The cytotoxic activity of the complexes against A549 lung cancer cells showed that the complexes have better cytotoxic activity than corresponding metal salts and [Cu(bdpab)Br]PF6 complex has best cytotoxic activity among the synthesized complexes.

Synthesis of mononuclear copper(II) complexes of N3O2 and N4O2 donors containing Schiff base ligands: Theoretical and biological observations

A new series of six mononuclear copper(II) complexes were synthesized from N3O2 and N4O2 donors containing Schiff base ligands, and characterized by various spectral methods. The geometry of the complexes was determined using UV–Vis, EPR and DFT calculations. The complexes of N3O2 donors (1–3) adopted square pyramidal geometry and the remaining complexes of N4O2 donors (4–6) show distorted octahedral geometry around copper(II) nuclei. Redox properties of the complexes show a one-electron irreversible reduction process in the cathodic potential (Epc) region from −0.74 to −0.98 V. The complexes show potent antioxidant activity against DPPH radicals. Molecular docking studies of complexes showed σ–π interaction, hydrogen bonding, electrostatic and van der Waals interactions with VEGFR2 kinase receptor. In vitro cytotoxicity of the complexes was tested against human breast cancer (MDA-MB-231) cell lines and one normal human dermal fibroblasts (NHDF) cell line through MTT assay. The morphological assessment data obtained by Hoechst 33258 and AO/EB staining revealed that the complexes induce apoptosis pathway of cell death.

The binding mode of pyrazolone derived copper(II), cobalt(II), nickel(II) and zinc(II) Schiff base coordination compounds with Calf-Thymus DNA

Transition metal complexes with Schiff base ligands possess remarkable biomedical activities that could be used to develop new metal-based anticancer agents. Anticancer metal complexes have attracted considerable interest since the successful application of platinum based anti-cancer drugs. Pyrazolone derivatives have been extensively studied and have shown a wide range of pharmacological activities and anticancer activities. A new class of mononuclear copper (II), cobalt(II), nickel(II) and zinc(II) complexes were synthesized using pyrazolone precursor Schiff base, obtained by the condensation of 4–aminoantipyrine with salicylaldehyde and respective metal(II) chloride. They have been characterized by elemental analysis, magnetic susceptibility, molar conductance measurements, UV-Vis., FT-IR, 1H NMR spectra and EPR studies. Their magnetic susceptibility values of the complexes at room temperature are consistent with octahedral geometry around the central metal ions. These complexes show lower conductance values, supporting their non-electrolytic nature. The data show that the complexes have composition of [ML2] type. In vitro DNA binding profiles of all complexes have been explored by absorption titrations, cyclic voltammetry technique and viscosity measurements. The corroborative results of above experiments suggest that these complexes are efficient metallo intercalators and can interact with CT-DNA. The binding constant values (Kb) clearly signify that the complexes bind to DNA through intercalation mode. The binding affinity of these complexes with CT DNA is found to be in the order, Cu(II)>Zn(II)>Co(II)>Ni(II), among them copper complex displaying a higher binding propensity as compared to other complexes.

Copper(II) and palladium(II) complexes with tridentate NSO donor Schiff base ligand: Synthesis, characterization and structures

Mononuclear copper(II) complex [CuL2] and palladium(II) complexes [Pd(X)L] where X = benzoate(bz) or salicylate(sal) and HL = 2-(methylthio)phenylimino)methyl)phenol, a Schiff base ligand with NSO coordination sites have been synthesized and characterized by microanalyses, IR, UV–Visible spectra, conductivity measurement and magnetic studies. Crystal structures of all the complexes have been solved by single crystal X-ray diffraction studies and showed that there are two molecules in a unit cell in the [CuL2] complex - one molecule has square planar geometry whereas second molecule has distorted square pyramidal geometry and palladium(II) complexes have distorted square planar geometry.

Synthesis, Characterization and Structure of Copper(II) complex involving Chloride and Tridentae NNS coordinate Schiff base ligand

Mononuclear copper(II) complex [CuLCl2] where L = (2-methylsulfanyl-phenyl)-(phenyl-pyridin-2-yl-methylene)amine, a tridentate NNS donor Schiff base ligand has been synthesized and characterized by microanalysis, IR, UV-Visible spectra and magnetic studies. Crystal structure of the complex has been solved by single crystal X-ray diffraction studies and shows the complex has distorted trigonal bipyramidal geometry.

