Aerial oxidation of primary alcohols and amines catalyzed by Cu(II) complexes of 2,2'-selenobis(4,6-di-tert-butylphenol) providing [O,Se,O]-donor atoms

Seven copper(II)-complexes 1-7 with the ligand 2,2'-selenobis(4,6-di-tert-butylphenol) providing [O,Se,O]-donor atoms have been isolated and characterized. Three of them 1, 2 and 3 are mononuclear, two 4 and 7 dinuclear and 5, 6 are trinuclear. The crystal structures of the complexes were determined by X-ray diffraction and the electronic structures were established by various physical methods including EPR and variable temperature (2-290 K) susceptibility measurements. The magnetic behaviour of the compounds 4-6 exhibits antiferromagnetic exchange coupling resulting in well-isolated S(t)= 1/2 ground state for 5 and 6 and a diamagnetic spin state for 4. Complexes 5 and 6 belong to the class of asymmetric trinuclear copper(II) complexes modelling the trinuclear copper site in multicopper oxidases. Complex 1 is a catalyst in the presence of a strong base for the aerial oxidation of primary alcohols to the corresponding aldehydes. A dinuclear complex, seemed to be 4, prepared in situ has been found to be a catalyst for the aerial oxidation of primary amines containing alpha-C-H atoms. Primary kinetic isotope effects show that H-abstraction from the alpha-carbon atom of a coordinated substrate (alcoholato or amine) is the rate-determining step in both cases. Two functional models for the metalloenzymes galactose oxidase and amine oxidases are thus described.     

A tetracopper(II)-tetraradical cuboidal core and its reactivity as a functional model of phenoxazinone synthase

The coordination chemistry of the tridentate ligand N-(2-hydroxy-3,5-di-tert-butylphenyl)-2-aminobenzylalcohol H3L has been studied with the copper(II) ion. The ligand is noninnocent in the sense that it is readily oxidized in the presence of air to its o-iminobenzosemiquinonato [L*]2- radical form. The crystal structure of the synthesized tetracopper(II)-tetraradical complex [CuII4(L*)4] (1), has been determined by X-ray crystallography at 100 K. Variable-temperature (2-290 K) magnetic susceptibility measurements of complex 1 containing eight paramagnetic centers establish the spin ground state to be diamagnetic (St=0) arising from the antiferromagnetic interactions. Electrochemical measurements (cyclic voltammograms and square wave voltammograms) indicate four one-electron reductions of the ligand prior to the reduction of the metal center. Complex 1 is found to catalyze the aerial oxidation of 2-aminophenol to 2-amino-phenoxazine-3-one, thus modeling the catalytic function of the copper-containing enzyme phenoxazinone synthase. Kinetic measurements together with electron paramagnetic resonance and electronic spectral studies have been used to decipher the complex six-electron oxidative coupling of 2-aminophenol. An "on-off" mechanism of the radicals together with redox participation of the metal center is proposed for the catalytic oxidation processes.     

Targeted oxidase reactivity with a new redox-active ligand incorporating N2O2 donor atoms. Complexes of Cu(II), Ni(II), Pd(II), Fe(III), and V(V)

