Synthesis and structural characterisation of new Re(III) complexes using aldimines of α-amino acids as coligands

Complexes of the general formula [Re^III(L)Cl(PPh₃)₂] have been synthesised by reacting H₂L and [ReOCl₃(PPh₃)₂] in ethanol. Here H₂L represents imines of α-amino acids (glycine, l-alanine, l-valine, l-phenylalanine) derived from salicylaldehyde and naphthaldehyde. The crystal structure of one complex has been determined. The complexes are mononuclear, paramagnetic and display paramagnetic ¹H NMR in CDCl₃ solution. Their spectral and redox properties are scrutinised.     

Metal‐based antibacterial and antifungal amino acid derived Schiff bases: their synthesis,characterization and in vitro biological activity

A new series of antibacterial and antifungal amino acid derived Schiff bases and their cobalt(II), copper(II), nickel(II) and zinc(II) metal complexes have been synthesized and characterized by their elemental analyses, molar conductances, magnetic moments, IR and electronic spectral measurements. The spectral data indicated the Schiff base ligands ( L ₁– L ₅) derived by condensation of salicylaldehyde with glycine, alanine, phenylalanine, methionine and cysteine, to act as tridentate towards divalent metal ions (cobalt, copper, nickel and zinc) via the azomethine‐N, deprotonated carboxyl group of the respective amino acid and deprotonated oxygen atom of salicylaldehyde by a stoichiometric reaction of M: L (1:2) to form complexes of the type K₂[M( L )₂] [where M = Co(II), Cu(II), Ni(II) and Zn(II)]. The magnetic moments and electronic spectral data suggested that all complexes have an octahedral geometry. Elemental analyses and NMR spectral data of the ligands and their Zn (II) complexes agree with their proposed structures. The synthesized ligands, along with their metal complexes, were screened for their in‐vitro antibacterial activity against four Gram‐negative (Escherichia coli, Shigella flexeneri, Pseudomonas aeruginosa and Salmonella typhi) and two Gram ‐ positive (Bacillus subtilis and Staphylococcus aureus) bacterial strains and for in‐vitro antifungal activity against Trichophyton longifusus, Candida albicans, Aspergillus flavus, Microsporum canis, Fusarium solani and Candida glaberata. The results of these studies show the metal complexes to be more antibacterial/antifungal against one or more species as compared with the uncomplexed Schiff base ligands. The brine shrimp bioassay was also carried out to study their in‐vitro cytotoxic properties. Only three compounds ( 2, 11 and 17 ) displayed potent cytotoxic activity as LD₅₀ = 8.196 × 10^?4, 7.315 × 10^?4 and 5.599 × 10^?4 M /ml respectively, against Artemia salina. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis,characterization, and spectroscopic studies of novel transition metal complexes with N,N′-bis(salicylaldehydene)-1,4-bis(4-chloro-2-aminophenoxy)butane

The metal complexes of Co(II), Cu(II), Ni(II), and Zn(II) with novel quadridentate Schiff base derived from 1,4-bis(4-chloro-2-aminophenoxy)butane and salicylaldehyde have been synthesized in DMF. These complexes have been characterized by microanalytical data, elemental analysis, magnetic measurements. ¹H NMR, ¹³C NMR, UV-vis and IR-spectra as well as conductance measurements were used to confirm the structures. On the basis of these observations it is suggested that these complexes exhibit the coordination number four. The text was submitted by the authors in English.     

Synthesis of Tetradentate Schiff Base Derivatives of Transition Bimetallic Complexes as Antimicrobial Agents

A series of Co(II), Cu(II), Mn(II) and Zn(II) bimetallic complexes have been synthesized with the schiff base ligand 2‐(bis‐2‐hydroxyl phenylidene) diimine (L) derived from the condensation of hydrazine and salicylaldehyde. The synthesized ligand and bimetallic complexes were characterized by different spectroscopic techniques. The characterization of ligand was carried out by FT‐IR, H¹NMR, C¹³NMR and MS while the bimetallic complexes were characterized by FT‐IR and X‐ray crystallographic techniques. The complexes and ligand were employed in vitro for antifungal and antibacterial activities using disc diffusion method. Different fungal strains such as Alternaria Alternate, Aspergillus Flavus and Aspergillus Niger were used to check antifungal activities of bimetallic complexes and ligand. Similarly, the bacterial strains used were Staphylococcus Aureus, Bacillus Subbtilis and Escheria Coli. The biological studies showed that the ligand exhibited lower value of antifungal and antibacterial activities than bimetallic complexes.     