New complexes of Cu(II) with dipicolinate and pyridyl-based ligands: An experimental and DFT approach

The three novel mononuclear copper(II) complexes with dipicolinate and pyridyl-based ligands [Cu(dipic)(L)(OH2)] (L=4-picoline, vinylpyridine, 4-styrylpyridine; dipic2−=dipicolinate) were afforded and structurally characterized. X-ray diffraction studies accounted for slight distorted square-pyramidal structures in which the dianion dipic2− acts as a tridentate ligand in a mer-fashion, the N-donor species occupy an in-plane position, and a water molecule was detected apically coordinated. To assess the effect of the nature of the pyridyl-substituent (para position) on electronic properties, other complexes were also synthesized: [Cu(dipic)(py)(OH2)], [{Cu(dipic)(OH2)}2(μ-pyz)] and [{Cu(dipic)(OH2)}(μ-pypy){Cu(dipic)}] (py=pyridine, pyz=pyrazine, pypy=(E)-1,2-bis(pyridine-4-yl)ethane). Absorptive behavior in the UV–VIS region was studied in solution and in the solid state (reflectance measurements).Additionally, geometry and population analyses were conducted by means of DFT calculations. Electronic UV–VIS spectra were simulated for both dinuclear complexes in the framework of the TD-DFT methodology to assign the origin of the absorption bands.

Synthesis, characterization, and crystal structures of mononuclear and dinuclear copper(II) complexes derived from similar tridentate Schiff bases

ABSTRACTA mononuclear copper(II) complex, [CuL1N3] (1), and a dinuclear copper(II) complex, [Cu2(L2)2(μ1,1-N3)2] (2), where L1 and L2 are the deprotonated forms of 2-[(2-diethylaminoethylimino)methyl]-4,6-difluorophenol (HL1) and 2,4-difluoro-6-[(2-isopropylaminoethylimino)methyl]phenol (HL2), respectively, were prepared. The complexes were characterized by elemental analysis, infrared (IR) and UV–Vis spectra, and single crystal X-ray determination. The crystal of complex 1 crystalizes in the orthorhombic space group Pbca, with unit cell a = 6.9327(7), b = 13.8926(13), c = 31.243(2) Å, V = 3009.1(5) Å3, Z = 8. The crystal of complex 2 crystalizes in the monoclinic space group P21/n, with unit cell a = 20.8686(16), b = 9.4893(16), c = 7.2440(12) Å, β = 94.020(2)°, V = 1431.0(4) Å3, Z = 4. The Cu atom in complex 1 is in square planar geometry, and that in complex 2 is in square pyramidal geometry.

N2O Formation via Reductive Disproportionation of NO by Mononuclear Copper Complexes: A Mechanistic DFT Study

The mechanism of the copper(I)-mediated reductive disproportionation reaction of NO to form N2O was investigated for five different 3,5-substituted tris(pyrazolyl)borate copper complexes (CuTpR1,R2) by means of DFT calculations. A thorough search of the potential surface was performed, using the B3LYP functional with the def2-SVP basis set for optimization purposes and def2-TZVP single-point calculations for constructing the potential energy surface for two of these complexes. The results can be condensed into six competing reaction mechanisms, two of which were more closely investigated using full def2-TZVP optimized potential and free energies. The results consistently predict the same mechanism to have the lowest overall barrier. For all five different complexes, this is found to be in good agreement with the experimental reaction barriers. The key intermediate for the transition from the N-bound reactant to the O-bound product contains a stable (NO)3 unit with one N-Cu and one O-Cu bond, which was not included in the mechanistic considerations reported in the literature. Further analysis of the charge distribution and the spin density demonstrates the formation of a Cu(II)-(N2O2-) intermediate and the electronic influence of the different ligands.

Isolation and characterization of hydrocarbon soluble NHC copper(I) phosphoranimide complex and catalytic application for alkyne hydroboration reaction

Novel NHC copper(I) phosphoranimide complexes have been isolated and characterized by NMR and X-ray crystallography studies. The feature of this hydrocarbon soluble mononuclear copper complex as effective hydroboration catalyst could be attributed to the rapid forming of copper hydride intermediate with the generating of more stable bulky borate by-product tBuPNB(pin), which is unveiled by excellent catalytic performance of [NHC]CuNPtBu3 for the alkyne hydroboration reaction with exclusive β-regio- and trans-stereo-selectivity in mild reaction condition. The copper hydride intermediate could also be observed from stoichiometric reaction of [NHC]CuNPtBu3 with HB(pin) compound by NMR analysis.

