Group II metal complexes with the N-(2-oxy-3,5-di-tert-butylphenyl)-4,6-di-tert-butyl-o-iminobenzoquinone ligand: an ESR study

The Group II metal (Mg, Ca, Sr, Ba, Zn, Cd) complexes based on the paramagnetic N-(2-oxy-3,5-di-tert-butylphenyl)-4,6-di-tert-butyl-o-iminobenzoquinone ligand were generated in solutions and studied by ESR spectroscopy. The magnesium, zinc, and cadmium complexes with trialkylphosphine ligands were prepared. Their molecular structures and electron density distribution were studied by ESR spectroscopy and DFT calculations.     

Synthesis and structural characterization of unsymmetrical osmocenes containing the pentamethylcyclopentadienyl ligand

Treatment of dibromo(pentamethylcyclopentadienyl)osmium(III) dimer with alkali metal salts of a variety of cyclopentadienyl derivatives provides a simple approach to the synthesis of unsymmetrical osmocenes containing the pentamethylcyclopentadienyl ligand. Furthermore, the reaction of dibromo(pentamethylcyclopentadienyl)osmium(III) with alkali metal salts of pyrrole and 3,5-di-tert-butylpyrazole afforded the corresponding pentamethylcyclopentadienylosmium complexes containing η⁵-pyrrolyl or η⁵-3,5-di-tert-butylpyrazolato ligands. This overall synthetic approach afforded pentamethylosmocene (64%), (η⁵-pentamethylcyclopentadienyl)(η⁵-indenyl)osmium (36%), (η⁵-pentamethylcyclopentadienyl)(η⁵-fluorenyl)osmium (30%), (η⁵-pyrrolyl)(η⁵-pentamethylyclopentadienyl)osmium (30%), and (η⁵-3,5-di-tert-butylpyrazolato)(η⁵-pentamethylcyclopentadienyl)osmium (38%). The new complexes were characterized by spectroscopic and analytical techniques, and by single crystal X-ray structural determinations. In the solid state, all of the new complexes exist as eclipsed metallocenes.     

Crystal structures of copper(II) and nickel(II) complexes with 1,3-bis(3,5-di-tert-butylsalicylideneamino)propan-2-ol

Mononuclear copper(II) and nickel(II) complexes with 1,3-bis(3,5-di-tert-butylsalicylideneamino)propan-2-ol (H₃L) of the general formula [M(HL)] were obtained and structurally characterized. It was demonstrated that the presence of the tert-butyl groups precludes intermolecular hydrogen bonding in the crystals of the complexes and that their molecules are only linked by hydrophobic interactions.     

Effect of two isomeric tetrapyrazolyl ligands on the catalytic oxidation of 3,5-di-tert-butylcatechol

Copper(II) salts were combined with a tetrapyrazolyl ligand ({N,N,N’,N’-tetrakis-[(3,5-dimethylpyrazol-1-yl)methyl)-1,4-phenylenediamine}L1 or {N,N,N’,N’-tetrakis-[(1,5-dimethylpyrazol-3-yl)methyl)-1,4-phenylenediamine}L2) and assessed as oxidation catalysts. The corresponding dioxygen complexes were generated in situ by mixing the copper salt and the pyrazolyl donor ligand in air. The oxidation of 3,5-di-tert-butylcatechol (DTBC), which affords 3,5-di-tert-butylquinone (DTBQ), was studied. The reaction rate was found to depend essentially on the nature of the junction linking two pyrazolyl neighbours.     

Synthesis and characterization of copper(II) and cobalt(II) complexes with two new potentially hexadentate Schiff base ligands. X-ray crystal structure determination of one copper(II) complex

Two new potentially hexadentate N₂O₄ Schiff base ligands 2-((z)-(2-(2-(2-((z)-3,5-di-tert-butyl-2-hydroxybenzylideneamino) phenoxy) phenoxy) phenylimino) methyl)-4,6-di-tert-butylphenol [H₂L¹] and 2-((z)-(2-(2-(2-((z)-3,5-di-tert-butyl-2-hydroxybenzylideneamino) phenoxy)-5-tert-butylphenoxy) phenylimino) methyl)-4,6-di-tert-butylphenol [H₂L²] were prepared from the reaction of 3,5-di-tert-butyl-2-hydroxy benzaldehyde with 1,2-bis(2′-aminophenoxy)benzene or 1,2-bis(2′-aminophenoxy)-4-t-butylbenzene, respectively. From the direct reaction of ligands [H₂L¹] and [H₂L²] with copper(II) and cobalt(II) salts in methanolic solution and in the presence of N(Et)₃ the neutral [CuL¹], [CuL²], [CoL¹] and [CoL²] complexes were prepared. All complexes were characterized by IR spectra, elemental analysis, magnetic susceptibility, mass spectra, molar conductance (Λ_m), UV-Vis spectra and in the case of [CuL²] with X-ray diffraction. X-ray crystal structure of [CuL²] showed that the complex contains copper(II) in a distorted square planar environment of N₂O₂ donors. Three CH/π interactions were observed in the molecular structure of latter complex.     