Ruthenium(II) Complexes Containing Lutidine‐Derived Pincer CNC Ligands: Synthesis,Structure, and Catalytic Hydrogenation of CN bonds

A series of Ru complexes containing lutidine‐derived pincer CNC ligands have been prepared by transmetalation with the corresponding silver‐carbene derivatives. Characterization of these derivatives shows both mer and fac coordination of the CNC ligands depending on the wingtips of the N‐heterocyclic carbene fragments. In the presence of tBuOK, the Ru‐CNC complexes are active in the hydrogenation of a series of imines. In addition, these complexes catalyze the reversible hydrogenation of phenantridine. Detailed NMR spectroscopic studies have shown the capability of the CNC ligand to be deprotonated and get involved in ligand‐assisted activation of dihydrogen. More interestingly, upon deprotonation, the Ru‐CNC complex 5 e (BF₄) is able to add aldimines to the metal–ligand framework to yield an amido complex. Finally, investigation of the mechanism of the hydrogenation of imines has been carried out by means of DFT calculations. The calculated mechanism involves outer‐sphere stepwise hydrogen transfer to the C?N bond assisted either by the pincer ligand or a second coordinated H₂ molecule.     

Kinetics of base hydrolysis of novel low spin Fe(II) amino acid Schiff base chelates—hydrophobic structural effects

The reactivity against OH^? ion of some novel Fe(II) complexes of Schiff base ligands derived from salicylaldehyde or o‐hydroxynaphth‐aldehyde and some variety of amino acids has been examined in aqueous and aqua‐ethanol mixtures. The rate law and relevant mechanism were assumed. Base hydrolysis kinetics measurements revealed pseudo‐first‐order doubly stage rates because of the presence of mer‐ and fac‐isomers. The evaluated rate constants and activation parameters are consistent with the stability constants of the investigated complexes. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 595–602, 2002     

Catalytic Enantioselective Reaction of Allenylnitriles with Imines Using Chiral Bis(imidazoline)s Palladium(II) Pincer Complexes

The first highly enantioselective reaction of allenylnitriles with imines has been developed. Excellent yields and enantioselectivities were observed for the reaction with various imines using chiral Phebim‐Pd^II complexes. This process offers a simple and efficient synthetic route for various functionalized α‐vinylidene‐β‐aminonitriles and their derivatives.     

Electrochemistry and oxygenation kinetics of tetradentate Schiff base manganese(II) complexes

The electrochemistry and oxygenation kinetics of a series of Mn(II) complexes containing ligands derived from substituted salicylaldehyde and linear diamines have been studied. Complexes prepared from ethylenediamine produce cyclic voltammograms with a quasi-reversible Mn(II)-Mn(III) couple and oxygenation reactions which are first-order in both complex and O₂, indicating formation of an Mn(III)-O⁻₂ species as the slow step in the reaction. The case of oxidation/oxygenation increases with increasing electron-donating ability of substituents on the salicyladehyde rings. Complexes with from six to 10 methylene groups in the diamine precursor produce highly irreversible voltammograms and oxygenation data which can not be interpreted in terms of a simple mechanism. Polymerization of the complexes is advanced as an explanation for these effects.     

Synthesis and characterization of coordination compounds of organotin(IV) with nitrogen and sulfur donor ligands

The reactions of dimethyltin dichloride with nitrogen and sulfur donor ligands derived by condensation of S‐benzyldithiocarbazate with indol‐3‐carboxylaldehyde, thiophene‐2‐aldehyde and furfuraldehyde have been investigated in 1:1 and 1:2 molar ratios in anhydrous alcohol. These ligands act as mononegatively charged bidentate species and coordinate to the central tin(IV) atom through the thiosulfur by proton exchange with the azomethine nitrogen. The newly synthesized complexes have been characterized by elemental analysis, conductance measurements and molecular weight determinations. The mode of bonding and the geometry of the complexes have been suggested on the basis of infrared, electronic and ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy, and probable structures have been assigned to these complexes. A few representative ligands and their tin(IV) complexes have also been screened for their antifungal and antibacterial activities and found to be quite active in this respect. Copyright © 2001 John Wiley & Sons, Ltd.     

Iron(III) Complexes of Tetradentate SCHIFF Bases

The iron(III) complexes of the Schiff bases derived from 1,3-diaminopropane-2-ol and salicylaldehyde (SBH₂), 3-aldehydosalicylic acid (SB′H₂) and acetylacetone (SB″H₂) have been isolated in the pure state and characterized. The structures of these complexes are discussed on the basis of elemental analyses, molecular weights, conductivities and magnetic susceptibilities. The Schiff bases behave as bivalent, tetradentate ligands. Room temperature (30°C) magnetic moments observed for these chelate compounds are lower than the spinonly value for high-spin d⁵ system.     