Oxygen Delivery as a Limiting Factor in Modelling Dicopper(II) Oxidase Reactivity.

Deprotonation of ligand-appended alkoxyl groups in mononuclear copper(II) complexes of N,O ligands L1 and L2 , gave dinuclear complexes sharing symmetrical Cu2 O2 cores. Molecular structures of these mono- and binuclear complexes have been characterized by XRD, and their electronic structures by UV/Vis, 1 H NMR, EPR and DFT; moreover, catalytic performance as models of catechol oxidase was studied. The binuclear complexes with anti-ferromagnetically coupled copper(II) centers are moderately active in quinone formation from 3,5-di-tert-butyl-catechol under the established conditions of oxygen saturation, but are strongly activated when additional dioxygen is administered during catalytic turnover. This unforeseen and unprecedented effect is attributed to increased maximum reaction rates vmax , whereas the substrate affinity KM remains unaffected. Oxygen administration is capable of (partially) removing limitations to turnover caused by product inhibition. Because product inhibition is generally accepted to be a major limitation of catechol oxidase models, we think that our observations will be applicable more widely.

Syntheses, crystal structures, spectral and DFT studies of copper(II) and nickel(II) complexes with N′-(pyridine-2-ylmethylene)acetohydrazide

Three new metal(II) complexes (copper(II)/nickel(II)) with N’-(pyridine-2-ylmethylene) acetohydrazide [Cu(HL)2]·(ClO4)21, [Ni(HL)2]·NO3·ClO4·0.5H2O 2 and [Cu(μ-CH3COO)(L)]2·4H2O 3 have been synthesized form N′-(pyridine-2-ylmethylene) acetohydrazide (HL/L). The synthesized complexes were characterized by means of elemental analysis, spectroscopic, magnetic susceptibility and cyclic voltammetric measurements. Single crystal X-ray analysis of complexes has revealed the presence of a distorted octahedral geometry around mononuclear copper(II) and nickel(II) complex (1 and 2) and distorted square pyramidal geometry around copper(II) centers of complex 3. In the solid state Schiff base remains in its keto-tautomeric form. On complexation with Cu(II)/Ni(II) ions in natural or slightly acidic medium it coordinates through ketonic oxygen (keto form, HL) whereas in basic medium it acts as monoprotic (enol form, L) ligand. Variable-temperature magnetic susceptibility data of the compound 3 indicates the presence of weak antiferromagnetic interaction with J = −12.3 cm−1. The cyclic voltammograms of homobinuclear complex 3 in DMSO gave two irreversible waves which correspond to the Cu(II,II)/Cu(II,I) and Cu(II,I)/Cu(I,I) redox processes. On the other hand, the mononuclear complex 1 exhibited M(II)/M(I) quasireversible wave E1/2 = 0.06 V vs Ag/AgCl. X-band electron paramagnetic resonance (epr) data of copper(II) mononuclear and binuclear complexes 1 and 3 have been collected to investigate magnetic properties of the complexes in detail. The electronic structures, spectral properties of the ligands and the complexes have been explained by DFT and TD-DFT calculations. In addition, biological activity ranking of present complexes 1–3 are investigated theoretically. Complexes catalyzed the dismutation of superoxide (O2▪─) at biological pH in alkaline nitroblue tetrazolium chloride assay and IC50 values were evaluated.

Synthesis, characterization, and structural determination of copper(II) complexes with alkyl derivatives of hydroxybenzophenones

Four mononuclear copper(II) complexes, [Cu(LFQM-115)2] (1), [Cu(LFQM-116)2] (2), [Cu(LFQM-117)2] (3) and [Cu(octyloxy)2] (4) [LFQM-115 = 2-hydroxy-4-O-methylbenzophenone (C14H11O3), LFQM-116 = 2-hydroxy-4-O-butylbenzophenone (C17H18O3), LFQM-117 = 2-hydroxy-4-O-(33-dimethylallyl)benzophenone (C18H18O3) and octyloxy = 2-hydroxy-4-O-octylbenzophenone (C21H25O3)], have been prepared and investigated by infrared spectroscopy, thermal analysis, and powder and single crystal X-ray diffraction. Even though the synthesis and infrared analysis of 1, 2, and 4 have been reported previously, their crystal structures were elucidated for the first time here. In addition, the crystal structures of LFQM-116 and LFQM-117 were also determined by single crystal X-ray diffraction. The pseudo-translational symmetry found in LFQM-116 and the isomorphism between LFQM-115 and LFQM-117 are discussed. The complexes were prepared from a reaction of copper(II) nitrate trihydrate and the respective ligand in a (1:2) molar ratio in methanol (for 1 and 2) or THF (for 3 and 4) with addition of NaOH. Furthermore, crystallographic studies show that each copper(II) exhibits a square planar geometry, coordinated by four oxygens of two ligands. The nature and crystal packing of the intermolecular interactions are discussed. Compounds 2 and 3 are isomorphic crystals and all structures have the same supramolecular synthon.

