Efficient initiators for the ring‐opening polymerization of L‐lactide: Synthesis and characterization of NNO‐tridentate Schiff‐base zinc complexes

A series of efficient catalysts, based on zinc alkoxides coordinated with NNO‐tridentate Schiff‐base ligands (L¹H‐L⁶H), for ring opening polymerization of L ‐lactide have been prepared. The reactions of diethyl zinc (ZnEt₂) with L¹H‐L⁶H yielded [(μ‐L)ZnEt]₂ ( 1a–6a ), respectively. Further reaction of compounds 1a–6a with benzyl alcohol (BnOH) produced the corresponding compounds of [LZn(μ‐OBn)]₂ ( 1b–6b), respectively. X‐ray crystal structural studies reveal that all of these compounds 1a–6a are dimeric bridging through the phenolato oxygen atoms of the Schiff‐base ligand. However, the molecular structures of 1b–6b show a dimeric character bridging through the benzylalkoxy oxygen atoms. Ring‐opening polymerization of L ‐lactide, initiated by 1b–6b , proceeds rapidly with good molecular weight control and yields polymer with a very narrow molecular weight distribution. Experimental results show that the substituents on the imine carbon of the NNO‐ligand affect the reactivity of zinc complexes dramatically. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6466–6476, 2008     

Molybdenum tetracarbonyl complexes with linear chain polyether‐containing Schiff base ligands and their reactivity in the polymerization of methyl methacrylate

Mo(CO)₆ was reacted with the Schiff base ligand obtained by condensation reaction of 2‐acetyl‐ or benzoylpyridine with poly(propylene glycol)bis(2‐aminopropyl ether) to obtain polymeric, dinuclear metal tetracarbonyl compounds. The long‐chain Schiff base complexes are highly soluble even in non‐polar solvents such as petroleum ether, diethyl ether and n‐hexane. These complexes, as free‐radical initiators, afforded methyl methacrylate polymerization in chlorinated solvents. Copyright © 2005 John Wiley & Sons, Ltd.     

Hybrid compounds of Schiff base Cu,Fe, Co complexes with molybdovanadophoric heteropolyacids: synthesis,characterization and their catalytic performance to hydroxylation of benzene with H2O2

Hybrid compounds of molybdovanadophoric heteropolyacids and a Schiff base transition metal complex, M‐saldmp or M‐fpdmp (M = Fe(II), Co(II), Cu(II)), were successfully prepared and found to be effective catalysts for direct hydroxylation of benzene with H₂O₂. The synergistic effect between Schiff base metal complex and heteropolyacid plays an important role in the promotion of catalytic activity. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis,characterization and catalytic properties of novel palladium(II) complexes containing aromatic sulfonamides: effective catalysts for the oxidation of benzyl alcohol

In this article, N‐(2‐aminophenyl)arylsulfonamides (1–5) were successfully synthesized by the reaction of o‐phenylenediamine and various benzenesulfonyl chlorides. The Schiff base derivatives (1a–f; 4e) of those compounds were obtained using different aldehydes. Then, a series of neutral‐four coordinate Pd(II) complexes (6–10) were prepared from the reaction of Pd(OAc)₂ and 1–5. On the other hand, when we tried to synthesize Pd(II) complexes containing Schiff base/sulfonamide ligands, two different situations were observed. Generally, when an electron‐donating group was attached to the imine fragment (1a–d) except for 1f, the Schiff base hydrolyzed and 6 was isolated. When an electron‐withdrawing group was attached to the imine fragment (1e, 4e), neutral four‐coordinate Pd(II) complexes (11–13) bearing Schiff base/sulfonamide ligands were isolated. The synthesized compounds were characterized by FT‐IR, elemental analysis and NMR spectroscopy. The complexes were used as a catalyst in the oxidation reaction of benzyl alcohol to benzaldehyde in the presence of H₅IO₆ in acetonitrile. All complexes showed satisfactory catalytic activity. The highest catalytic activity was obtained with 9. Copyright © 2012 John Wiley & Sons, Ltd.     

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.     

