Asymmetric synthesis of aspartic and α-methylaspartic acids via Ni(II) complexes with schiff bases of glycine and alanine and chiral carbonyl-containing reagents

We propose a method for the synthesis of aspartic and -methylaspartic acids by alkylation with ethyl bromoacetate of the -carbon atom of the amino acid moiety in Ni(II) complexes of Schiff bases of glycine with (S)-2-[(N-benzylprolyl)amino]benzophenone and alanine with (S)-2-[(N-benzylprolyl)amino]-benzaldehyde, respectively. Attempts to synthesize -methylaspartic acid by oxidative cleavage of the C=C bond to a COOH group in the complex of the Schiff base of -allylalanine with (S)-2-[(N-benzylprolyl)amino]benzophenone were unsuccessful.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1542–1547, July, 1991.     

Reaction of Schiff bases anions with 4-halo-2-butenoates: Selective synthesis of α-cyclopropyl and γ,δ unsaturated α-amino acid derivatives.

Copper-catalyzed substitution reactions.     

New diorganotin(IV) complexes with some Schiff bases derived from β-diketones: synthesis,spectral properties,thermal analysis,and antibacterial activity

The Schiff bases H₂L^a, H₂L^b, and H₂L^c have been prepared from the reaction of 2-amino-4-chlorophenol with acetylacetone, benzoylacetone, and dibenzoylmethane, respectively. Organotin(IV) complexes [SnPh₂(L^a)] (1), [SnPh₂(L^b)] (2), [SnPh₂(L^c)] (3), and [SnMe₂(L^c)] (4) have been synthesized from the reaction of SnPh₂Cl₂ and SnMe₂Cl₂ with these Schiff bases. The synthesized complexes have been characterized by elemental analysis and FT-IR, ¹H, ¹³C, and ¹¹⁹Sn NMR spectroscopy. Spectroscopic data suggest the Schiff bases are completely deprotonated and coordinated tridentate to tin via imine nitrogen and phenolic and enolic oxygen atoms; the coordination number of tin is five. Thermal decomposition of the complexes has been studied by thermogravimetry. The in vitro antibacterial activities of the Schiff bases and their complexes have been evaluated against Gram-positive (Bacillus subtilis and Staphylococcus aureus) and Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria. H₂L^a, H₂L^c, and all complexes exhibited good activities and have potential as drugs.     

Preparation of a simple biocompatible magnetite@citric acid: An efficient reusable solid acid catalyst for the rapid synthesis of antipyrine Schiff’s bases and study of their radical scavenging potential

Citric acid immobilized magnetic nanoparticles (MNPs@CA) have been synthesized and used for the preparation of bio-important antipyrine (1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one) derived Schiff’s bases (3a–k) in lesser reaction time with very high yield under ultrasonication. The catalyst was characterized by FT-IR, powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), and thermogravimetric analysis (TGA). The functionalized nanoparticles were easily separated using an external magnet during work-up procedure and show excellent reusability upto 8 cycles without any significant loss in catalytic activity. All the synthesized compounds (3a–k) were screened by DPPH (2,2-diphenyl-1-picrylhydrazyl) method with respect to ascorbic acid for their antioxidant activity and some of them gave promising results.     

Catalytic activity correlation of Ni(Ⅱ),Co(Ⅱ) and Pd(Ⅱ) complexes to metal atom net charge

The metal atom net charge correlation(MANCC) method was developed in prediction of catalyst activity of asymmetric late-transition metal complexes,2-quinoxalinyl-6-iminopyridine Ni(Ⅱ),2-imino-1,10-phenanthroline Co(Ⅱ) and 2-methoxycarbonyl-6-iminopyridine Pd(Ⅱ) complexes,from the net charge of the metal atom for ethylene polymerization.Dreiding force field was modified according to the X-ray diffraction data.We found that the asymmetric structure of the complexes resulted in a charge differ-ence between two...     