Synthesis,characterization and in vitro biological activity of cobalt(II), copper(II) and zinc(II) Schiff base complexes derived from salicylaldehyde and D,L‐selenomethionine

New cobalt(II), copper(II) and zinc(II) complexes of Schiff base derived from D,L ‐selenomethionine and salicylaldehyde were synthesized and characterized by elemental analysis, IR, electronic spectra, conductance measurements, magnetic measurements and biological activity. The analytical data showed that the Schiff base ligand acts as tridentate towards divalent metal ions (cobalt, copper, zinc) via the azomethine‐N, carboxylate oxygen and phenolato oxygen by a stoichiometric reaction of M:L (1:1) to form metal complexes [ML(H₂O)], where L is the Schiff base ligand derived from D,L ‐selenomethionine and salicylaldehyde and M = Co(II), Cu(II) and Zn(II). ¹H NMR spectral data of the ligand and Zn(II) complex agree with proposed structures. The conductivity values between 12.87 and 15.63 S cm² mol^?1 in DMF imply the presence of non‐electrolyte species. Antibacterial and antifungal results indicate that the metal complexes are more active than the ligand. Copyright © 2010 John Wiley & Sons, Ltd.     

Metal Chelate Complexes of the Schiff Bases Derived from Salicylaldehyde and Methyl Ethers of Aminophenols (Anisidines)

Some transition metal chelates of the Schiff's bases derived from salicylaldehyde and o -anisidine, m -anisidine and p -anisidine have been isolated and characterized. The structures of these complexes have been discussed on the basis of their elemental analyses, conductivities, magnetic moment values, electronic and infrared spectral data. The Ni²⁺, Cu²⁺ and Zn²⁺ form ML₂ type compounds, UO₂²⁺ and Fe³⁺ form dimeric [UO₂ L₂]and [Fe L₂ Cl]₂ respectively.     

Oxomolybdenum(VI) and (IV) complexes of pyrazole derived ONO donor ligands – synthesis,crystal structure studies and spectroelectrochemical correlation

Four cis-dioxomolybdenum complexes of general formula [MoO₂(Lⁿ)EtOH] (n = 1–4) and one oxomolybdenum(IV) complex [MoO(L⁴)EtOH], with potentially tridentate Schiff bases derived from 5-methyl pyrazole-3-carbohydrazide and salicylaldehyde/substituted salicylaldehyde/o-hydroxy acetophenone have been prepared. The Mo(IV) complex is derived from the Mo(VI) dioxo complex by oxotransfer reaction with PPh₃. The complexes are characterized by elemental analysis, electronic spectra, IR, ¹H NMR, and by cyclic voltammetry. All the Mo(VI) species are crystallographically characterized. The complexes have a distorted octahedral structure in which the ligand behaves as a binegative donor one, leaving the pyrazole –N uncoordinated towards the metal center. It is also revealed from the crystal structure that the Mo(VI) center enjoys an NO₅ donor environment.     

Reactions of cyanoacetylhydrazine complexes with salicylaldehyde and consequent metal-promoted reactions

The reactions of salicylaldehyde with a suspension of cyanoacetylhydrazine and/or malonic acid amido-hydrazide complexes in aqueous ethanolic solutions afford novel complexes. The structures of the isolated complexes have been elucidated by conventional physical and chemical measurements. The absence of the cyano group band at 2270 cm⁻¹ in the IR spectra of all complexes, except those of CO(II) and Ni(II) complexes, suggests the promotion of H₂O to the cyano group (CN) forming amido group. Several structures have been proposed in which salicylaldehyde behaves differently toward the cyanoacetylhydrazine complexes. Also, 1-salicylhydrazo-3-imino-3-(o-formyl) phenoxy propionic acid hydrazide is synthesized either by extraction from the isolated solid complexes using disodium ethylene-diaminetetraacetate or during refluxing of Co(II) and/or Fe(II) complexes with salicylaldehyde. This novel compound is confirmed by elemental analysis, spectra (IR and ¹H NMR) and mass spectra.     

Nickel‐Catalyzed Synthesis of N‐Aryl‐1,2‐dihydropyridines by [2+2+2] Cycloaddition of Imines with Alkynes through T‐Shaped 14‐Electron Aza‐Nickelacycle Key Intermediates

Despite there being a straightforward approach for the synthesis of 1,2‐dihydropyridines, the transition‐metal‐catalyzed [2+2+2] cycloaddition reaction of imines with alkynes has been achieved only with imines containing an N‐sulfonyl or ‐pyridyl group. Considering the importance of 1,2‐dihydropyridines as useful intermediates in the preparation of a wide range of valuable organic molecules, it would be very worthwhile to provide novel strategies to expand the scope of imines. Herein we report a successful expansion of the scope of imines in nickel‐catalyzed [2+2+2] cycloaddition reactions with alkynes. In the presence of a nickel(0)/PCy₃ catalyst, a reaction with N‐benzylidene‐P,P‐diphenylphosphinic amide was developed. Moreover, an application of N‐aryl imines to the reaction was also achieved by adopting N‐heterocyclic carbene ligands. The isolation of an (η²‐N‐aryl imine)nickel(0) complex containing a 14‐electron nickel(0) center and a T‐shaped 14‐electron five‐membered aza‐nickelacycle is shown. These would be considered as key intermediates of the reaction. The structure of these complexes was unambiguously determined by NMR spectroscopy and X‐ray analyses.     

