Catalytic activities of polymer‐supported metal complexes in oxidation of phenol and epoxidation of cyclohexene

The metal complexes of N, N′‐bis (o‐hydroxy acetophenone) propylene diamine (HPPn) Schiff base were supported on cross‐linked polystyrene beads. The complexation of iron(III), copper(II), and zinc(II) ions on polymer‐anchored HPPn Schiff base was 83.4, 85.7, and 84.5 wt%, respectively, whereas the complexation of these metal ions on unsupported HPPn Schiff base was 82.3, 84.5, and 83.9 wt%. The iron(III) complexes of HPPn Schiff base were octahedral in geometry, whereas copper(II) and zinc(II) ions complexes were square planar and tetrahedral. Complexation of metal ions increased the thermal stability of HPPn Schiff base. Catalytic activity of metal complexes was tested by studying the oxidation of phenol and epoxidation of cyclohexene in the presence of hydrogen peroxide. The polymer‐supported HPPn Schiff base complexes of iron(III) ions showed 73.0 wt% conversion of phenol and 90.6 wt% conversion of cyclohexene at a molar ratio of 1:1:1 of substrate to catalyst and hydrogen peroxide, but unsupported complexes of iron(III) ions showed 63.8 wt% conversion for phenol and 83.2 wt% conversion for cyclohexene. The product selectivity for catechol (CTL) and epoxy cyclohexane (ECH) was 93.1 and 98.3 wt%, respectively with supported HPPn Schiff base complexes of iron(III) ions but was lower with HPPn Schiff base complexes of copper(II) and zinc(II) ions. Activation energy for the epoxidation of cyclohexene and phenol conversion with unsupported HPPn Schiff base complexes of iron(III) ions was 16.6 kJ mol^?1 and 21.2 kJ mol^?1, respectively, but was lower with supported complexes of iron(III) ions. Copyright © 2007 John Wiley & Sons, Ltd.     

Recent advances in anticancer ruthenium Schiff base complexes

Nowadays in cancer treatment, both metal complexes and organic molecules are being widely used. Current years have seen a surge of interest in the application of organometallic compounds to treat cancer and other diseases. Undeniably, the unique properties of organometallic compounds, intermediate between those of classical inorganic and organic materials, provide new opportunities in the field of medicinal chemistry. Since the discovery of cisplatin, many transition metal complexes have been synthesized and assayed for anticancer activity. In recent years, ruthenium-based Schiff base complexes have emerged as promising antitumor and antimetastatic agents with potential uses in treatment of platinum-resistant tumors or as alternatives to platinum-based chemotherapy. Advantages of utilizing ruthenium complexes in drug development include reliable methods of synthesizing stable complexes; the ability to tune ligand affinities, electron transfer and substitution rates, and reduction potentials; and an increasing knowledge of the biological effects of such complexes. This great expansion of ruthenium-based Schiff base complexes is mainly due to the unique ability of the ruthenium core to permit multiple oxidation states, hence versatile electron-transfer pathways, and because of the ease of preparation with versatile and variable-denticity Schiff base ligands. This review aims to bring the reader up to date with the more recent Ru(II)/(III)-based Schiff base complexes that have been synthesized and investigated for their cytotoxicity.     

Syntheses of Some New Group 4 non-Cp Complexes Bearing Schiff-base, Thiophene Diamide Ligands Respectively and Their Catalytic Activities for a-Olefin Polymerization

Totally sixteen new titanium and zirconium non-Cp complexes supported by Schiff-base, or thiophene diamide ligands have been synthesized. The complexes are obtained by the reaction of M(OPr-i)4(M=Ti,Zr) with the corresponding Schiff-base ligand in 1:1 molar ratio in good yield. The thiophene diamide titanium complex has been prepared from trimethylsilyl amine [N,S,N] ligand and TiCl4 in toluene at 120℃. All complexes are well charac-terized by ^1H NMR, IR, MS and elemental analysis. When activated by excess methylaluminoxane (MAO), complexes show moderate catalytic activity for ethylene polymerization, and complex If (R^1=CH3,R^2=Br) exhibits the highest activity for ethylene and styrene polymerization. When the complexes were preactivated by triethylaluminum (TEA), both polymerization activities and syndiotacticity of the polymers were greatly improved.     