The coordination chemistry of the tetradentate ligand N,N'-bis(2-hydroxy-3,5-di-tert-butylphenyl)-2,2'-diaminobiphenyl H(4)L has been studied with the copper(II), nickel(II), palladium(II), iron(III), and vanadium(V) ions. The ligand is non-innocent in the sense that it is readily oxidized in the presence of air to its o-iminobenzosemiquinonato (L(**))(2-) radical form. The crystal structures of the diradical compounds, [Cu(II)(L(**))] 1, [Ni(II)(L(**))] 2, [Pd(II)(L(**))] 3, the monoradical high-spin compound [Fe(III)(HL(*))Cl] 4, and the di(mu-methoxo)divanadium(V) compound [L(2)V(2)(mu-OCH(3))(2)] 5 without a radical have been determined by X-ray crystallography at 100 K. The biphenyl backbone of the ligand induces a tetrahedral distortion of the metal(II) geometry in 1, 2, and 3 having a N(2)O(2) coordination environment. The dihedral angles between the metal planes are 35.5 degrees for 1, 30.8 degrees for 2, and 22.2 degrees for 3. Variable-temperature (2-290 K) magnetic susceptibility measurements together with Mossbauer and electron paramagnetic resonance (EPR) spectroscopy establish the electronic structures of the complexes. Electrochemical cyclic voltammetric measurements indicate four one-electron reversible redox processes of the ligand for 1, 2, and 3. Complex 1 is found to catalyze the aerial oxidation of benzylalcohol to benzaldehyde, thus modeling the catalytic function of the copper-containing enzyme Galactose Oxidase (GO). Kinetic measurements in conjunction with EPR and UV-vis spectroscopic studies have been used to decipher the catalytic oxidation process. A ligand-derived redox activity has been proposed as a mechanism in which complex 1 disproportionates in a basic medium to generate the catalytically active species. An "on-off" mechanism of the radicals without apparent participation of the metal center is invoked for the catalytic process, whose intimate mechanism thus differs from that of the enzyme Galactose Oxidase.     

Structurally diverse copper(II) complexes of polyaza ligands containing 1,2,3-triazoles: site selectivity and magnetic properties

Copper(II) acetate mediated coupling reactions between 2,6-bis(azidomethyl)pyridine or 2-picolylazide and two terminal alkynes afford 1,2,3-triazolyl-containing ligands L(1)-L(6). These ligands contain various nitrogen-based Lewis basic sites including two different pyridyls, two nitrogen atoms on a 1,2,3-triazolyl ring, and the azido group. A rich structural diversity, which includes mononuclear and dinuclear complexes as well as one-dimensional polymers, was observed in the copper(II) complexes of L(1)-L(6). The preference of copper(II) to two common bidentate 1,2,3-triazolyl-containing coordination sites was investigated using isothermal titration calorimetry and, using zinc(II) as a surrogate, in (1)H NMR titration experiments. The magnetic interactions between the copper(II) centers in three dinuclear complexes were analyzed via temperature-dependent magnetic susceptibility measurements and high-frequency electron paramagnetic resonance spectroscopy. The observed magnetic superexchange is strongly dependent on the orientation of magnetic orbitals of the copper(II) ions and can be completely turned off if these orbitals are arranged orthogonal to each other. This work demonstrates the versatility of 1,2,3-triazolyl-containing polyaza ligands in forming metal coordination complexes of a rich structural diversity and interesting magnetic properties.     

Oxidation of an o-iminobenzosemiquinone radical ligand by molecular bromine: structural, spectroscopic, and reactivity studies of a copper(II) o-iminobenzoquinone complex

The bis(o-iminobenzosemiquinonato)copper(II) complex 1, containing the radical form [L(*)SQ](1-) arising from the aerial oxidation of the noninnocent ligand 2-anilino-4,6-di- tert-butylphenol, H2L, is readily oxidized by molecular bromine to a bis(o-iminobenzoquinone)copper(II) complex, 2. Thus, a ligand-based oxidative addition is reported for complex 1 containing an electron-rich Cu(II) d(9) metal ion. The crystal structure of the synthesized hexacoordinated complex [Cu(II)(LBQ)2Br2] (2) has been determined by X-ray crystallography at 100 K. Variable-temperature (2-290 K) magnetic susceptibility measurements and an X-band electron paramagnetic resonance spectrum establish the spin state to be St = 1/2 because of localized spin moments mainly in the (d(x(2)-y(2)))(1) orbital of a Cu(II) d(9) ion, indicating clearly the presence of a neutral iminobenzoquinone form, [LBQ](0), of the ligand in 2, as is found also in the X-ray structure. Electrochemical measurements (cyclic voltammograms and coulometry) indicate two successive one-electron reductions of the ligand. The reactivity of complex 2 as an oxidizing agent toward ethanol and triethylamine has been investigated.     