Dinuclear (Fe(II), Gd(III)) complexes deriving from hexadentate Schiff bases: synthesis,structure, and Mössbauer and magnetic properties

The dinuclear (Fe(II), Gd(III)) complexes studied in this report derive from hexadentate Schiff base ligands abbreviated H(2)L(i)() (i = 1, 2, 3). H(2)L(1) = N,N'-bis(3-methoxysalicylidene)-1,3-diamino-2,2'-dimethyl-propane, H(2)L(2) = N,N'-bis(3-methoxysalicylidene)-1,2-diamino-2-methylpropane, and H(2)L(3) = N,N'-bis(3-methoxysalicylidene)-1,2-diaminoethane. The crystal and molecular structures of three complexes have been determined at 160 K. Depending on the solvent used in the preparation, L(1)Fe(CH(3)OH)Gd(NO(3))(3)(CH(3)OH)(2), 1, or L(1)Fe((CH(3))(2)CO)Gd(NO(3))(3), 1', is obtained from H(2)L(1). A similar complex, L(2)Fe((CH(3))(2)CO)Gd(NO(3))(3), 2, is obtained from H(2)L(2). Complex 1 crystallizes in the orthorhombic space group Pca2(1) (No. 29): a = 22.141(3) A, b = 9.4159(16) A, c = 15.2075(17) A, V = 3170.4(7) A(3), Z = 4. Complexes 1' and 2 crystallize in the monoclinic space group P2(1)/c (No. 14): 1', a = 9.6264(17) A, b = 19.662(3) A, c = 16.039(3) A, beta = 95.15(2) degrees, V = 3023.6(9) A(3), Z = 4; 2, a = 9.7821(13) A, b = 18.7725(17) A, c = 16.100(2) A, beta = 96.497(16) degrees, V = 2937.5(6) A(3), Z = 4. Complexes 1, 1', and 2 possess an Fe(O(phenoxo))(2-)Gd core. The mononuclear L(3)Fe complex could be prepared from H(2)L(3) but not the related dinuclear (Fe, Gd) species. M?ssbauer spectroscopy evidences that the iron center is in the +2 oxidation state for the six complexes. The experimental magnetic susceptibility and magnetization data of complexes 1, 1', and 2 indicate the occurrence of weak Fe(II)-Gd(III) ferromagnetic interactions. Single ion zero-field splitting of the iron(II) must be taken into account for satisfactorily fitting the data by exact calculation of the energy levels associated to the spin Hamiltonian through diagonalization of the full matrix for axial symmetry (1, J = 0.50 cm(-1), D = 2.06 cm(-1); 1', J = 0.41 cm(-1), D = 3.22 cm(-1); 2, J = 0.08 cm(-1), D = 4.43 cm(-1)).     

Solid–solid synthesis,characterization, thermal decomposition and antibacterial activities of zinc(II) and nickel(II) complexes of glycine–vanillin Schiff base ligand

The zinc(II) and nickel(II) complexes of glycine–vanillin Schiff base were synthesized by one-step solid–solid reaction at room temperature. The composition and structure of the complexes were characterized by elemental analyses, Fourier transform infrared spectra (FTIR), X-ray powder diffraction (XRD), and thermogravimetry and differential scanning calorimetry (TG–DSC). The crystal structure of the complexes belongs to monoclinic system with the lattice parameters: a = 0.6807 nm, b = 1.3818 nm, c = 1.2011 nm, β = 95.80° for [Zn(C₁₀H₉O₄N)(H₂O)₃], and a = 0.7457 nm, b = 1.3331 nm, c = 1.2560 nm, β = 91.89° for [Ni(C₁₀H₉O₄N)(H₂O)₃]·1.5H₂O. The experimental results indicate that the zinc and nickel ions are all six-coordinated by imino nitrogen, carboxylic oxygen, and phenolic oxygen from the Schiff base ligand, and oxygen from three coordinated water molecules, respectively. The possible pyrolysis reactions in the thermal decomposition processes of the complexes and the experimental and calculated percentage mass loss are also given. The two complexes have the most intense antibacterial activities against Escherichia coli.     

Electrochemical synthesis of neutral transition metal(II) (Fe,Co, Ni,Cu, Zn) complexes of pyridine-2-carbaldehyde pyridin-2′-ylhydrazone and several analogues

Summary Neutral transition metal(II) complexes of pyridine-2-carbaldehyde pyridin-2-ylhydrazone (papyH) and several analogues have been prepared by electrochemical synthesis. The [M(papy)₂] compounds (M = Fe, Co, Ni, Cu or Zn) were obtained mostly as red-green dichroic substances as a result of the extended -conjugation system in the anionic hydrazone. Vibrational and electronic spectra confirm the presence of the anionic hydrazone and its tridentate coordination to the metal centre.     