The Synthesis and Characterization of s‐Triazine‐Cored Tripodal Structure and Its Salen/Salophen‐Bridged Fe/Cr(III) Capped Complexes

A novel Schiff base compound was synthesized, and its complexation properties with Fe(III) and Cr(III) were investigated. Tripodal ligand was synthesized by the reaction of s‐triazine and 4‐hydroxybenzaldehyde. Then a Schiff base involving 8‐hydroxyquinoline was synthesized by the reaction of 5‐aminomethyl‐8‐hydroxyquinoline ( QN ) and 2,4,6‐tris(p‐formylphenoxy)‐1,3,5‐triazine ( TRIPOD ) in methanol/chloroform media. The obtained Schiff base ( QN-TRIPOD ) was then reacted with four trinuclear Fe(III) and Cr(III) complexes including tetradentate Schiff bases N ,N ′‐bis(salicylidene)ethylenediamine (salenH₂)/bis(salicylidene)‐o‐phenylenediamine (SalophenH₂). The synthesized ligand and complexes were characterized by means of elemental analysis carrying out ¹H NMR, FTIR spectroscopy, thermal analyses, and magnetic susceptibility measurements. Finally, metal ratios of the prepared complexes were determined by using atomic adsorption spectrometry.     

Synthesis,structure and catalytic polymerization activity of half‐sandwich cyclometallated iridium complexes

A series of mononuclear half‐sandwich cyclometallated iridium complexes with Schiff base ligands were synthesized in good yields. Five air‐stable C,N‐chelate mode complexes were obtained smoothly through metal‐mediated C─H bond activation. Treatments of dimeric metal complexes [Cp*IrCl₂]₂ with ligands L1–L5 afforded the corresponding C,N‐chelate mononuclear half‐sandwich iridium(III) complexes 1 – 5 . These iridium complexes exhibit high catalytic activity for norbornene polymerization. Both steric and electronic effects of the substituted groups have influences on the behaviors of the polymerization process. All complexes were characterized using infrared and NMR spectroscopies and elemental analysis. Molecular structures of complexes 1 , 2 and 5 were further confirmed using single‐crystal X‐ray analysis.     

Metal complexes of novel Schiff base derived from iron sandwiched organometallic and 4‐nitro‐1,2‐phenylenediamine: Synthesis,characterization, DFT studies,antimicrobial activities and molecular docking

The condensation of 2‐acetylferrocene with 4‐nitro‐1,2‐phenylenediamine in a 1:1 molar ratio, resulting in formation of a novel bi‐dentate organometallic Schiff base ligand (L), (2‐(1‐((2‐amino‐5‐nitrophenyl)imino)ethyl)cyclopenta‐2,4‐dien‐1‐yl)(cyclopenta‐2,4‐dien‐1‐yl)iron. Also, its Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes have been synthesized. The stoichiometric ratios of the prepared compounds were estimated using elemental analysis (C, H, N, M), molar conductivity, FT‐IR, UV‐Vis, ¹H‐NMR, SEM and mass spectral analysis. Furthermore, their TG and DTG properties were studied. The geometrical structure of the complexes was found to be octahedral. From spectral analysis, the Schiff base coordinated to metal ions through the azomethine and amine groups. DFT‐based molecular orbital energy calculations of the synthesized ligand have been studied, in which the ligand was theoretically optimized. The Schiff base and its metal complexes have been screened for their antimicrobial activities against different bacterial and fungal species by using disc diffusion method. The anticancer activities of the ligand and its metal complexes have also been studied towards breast cancer (MCF‐7) and human normal melanocytes (HFB‐4) cell lines. Molecular docking was also used to identify the interaction between the Schiff base ligand and its Cd(II) complex with the active site of the receptors of breast cancer mutant oxidoreductase (PDB ID: 3HB5), crystal structure of Staphylococcus aureus (PDB ID: 3Q8U) and yeast‐specific serine/threonine protein phosphatase (PPZ1) of Candida albicans (PDB ID:5JPE).     