Spectroscopic characterization of copper(II) complexes of indoxyl N(4)-methyl thiosemicarbazone

New copper(II) complexes of indoxyl thiosemicarbazone (ITSC) of general composition CuL2X2 (where L: ITSC; X: Cl-, NO3-, ClO4-, NCS-) have been synthesized and characterized by elemental analysis, molar conductance, magnetic susceptibility measurements and spectral (electronic, IR, EPR, 1H NMR, Mass) studies. Cyclic voltammetry measurements show quasi-reversible Cu2+/Cu1+ couple. Various physico-chemical techniques suggest a tetragonal structure for these copper(II) complexes.     

Spectral,biological screening,and DNA studies of metal chelates of 4-[N,N-bis-(3,5-dimethyl-pyrazolyl-1-methyl)]aminoantipyrine

Tridentate chelate complexes of Co(II), Ni(II), and Cu(II) have been synthesized from 4-[N,N-bis-(3,5-dimethyl-pyrazolyl-1-methyl)]aminoantipyrine. Microanalytical data, UV-Vis, magnetic susceptibility, Infrared, ¹H- ¹³C-NMR, mass, thermal gravimetric analysis and electron paramagnetic resonance (EPR) techniques were used to confirm the structures. The electronic absorption spectra and magnetic susceptibility measurements suggest a distorted octahedral geometry for the metal. EPR spectra of the copper(II) complex at 77?K confirm the distorted octahedral geometry of the copper(II) complex. The antimicrobial activities of the ligand and metal complexes against the bacteria such as Xanthomonas maltophilia, Chromobacterium violaceum, Acinetobacter, Staphylococci, Streptococci, and the fungus Candida albicans have been carried out. A comparative study of minimum inhibitory concentration values of the ligand and its metal complexes indicates that metal complexes exhibit higher antibacterial and antifungal activity than the free ligand. The electrochemical behavior of copper(II) complex was studied by cyclic voltammetry. The complexes show nuclease activity in the presence of oxidant.     

Synthesis,Spectral, Thermal and Biological Studies of Mn(II), Co(II), Ni(II) and Cu(II) Complexes with 1‐(((5‐Mercapto‐1H‐1,2,4‐triazol‐3‐yl)imino)‐methyl)naphthalene‐2‐ol

Mn(II), Co(II), Ni(II) and Cu(II) complexes of 5‐mercapto‐1,2,4‐triazol‐3‐imine‐2′‐hydroxynaphthaline have been synthesized and characterized by elemental analysis, IR, ¹H NMR, EI‐mass, UV‐Vis, and ESR (electron spin resonance) spectra, molar conductance, magnetic moment measurements, DC conductivity and thermogravimetric analysis. IR spectra confirm that the ligand molecule existed in both thione and thiole forms. The molar conductance values indicate the complexes are nonelectrolyte. The magnetic moment values of the complexes display paramagnetic behavior. All studies confirm the formation of an octahedral geometry for complex 1 and the other complexes have tetrahedral geometrical structures. The structures of the complexes have also been theoretically studied by using the molecular mechanic calculations by the hyperchem. 8.03 molecular modeling program which confirm the proposed structures. The Schiff‐base ligand and its metal complexes have also been screened for their antimicrobial activities.     

Tridentate facial ligation of tris(pyridine-2-aldoximato)nickel(II) and tris(imidazole-2-aldoximato)nickel(II) To generate NiIIFeIIINiII, MnIIINiII, NiIINiII, and ZnIINiII and the electrooxidized MnIVNiII, NiIINiIII, and ZnIINiIII species: a magnetostructural, electrochemical, and EPR spectroscopic study

