Potentiometric and antimicrobial studies on the asymmetric Schiff bases and their binuclear Ni(II) and Fe(III) complexes; synthesis and characterization of the complexes

The protonation constants of two nitro-Schiff bases SB¹, SB² and three asymmetric tetradentate diimines H₂L¹, H₂L² and H₂L³ and the stability constants of their ML type binuclear Ni(II) and Fe(III) complexes have been determined potentiometrically. The asymmetric diimines are (2OH) RCHNC₆H₄CHNR′ (2OH) type compounds [where R = R′ = phenyl for H₂L¹; R = naphthyl, R′ = phenyl for H₂L² and R = R′ = naphthyl for H₂L³]. The effect of tautomeric forms on the acid-base properties of the diimines has been investigated and discussed. In addition, dimeric and binuclear Ni(II) and Fe(III) complexes of the diimines have been synthesized and characterized by physical and spectroscopic techniques. Also, in vitro antimicrobial activities of the diimines and the complexes have been evaluated against three bacteria: Micrococcus luteus (NRLL B-4375), Bacillus cereus (RSKK 863), Escherichia coli (ATCC 11230) and the fungus: Candida albicans (ATCC 10239).     

Catalytic, asymmetric aza-Baylis-Hillman reaction of N-sulfonated imines with activated olefins by quinidine-derived chiral amines

The chiral nitrogen Lewis base, tricyclic cinchona alkaloid derivative TQO, is an effective promoter in the catalytic, asymmetric aza‐Baylis–Hillman reaction of N‐sulfonated imines Ar? CH?NR′ 1 (R′ = Ts, Ms, Ns, SES) with various activated olefins such as methyl vinyl ketone (MVK), ethyl vinyl ketone (EVK), acrolein, methyl acrylate, phenyl acrylate, or α‐naphthyl acrylate to give the corresponding adducts in moderate to good yields with good to high ee (up to 99 %) at ?30 °C or 45 °C in various solvents, including DMF/MeCN (1:1, v/v). The first such reaction of 1 with the simplest Michael acceptor MVK and methyl acrylate has been achieved with excellent enantioselectivity. The adducts derived from MVK and EVK had the opposite absolute configuration to those from acrolein, methyl acrylate, phenyl acrylate, and α‐naphthyl acrylate. A plausible mechanism has been proposed on the basis of previous reports and the authors’ investigations. An effective bifunctional chiral nitrogen Lewis base–Brønsted acid system has been revealed in this type of aza‐Baylis–Hillman reaction.     

Acidichromism in the Mixed Langmuir—Blodgett Films of Stearic Acid with a Carbazole—containing Schiff Base

ＩｎｔｒｏｄｕｃｔｉｏｎＲｅｖｅｒｓｉｂｌｅｃｏｌｏｒｃｈａｎｇｅｓｕｐｏｎｅｘｔｅｒｎａｌｏｒｉｎｔｅｒｎａｌｓｔｉｍｕｌａｔｉｏｎｓｈａｖｅｂｅｅｎａｔｔｒａｃｔｉｎｇｍｕｃｈａｔｔｅｎｔｉｏｎｄｕｅｔｏｔｈｅｉｒｕｔｉｌｉｔｙａｓｆｕｎｃｔｉｏｎａｌｍａｔｅｒｉａｌｓ .Ｆｏｒｅｘａｍｐｌｅ ,ｐｈｏ ｔｏｃｈｒｏｍｉｓｍｄｅｓｃｒｉｂｅｓｔｈｅｃｏｌｏｒｃｈａｎｇｅｓｉｎｄｕｃｅｄｂｙｐｈｏ ｔｏｉｒｒａｄｉａｔｉｏｎａｎｄｃａｎｂｅｕｓｅｄａｓｐｈｏｔｏ ｒｅｃｏｒｄｉｎｇｍａｔｅｒｉ ａｌｓ…     

Conformational state of benzilidene aniline derivatives from ab initio calculation and NMR spectroscopy data

Quantum chemical calculations of the structure and conformational state of a number of Shiff bases have been performed. ¹³C NMR spectra of investigated molecules were calculated and compared with experimental data to test verification of the used calculation model. The effect of terminal substituents on the conformation of azomethines and a relation between the conformation and ¹³C NMR chemical shift were examined.     

Interaction of vinylpyridines with 1,3-dienes catalyzed by transition metal complexes

The linear and cyclic cooligomerization of 2-vinyl-, 2-methyl-5-vinyl-, and 4-vinylpyridines with 1,3-dienes and trienes catalyzed by complexes of transition metals (Fe, Co, Ni, Mn, Cr, Pd, Ru, Rh, and Zr) was carried out to give unsaturated pyridines containing alkenyl and cycloalkenyl substituents.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 916–921, May, 1993.     