Preconcentration and Determination of Copper(II) by Novel Solid-Phase Extraction and High-Resolution Continuum Source Flame Atomic Absorption Spectrometry

Amberlite XAD-4 modified with N-para-anisidine-3,5-di-tert-butylsalicylaldimine was investigated as a new chealting sorbent for the selective separation and preconcentration of Cu(II). The metal ion was retained by chemical sorption on the modified resin, eluted by hydrochloric acid, and determined by high-resolution continuum source flame atomic absorption spectrometry. The prepared resin was characterized for the solid-phase extraction of Cd²⁺, Co²⁺, Cr³⁺, Cu²⁺, Fe³⁺, Mn²⁺, Ni²⁺, Pb²⁺, and Zn²⁺ in a column. The influence of the pH, the mass of solid phase, eluent, flow rate, and sample volume was optimized. Using the optimum conditions, only Cu(II) showed quantitative sorption at the 95% confidence level, and the recoveries of the other metal ions were below 80%. A preconcentration factor 125 was obtained for Cu(II) with a limit of detection of 0.56?µg?L^?1. The method was used for the determination of Cu(II) in tap water, river water, tomato leaves, and fish. The relative standard deviation and the relative error were lower than 7%.     

Hexanuclear Zn(II) and Mononuclear Cu(II) Complexes containing imino phenol ligands: Exploitation of their Catalytic and Biological Perspectives

A unique hexanuclear zinc(II) ( 1 ) and two mononuclear copper(II) ( 2 and 3 ) complexes anchored with imino phenol ligand HL ¹ and HL ² were synthesized with good yield and purity (where HL ¹  = 4‐tert‐butyl‐2,6‐bis((mesitylimino)methylphenol and HL ²   =  5‐tert‐butyl‐2‐hydroxy‐3‐((mesitylimino)methyl)benzaldehyde). These complexes were characterized by utilizing various spectroscopic protocols like NMR, FTIR, UV as well as ESI‐Mass spectrometry, elemental analysis and single crystal X‐ray diffraction studies. Their potential to bind calf thymus DNA (CT‐DNA) was tested utilizing different techniques such as UV–visible and fluorescence spectroscopy. The experiment implies that they interact with CT‐DNA via non‐intercalative mode with moderate capabilities (K_b ~ 10⁴ M^?1). On the other hand, these complexes have high capabilities to quench the fluorescence of bovine serum albumin (BSA) following the static pathway. In addition, they are active catalysts for the oxidation reaction of 3,5‐di‐tert‐butylcatechol (3,5‐DTBC) to 3,5‐di‐tert‐butylquinone (3,5‐DTBQ) under aerobic condition. From the recorded EPR signals of all complexes, it has been concluded that the oxidation reaction proceeds via ligand oriented radical pathway instead of metal based redox participation. Kinetic studies using 1 – 3 indicate that it follows Michaelis–Menten type of equation with moderate to high turnover number (k_cat). Apart from these aspects, complexes 1 – 3 were screened for their cytotoxic behavior towards HeLa cells (human cervical carcinoma) and found quite active with comparable IC₅₀ values to cisplatin.     

Homo-and heterometal complexes with sterically eclipsed ortho-nitrosophenol

Novel homo-and heterometal complexes based on 4,6-di-tert-butyl-2-nitrosophenol (HL) were synthesized, and their physicochemical properties were studied. The data of the ¹H NMR, electronic spectroscopy, magnetochemical measurements, and the atomic absorption study suggest that the nitroso group of a ligand can be bidentate in polynuclear coordination compounds. The experimental data were obtained for the first time on self-assembling of both homo-and heterometal trinuclear complexes with predicted properties from the initial metal chelates of ortho-nitrosophenols.     

