Synthesis,characterization, and biological activity of metal complexes of azohydrazone ligand

A new azohydrazone, 2-hydroxy-N′-2-hydroxy-5-(phenyldiazenyl)benzohydrazide (H₃L) and its copper(II), nickel(II), cobalt(II), manganese(II), zinc(II), cadmium(II), mercury(II), vanadyl(II), uranyl(II), iron(III), and ruthenium(III) complexes have been prepared and characterized by elemental and thermal analyses as well as spectroscopic techniques (¹H-NMR, IR, UV-Vis, ESR), magnetic, and conductivity measurements. Spectral data showed a neutral bidentate, monobasic bidentate, monobasic tridentate, and dibasic tridentate bonding to metal ions via the carbonyl oxygen in ketonic or enolic form, azomethine nitrogen, and/or deprotonated phenolic hydroxyl oxygen. ESR spectra of solid vanadyl(II) complex (2), copper(II) complexes (3–5), and (7) and manganese(II) complex (10) at room temperature show isotropic spectra, while copper(II) complex (6) shows axial symmetry with covalent character. Biological results show that the ligand is biologically inactive but the complexes exhibit mild effect on Gram positive bacteria (Bacillus subtilis), some octahedral complexes exhibit moderate effect on Gram negative bacteria (Escherichia coli), and VO(II), Cd(II), UO(II), and Hg(II) complexes show higher effect on Fungus (Aspergillus niger). When compared to previous results, metal complexes of this hydrazone have a mild effect on microorganisms due to the presence of the azo group.     

Structural characterization of alachlor complexes with transition metal ions by electrospray ionization tandem mass spectrometry

Electrospray ionization mass (ESI-MS) spectrometry was used to investigate the nature of metal complexes of alachlor and their dissociations on activation. Ions of the first row transition metal series were employed to react with alachlor and the products were subjected to collision-induced dissociation (CID) for further structural characterization. The formation of diverse complex ions including doubly charged metal/alachlor complexes; [3L + M]²⁺ and [4L + M]²⁺ (L: alachlor and M: transition metal ions) were observed depending on the experimental conditions including the tube lens offset voltage (TLOV) and relative concentrations of alachlor and transition metal ions. It is clear that complexation with transition metal ions alters the reactive site of alachlor, promoting the loss of chlorine over the loss of CH₃OH that is the major reaction pathway in uncomplexed system. Direct elimination of chlorine from alachlor molecule was confirmed by the use of MnBr₂ instead of MnCl₂. These evidences clearly illustrate the catalytic activities of the metal ions through insertion mechanism. The function of transition metal ions in complexation was emphasized comparing the fragmentation patterns with those of protonated molecule. A change in the oxidation state of copper from + 2 to + 1 during the dissociation of metal complex was observed in company with elimination of radicals which is specific for the copper complex ions.     

A new one pot and solvent-free synthesis of nickel porphyrin complex

Abstract

A new one pot and solvent-free synthesis of nickel porphyrin complex is described. This is prepared by condensing pyrrole, benzaldehyde, nickel (II) chloride, and 1,8-diazabicyclo [5.4.0] undec-7-ene as a base. This new method allows higher yields, reduced reaction times, ease of handling, and follows principles of green chemistry. The same complex is also prepared by an alternative route, i.e. first, the porphyrin is prepared and then the insertion of metal ion.     

Stability constants of metal complexes of macrocyclic ligands with pendant donor groups

Abstract

In our studies of the stability constants of metal complexes, we have investigated a number of macrocyclic ligands with pendant donor groups. The ligands are characterized by the fact that they have nitrogen donors in the macrocyclic ring and oxygen or sulfur donors in the pendant arms. These ligands represent seven different macrocycles, and by varying the pendant donor groups, ten different ligands are indicated. The affinities of these ligands for fifteen metal ions will be described. The Fe(III) complex of triazanonane with o-hydroxypyridyl or o-hydroxybenzyl pendant donor groups are the most stable ferric complexes ever reported. The In(III) complex of triazacyclononane with pendant mercaptoethyl donor groups, is exceptionally stable. Also, the Ca(II) complex of DOTA probably has the highest stability of any calcium(II) complex. These, and other comparisons will be made on the basis of the thermodynamic stability constant data for the ligands described.     