One-pot aqueous-phase synthesis of quinoxalines through oxidative cyclization of deoxybenzoins with 1,2-phenylenediamines catalyzed by a zwtterionic Cu(II)/calix[4]arene complex

A green protocol for the synthesis of quinoxalines has been developed from catalytic oxidative cyclization of deoxybenzoins with 1,2-phenylenediamines in water. The optimal conditions are involved in the use of a water-soluble mononuclear copper(II) complex of a zwitterionic calix[4]arene [Cu(II)L(H2O)]I2 (1, H4L=[5,11,17,23–tetrakis (trimethylammonium)–25,26,27,28–tetrahydroxycalix[4]arene]) as a catalyst in alkali solution after refluxing for 15h in O2. The target quinoxaline and its derivatives were obtained in good yields (up to 88%). The procedure described in this paper is simple, practical and environmentally benign.

Reversible luminescent colour changes of mononuclear copper(i) complexes based on ligand exchange reactions by N-heteroaromatic vapours.

[CuCl(PPh3)2(4-Mepy)] (PPh3 = triphenylphosphine, 4-Mepy = 4-methylpyridine), a highly blue-luminescent mononuclear copper(i) complex, shows reversible emission colour change ranging from blue-green to red by vapour exposure to N-heteroaromatics, such as pyridine, pyrimidine, and 2-methylpyrazine. The remarkable colour changes occur due the ligand exchange reaction between the solid and gas. Such ligand exchange reactions would be applicable to various vapours with coordination ability and be useful for the sensing of such volatile organic compounds as well as a new convenient methodology for the preparation of luminescent complexes.

Mono-, tri- and polynuclear copper(ii) complexes of Schiff-base ligands: synthesis, characterization and catalytic activity towards alcohol oxidation

A mononuclear copper(ii) complex acts as a superior catalyst compared to a tri- or polynuclear complex towards oxidation of alcohols to the corresponding aldehydes.

μ-Pyridine-bridged copper complex with robust proton-reducing ability.

The binuclear copper complex [Cu(DQPD)]2 (where DQPD = deprotonated N2,N6-di(quinolin-8-yl)pyridine-2,6-dicarboxamide (DQPDH2)) was synthesised and characterised by various spectroscopic as well as electrochemical techniques. The binuclear copper complex was converted into a mononuclear one by the addition of 2 equivalents of pTsOH into [Cu(DQPD)]2. The interconversion between the dimer and monomer complex was studied through UV-Vis spectroscopy and cyclic voltammetry. The mononuclear copper complex showed high catalytic activity towards electrochemical proton reduction using acetic acid as the external proton source in 95 : 5 (v/v) DMF/H2O. It showed an ic/ip (where ic is the catalytic current in the presence of acetic acid and ip is the reduction peak current in absence of acid) value of 24 and a turnover rate (TOF) of 111.70 s-1 at a scan rate of 100 mV s-1 at 25 °C. The [Cu(DQPD)]2 complex evolved hydrogen under the irradiation of visible light in the presence of fluorescein (Fl) as a photosensitizer and triethylamine (TEA) as the sacrificial electron donor with an initial TOF of 0.03 s-1 with respect to the catalyst.