Hexacoordinate triphenylantimony(V) complex with tridentate bis-(3,5-di-tert-butyl-phenolate-2-yl)-amine ligand: Synthesis,NMR and X-ray study

The oxidative addition reaction of 4,6-di-tert-butyl-N-(2-hydroxy-3,5-di-tert-butyl-phenyl)-o-iminobenzoquinone (IBQ) to triphenylantimony(III) proceeds with the migration of hydroxyl-proton to a nitrogen atom to form tridentate O,N,O′-coordinated bis-(3,5-di-tert-butyl-phenolate-2-yl)-amine ligand. In accordance with ¹H, ¹³C, DEPT NMR data, the new hexacoordinate complex [bis-(3,5-di-tert-butyl-phenolate-2-yl)-amine]triphenylantimony(V), [(AP-AP)H]SbPh₃ (1) in solution has a C_s symmetry plane leading to the equivalence of two O,N-chelate o-aminophenolato moieties. The molecular structure of 1 · acetone was studied by a single-crystal X-ray. Compound 1 was found to be air-stable both in solid and in solution. Its oxidation by PbO₂ leads to paramagnetic [4,6-di-tert-butyl-N-(3,5-di-tert-butyl-phenolate-2-yl)-o-iminobenzosemiquinolato]triphenylantimony(V), [(AP-ISQ)]SbPh₃ (2).     

A facile synthesis and properties of quinone from a polyvalent porphyrin,tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)phorphyrin

The quinone 5,15-di-(3,5-di-tert-butyl-4-hydroxyphenyl)-10,20-di-(3,5-di-tert-butyl-4-quinomethane)porpho-10,20-dimethene (2) was obtained in high yield by the oxidation of the polyvalent porphyrin tetrakis(3,5-ditert-butyl-4-hydroxyphenyl)phorphyrin (1) with an Mn²⁺-O₂ system in dimethylformamide. 2 was reduced to 1 by ascorbic acid or hydroquinone.     

3,5-di-tert-butyl-1,4-benzoquinone ferrocenoylhydrazone and its zinc(II), palladium(II), and mercury(II) complexes: Structure and properties

A new ligand system, 3,5-di-tert-butyl-1,4-benzoquinone ferrocenoylhydrazone, was synthesized and its complexes with zinc(II), Hg(II), and palladium(II) were prepared. The compounds were studied by IR, electron absorption, and ¹H NMR spectroscopy. Structure of the compounds obtained is discussed.     

Synthesis,characterization, and crystal structures of cobalt(II), copper(II), and zinc(II) complexes of a bidentate iminophenol

A bidentate iminophenol (HL = 2-((4-methoxyphenylimino)methyl)-4,6-di-tert-butylphenol derived from condensation of 4-methoxyaniline and 3,5-di-tert-butyl-2-hydroxybenzaldehyde) was mixed with divalent metal salts to form the corresponding mononuclear metal complexes [M^II(L)₂] (M = Co (1), Cu (2), and Zn (3)). The complexes are characterized by different spectroscopic and analytical tools. X-ray crystal structures of the complexes revealed homoleptic mononuclear complexes with MN₂O₂ coordination. The cobalt(II) (1) and zinc(II) (3) complexes display a pseudo-tetrahedral coordination geometry, whereas the copper(II) complex (2) exhibits a distorted square-planar coordination. The zinc(II) complex (3) emits at 460 nm with a twofold enhancement of emission with respect to the free iminophenol.     

Synthesis, structural, spectroscopic and reactivity properties of a new N-2,3,4-trifluorophenyl-3,5-di-tert-butylsalicylaldimine ligand and its Cu(II) and Pd(II) complexes

A new N-2,3,4-trifluorophenyl-3,5-di-tert-butylsalicylaldimine (1) complexes with Cu(II) (2) and Pd(II) (3) have been synthesized and characterized by X-ray crystallography, UV-Vis, IR, ¹H NMR and EPR spectroscopic techniques. The X-ray crystal structure of complex 2 reveals tetrahedrally distorted square-planar coordination geometry around Cu(II). The UV/Vis and EPR results indicate that the solid state geometry of 2 remains unchanged in solutions. Chemical oxidation of 3 with Ce(IV) in CHCl₃ generates relatively stable Pd(II)-phenoxyl radical complex (g = 2.0073). The results related with the chemical oxidation of 2 and 3 as well as the catalytic activity of 3 in the hydrogenation of PhNO₂ are presented.     