Solid state synthesis,spectroscopic and X-ray studies of metal complexes of 2-picolinic acid and vapochromic behavior of [Co(Pic)2(H2O)2]·2H2O

Three compounds, [Cu(Pic)₂(H₂O)] (1a), [M(Pic)₂(H₂O)₂]·2H₂O] (M=Co (2a), Zn (3a), Pic = 2-picolinic acid) were obtained by solvent-free synthesis through grinding of metal acetate salt with 2-picolinic acid. Favorable comparison of solvent-free with solution based method of 1b, 2b and 3b was observed. Good resemblance of identity of compounds obtained through the two methods was confirmed by elemental analysis, spectroscopic techniques (UV-Vis and FTIR), TGA and PXRD. The single crystal diffraction data for [Co(Pic)₂(H₂O)₂]·2H₂O obtained from the Cambridge structure database (CSD), its PXRD simulated patterns closely matched that of complex 2a by solvent-free synthesis. Vapochromic behavior of this complex was studied using colour change, FT-IR, TGA, PXRD and solid state UV-visible spectroscopies. This complex generated specific colour which is also evident in the shifting of the vibrational frequencies (νO-H and ν C=O bands). The resulting inclusion compounds have different colours depending on the solvent used. In addition, exposure of the resultant inclusion compounds to ambient environment or heating for a few minutes regenerate the original material without degradation even after exposure/heating cycles as evident from TGA/DTG thermograms.     

Metal-based antibacterial agents: synthesis,characterization, and in vitro biological evaluation of cefixime-derived Schiff bases and their complexes with Zn(II), Cu(II), Ni(II), and Co(II)

The zinc(II), copper(II), nickel(II), and cobalt(II) complexes of Schiff bases, obtained by the condensation of cefixime with furyl-2-carboxaldehyde, thiophene-2-carboxaldehyde, salicylaldehyde, pyrrol-2-carboxaldehyde, and 3-hydroxynaphthalene-2-carboxaldehyde, were synthesized and characterized by their elemental analyses, molar conductances, magnetic moments, IR, and electronic spectral measurements. Analytical data and electrical conductivity measurements indicated the formation of M?:?L (1?:?2) complexes, [M(L)₂(H₂O)₂] or [M(L)₂(H₂O)₂]Cl₂ [where M?=?Zn(II), Cu(II), Ni(II), and Co(II)] in which ligands are bidentate via azomethine-N and deprotonated-O of salicyl and naphthyl, furanyl-O, thienyl-S, and deprotonated pyrrolyl-N. The magnetic moments and electronic spectral data suggest octahedral complexes. The synthesized ligands, along with their metal complexes, were screened for their antibacterial activity against different bacterial strains. The studies show the metal complexes to be more active against one or more species as compared to the uncomplexed ligands.     

Synthesis,crystal structures,thermal, and spectroscopic properties of four new metal(II) (M = Co,Ni, Cu,Hg) complexes of 2-benzoylbenzoate with 3-picoline

Four 2-benzoylbenzoate (bba) complexes, [Co(bba)₂(H₂O)₂(3-pic)₂] (1), [Ni(bba)₂(H₂O)₂(3-pic)₂] (2), [Cu(bba)₂(3-pic)₂] (3), and [Hg(bba)₂(3-pic)₂] (4), have been synthesized and characterized by IR spectra, thermal (TG, DTG, and DTA) analysis, and single crystal X-ray diffraction. All the complexes consist of neutral monomeric units with 1 and 2 crystallizing in the orthorhombic (P n a 2₁), 3 in triclinic (P 1), and 4 in monoclinic (P2₁/c) crystal systems. The metal(II) ions exhibit distorted octahedral coordination for 1, 2, and 3 and mercury(II) exhibits distorted trigonal prism coordination. In 1 and 2, bba is monodentate, whereas in 3 and 4 bba is bidentate. 3-Picoline (3-pic) is a classical N-monodentate ligand. Bba are coordinated to metal(II) with carboxylates and IR spectra of all complexes display characteristic absorptions of carboxylate {υ(OCO)_asym and υ(OCO)_sym}. Thermogravimetric (TG) analyses show that 1 and 2 are thermally stable (T_decomp.?>?60°C) and 3 and 4 are thermally stable (T_{decomp .} ?>?120°C).     