Syntheses of Polythioethers Tethered with Bulky Aryl Groups and Their Complexation with Late-Transition Metals

Abstract

New types of o-phenylene-bridged polythioethers tethered with extremely bulky aryl groups at their terminal sulfur atoms, such as TbtS(o-Phen)S(o-Phen)S(o-Phen)STbt (1) and TbtS(o-Phen)S(o-Phen)SS(o-Phen)S(o-Phen)STbt (2) (Tbt = 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, o-Phen = o-phenylene), were synthesized and subjected to the complexation with several kinds of late-transition metals. In the case of polythioether 1, the reaction with RhCl₃·3H₂O in benzene/EtOH resulted in the formation of a unique bimetallic complex, in which a part of ligand 1 is lost and the resulting sulfur atom is directly bound to the other Rh metal center. Interestingly, similar treatment of 1 with IrCl₃·3H₂O afforded ethyl-coordinated mononuclear Ir complex. Furthermore, 1 underwent complexation with Na₂PdCl₄ in EtOH to give the corresponding square planar dichloropalladium complex coordinated with two inner sulfur atoms of 1, while the S₆-ligand 2 reacted with excess of Pd(PPh₃)₄ in benzene to afford a quite interesting trinuclear Pd complex multi-step metal insertion reactions.     

Ligand and solvent effects on CO2 insertion into group 10 metal alkyl bonds

The insertion of carbon dioxide into metal element σ-bonds is an important elementary step in many catalytic reactions for carbon dioxide valorization. Here, the insertion of carbon dioxide into a family of group 10 alkyl complexes of the type (^RPBP)M(CH₃) (^RPBP = B(NCH₂PR₂)₂C₆H₄⁻; R = Cy or ^tBu; M = Ni or Pd) to generate κ¹-acetate complexes of the form (^RPBP)M{OC(O)CH₃} is investigated. This involved the preparation and characterization of a number of new complexes supported by the unusual ^RPBP ligand, which features a central boryl donor that exerts a strong trans-influence, and the identification of a new decomposition pathway that results in C–B bond formation. In contrast to other group 10 methyl complexes supported by pincer ligands, carbon dioxide insertion into (^RPBP)M(CH₃) is facile and occurs at room temperature because of the high trans-influence of the boryl donor. Given the mild conditions for carbon dioxide insertion, we perform a rare kinetic study on carbon dioxide insertion into a late-transition metal alkyl species using (^tBuPBP)Pd(CH₃). These studies demonstrate that the Dimroth–Reichardt parameter for a solvent correlates with the rate of carbon dioxide insertion and that Lewis acids do not promote insertion. DFT calculations indicate that insertion into (^tBuPBP)M(CH₃) (M = Ni or Pd) proceeds via an S_E2 mechanism and we compare the reaction pathway for carbon dioxide insertion into group 10 methyl complexes with insertion into group 10 hydrides. Overall, this work provides fundamental insight that will be valuable for the development of improved and new catalysts for carbon dioxide utilization.

The kinetics of carbon dioxide insertion into a pincer-supported palladium methyl complex are studied. The complex inserts carbon dioxide at room temperature, and we explore both solvent and Lewis acid effects on carbon dioxide insertion.     

Chalcogen-containing metal chelates as single-source precursors of nanostructured materials: recent advances and future development

Abstract

The analysis of the use of chalcogenide metal chelates as single-source precursors of nanostructured materials has been carried out. The influence of the nature of the ligand, temperature, capping agents, thermolysis time, and solvent on the kinetic laws of thermolysis and the properties of the resulting nanomaterials is considered. Particular attention is paid to thermolysis of polynuclear chalcogenide metal chelates. The basic data on the synthesis of metal-polymer nanocomposites by thermolysis of chalcogenide metal chelates in the presence of polymers are summarized. The problems and future prospects of obtaining nanostructured materials by thermolysis of chalcogenide metal chelates are outlined. The bibliography includes articles published during the last 5 years.     