Ring‐opening polymerization of rac‐lactide catalyzed by Al(III) and Zn(II) complexes incorporating Schiff base ligands derived from pyrrole‐2‐carboxaldehyde

A series of Al(III) chloride [LAl‐Cl]; Al(III) alkoxide [LAl‐OR]₂; and Zn(II) [LZn]₂ complexes with Schiff base ligands were obtained. ¹H NMR and X‐ray diffraction studies indicate that [LAl‐Cl] complexes have C_s symmetry and the Al center is penta‐coordinated. The Al(III) alkoxide complex [L⁵Al‐OⁱPr]₂ is a dimer bridged by OⁱPr^? with the Al center in a distorted octahedral environment. Zn complexes [LZn]₂ are double helix dimers with tetra‐coordinated Zn centers. The catalytic activity for the ring‐opening polymerization of rac‐lactide was evaluated. The best activity in this series is shown by the aluminium chloride complex with a flexible three‐carbon bridge; more flexible four‐carbon bridges lower the activity.     

Syntheses, characterization, antimicrobial and genotoxic activities of new Schiff bases and their complexes

Two new Schiff base ligands (L¹, L²) have been prepared from the reaction of 2,6-diacetylpyridine and 2-pyridinecarboxyaldehyde with 4-amino-2,3-dimethyl-1-phenyl-3-pyrozolin-5-on, and their Co(II), Cu(II), Ni(II), Mn(II), and Cr(III) metal complexes have also been prepared. The complexes are formed by coordination of N and O atoms of the ligands. Their structures were characterized by physico-chemical and spectroscopic methods. The analytical data shows that the metal to ligand ratio in the Schiff base complexes is 1:2. The Schiff base ligands and all complexes were evaluated for their in vitro antibacterial and antifungal activities by the disc diffusion method. In addition, the genotoxic properties of the ligands were studied.     

Synthesis,spectroscopy, thermal and biological aspect of novel six‐coordinated dimeric iron(III) mixed‐ligand complexes

The mixed‐ligand complexes of iron(III) with 1‐cyclopropyl‐6‐fluoro‐4‐oxo‐7‐piperazin‐1‐yl‐1,4‐dihydroquinoline‐3‐carboxylic acid and various neutral bidentate Schiff base ligands were prepared. The structure of mixed‐ligand complexes was investigated using spectral, physicochemical and elemental analyses. Biocidal activity was determined using agar plate technique against Staphylococcus aureus, Bacillus subtilis, Bacillus cereus, Salmonella typhi, Escherichia coli and Serratia marcescens . The result showed a significant increase in a biocidal activity compared with parent ligands, metal salts and standard drugs (ofloxacin, levofloxacin). DNA binding and cleavage studies were carried out using absorption titration and gel electrophoresis techniques, respectively. The binding constant of Fe(III) complexes was obtained in the range 2.5–4.0 × 10⁴ M ^?1. The DNA binding and cleavage efficacy were raised in mixed‐ligand complexes as compared with parental ligands and metal salts. Copyright © 2008 John Wiley & Sons, Ltd.     

p‐Nitrophenyl Picolinate Cleavage by Unsymmetrical Bis‐Schiff Base Manganese(III) and Cobalt(II) Complexes with Aza‐Crown Ether or Morpholino Pendants

The unsymmetrical bis‐Schiff base manganese(III) and cobalt(II) complexes with either benzo‐10‐aza‐crown ether pendants (MnL¹Cl, MnL²Cl) or morpholino pendant (MnL³Cl, CoL³) have been employed as models for hydrolase by studying the kinetics of their hydrolysis reactions with p‐nitrophenyl picolinate (PNPP). A kinetic model of PNPP cleavage catalyzed by these complexes is proposed. The effects of complex structures and reaction temperature on the rate of PNPP hydrolysis have been examined. All four complexes exhibit high catalytic activity and the rate increases with pH under 25°C. The complexes of ligands containing a crown ether group exhibit higher catalytic activities than the non‐crown analogues. The catalytic activity of the complexes follows the order Mn(III)>Co(II) under the same ligands.     