Eight hetero- and homometal complexes 1-6, containing the metal centers Ni(II)Fe(III)Ni(II) (1), Mn(III)Ni(II) (2), Ni(II)Ni(II) (3a-c and 4), Zn(II)Ni(II) (5), and Zn(II)Zn(II) (6), are described. The tridentate ligation property of the metal complexes tris(pyridine-2-aldoximato)nickel(II) and tris(1-methylimidazole-2-aldoximato)nickel(II) with three facially disposed pendent oxime O atoms has been utilized to generate the said complexes. Complex 1 contains metal centers in a linear arrangement, as is revealed by X-ray diffraction. Complexes were characterized by various physical methods including cyclic voltammetry (CV), variable-temperature (2-290 K) magnetic susceptibility, electron paramagnetic resonance (EPR) measurements, and X-ray diffraction methods. Binuclear complexes 2-6 are isostructural in the sense that they all contain a metal ion in a distorted octahedral environment MN(3)O(3) and a second six-coordinated Ni(II) ion in a trigonally distorted octahedral NiN(6) geometry. Complexes 1-4 display antiferromagnetic exchange coupling of the neighboring metal centers. The order of the strength of exchange coupling in the isostructural Ni(II)2 complexes, 3a-c, and 4, demonstrates the effects of the remote substituents on the spin coupling. The electrochemical measurements CV and square wave voltammograms (SQW) reveal two reversible metal-centered oxidations, which have been assigned to the Ni center ligated to the oxime N atoms, unless a Mn ion is present. Complex 2, Mn(III)Ni(II), exhibits a reduction of Mn(III) to Mn(II) and two subsequent oxidations of Mn(III) and Ni(II) to the corresponding higher states. These assignments of the redox processes have been complemented by the X-band EPR measurements. That the electrooxidized species [3a]+, [3b]+, [3c]+, and [4]+ contain the localized mixed-valent NiIINiIII system resulting from the spin coupling, a spin quartet ground state, S(t) = 3/2, has been confirmed by the X-band EPR measurements.     

Manganese(II) and copper(II) complexes of some nitrogenoxygen and nitrogensulphur donor ligands

Manganese(II) and copper(II) complexes of the type M(ligandH)₂ with some nitrogenoxygen and nitrogensulphur donor ligands (HL) viz. phenylpyruvic acid semicarbazone (ppysc), 4-methylphenylpyruvic acid semicarbazone (4-mppysc), phenylpyruvic acid thiosemicarbazone (ppytsc) and 4-methylphenyl pyruvic acid thiosemicarbazone (4-ppytsc), have been synthesised. All the complexes have been characterised by magnetic moment measurements, IR electronic and electron spin resonance special studies. All the ligands behave as tridentate.     

Spectral and magnetic properties of copper(II) furoate and copper(II) thiophene-2-carboxylate

Anhydrous copper(II) furoate and copper(II) thiophene-2-carboxylate have been Synthesized. They are formulated as dimeric species with four carboxylate bridges. The thiophene and furan moieties give rise to polymeric structures. Electron spin resonance spectra and magnetic susceptibility measurements show that the dimers have a singlet ground state and a thermally populated triplet state. The exchange coupling constants, 2J, are ?322 and ?312 cm^?1 for the furoate and thiophene-2-carboxylate complexes, respectively. The electronic and infrared spectra are also discussed.     

New Copper（Ⅱ） and Nickel（Ⅱ） Complexes of 4-Morpholinoacetophenone Thiosemicarbazone： Structural, Electrochemical and Antimicrobial Studies

4-Morpholinoacetophenone thiosemicarbazone, MAPT, and its nickel（Ⅱ） and copper（Ⅱ） complexes have been prepared and characterized by elemental analysis, magnetic susceptibility, spectral methods （FT-IR, ^1H NMR） and cyclic voltammetry. Electrochemical behaviors of the complexes have been studied by cyclic voltammetry in DMF media showing metal centered reduction processes for both of them. The redox properties, nature of the electrode processes and the stability of the complexes were discussed. [Cu（MAPT）2]Cl2 complex shows Cu（Ⅱ）/Cu（Ⅰ） couple and quasi-reversible wave associated with the Cu（Ⅲ）/Cu（Ⅱ） process. The reduction/oxidation potential values depend on the structures of complexes. Also, the antimicrobial activities of these complexes were determined against S. aureus, E. coli and B. subtilis.     