A Schiff basep-tent-butylcalix[4]arene. Synthesis and metal ion complexation

This communication describes the synthesis of Schiff base calix[4]arene (1) in which the Schiff base unit bridges two opposite hydroxy groups ofp-tert-butylcalix[4]arene. The synthesis of (1) has been achieved by refluxing in acetonitrile-methanol the appropriate 1,3-dicarbaldehyde-p-tert-butyl-calix[4]arene (4) with 1,3-diaminopropane. The yield of the reaction is 19%. Ligand (1) possesses a compartment containing two nitrogen atoms, four ether-type oxygen atoms, and two ionizable hydroxy groups likely to complex metal cations.     

New Method for the Synthesis of Lactones via Nickel-Catalyzed Isocyanides Insertion

A novel nickel catalyst for the reaction of tert-butyl isocyanide insertion was discovered. In this approach, 1,2-bis(diphenylphosphino)ethane (L3) serves as an efficient ligand, thereby allowing the preparation of lactones from (o-bromophenyl)phenylethanone derivatives. It is noteworthy that this is the first example of nickel acting as a metal catalyst in the reactions of tert-butyl isocyanide insertion. The significance of this methodology may draw many chemists’ attention in the field of isocyanide-incorporating reactions.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]     

Transition metal complex cations as reagents for gas-phase transformation of multiply deprotonated polypeptides

Triply deprotonated DGAILDGAILD was reacted in the gas-phase with doubly charged copper, cobalt, and iron metal complexes containing either two or three phenanthroline ligands. Reaction products result from two major pathways. The first pathway involves the transfer of an electron from the negatively charged peptide to the transition-metal complex. The other major pathway consists of the displacement of the phenanthroline ligands by the peptide resulting in the incorporation of the transition-metal into the peptide to form [M − 3H + X^II]⁻ ions, where X is Cu, Co, or Fe, respectively. The extent to which each pathway contributes is dependent on the nature of transition-metal complex. In general, bis-phen complexes result in more electron-transfer than the tris—phen complexes, while the tris—phen complexes result in more metal insertion. The metal in the complex plays a large role as well, with the Cu containing complexes giving rise to more electron transfer than the corresponding complexes of Co and Fe. The results show that a single reagent solution can be used to achieve two distinct sets of products (i.e., electron-transfer products and metal insertion products). These results constitute the demonstration of novel means for the gas-phase transformation of peptide anions from one ion type to another via ion/ion reactions using reagents formed via electrospray ionization.     

Influence of metal complex formation on the antimicrobial activity of nifuroxazide: spectroscopic,electrochemical, and DFT studies

[M(HL)₂] complexes (M = Co(II) (1), Ni(II) (2), and Cu(II) (3); H₂L = 4-hydroxybenzoic[(5-nitro-2-furanyl)methylene]hydrazide acid, nifuroxazide) were synthesized, characterized (by elemental analysis, TG, IR, UV–vis., EPR, magnetic, and conductance measurements) and tested for their antimicrobial activities. H₂L is a mono-negative bidentate ligand via hydrazone N and C–O^? forming intermediate complexes between tetrahedral and square-planar geometries (“flattened” tetrahedron, D_2d symmetry) for 1 and 2, as well as square-planar for Cu(II) complex 3. Natural bond orbital analysis revealed that the interaction of oxygen with metal ion is the main factor which determines the stability of 1–3 as the binding energy decreases with an increase in the M–O bond length. Time-dependent density functional theory calculations were carried out to understand the electronic transitions in related experimental observations. The reduction potential values of the nitro group are affected by the metal center. Ni(II) complex 2 displayed the highest activity among the tested complexes against Escherichia coli with a MIC₅₀ value of 0.098 μmol mL^?1 compared with 0.131 (1) and 0.117 μmol mL^?1 (3).     

Design and synthesis of multidentate ligands via metal promoted C-N bond formation processes and their coordination chemistry

This presentation reports some novel examples of organic ring amination reactions via metal mediation. The organic transformations are highly regioselective and can be controlled by the proper selection of the mediator complex. The two isomeric organic ligands viz. HL¹ and HL² were isolated in their pure states by the removal of the metal ions. These were fully characterized. The ligand HL¹ has lowpKa, 8.5. Upon deprotonation, it behaves as a potentialbis chelating N,N,N-donors. The coordination chemistry of the HL¹ ligand involving some 3d-metal ions is described. Two unusual low-spin complexes of manganese(II) and iron(III) are reported. The ferric complex displayed a rhombic EPR while, the corresponding manganese compound showed a complex pattern due to hyperfine coupling. All the complexes displayed large number of redox responses. A brief mention about the future projection of this work is noted.     