Photoluminescence property of polymer–rare earth complexes containing acetaldehyde/aminophenol type bidentate Schiff base ligand

Acetaldehyde was introduced onto the side chains of polysulfone, and then Schiff base reactions were carried out between the introduced acetaldehyde and ortho-aminophenol (OAP) or meta-aminophenol (MAP). Two bidentate Schiff base (B) ligands of acetaldehyde/aminophenol type, OAPB and MAPB, were bonded on the side chains of polysulfone, and two new bidentate Schiff base ligand functionalized-polysulfones, PSF-OAPB and PSF-MAPB, were obtained. The triplet state energies of OAPB and MAPB are well matched with the resonant level energy of Tb(III), and the Tb(III) complexes emit the strong characteristic fluorescence of Tb(III) (green luminescence). Complexes of Eu(III) have no fluorescence emission because of the mismatching of the energy levels. In comparison, the fluorescence intensity of the binary complex PSF-(MAPB)₃-Tb(III) is stronger than that of the binary complex PSF-(OAPB)₃-Tb(III) because of the structured difference of the chelating ring. The ternary complexes PSF-(MAPB)₃-Tb(III)-(Phen)₁ (Phen represents 1,10-phenanthroline) and PSF-(OAPB)₃-Tb(III)-(Phen)₁ have stronger fluorescence emissions than the corresponding binary complexes. The fluorescence emission intensities of solid films of the complexes are stronger than that of their solutions. The prepared luminescent polymer-Tb(III) complexes containing acetaldehyde/aminophenol type bidentate Schiff base ligands have very high quantum yields (80–86%), reflecting the high intramolecular energy transfer efficiencies from the ligands to Tb(III).     

Binuclear Ru(III) Schiff base complexes: synthesis,spectral characterization,oxidation, C?C coupling reactions and antibacterial activities

New hexa‐coordinated binuclear Ru(III) Schiff base complexes of the type {[(B)₂X₂Ru]₂L} (where B = PPh₃ or AsPh₃; X = Cl or Br; L = binucleating N₂O₂ Schiff bases) were synthesized and characterized by elemental analysis, magnetic susceptibility measurement, FT‐IR, UV–vis, ¹³C{¹H}‐NMR, ESR at 300 and 77 K, cyclic voltammetric technique, powder X‐ray diffraction pattern and SEM. The new complexes were used as catalysts in phenyl–phenyl coupling reaction and the oxidation of alcohols to their corresponding carbonyl compounds using molecular oxygen atmosphere at room temperature. Further, the new Schiff base ligands and their Ru(III) complexes were also screened for their antibacterial activity against K. pneumoniae, Shigella sp., M. luteus, E. coli and S. typhi. From this study, it was found that the activity of the ruthenium(III) Schiff base complexes almost reaches the effectiveness of the conventional bacteriocide standards. Copyright © 2009 John Wiley & Sons, Ltd.     

Schiff base complexes of vanadium(III, IV, V) as catalysts for the electroreduction of O2 to H2O in acetonitrile

Fifteen Schiff base ligands were synthesized and used to form complexes with vanadium in oxidation states III, IV, and V. Electrochemical and spectral characteristics of the complexes were evaluated and compared. In acidified solutions in acetonitrile the vanadium(IV) complexes undergo reversible disproportionation to form V(III) and V(V) complexes. With several of the ligands the V(III) complexes are much more stable in the presence of acid than is the previously studied complex with salen, an unelaborated Schiff base ligand (H(2) salen = N,N'-ethylenebis(salicylideneamine)). Equilibrium constants for the disproportionation were evaluated. The vanadium(III) complexes reduce dioxygen to form two oxo ligands. The reaction is stoichiometric in the absence of acid, and second-order rate constants were evaluated. In the presence of acid some of the complexes investigated participate in a catalytic electroreduction of dioxygen.     