Structural and electrochemical studies of novel bis(mu-methoxo)diiron complexes: observation of Fe(III)Fe(IV) and Fe(IV)Fe(IV) states resonating with phenoxyl radicals

Novel diiron complexes with an Fe2(mu-OMe)2 core were studied as models of the active site of nonheme iron-containing enzymes. X-ray crystal structures of the complexes showed the existence of two types of ligand folding-parallel and twisted-both of which have four virtually equivalent phenolato groups sticking out from the Fe2O2 rhombic plane. Cyclic voltammetry measurements revealed two or more distinct redox waves in a region of relatively high potential, in addition to known Fe(II)/Fe(III) redox waves in a region of lower potential. These new peaks were assigned to the high-valence state of iron atoms, that is, Fe(III)Fe(IV) and Fe(IV)Fe(IV), resonating with the phenoxyl radical(s). The split width of the redox waves ranged from 0.14 to 0.20 eV, which may be a measure of the electronic interaction of the phenolate groups through the Fe2(mu-OMe)2 core.     

Basicity of 2-phenyl-5-R-1,3,4-oxadiazoles

We have studied the basicity of 2-phenyl-5-R-1,3,4-oxadiazoles (R = H, Me, CH₂Ph, t-Bu, CH₂Cl, CCl₃, CF₃) in aqueous sulfuric acid solutions. These compounds are weak organic bases (pK_BH ⁺ is −1.8 to −5.2). The values of pK_BH ⁺ determined on the H₀ and X acidity function scales agree well with each other. The substituent at the 5 position has a substantial effect on the basicity of the 1,3,4-oxadiazole ring. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 748–756, May, 2006.     

Syntheses,Characterization and Crystal Structures of Three Structurally Similar Dinuclear Schiff Base Cadmium(II) Complexes with Bridging Azide or Thiocyanate Ligands

Three novel Schiff base cadmium(II) complexes, derived from the end‐on (μ‐1,1‐N₃) azide or end‐to‐end (μ‐1,3‐NCS) thio cyanate bridges and similar tridentate Schiff base ligands, have been synthesized under similar synthetic procedures and their crystal structures determined by X‐ray diffraction methods. They are the dinuclear double end‐on azide‐bridged [Cd₂(L1)₂(N₃)₂(μ‐1,1‐N₃)₂] ( 1 ), the dinuclear double end‐on azide‐bridged [Cd₂(L2)₂(N₃)₂(μ‐1,1‐N₃)₂] ( 2 ), and the dinuclear double end‐to‐end thiocyanate‐bridged [Cd₂(L3)₂(NCS)₂(μ_1,3‐NCS)₂] ( 3 ), where L1, L2 and L3 are three similar tridentate Schiff bases obtained by condensation of 2‐pyridylaldehyde with N,N‐diethylethane‐1,2‐diamine, of 2‐pyridylaldehyde with N‐isopropylethane‐1,2‐diamine, and of 2‐pyridylaldehyde with N,N‐dimethylpropane‐1,3‐diamine, respectively. Each cadmium(II) centre in the complexes is in a distorted octahedral coordination. There is a crystallographic inversion centre in each of the complexes. The similar small ligands used as the secondary ligands in the preparation of the cadmium(II) complexes with similar Schiff bases can result in similar structures.     

Electrochemical synthesis of Co,Ni, and Zn complexes with 2-Pyrrole-[N-(o-hydroxyphenyl)methylimines]: The crystal structure of 2,2′-Bipyridine bis{2-[(2-pyrrole)methylimino]5-methylphenolato}nickel(II)

The electrochemical oxidation of anodic cobalt, nickel, and zinc in acetonitrile containing both 2-pyrrole-[N-(o-hydroxyphenyl)methylimines] (H₂L) and a bidentate ligand (1, 10-phenanthroline(phen) or 2,2′-bipyridine(bipy)) yielded compounds of general formula M(HL)₂ · phen and M(HL)₂ · bipy (M = Co, Ni, Zn). The crystal structure of 2,2′-bipyridine bis{2-[(2-pyrrole)methylimino]5-methylphenolato}nickel(II) was determined by X-ray diffraction. This compound crystallizes in the orthorhombic space group Pccn with a = 19.430(2), b = 28.488(2), c = 17.567(1) Å. The nickel atom has a distorted octahedral geometry, and the pyrrole nitrogen is not coordinated. The IR, ¹H-NMR and UV-visible spectra of the complexes are discussed and related to the structure.