Synthesis of 4‐substituted styrene compounds via palladium catalyzed Suzuki–Miyaura reaction using bidentate Schiff base ligands

Air‐stable symmetric Schiff base have been synthesized and proved to be efficient ligands for Suzuki–Miyaura reaction between aryl bromides and arylboronic acids using PdCl₂(CH₃CN)₂ as palladium source under aerobic conditions. The coupling reaction proceeded smoothly using N,N‐bis(anthracen‐9‐ylmethylene)benzene‐1,2‐diamine (L₇) as ligand to provide 4‐substituted styrene compounds in good yields. Copyright © 2009 John Wiley & Sons, Ltd.     

Crown‐like macrocycle zinc complex derived from β‐diketone ligand for the polymerization of rac‐lactide

Enolic Schiff base zinc (II) complex 1 was synthesized. XRD revealed 1 was a novel crown‐like macrocycle structure consisted of hexanuclear units of (LZnEt)₆ via the coordination chelation between the Zn atom and adjacent amine nitrogen atom. Further reaction of 1 with one equivalent 2‐propanol at RT produced Zn‐alkoxide 2 by in situ alcoholysis. Complex 2 was used as an initiator to polymerize rac‐lactide in a controlled manner to give heterotactic enriched polylactide. Factors that influenced the polymerization such as the polymerization time and the temperature as well as the monomer concentration were discussed in detail in this paper. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 643–649, 2008     

Spectroscopic,thermal and antimicrobial properties of the copper(II) complex of Schiff base derived from 2‐(salicylidene) aminopyridine

Schiff bases and their complex combinations with metallic ions represent a class of compounds with antimicrobial activity. A ligand was prepared by condensation of the salicylaldehyde with 2‐aminopyridine obtaining 2‐(salicylidene) aminopyridine (SB) with a high capacity for complexing Cu(II) ions. The new compound has been characterized by physical constants (melting point, solubility, stability) and the chemical structure was confirmed by elemental, spectral (IR, UV–visible, ¹H NMR and ¹³C‐NMR) and thermal analyses. The elemental analysis gives a coordination ratio of 1:2 metal:Schiff base. Lethal dose 50 (DL₅₀) values of new Schiff base and their complex with metallic ions were established. The antimicrobial activity of this complex was tested in comparison with the activity of the corresponding Schiff base on strains of Staphylococcus aureus, Bacillus cereus, Bacillus subtilis, Escherichia coli, Candida albicans, and Klebsiella. These were compared with the activity of the reference drugs (chloramphenicol, tetracycline, ofloxacin and nystatin) on the above‐mentioned strains. It has been established that all compounds tested were very active against both Gram‐positive and Gram‐negative bacteria. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis,characterization, and computational study of some new organotellurium compounds containing azomethine groups

The reaction of ortho‐mercurated anilines with benzaldehyde gave the ortho‐mercurated Schiff bases. The reaction of the mercurated Schiff bases with tellurium tetrabromide in 1:1 and 2:1 mole ratio using dry chloroform as solvent gave the ortho‐tellurated Schiff bases compounds ArTeBr₃ and Ar₂TeBr₂, respectively, in good yields (where Ar = 5‐ClC₆H₃N=CHC₆H₅, 5‐BrC₆H₃N=CHC₆H₅, 5‐CH₃OC₆H₃N=CHC₆H₅, and 5‐NO₂C₆H₃N=CHC₆H₅). The reduction of ArTeBr₃ by hydrazine hydrate gave the corresponding ditelluride (i.e., Ar₂Te₂). Treatment of Ar₂TeBr₂ with hydrazine hydrate afforded tellurides (Ar₂Te) in good yields. Attempts to prepare the corresponding aryl tellurenyl bromides, ArTeBr, by partial reduction of ArTeBr₃ with various reducing agents were unsuccessful. All these new compounds were characterized by microanalysis, ¹H, and ¹³C NMR, IR, and mass spectroscopic data. A computational study for the Te → N interactions of all compounds was calculated using the GAUSSIAN 03 program package. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:307–315, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20437     

Stereochemical aspects of the hypophosphorous acid addition to terephthalic schiff bases. Synthesis of new 1,4‐phenylene‐bis‐aminomethane‐bis‐phosphonous acids

Terephthalic Schiff bases react with hypophosphorous acid to form 1,4‐phenylene‐bis‐N‐alkyl‐aminomethanephosphonous acids in moderate yields. NMR studies demonstrated that—for several examples—this reaction led to the exclusive formation of only one diastereomeric form. NMR investigation of a chiral salt identified the meso form. In contrast hereto, a corresponding addition of hypophosphorous acid to a chiral Schiff base proved to be not stereoselective; all three possible diastereoisomers were formed in a 4:1:1 ratio. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:283–287, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20422     