Tale of a twist: magnetic and optical switching in copper(II) semiquinone complexes

An intermediate (C) that is observed in both phenol hydroxylation and catechol oxidation with the side-on peroxide species [Cu(2)O(2)(DBED)(2)](2+) (DBED = N(1),N(2)-di-tert-butylethane-1,2-diamine) is identified as a copper(II) semiquinone species ([1](+)) through independent synthesis and characterization. The reaction of the redox-active 3,5-di-tert-butylquinone ligand with [(DBED)Cu(I)(MeCN)](+) yields a copper(II) semiquinone [1](+) complex with a singlet ground state and an intense purple chromophore (ε(580) ~ 3500 M(-1) cm(-1)). All other copper(II) semiquinone complexes characterized to date are paramagnetic and weakly colored (ε(800) ~ 500 M(-1) cm(-1)). Antiferromagnetic coupling between the Cu(II) center and the semiquinone radical in [1](+) is characterized by paramagnetic (1)H NMR and SQUID magnetometry. Comparative X-ray crystal structures along with density functional theory calculations correlate the geometric structures of copper(II) semiquinone complexes with their magnetic and optical properties. The unique observable properties of [1](+) originate from an increase in the overlap of the Cu 3d and semiquinone π orbitals resulting from a large rhombic distortion in the structure with a twist of 51°, attributable to the large isotropic demands of the tert-butyl substituents of the DBED ligand. Independent characterization of [1](+) allows the spectroscopic yields of intermediate C to be quantified in this intriguing hydroxylation reaction.     

Synthesis and characterization of transition metal complexes of N′-[(1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)methylene]thiophene-2-carbohydrazide

A hydrazone ligand (HL) containing the thiophene moiety has been prepared via condensation of thiophene-2-carbohydrazide with 1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazole-4-carbaldehyde. The complexes of copper(II), nickel(II), cobalt(II), manganese(II), zinc(II), palladium(II), iron(III), ruthenium(III), uranyl(VI), and titanium(IV) with the ligand were prepared in good yield from the reaction of the ligand with the corresponding metal salts. The ligand and complexes were characterized using infrared, mass spectra, nuclear magnetic resonance, electronic absorption spectra, electron spin resonance, and magnetic moment measurements as well as elemental and thermal analyses. The results showed that the complexes are enolic by nature, whilst the ratio between the metal ion and the ligand depends on the acidity of the metallic ions and their oxidation numbers.     

Kupfer(II)-Komplexe mit monofunktionellen dreizähnigenSchiffbasen mit O,N,O-Sequenzen

A few complexes of copper(II) have been prepared by reacting copper(II) acetate with salicylidene methyl anthranilates in alcohol medium. Analytical data indicate 1 : 2 stoichiometry. These copper(II) complexes show normal magnetic moments indicating no spin interactions. With the help of electronic and infrared spectral evidences it has been suggested that in these complexes copper(II) exhibits coordination number six.     

Bis -(3,5-dimethyl-pyrazolyl-1-methyl)-(3-phosphanyl-propyl)-amine complexes of copper(II), nickel(II), and cobalt(II)

A series of Cu(II), Co(II), and Ni(II) complexes of bis-(3,5-dimethyl-pyrazolyl-1-methyl)-(3-phosphanyl-propyl)-amine C₁₅H₂₆N₅P (1), prepared from 3-aminopropylphosphine and 1-hydroxymethyl-3,5-dimethylpyrazole were characterized. The nature of bonding and the geometry of the complexes have been deduced from elemental analysis, infrared, electronic, ¹H NMR, ³¹P NMR spectra, magnetic susceptibility, and conductivity measurements. The studies indicate octahedral geometry for nickel complex and square pyramidal geometry for copper and cobalt complexes. The EPR spectra of copper complex in acetonitrile at 300 K and 77 K were recorded. Biological activities of the ligand and metal complexes have been studied on Staphylococcus aureus, Escherichia coli, Aspergillus niger, and Aspergillus flavus by well-diffusion method. The zone of inhibition values were measured at 37°C for a period of 24 h. The electrochemical behavior of copper complexes was studied by cyclic voltammetry. Catalytic study indicates the copper complex has efficient catalytic activity in oxidation of amitriptyline.     