Novel naphthalimide–aminobenzamide dyads as OFF/ON fluorescent supramolecular receptors in metal ion binding

A series of novel naphthalimide–aminobenzamide (NAPIM-2ABZ) dyads 3 connected by different length polymethylene chains were synthesized and studied as fluorescent supramolecular receptors in metal ion binding. The photophysical properties were evaluated and compared with separated chromophores. The electronic absorption spectra of dyads 3 showed no interaction between chromophores in the ground state. The fluorescence quantum yields were lower in dyads 3 in comparison with N-propyl-2-aminobenzamide (8). The fluorescence quenching is attributed to a PET mechanism between fluorophores (from 2ABZ to NAPIM), which is dependent on the polymethylene chain length. In metal binding study was found a response towards transition metal ions such as Hg(II), Cu(II), Zn(II) and Ni(II). Dyad 3b presented selectivity towards Cu(II). The UV-vis, IR and ¹H-NMR studies demonstrated the interaction with 2ABZ moiety in the ground state, and interestingly dyads with shorter polymethylene chains 3a (n = 0), 3b (n = 1) and 3c (n = 2) exhibited an OFF/ON fluorescence behaviour due to the PET inhibition and the quenching of 2ABZ fluorescence. Dyads 3d (n = 4) and 3e (n = 6) presented opposite response ON/OFF in the complex with metal ions evidencing the absence of PET in these dyads.     

Synthesis and characterization of single-source molecular precursors for the preparation of metal chalcogenides

Metal chalcogenides constitute an important family of functional materials. Subtle changes in shape, size and phase of these materials result in variations in physical properties (e.g. electronic and optical), which can be exploited for various technological applications. Several strategies have evolved recently for controlling shape, size and phase of these materials. This work discusses design and synthesis of single-source molecular precursors for the preparation of metal chalcogenides both in bulk and nano-size regime. Precursors for palladium chalcogenides, indium sulphides andII–VI materials are presented. Synthesis of a variety of palladium(II)/platinum(II) complexes with internally functionalised chalcogenolate ligands, selenocarboxylates; gallium and indium dithiolate complexes and zinc/cadmium/ mercury complexes with N,N′-dimethylaminoalkylselenolate ligands and their characterization by NMR and X-ray crystallography are also discussed. Data on thermal behaviour of a few representative complexes, [Pd(SeCOAr)₂(PR₃)₂], [PdCl(E∩N)(PR₃)], [InMe₂(S∩S)], [In(S∩S)₃] and [M(E(CH₂)_nNMe₂)₂] (M = Zn, Cd, Hg;n = 2 or 3) are presented.     

Structures,luminescence, and antibacterial studies of two transition metal complexes involving Schiff bases

Two new transition metal complexes of Schiff bases, [Pd₂(L1)₂Cl₂] (1) and [Zn(L2)₂] (2), [L1?=?N-(4-fluorobenzylidene)-2,6-diisopropylbenzenamine and L2?=?2,4-dibromo-6-((E)(mesitylimino)methyl)phenol], have been synthesized solvothermally and characterized by elemental analysis, IR-spectroscopy, thermogravimetric analysis, powder X-ray diffraction, UV-vis absorption spectra, and single-crystal X-ray diffraction. Complex 1 is a μ-chloro-bridged dinuclear cyclometallated Pd(II) complex, whereas 2 is mononuclear with the Zn^II tetrahedrally coordinated by two L2. Both 1 and 2 display photoluminescence in the solid state at 298?K (fluorescence lifetimes τ?=?22.516?ns at 468?nm for 1, τ?=?3.697?μs at 490?nm for 2). These Schiff bases and their metal compounds have been screened for antibacterial activity against several bacteria, and the results are compared with the activity of penicillin.     