Synthesis,Characterization, and Crystal Structure of Mononuclear and Dinuclear Dioxomolybdenum(VI) Complexes with Tridentate Schiff‐base Ligands. Part 2

Mononuclear [MoO₂LD], and dinuclear [MoO₂L]₂ or [MoO₂L]₂ · D dixomolybdenum(VI) complexes have been prepared by the reaction of tridentate Schiff‐base ligands L with [MoO₂(acac)₂]. The Schiff‐base ligands have been synthesized from salicylaldehyde ( 1 , 1a , 1c , 1d ), 2‐hydroxy‐1‐naphthaldehyde ( 2 , 2c ) and 2‐hydroxy‐3‐methoxybenzaldehyde ( 3a , 3b , 3c , 3d , 3e ) with 2‐amino‐p‐cresol. All prepared complexes consist of cis‐MoO₂²⁺core coordinated by Schiff‐base ligand through two deprotonated hydroxyl groups and one imino nitrogen atom. The usual octahedral coordination around the molybdenum atoms is completed by the neutral ligand D (methanol, ethanol, dimethyl sulfoxide, imidazole or 4, 4′‐bipyridine). All compounds were characterized by elemental analyses, IR spectroscopy and some of them by X‐ray crystallography ( 1a , 2c , 3a , 3b , 3c and 3e ).     

Synthesis,characterization and antibacterial properties of symmetric 1,1′‐ferrocene derived Schiff‐base ligands and their Co(II), Cu(II), Ni(II) and Zn(II) chelates

Symmetric 1,1′‐dimethylferrocene derived Schiff‐base ligands have been prepared by the condensation reaction of 1,1′‐diacetylferrocene with 2‐aminopyrazine, 2‐aminopyridine and 2‐aminothiazole respectively. Their transition metal chelates, of the type [M(L)]Cl₂ [M = Cu(II)] and [M(L)(Cl₂)] [M = Co(II), Ni(II) and Zn(II)] have been prepared. The synthesized Schiff‐base ligands and their metal(II) chelates have been characterized by their physical, analytical and spectral data. Copyright © 2000 John Wiley & Sons, Ltd.     

Synthesis,characterization, and biological activity of phosphorylated/thiophosphorylated compounds of 2‐substituted benzimidazoles

A series of phosphorylated and thiophosphorylated compounds of 2‐substituted benzimidazoles have been synthesized by the reaction of POCl₃ and PSCl₃ with 2‐substituted benzimidazoles in different molar ratios. The compounds have been characterized by elemental analyses, infrared, and ¹H NMR and ³¹P NMR spectral studies. These compounds were found to be insecticidal when tested against Periplenata americana. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:154–157, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20385     

Functional zinc(II) phthalocyanines bearing Schiff base complexes as oxidation catalysts for bleaching systems

Oxidation catalysis is used to increase the performance of hydrogen peroxide in laundry bleach applications. Bleach catalysts provide cost‐effective, energy‐saving and environmentally friendly bleach systems yielding perfect stain removal at lower temperatures. This comparative study is based on the synthesis of bis[bis(salicylhydrazonephenoxy)manganese(III)] phthalocyaninatozinc(II) ( 2 ), bis[bis(salicylhydrazonephenoxy)cobalt(III)] phthalocyaninatozinc(II) ( 3 ) and bis[bis(salicylhydrazonephenoxy)iron(III)] phthalocyaninatozinc(II) ( 4 ) as tri‐nuclear complexes consisting of two Schiff base complexes substituting a zinc phthalocyanine. Complexion on the periphery to obtain complexes 2 , 3 , 4 was performed through the reaction of a Schiff base‐substituted phthalocyanine using MnCl₂?4H₂O, CoCl₂?6H₂O or FeCl₃?6H₂O salts in basic condition in dimethylformamide. Fourier transform infrared, ¹H NMR, ¹³C NMR, UV–visible, inductively coupled plasma optical emission and mass spectra were applied to characterize the prepared compounds. The bleach performances of the three phthalocyanine compounds 2 , 3 , 4 were examined by the degradation of morin as hydrophilic dye. The degradation progress in the presence of catalysts 2 , 3 , 4 /H₂O₂ combination in aqueous solution was investigated using an online spectrophotometric method. It was found that the catalysts 2 , 3 , 4 exhibited better bleaching performance at 25 °C than tetraactylethylethylenediamine as bleach activator used in powder detergent formulations for stain removal. Copyright © 2015 John Wiley & Sons, Ltd.     