Molecular encapsulation of transition metal complexes in cyclodextrins. Part 2. Synthesis and crystal structures of 2:1 adducts between α-cyclodextrin and metallocenium hexafluorophosphates [η5-C5H5)2M]PF6(M = Fe,Co, Rh)

The title metallocenium salts form crystalline 2:1 host:guest inclusion compounds with-cyclodextrin, [(⁵-C₅H₅)₂M]PF₆ · 2-CD · 8H₂O (1, M = Fe;2, M = Co;3, M = Rh). The X-ray crystal structures of1 and3, and the lattice constants, crystal system and space group of2 have been determined. Crystal data: triclinic, space groupP1 (No. 1),Z = 1;1,a = 13.865 (2) Å,b = 13.839 (2) Å,c = 15.520 (2) Å, = 91.43 (2)°, = 85.81 (2)°, = 120.22 (2)°, andR _F = 0.089 for 4257 observed MoK reflections [I > 3(I)];2,a = 13.810 (2) Å,b = 13.872 (2) Å,c = 15.560 (2) Å, = 93.99 (2)°, = 87.06 (2)°, = 120.04 (2)°;3,a = 13.756 (1) Å,b = 13.863 (1) Å,c = 15.561 (2) Å, =94.39 (1)°, = 86.92 (1)°, = 119.89 (1)°, andR _F = 0.061 for 11142 observed MoK reflections [I > 3(I)]. In the crystals of1 and3, two -cyclodextrin molecules are arranged head-to-head to form a dimer by means of intermolecular hydrogen bonding across the secondary hydroxyl faces of adjacent -CD monomers. The dimers are stacked along the crystallographicc axis to form a channel-type structure. The metallocenium cation is encapsulated within the cavity of the dimer, while the PF ₆ ^– anion is located outside the cavity, being centered between the primary hydroxyl faces of adjacent dimers. Eight water molecules of hydration per asymmetric unit reside in the spaces between the -CD columns. In view of the almost identical crystal data for2 a similar structure can be assumed for the cobaltocenium adduct.     

Ni(II), Co(II), and Cu(II) complexes incorporating 2-pyrazinecarboxylic acid：Synthesis,characterization, electrochemical evaluation,and catalytic activity for the synthesis of 2H-indazolo[2,1-b]phthalazine-triones

Three complexes containing 2-pyrazinecarboxylate (pzca–), including [Ni(pzca)2(H2O)2], [Co(pzca)2(H2O)2], and [Cu(pzca)2(H2O)2], have been synthesized and characterized using physico-chemical and spectroscopic methods. Furthermore, the structure of each complex was determined by single-crystal X-ray diffraction. All three complexes have an octahedral geometry, where the metal ion chelated by two carboxylate oxygens, two nitrogen atoms belonging to pyrazinic acid molecules, and two oxygen atoms of two water molecules. The catalytic activities of these complex-es were also investigated in the green synthesis of 2H-indazolo[2,1-b]phthalazine-triones by the reaction of hydrazine hydrate with an arylaldehyde, phthalic anhydride, and dimedone in acetic acid.     

M(II) Schiff base complexes (M = zinc,manganese, cadmium,cobalt, copper,nickel, iron,and palladium) supported on superparamagnetic Fe3O4@SiO2 nanoparticles: synthesis,characterization and catalytic activity for Sonogashira–Hagihara coupling reactions

A series of magnetically separable catalysts consisting of Schiff base complexes of metal ions (Zn, Mn, Cd, Co, Cu, Ni, Fe and Pd) supported on superparamagnetic Fe₃O₄@SiO₂ nanoparticles has been prepared. The structural features of the catalysts were characterized by XRD, FTIR, TEM, FE-SEM, DLS, VSM, UV–Vis, TGA, AFM and N₂ adsorption–desorption. Some of the Fe₃O₄@SiO₂/Schiff base complexes were found to be efficient catalysts for the Cu-free and the phosphine free Sonogashira–Hagihara coupling reaction of aryl halides and phenylacetylene. The catalysts are superparamagnetic, and thus could be easily separated by the utilization of an external magnetic field, and could be reused for six cycles without significant loss of activity.     