Synthesis,characterization and catalytic studies of iron(III), cobalt(II), nickel(II) and copper(II) complexes containing triphenylphosphine and β-diketones

A series of new β-diketonato complexes have been synthesized from the reactions of iron(III), cobalt(II), nickel(II) and copper(II) Ph₃P complexes with β-diketones (acetylacetone, benzoylacetone and dibenzoylmethane). All the complexes have been characterized by elemental analyses, spectral studies (i.r., electronic., magnetic., e.p.r., ¹H-n.m.r.) and cyclic voltammetry. The new complexes have been used as catalysts for aromatic coupling and oxidation reactions. Higher catalytic activity has been observed for the nickel(II) complexes compared to the other complexes.     

Unraveling the electronic structures of low-valent naphthalene and anthracene iron complexes: X-ray, spectroscopic, and density functional theory studies

Naphthalene and anthracene transition metalates are potent reagents, but their electronic structures have remained poorly explored. A study of four Cp*-substituted iron complexes (Cp* = pentamethylcyclopentadienyl) now gives rare insight into the bonding features of such species. The highly oxygen- and water-sensitive compounds [K(18-crown-6){Cp*Fe(η(4)-C(10)H(8))}] (K1), [K(18-crown-6){Cp*Fe(η(4)-C(14)H(10))}] (K2), [Cp*Fe(η(4)-C(10)H(8))] (1), and [Cp*Fe(η(4)-C(14)H(10))] (2) were synthesized and characterized by NMR, UV-vis, and (57)Fe M?ssbauer spectroscopy. The paramagnetic complexes 1 and 2 were additionally characterized by electron paramagnetic resonance (EPR) spectroscopy and magnetic susceptibility measurements. The molecular structures of complexes K1, K2, and 2 were determined by single-crystal X-ray crystallography. Cyclic voltammetry of 1 and 2 and spectroelectrochemical experiments revealed the redox properties of these complexes, which are reversibly reduced to the monoanions [Cp*Fe(η(4)-C(10)H(8))](-) (1(-)) and [Cp*Fe(η(4)-C(14)H(10))](-) (2(-)) and reversibly oxidized to the cations [Cp*Fe(η(6)-C(10)H(8))](+) (1(+)) and [Cp*Fe(η(6)-C(14)H(10))](+) (2(+)). Reduced orbital charges and spin densities of the naphthalene complexes 1(-/0/+) and the anthracene derivatives 2(-/0/+) were obtained by density functional theory (DFT) methods. Analysis of these data suggests that the electronic structures of the anions 1(-) and 2(-) are best represented by low-spin Fe(II) ions coordinated by anionic Cp* and dianionic naphthalene and anthracene ligands. The electronic structures of the neutral complexes 1 and 2 may be described by a superposition of two resonance configurations which, on the one hand, involve a low-spin Fe(I) ion coordinated by the neutral naphthalene or anthracene ligand L, and, on the other hand, a low-spin Fe(II) ion coordinated to a ligand radical L(?-). Our study thus reveals the redox noninnocent character of the naphthalene and anthracene ligands, which effectively stabilize the iron atoms in a low formal, but significantly higher spectroscopic oxidation state.     

Synthesis,characterization, NLO study,and antimicrobial activities of metal complexes derived from 3-(3-(2-hydroxyphenyl)-3-oxoprop-1-enyl)-4H-chromen-4-one and sulfanilamide

A series of metal(II) complexes ML (where M?=?Cu(II), Co(II), Ni(II), Zn(II), Mn(II), Cd(II), and VO(II)) have been prepared from 3-(3-(2-hydroxyphenyl)-3-oxoprop-1-enyl)-4H-chromen-4-one and sulfanilamide. The structures of the complexes have been investigated by elemental analysis, magnetic susceptibility, molar conductance, IR, UV-Vis, NMR, mass, and ESR spectral studies. Conductivity measurements reveal that the complexes are non-electrolytes, except the oxovanadium complex. Spectral and other data show square pyramidal geometry for oxovanadium and octahedral for the other complexes. The redox behaviors of the copper and vanadyl complexes have been studied through cyclic voltammetry. Antimicrobial activities of the compounds against several microorganisms indicate that some complexes have higher activity than free ligand. The compounds may serve as photoactive materials as indicated from their characteristic fluorescence properties. The second harmonic generation efficiency of the ligand was found to be higher than that of urea and KDP.