Oxocation complexes,Part X. Oxomolybdenum(V) and dioxomolybdenum(VI) complexes with tri- and tetra-dentate Schiff bases

Summary Many new oxomolybdenum(V) and dioxomolybdenum(VI) complexes have been synthesized with tri- and tetradentate Schiff bases derived by the condensation of salicylaldehyde, thiosalicylaldehyde,o-hydroxyacetophenone, 3-carboxysalicyclaldehyde or acetylacetone with aminoalcohols, polymethylenediamines ando-phenylenediamines. Mononuclear oxothiolato Schiff base complexes of molybdenum(V) have been prepared for the first time. Quadridentate Schiff bases derived from salicylaldehyde and substituted salicylaldehydes ando-phenylenediamine have also been successfully employed to isolate dioxomolybdenum(VI) complexes in the solid state, in which two oxygen atoms of the MoO₂ group arecis- to each other, similar to the situation observed for other dioxomolybdenum(VI) complexes of salicylaldehyde-polymethylenediamine Schiff base ligands.Structures have been determined with the help of elemental analyses, magnetic susceptibilities, molar conductances, i.r., electronic and¹H n.m.r. spectral data.For Part IX, K. Dey, R. K. Maiti and J. K. Bhar,Indian J. Chem., in press.     

Synthesis,Characterization, and Structure of Quinoline‐based Benzimidazole Derivatives

Quinoline‐based benzimidazole compounds have been successfully synthesized and characterized by various spectroscopic techniques like FT‐IR, ¹H NMR, ¹³C NMR, and mass spectral analysis, and the structures have been authenticated by single crystal X‐ray diffraction method. Here, we report an economical, mild, and efficient procedure that involves condensation of 8‐hydroxyquinoline‐2‐carbaldehyde with various diamines as substrates to give bis‐imines. A systematic study towards both aliphatic and aromatic bis‐imines has been conducted to investigate the ring‐closure reaction that generates the benzimidazole moiety in the heterocyclic compounds discussed in this study. Aliphatic bis‐imines does not undergo cyclization; however, the bis‐imines derived from o‐phenylenediamine and derivatives generates heterocyclic compounds with benzimidazole moiety. In contrast to synthetic procedures reported earlier for benzimidazoles, the reaction conditions herein reported are simpler. Path for reactions holds initial condensation with one equivalent of 8‐hydroxyquinoline‐2‐carbaldehyde to form mono‐imine followed by immediate intramolecular ring closure. The subsequent nupleophilic attack to another equivalent of 8‐hydroxyquinoline‐2‐carbaldehyde and migration of hydride generates the benzimidazole moiety and the active methylene group. The ─CH₂ group was confirmed from ¹H and ¹³C NMR, wherein the two hydrogens appeared at around 6.40–6.52 ppm and the carbon center appeared at 51.54–51.77 ppm. The single crystal X‐ray diffraction also confirmed the formation of benzimidazole moiety and the active methylene group in the heterocyclic compounds discussed in this study.     

Synthesis and magnetic properties of novel poly(Schiff base)‐Fe2+ complexes

Three polymer‐Fe²⁺ complexes were synthesized from Fe²⁺ and poly(Schiff base)s. The poly(Schiff base)s were prepared from 2,2′‐diamino‐4,4′‐bithiazole (DABT) with phthalaldehyde, 5,5′‐methylenebis(salicylaldehyde) (MBSA) and terephthalaldehyde, respectively, and characterized by IR, XPS, NMR and ESR spectroscopy. The magnetic behavior of these polymer‐Fe²⁺ complexes was examined as a function of magnetic field strength and temperature (5–300 K), respectively. The hysteresis loops were also studied. Based on these results, several novel ferromagnets were obtained.     

Transition metal complexes of the Schiff bases from 2-phenylethylamine and 2-hydroxyarylcarbonyl compounds

Summary A series of complexes of the type Co^IIIL₃, NiL₂, Ni(HL)₂(OAc)₂ and CuL₂ where HL is a Schiff base derived from 2-phenylethylamine and 2-hydroxy-1-naphthaldehyde, salicylaldehyde, 2-hydroxyacetophenone and its 5-methyl and 5-chloro-derivatives and 2-hydroxypropiophenone and its 5-methyl and 5-chloro-derivatives have been synthesised and characterized. The cobalt(III) complexes are octahedral, the copper complexes are planar, the complexes NiL₂ of Schiff bases derived from aldehydes are also planar, whereas those derived from ketones formulated Ni(HL)₂(OAc)₂ are octahedral.