Spectral, thermal and electrochemical characterization of novel homo-dinuclear complexes [M2(H3DTPA)(H2O)6]Cl2·xH2O (M=Cr2+, Mn2+, Co2+, Ni2+ or Cu2+)

The title complexes were prepared and characterized employing spectral (FAB-Mass, IR, electronic, (1)H and (13)C NMR), thermal and electrochemical techniques. Analytical and FAB-Mass data suggested a homo-dinuclear stoichiometry. IR and electronic ligand field spectral studies coupled with molecular model computations have indicated a distorted octahedral geometry where the ligand coordinates as a hexadentate dianionic [H(3)DTPA](2-)(H(5)DTPA=diethylenetriaminepentaacetic acid) moiety. The electrochemical redox properties and the antibacterial activities of the compounds were also investigated.     

Interaction of hydantoins with transition metal ions: synthesis,structural, spectroscopic,thermal and magnetic properties of [M(H<Subscript>2</Subscript>O)<Subscript>4</Subscript>(phenytoinate)<Subscript>2</Subscript>] M = Ni(II), Co(II)

Complexes of Ni(II) and Co(II) of the formulae [Ni(H₂O)₄(pht)₂] (1) and [Co(H₂O)₄(pht)₂]·1,5NH₃·H₂O (2) (where pht = phenotoinate anion) were obtained and characterized physicochemically. [Ni(H₂O)₄(pht)₂] (1) crystallizes in a monoclinic space group P2₁/c; a = 11.7358(8), b = 11,1250(8), 11.4182(7) Å; β = 97.076(5)°; V = 1479.41 Å³; Z = 2. The environment around the nickel and cobalt ions can be described as a distorted octahedron. The metal ion was found to bind to four water molecules and two nitrogen atoms derived from two anions of the monodentate phenytoinate. Four intramolecular hydrogen bonds designated as S(6) graph set are found in one [Ni(H₂O)₄(pht)₂] (1) molecule. Two chain HB patterns, constructed by the [Ni(H₂O)₄(pht)₂] molecules extending along the c and b axes, respectively, have been observed. The cobalt complex precipitates with the additional solvent molecules: one and a half of ammonia and one water. The results document the preferential binding of hydantoins to the metal ions through N(3) atom.     

Synthesis,characterization, spectroscopic,and thermal studies of imidazole complexes of metal benzenesulfonates. Crystal structure of [M(imH)<Subscript>3</Subscript>(H<Subscript>2</Subscript>O)<Subscript>3</Subscript>]·(BS)<Subscript>2</Subscript> [M=Ni(II) and Co(II)]

Four novel transition metal benzenesulfonate (BS) complexes of imidazole (im) with a general formula [M(imH)₃(H₂O)₃]·(BS)₂ [M=Mn(II) (1), Ni(II) (2), Co(II) (3)] and [Cu(BS)(imH)₃]·(BS) (4) have been synthesized and characterized by physicochemical and spectroscopic methods. The complexes 2 and 3 have also been characterized by single X-ray diffraction technique. The BS anion in complexes 1–3 acts as a counter anion, while in complex 4, it acts as both ligand and counter anion. The Ni and Co complexes are isomorphous, crystallizing in the monoclinic crystal system with C2/c space group. Each metal(II) atom in 2 and 3 is octahedrally coordinated by three imidazole and three aqua ligands, adopting a mer-coordination mode with Ni(II) or Co(II) centers. In both 2 and 3, the H2C atom has bifurcated donor (O3 and O5) atoms, forming a bifurcated hydrogen bond. This hydrogen bond links the complex cation and BS anion, forming one-dimensional hydrogen-bonded supramolecular chains. The complexes exhibit different decomposition characteristics. Magnetic susceptibility measurement shows that complex 3 has orbital interactions.