Oxotitanium(IV) complexes of some bis‐unsymmetric Schiff bases: Synthesis,structural elucidation and biomedical applications

A number of oxotitanium(IV) complexes of the type TiOL with bis‐unsymmetric dibasic tetradentate Schiff base (LH₂) containing ONNO donor atoms have been synthesized. Mono‐Schiff base (OPD‐HNP) was prepared by the condensation of 1:3 molar ratio of 2‐hydroxy‐1‐naphthaldehyde (HNP) with o‐phenylenediamine (OPD). Dibasic unsymmetric tetradentate diamine Schiff bases were prepared by the reaction of OPD‐HNP with 2‐hydroxyacetophenone, 2‐hydroxypropeophenone, benzoylacetone, acetylacetone and ethylacetoacetate. Further, titanylacetylacetonate was reacted with these ligands to obtain their metal complexes. On the basis of analytical and physiochemical data, the formation of complexes as TiOL was suggested having square pyramidal geometry. Quantum mechanical approach also confirmed this geometry. The assessment of the synthesized ligands and their complexes showed that some behave as good inhibitors of mycelial growth against selected phytopathogic fungi but weak inhibitors against some selected bacteria. A few of them also showed antioxidant properties.     

Trans‐ and cis‐ Cobalt(III), Iron(III), and Chromium(III) Complexes Based on α‐ and γ‐Diimine Schiff Base Ligands: Synthesis and Evaluation of the Complexes as Catalysts for Oxidation of L‐Cysteine

The synthesis of a new series of trans and racemic cis isomers of cobalt(III)‐, iron(III)‐, and chromium(III)‐based complexes with the α‐ and γ‐diimine Schiff base ligands, N,N′‐bis(X)‐2,3‐butandiimine and N,N′‐bis(X)‐1,2‐phenyldiimine (X = cyclohexyl, 2‐isopropylphenyl, 1‐naphthyl) is described. To confirm the identity of the complexes prepared in the present study, a variety of techniques including elemental analysis, magnetic susceptibility, infrared‐, mass‐ (EI), and UV/Vis‐ spectroscopy have been utilized. Some of the isolated complexes have been evaluated as catalysts for the oxidation of L‐cysteine. Preliminary results showed that the metal atoms, geometry of the complexes, auxiliary substituents, and the backbone of the ligand influenced the rate of oxidation reaction.     

Catalytic oxidation and C–C coupling reactions of new ruthenium(III) Schiff base complexes containing PPh<Subscript>3</Subscript> or AsPh<Subscript>3</Subscript> co-ligands

New mononuclear ruthenium(III) Schiff base complexes of the type [RuX₂(EPh₃)(L)] (X = Cl or Br; E = P or As; L = monobasic tridentate Schiff base derived from o-aminophenol or o-aminothiophenol with ethylacetoacetate or ethylbenzoylacetate) have been synthesized. The Schiff base ligands chelate to ruthenium through O, N, and O/S by dissociation of the phenolic proton/thiophenolic proton forming chelate rings. These complexes have been characterized by physico-chemical and spectroscopic methods. Cyclic voltammetric data of all the complexes showed Ru(III)/Ru(IV) oxidation and Ru(III)/Ru(II) reduction within the range of 0–1.5 V and 0 to −1.5 V with respect to Ag/AgCl, respectively. The complexes were tested as catalysts in the oxidation of alcohols using molecular oxygen at ambient temperature, and also in C–C coupling reactions. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Iron(III) Schiff base complexes with asymmetric tetradentate ligands: synthesis,spectroscopy, and antimicrobial properties