Cu(II), Co(II), Ni(II), Mn(II), and Fe(II) metal complexes containing N,N′-(3,4-diaminobenzophenon)-3,5-But2-salicylaldimine ligand: Synthesis,structural characterization,thermal properties,electrochemistry, and spectroelectrochemistry

The synthesis, structure, spectroscopic and electro-spectrochemical properties of steric hindered Schiff-base ligand [N,N′-(3,4-benzophenon)-3,5-Bu^t₂-salicylaldimine (LH₂)] and its mononuclear Cu(II), Co(II), Ni(II), Mn(II) and Fe(II) complexes are described in this work. The new dissymmetric steric hindered Schiff-base ligand containing a donor set of NONO was prepared through reaction of 3,4-diaminobenzophenon with 3,5-Bu^t₂-salicylaldehyde. Certain metal complexes of this ligand were synthesized by treating an ethanolic solution of the ligand with an equimolar amount of metal salts. The ligand and its complexes were characterized by FT-IR, UV–vis, ¹H NMR, elemental analysis, molar conductivity and thermal analysis methods in addition to magnetic susceptibility, electrochemistry and spectroelectrochemistry techniques. The tetradentate and mononuclear metal complexes were obtained by reacting N,N′-(3,4-benzophenon)-3,5-Bu^t₂-salicylaldimine (LH₂) with some metal acetate in a 1:1 mole ratio. The molar conductance data suggest metal complexes to be non-electrolytes.     

Chromone-based Schiff base metal complexes as catalysts for catechol oxidation: Synthesis,kinetics and electrochemical studies

Two new Schiff base ligands with chromone moiety and their transition metal complexes were synthesized and characterized by elemental analyses, magnetic susceptibility, molar conductance and TGA analyses, FT IR, UV-Vis, NMR and mass spectroscopy. All the complexes synthesized have been investigated as functional models for catechol oxidase (catecholase) activity by employing 3,5-di-tert-butylcatechol as a model substrate. The two mononuclear copper(II) and two mononuclear iron(II) complexes show catecholase activity with turnover (k_cat) numbers lying in the range 27.2–1328.4 h^?1. According to the kinetic measurement results, the rate of catechol oxidation follows first order kinetics and iron(II) complexes were found to have higher catalytic activity than those of copper(II) complexes. Electron-donating substituent on Schiff base ligand enhanced the catalytic activity of metal complexes while the electron-withdrawing substituent led to a decrease in activity. The electrochemical properties of two Schiff bases and their metal complexes were also investigated by Cyclic Voltammetry (CV) using glassy carbon electrode (GCE) at various scan rates. Electrochemical processes of all the compounds were observed as irreversible.     

Complexes of the 14th group elements with tridentate redox-active ligand

New methods of synthesis of the 14th group metal (Si, Sn, Pb) complexes containing a redox-active ligand, 3,5-di-tert-butyl-1,2-quinone-1-(2-hydroxy-3,5-di-tert-butylphenyl)imine, in various redox states were developed. New compounds were studied by the ESR spectroscopy in solutions. The redox properties of the paramagnetic tin compounds are characterized by the cyclic voltammetry. The solvent and temperature effect on the ESR spectra parameters of paramagnetic complexes of Sn(IV)and Pb(IV) was revealed.     

Influence of the redox state of the ligand on the dealkylation of substituted methylcobaloximes in the presence of heavy metal ions

The synthesis of cobaloxime and methylcobaloxime containing sterically hindered 2,6-di-tert-butylphenol fragments in the ligand is described. Spectral studies of the demethylation of methylbis(dimethylglyoximato)cobalt (1a), methylbis(diphenylglyoximato)cobalt (1b), methylbis[methyl-(3,5-di-tert-butyl-4-hydroxyphenyl)glyoximato]cobalt (1c) pyridinates were carried out in the presence of Cd²⁺, Hg²⁺, Sn⁴⁺, Pb²⁺, and Pb⁴⁺ ions, The free radical forms of the complexes containing a phenoxy radical W the ligand are formed during oxidation. The ESR spectra are given. The unpaired electron in the periphery of the methylcobaloxime ligand1c interacts with the Co-CH₃ fragment through the conjugated systems, enhancing the donating properties of the equatorial ligand of the complex, which leads to the rapid cleavage of the Co-C bond. Therefore the demethylation of methylcobaloxime in the presence of heavy metal ions occurs in a significantly shorter time.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp, 1822–1827, July, 1996.     