Organotin(IV) complexes with various donor ligands and their cytotoxicity against tumour cell lines. Part(I): R2SnCl2 with Schiff bases; unusual CN bond cleavage of the bases and X‐ray structures of the ionic products formed

Several Schiff bases derived from salicylaldehyde and aminopyridines were found to coordinate with Me₂SnCl₂ in 1:1 or 1:2 (tin:base) molar ratio in diethylether, depending on the nature of the Schiff base used, to form complexes of the general formula Me₂SnCl₂·L or Me₂SnCl₂·2L respectively. These Schiff bases coordinate with Ph₂SnCl₂ in a similar manner, but if the reaction is carried out in chloroform or if the product formed in ether is dissolved in chloroform then colourless to pale yellow crystals precipitated. The latter were analysed and found to be due to the ionic compounds [H₂NpyN–H⁺]₂ [Ph₂SnCl₄]^2? which were formed as a result of an unusual cleavage of the C?N bond of the Schiff bases. The Schiff bases, their Me₂SnCl₂ complexes and the ionic compounds were analyzed physicochemically and spectroscopically. The crystal structures of two of the ionic compounds showed that the cation [H₂NpyN–H⁺] binds with the anion [Ph₂SnCl₄]^2? via hydrogen bonds. The Schiff bases, their Me₂SnCl₂ complexes and the ionic compounds were screened against the three tumour cell lines, L₉₂₉, K₅₆₂ and HeLa, and the results were compared with those of the anticancer drugs, cisplatin, carboplatin and oxaliplatin. Copyright © 2003 John Wiley & Sons, Ltd.     

Some divalent metal(II) complexes of novel potentially tetradentate Schiff base N,N′‐bis(2‐carboxyphenylimine)‐2,5‐thiophenedicarboxaldhyde: Synthesis,spectroscopic characterization and bioactivities

A novel tetradentate dianionic Schiff base ligand, N ,N ′‐bis(2‐carboxyphenylimine)‐2,5‐thiophenedicarboxaldhyde (H₂L) and some first row d‐transition metal chelates (Co(II), Cu(II), Ni(II) and Zn(II)) were synthesized and characterized using various physicochemical and spectroscopic methods. The spectroscopic data suggested that the parent Schiff base ligand coordinates through both deprotonated carboxylic oxygen and imine nitrogen atoms. The free Schiff base and its metal chelates were screened for their antimicrobial activities for various pathogenic bacteria and fungi using the agar well diffusion method. The antibacterial and antifungal activities of all the newly synthesized compounds are significant compared to the standard drugs ciprofloxacin and nystatin. The antioxidant activities of the compounds were determined by reduction of 1,1‐diphenyl‐2‐picrylhydrazyl and compared with that of vitamin C as a standard. DNA binding ability of the novel Schiff base and its complexes was investigated using absorption spectroscopy, fluorescence spectroscopy, viscosity measurements and thermal denaturation. The obtained results clearly demonstrate that the binding affinity with calf thymus DNA follows the order: Cu(II) complex > Ni(II) complex > Zn(II) complex > Co(II) complex >H₂L. Furthermore, the DNA cleavage activity of the newly synthesized ligand and its metal complexes was investigated using supercoiled plasmid DNA (pUC18) gel electrophoresis.     

Observation and Kinetic Characterization of Transient Schiff Base Intermediates by CEST NMR Spectroscopy

In aqueous solution, many biochemical reaction pathways involve reaction of an aldehyde with an amine, which progresses through generally unstable, hydrated and dehydrated, Schiff base intermediates that often are unobservable by conventional NMR. There are 4 states in the relevant equilibrium: 1) gem‐diol, 2) aldehyde, 3) hemiaminal, and 4) Schiff base. For the reaction between protein amino groups and DOPAL, a highly toxic metabolite of dopamine, the ¹H resonances of both the hemiaminal and the dehydrated Schiff base can be observed by CEST NMR, even when their populations fall below 0.1 %. CEST NMR reveals the quantitative exchange kinetics between reactants and Schiff base intermediates, explaining why the Schiff base NMR signals are rarely observed. The reactivity of DOPAL with N^α‐amino groups is greater than with lysine N^?‐amines and, in the presence of O₂, both types of Schiff base DOPAL–peptide intermediates rapidly react with free DOPAL to irreversibly form dicatechol pyrrole adducts.     