The synthesis and characterization is reported of four iron(III) complexes of general formula [Fe(pythsalX)(H₂O)₂]Cl₂, derived from the NSNO-donor tetradentate Schiff base ligands pythsalHX ([5-X-N-(2-pyridylethylsulfanylethyl)salicylideneimine] (X = OMe, N₂Ph, I, NO₂). The complexes were characterized by physico-chemical and spectroscopic methods. The thermal stabilities of both the free Schiff bases and their complexes were studied by differential scanning calorimetry and thermogravimetric analyses. The spectroscopic data suggest that the Schiff base ligands coordinate through deprotonated phenolic oxygen, imine, and pyridine-type nitrogens and the thioether sulfur atoms to give an octahedral geometry around the iron(III) atom in all these complexes. The free Schiff bases and their complexes have been screened for antimicrobial activities and the results show that the free Schiff bases are more potent antibacterials than the complexes.     

Synthesis and studies of Schiff base complexes with aza-crown ether or morpholino pendants as synthetic hydrolases for <Emphasis Type="Italic">p</Emphasis>-nitrophenyl picolinate

Three symmetrical bis-Schiff bases with either benzo-10-aza-crown ether or morpholino pendants and their Mn(III) and Co(II) complexes have been synthesized and employed as models for hydrolase enzymes by studying the kinetics of their hydrolysis reactions with p-nitrophenyl picolinate (PNPP). A kinetic model of PNPP cleavage catalyzed by these complexes is proposed. The effects of complex structures and reaction temperature on the rate of PNPP hydrolysis have been examined. All four complexes exhibit high catalytic activity and the rate increases with pH. The complexes of ligands containing a crown ether group exhibit higher catalytic activities than the non-crown analogs, and the catalytic activity of the phenyl-bridged Schiff base complex is larger than that of ethyl-bridged analogue for the same substituents and metal.     

氮杂冠醚取代单Schiff碱过渡金属配合物催化氧化对二甲苯研究

本文将苯并-10-氮杂-15-冠-5或吗啉基取代的单Schiff碱过渡配合物作为催化剂,在常压和120℃条件下,以空气为氧源,研究了对二甲苯催化氧化反应。实验探讨了Schiff碱配合物中心金属离子、Schiff碱配体中挂接的氮杂冠醚环、配体芳环上取代基和反应时间等对对二甲苯催化氧化反应的影响。实验结果表明:Schiff碱配合物中氮杂冠醚的存在能显著缩短反应诱导期,提高催化反应活性和产物选择性;Schiff碱Mn(III)配合物比Schiff碱Co(II)具有更高的催化反应活性;氮杂冠醚Schiff碱Mn(III)配合物对于二甲苯的催化氧化反应转化率大于60%,对甲苯甲酸产物的选择性均高于70%。     

Synthesis of di‐nitrogen Schiff base complexes of methyltrioxorhenium(VII) and their application in epoxidation with aqueous hydrogen peroxide as oxidant

Several di‐nitrogen Schiff bases were synthesized through the condensation of 2‐pyridinecarboxaldehyde with primary amines. The Schiff bases as ligands coordinated with methyltrioxorhenium (MTO) smoothly to afford the correspondent complexes which were characterized by IR, ¹H NMR, ¹³C NMR, MS and elemental analysis. One of the complexes was analyzed by X‐ray crystallography as well. The results revealed that the complexes display distorted octahedral geometry in the solid state with a trans‐position of Schiff base. Catalytic results indicated that the complexes as catalysts increased the selectivity of epoxides remarkably compared with MTO in the epoxidation of alkenes with 30% hydrogen peroxide as oxidant and the increasing rate depended on the structure of the Schiff base ligands of the complexes. The results indicated that the stronger the donating ability of the ligand, the higher selectivity of epoxides the complex gave in the epoxidation of alkenes with 30% hydrogen peroxide as oxidant. Copyright © 2010 John Wiley & Sons, Ltd.