Salen and half-salen palladium(II) complexes: synthesis, characteriztion and catalytic activity toward Suzuki-Miyaura reaction

Salen and half-salen palladium(II) complexes (salden)Pd (1, salden=N,N′-bis(3,5-di- tert-butylsalicylidene)-1,2-dimethylethylenediamine), (hsalph)PdCl (2, hsalph=3,5-di-tert- butylsalicylidene-1-iminophenylene-2-amine), and (salph)Pd (4, salph=N,N′-bis(3,5-di-tert- butylsalicylidene)-1,2-phenylenediamine) were prepared and structurally characterized by X-ray crystallography. Complex 2 proved to exhibit high catalytic activity toward Suzuki-Miyaura reaction. Polyaromatic C₃-symmetric derivatives and various fluorinated biphenyl derivatives were readily achieved in good yields using Suzuki-Miyaura reaction catalyzed by complex 2.     

Effects of solvation on charge distribution of 1,2-semiquinonato/catecholatocobalt complexes containing bis(3-pyridyl) phenylvinylsilane

Recrystallization of [Co(3,5-dbbq)₂(L)₂] (3,5-dbbq?=?3,5-di-tert-butyl-1,2-benzoquinone; L?=?bis(3-pyridyl)phenylvinylsilane) from diethyl ether at ?20?°C produces trans-[Co(3,5-dbbq)₂(L)₂] while the recrystallization from toluene at ?20?°C gives trans-[Co(3,5-dbbq)₂(L)₂]·2PhMe. The complex exists as trans-[Co^III(3,5-dbsq)(3,5-dbcat)(L)₂] (3,5-dbsq?=?3,5-di-tert-butyl-1,2-semiquinonato; 3,5-dbcat?=?3,5-di-tert-butylcatecholato) in the solid state at 173?K. Differences in charge distribution between trans-[Co(3,5-dbbq)₂(L)₂] and trans-[Co(3,5-dbbq)₂(L)₂]·2PhMe have been observed based on the effective magnetic moments and IR spectra of the complexes along with their X-ray crystal structures.     

Synthesis,electrochemical and in situ spectroelectrochemical studies of new transition metal complexes with two new Schiff-bases containing N2O2/N2O4 donor groups

New Schiff-base copper and cobalt complexes, [Cu(L¹)], [Cu(L²)] and [Co(L¹)], [Co(L²)] (where L¹ = N-N′-bis(3,5-di-tert-butylsalicylaldimine)-1,4-cyclohexane bis(methylamine) and L² = N-N′-bis(3,5-di-tert-butylsalicylaldimine)-1,8-diamino-3,6-dioxaoctane), were synthesized and characterized using elemental analysis, IR spectra, UV–Vis spectra, magnetic susceptibility measurements, ¹H and ¹³C NMR spectroscopy, thermal analysis and molar conductance (Λ_M). Their electro-spectrochemical properties were investigated using cyclic voltammetric (CV) and thin-layer spectroelectrochemical techniques in a dichloromethane solution (CH₂Cl₂). The CV of [Cu(L²)] showed a lower oxidation potential than that of [Cu(L¹)] under the same experimental conditions. The oxidation wave (II) of [Cu(L²)] was accompanied by an EC process (II′), which was not observed for [Cu(L¹)]. Also, [Cu(L²)] exhibited a reduction process, but [Cu(L¹)] did not. These results indicate that the Cu(II) ion in [Cu(L²)] is coordinated by N₂O₄ donor sites while [Cu(L¹)] presents a square-planar structure with N₂O₂ donor sites. Both oxidation processes for [Co(L¹)] and [Co(L²)] are based on the cobalt center, and they are assigned to Co(II)/Co(III) couples. The spectroelectrochemical results indicate that the oxidized species of [Cu(L²)] is similar to that of [Cu(L¹)], the only difference being that the absorption bands of the oxidized species for [Cu(L²)] shift to lower energy compared with those of [Cu(L¹)] because of their different coordination environment. The geometry of [Cu(L²)] changed into square-planar after the complex was totally oxidized and the neutral complex was only recovered following the EC process, as observed from the CV of [Cu(L²)]. For the two cobalt complexes, the bands corresponding to the π → π^∗transitions disappeared and new bands with small red shifts and of lower intensity were observed during the oxidation process. These new bands are attributed to the LMCT transition as observed in the case of the oxidation processes of the cobalt complexes.