Synthesis and characterization of a novel magnetic nano‐palladium Schiff base complex: application in cross‐coupling reactions

A novel and task‐specific nano‐magnetic Schiff base ligand with phosphate spacer using 2‐aminoethyl dihydrogen phosphate instead of usual coating agents, i.e. tetraethoxysilane and 3‐aminopropyltriethoxysilane, for coating of nano‐magnetic Fe₃O₄ is introduced. The nano‐magnetic Schiff base ligand with phosphate spacer as a novel catalyst was synthesized and fully characterized using infrared spectroscopy, X‐ray diffraction, scanning and transmission electron microscopies, thermogravimetry, derivative thermogravimetry, vibrating sample magnetometry, atomic force microscopy, X‐ray photoelectron spectroscopy and energy‐dispersive X‐ray spectroscopy. The resulting task‐specific nano‐magnetic Schiff base ligand with phosphate spacer was successfully employed as a magnetite Pd nanoparticle‐supported catalyst for Sonogashira and Mizoroki–Heck C–C coupling reactions. To the best of our knowledge, this is the first report of the synthesis and applications of magnetic nanoparticles of Fe₃O₄@O₂PO₂(CH₂)₂NH₂ as a suitable spacer for the preparation of a designable Schiff base ligand and its corresponding Pd complex. So the present work can open up a new and promising insight in the course of rational design, synthesis and applications of various task‐specific magnetic nanoparticle complexes. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis,Electrochemical and Luminescence Studies of Nickel and Vanadium Complexes Containing Tetradentate Schiff Base Ligand with N2O2 Donor Atoms

A symmetrical tetradentate Schiff base ligand was derived by the condensation of ortho‐vanillin and thiourea in 2:1 molar ratio and adjusted pH. Nickel and vanadyl complexes were obtained using the template method by the reaction of ortho‐vanillin and thiourea with Ni(OAc)₂. 4H₂O and VO(acac)₂ (2:1:1 molar ratio) in absolute ethanol and adjusted pH. The Schiff base ligand and its complexes have been characterized by FT‐IR, ¹H NMR, UV/Vis, elemental analysis and conductometry measurements. In nickel and also vanadyl complexes the ligands were coordinated to the metals via the imine N and enolic O atoms. The complexes have been found to possess 1:1 metal to ligand stoichiometry and the molar conductance data revealed that the metal complexes were non‐electrolytes. The nickel and vanadyl complexes exhibited tetrahedral and square pyramidal coordination geometry, respectively. The emission spectra of the ligand and its complexes were studied in DMSO. Electrochemical properties of the ligand and its complexes were also investigated in the DMF solvent at the 150 mVs^‐1 scan rate. The ligand and its complexes showed irreversible processes at this scan rate.     

Copper(II) Schiff Base Complex Immobilized on Superparamagnetic Fe3O4@SiO2 as a Magnetically Separable Nanocatalyst for Oxidation of Alkenes and Alcohols

A new heterogeneous catalyst containing a copper(II) Schiff base complex covalently immobilized on the surface of silica‐coated Fe₃O₄ nanoparticles (Fe₃O₄@SiO₂‐Schiff base‐Cu(II)) was synthesized. Characterization of this catalyst was performed using various techniques. The catalytic potential of the catalyst was investigated for the oxidation of various alkenes (styrene, α‐methylstyrene, cyclooctene, cyclohexene and norbornene) and alcohols (benzyl alcohol, 3‐methoxybenzyl alcohol, 3‐chlorobenzyl alcohol, benzhydrol and n ‐butanol) using tert ‐butyl hydroperoxide as oxidant. The catalytic investigations revealed that Fe₃O₄@SiO₂‐Schiff base‐Cu(II) was especially efficient for the oxidation of norbornene and benzyl alcohol. The results showed that norbornene epoxide and benzoic acid were obtained with 100 and 87% selectivity, respectively. Moreover, simple magnetic recovery from the reaction mixture and reuse for several times with no significant loss in catalytic activity were other advantages of this catalyst