Synthesis, crystal structure, stability studies, DNA/albumin interactions, and antimicrobial activities of two Cu(II) complexes with amino acids and 5-nitro-1,10-phenanthroline

One-dimensional (1-D) coordination polymer and mononuclear copper(II) complexes, ([Cu(nphen)(asn)]ClO4)n (1) and [Cu(nphen)(gln)(H2O)]ClO4·H2O (2) (nphen = 5-nitro-110-phenanthroline, asn = asparagine, gln = glutamine), have been synthesized and characterized by IR spectroscopy, ESI-MS, CHN analysis, and single-crystal X-ray diffraction. These binary and ternary complexes of copper(II) with nphen, asn, and gln have been investigated using potentiometric methods in 0.1 M KCl aqueous ionic media at 298.2 K. The protonation constants of the ligands and the stability constants of 1 and 2 have been calculated from the potentiometric data using the “BEST” software package. The potentiometric results have been analyzed using the “SPE” software package, and the distribution curves for the copper-containing species have been determined for the ternary systems. The CT-DNA-binding properties of these complexes have been investigated by thermal denaturation measurements and both absorption and emission spectroscopy. Further, the interaction of these complexes with bovine serum albumin (BSA) and human serum albumin (HSA) has been investigated using absorption and emission spectroscopy. The thermodynamic parameters, free energy change (ΔG), enthalpy change (ΔH), and entropy change (ΔS) were calculated by the van’t Hoff equation and discussed. The distances between the serum albumins and 1 and 2 have been obtained according to fluorescence resonance energy transfer (FRET). Conformational changes of serum albumins have been observed from synchronous fluorescence technique. The antimicrobial activity of the complexes has also been tested on some bacteria. The effect of different amino acids on the copper(II) complexes are discussed.

Catalytic promiscuity of mononuclear copper(II) complexes in mild conditions: Catechol and cyclohexane oxidations

Two copper(II) mononuclear complexes were synthesized and investigated as promiscuous oxidative catalysts: [Cu(pymimi)Cl2]: [(2-(pyridyl-2-yl)ethyl)((1-methylimidazol-2-yl)methyl)imine](bischlorido)copper(II), C1, and [Cu(pymima)Cl2]: [(2-(pyridyl-2-yl)ethyl)((1-methylimidazol-2-yl)methyl)amine] (bischlorido)copper(II), C2. Both complexes were characterized by the following techniques: X-ray crystallography, decomposition point, elemental analysis, IR, UV–Vis and EPR spectroscopies, conductimetric analysis and electrochemistry. DFT calculations at the B3LYP level were carried out to corroborate structural, vibrational and spin Hamiltonian parameters (gx, gy and gz). TDDFT electronic spectra were calculated at CAMB3LYP level. Cyclohexane peroxidation promoted by C1 and C2 yielded the following overall conversions/turnover numbers: 48%/531s−1 and 46%/508s−1, respectively. Both complexes also catalyze the conversion of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylquinone (3,5-DTBQ) with turnover numbers of 6.0×10−2s−1 for C1 and 11.0×10−2s−1 for C2. Complexes C1 and C2 can be classified as substrate promiscuous catalysts due to their ability to promote the oxidation of two different substrates, in the presence of distinct oxidants (O2, for catechol and H2O2 for cyclohexane).

Control of Complex Formation through Peripheral Substituents in Click-Tripodal Ligands: Structural Diversity in Homo- and Heterodinuclear Cobalt-Azido Complexes.

The azide anion is widely used as a ligand in coordination chemistry. Despite its ubiquitous presence, controlled synthesis of azido complexes remains a challenging task. Making use of click-derived tripodal ligands, we present here various coordination motifs of the azido ligands, the formation of which appears to be controlled by the peripheral substituents on the tripodal ligands with otherwise identical structure of the coordination moieties. Thus, the flexible benzyl substituents on the tripodal ligand TBTA led to the formation of the first example of an unsupported and solely μ1,1-azido-bridged dicobalt(II) complex. The more rigid phenyl substituents on the TPTA ligand deliver an unsupported and solely μ1,3-azido-bridged dicobalt(II) complex. Bulky diisopropylphenyl substituents on the TDTA ligand deliver a doubly μ1,1-azido-bridged dicobalt(II) complex. Intriguingly, the mononuclear copper(II) complex [Cu(TBTA)N3]+ is an excellent synthon for generating mixed dinuclear complexes of the form [(TBTA)Co(μ1,1-N3)Cu(TBTA)]3+ or [(TBTA)Cu(μ1,1-N3)Cu(TPTA)]3+, both of which contain a single unsupported μ1,1-N3 as a bridge. To the best of our knowledge, these are also the first examples of mixed dinuclear complexes with a μ1,1-N3 monoazido bridge. All complexes were crystallographically characterized, and selected examples were probed via magnetometry and high-field EPR spectroscopy to elucidate the electronic structures of these complexes and the nature of magnetic coupling in the various azido-bridged complexes. These results thus prove the power of click-tripodal ligands in generating hitherto unknown chemical structures and properties.