Chemical and morphological modification of complex manganese oxides with different sizes of structural tunnels

The methods for the synthesis of protonated forms of complex manganese oxides Mg _x Mn₄O₈·H₂O and Ba₆Mn₂₄O₄₈ (1h and 2h, respectively) in the form of whisker crystals possessing tunnel crystal structures of different sizes were optimized. The microstructural features and physicochemical properties of the synthesized materials were studied. The treatment with nitric acid leads to the formation of the Mn-O-H hydroxy groups due to the insertion of protons into the structural tunnels. The protonated forms of the 1h and 2h phases are active in ion-exchange processes in aqueous solutions, the tunnel size being the determining factor for the sorption of heavy metal cations. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1130—1135, June, 2008.     

Spin-state dynamics of a photochromic iron(II) complex and its immobilization on oxide surfaces via phenol anchors

This work presents a detailed study of the photo-induced spin-state dynamics of the photochromic iron(II) complex 1, where the metal ion is in the field of a tripodal hexa-imine ligand with protolysable phenol groups. The nature of the complex’s ground state has been identified as a spin singlet by ¹H NMR and steady-state UV/vis spectroscopies, and its distorted octahedral structure was analyzed via crystal structure determination. Sub-picosecond and nanosecond time-resolved laser flash photolysis experiments identify the long-lived quintet state of 1 as the selective product of photoexcitation in the UV/vis spectral region. Thermal barriers of spin-state interconversion as a function of solvent and added base are derived from temperature-dependent rates of transient decay. Ground-state recovery is found to be significantly affected by the solvent and is strongly enhanced, in particular, by base-driven solvolysis of the ligand’s phenol groups. Partial spontaneous deprotonation of the phenolic hydroxyl groups of 1 seems to prevail on metal oxide surfaces, i.e. on alumina. Composite materials, like 1 at Al₂O₃, that retain the characteristic spectral features of the parent iron(II) complex can be readily obtained by wet impregnation of hydrous alumina with solutions of 1.     

Complexation of aminoglycoside antibiotics with metal cations as a derivatization reaction: Determination of gentamicin by equilibrium electrochemical and spectrophotometric methods

The complexation of aminoglycoside antibiotics with metal cations was proposed as a derivatization method for the further determination of the complex obtained by potentiometry with ion-selective electrodes (ISE), voltammetry at the interface between two immiscible electrolyte solutions (ITIES), and spectrophotometry. It was shown by the spectrophotometric method that gentamicin formed a 1: 1 complex with copper(II). For the potentiometric determination of gentamicin, we obtained ionophores that were ion associates formed by the gentamicin complex of copper(II) and tetraphenylborate derivatives as counterions. The transfer of the gentamicin complex of copper(II) was studied voltammetrically at the ITIES. The results obtained indicate that l antibiotic gentamicin can be directly determined as a complex with copper(II) by potentiometric, voltammetric, and spectrophotometric methods.     

New homodi-and heterotrinuclear metal complexes of Schiff base compartmental ligand: interaction studies of copper complexes with calf thymus DNA

The new homodinuclear complexes 1–4 of the type [LM^II ₂Cl₂], heterotrinuclear complexes 5 and 6 of the type [LM^II ₂Sn^IVCl₆] where M = Cu^II, Mn^II, Co^II, Ni^II and Cu^II and Ni^II, respectively have been synthesized and characterized by elemental analysis and various spectroscopic techniques. The homodinuclear complexes possess two different environments (N₂ and N₂O₂donor sets) for holding the metal ions. The metal ion in N₂ set exhibits square planar geometry with two chloride ions in the inner sphere but rhombic structure is found in tetradentate N₂O₂ Schiff base cavity while in heterotrinuclear complexes Sn^IV atom is in the octahedral environment. The interaction of complexes 1 and 5 with calf thymus DNA was carried out by absorption spectroscopy and cyclic voltammetry. The intrinsic binding constants (K _b ) of complex 1 and 5 were determined as 3.2 × 10³ M⁻¹ and 9.6 × 10³ M⁻¹, respectively suggesting that complex 5 binds more strongly to CT-DNA than complex 1. Fluorescence studies along with viscosity measurements have also been checked to authenticate the binding of metal complexes with DNA.