Binuclear organometallic ruthenium complexes of a Schiff base expanded porphyrin

The synthesis of binuclear organometallic ruthenium complexes of an expanded porphyrin-type macrocycle is reported; pyrrolic hydrogen bonding donors were found to interact with ancillary ligands in the primary coordination sphere and to stabilize coordinated dioxygen in an eta(2)-fashion.     

1,2,3-Triazolylidenes as versatile abnormal carbene ligands for late transition metals

The [3 + 2] cycloaddition of azides and acetylenes followed by nitrogen quaternization was applied for the generation of novel and highly modular triazolium salts. The selective substitution of the 1,3,4-substitution pattern presets such salts as precursors for a new class of abnormal carbene ligands, thus expanding the family of these high-impact ligands. Metalation of the triazolium salts is highly versatile and is illustrated by direct C-H bond activation as well as by applying a transmetalation protocol, thus providing access to Pd(II), Ru(II), Rh(I), and Ir(I) abnormal carbene complexes. The donor properties of these carbenes were analyzed by using Tolman electronic parameters and were found to be slightly stronger than those the most basic normal carbenes.     

Formation of a silicon‐containing macrocycle with a pyridoxalimine Schiff base ligand

The reaction of dichlorodiphenylsilane with a polydentate Schiff base ligand derived from pyridoxal and 2‐hydroxyaniline yields the macrocyclic centrosymmetric silicon compound 9,27‐dimethyl‐3,3,21,21‐tetraphenyl‐2,4,20,22‐tetraoxa‐8,13,26,31‐tetraaza‐3,21‐disilapentacyclo[30.4.0.0^6,11.0^14,19.0^24,29]hexatrideca‐1(32),6,8,10,12,14,16,18,24,26,28,30,33,35‐tetradecaene‐10,28‐diol chloroform tetrasolvate, C₅₂H₄₄N₄O₆Si₂·4CHCl₃. The asymmetric unit contains half of the macrocycle and two molecules of chloroform, with C—H...O and C—H...N contacts binding the two guests to the host in the crystal structure. This macrocyclic silicon compound represents a promising host for molecular‐recognition processes and for the construction of nanostructures.     

Modern spectroscopic techniques in the characterization of Schiff base macrocyclic ligand and its complexes with transition metals

Mn(II), Co(II), Ni(II), and Cu(II) complexes with a new azamacrocyclic tetradentate [N(4)] ligand i.e. 2,3,9,10-tetraphenyl;l,4,8,11-tetraazacyclotetradeca;1,3,8,10-tetraene (L) have been synthesized and characterized by elemental analysis, molar conductance measurements, magnetic susceptibility measurements, mass, (1)HNMR, IR, electronic and EPR spectral studies. On the basis of their non-electrolytic nature, the probable formula of the complexes is proposed to be [M(L)X(2)], where M=Mn(II), Co(II), Ni(II), and Cu(II), X=Cl(-) and NO(3)(-), in dimethylformamide (DMF). All the complexes are of high-spin type and found to have six coordinated, octahedral geometry for Mn(II), Co(II), and Ni(II) complexes, and tetragonal for Cu(II) complexes. Macrocyclic ligand and its complexes have also been screened against pathogenic bacteria and fungi in vitro as growth inhibiting agent.     

A 1D Schiff base zinc polymer as a versatile metallo-ligand for the synthesis of polynuclear zinc cages

The 1D polymeric Schiff base zinc complex, [LZn(2)Et(2)](n), where LH(2) = (NN'-ethylene-bis(4-iminopentan-2-one)) has been demonstrated as a useful synthetic metallo building block for the synthesis of homo and heteronuclear zinc cages. The reaction of [LZn(2)Et(2)](n) with CdI(2) afforded the hetero-nuclear cage, 1, [L(2)Zn(4)(Et)(2)CdI(4)], while reaction with HgI(2) afforded a hexanuclear zinc cage, [L(2)Zn(6)(Et)(4)(μ(4)O)(μ(3)OEt)I], 2. The versatility of [LZn(2)Et(2)](n) as a metallo building block is demonstrated through the reaction with ferrocenyl carboxylic acid, affording the ferrocenyl supported zinc cage, [L(2)Zn(8)(FcCO(2))(4)(Et)(2)(OEt)(2)(μ(4)O)(2)], 3, while the reaction with Er(III) acetate afforded the decanuclear zinc cage, [L(3)Zn(10)(μ(4)O)(4)(Et)(6)], 4.     

New chiral Schiff base as a tridentate ligand for catalytic enantioselective addition of diethylzinc to aldehydes

We have developed new chiral Schiff base catalysts for the enantioselective addition of diethylzinc reagents to aldehydes. The reaction of benzaldehyde with diethylzinc in the presence of 1 mol % of the chiral Schiff base catalyst proceeded to afford 1-phenyl-1-propanol in 96% enantiomeric excess (ee).     

Titanium(IV) phosphinoamide as a unique bidentate ligand for late transition metals II: TiRu heterobimetallics bearing a bridging chlorine atom

Treatment of a titanium phosphinoamide, (Ph₂PN^tBu)₂TiCl₂ (1), with [Cp^∗RuCl]₄ in THF at room temperature afforded a TiRu heterobimetallic complex, of which crystallographic study showed the molecular structure to be a six-membered dimetallacyclohexane, Cp^∗Ru(μ-Cl)(Ph₂PN^tBu)₂TiO (3). A boat conformation of the dimetallacycle leads to effective linking of the two metal centers by two phosphinoamide ligands, and bridging of a chlorine atom over the TiRu axis. The TiRu heterobimetallics were synthesized by the reaction of 1 with Cp^∗Ru(COD)Cl or Cp^∗Ru(TMEDA)Cl, whereas no reaction occurred between 1 and Cp^∗Ru(PCy₃)Cl. A primary product of this reaction would be a trichloride, Cp^∗Ru(μ-Cl)(Ph₂PN^tBu)₂TiCl₂ (2). In fact, careful treatment of 1 with [Cp^∗RuCl]₄ afforded 2 as the main product which was detected by NMR and ESI-MS spectra; 2 was converted to 3 in contact with 1 equivalent of water.     

A tetrameric neptunyl(v) cluster supported by a Schiff base ligand

The first tetrameric cation-cation neptunyl(v) cluster, [{NpO(2)(salen)}(4)(μ(8)-K)(2)][K(18C6)Py](2), has been synthesized in non-aqueous solution from the reaction of [(NpO(2)Py(5))(KI(2)Py(2))](n) with K(2)salen and its structure determined in the solid state and in solution where the complex retains its tetrameric form.     

A periodic walk: a series of first-row transition metal complexes with the pentadentate ligand PY5

A series of transition metal complexes derived from the pentadentate ligand PY5, 2,6-(bis-(bis-2-pyridyl)methoxymethane)pyridine, illustrates the intrinsic propensity of this ligand to complex metal ions. X-ray structural data are provided for six complexes (1-6) with cations of the general formula [M(II)(PY5)(Cl)](+), where M = Mn, Fe, Co, Ni, Cu, Zn. In complexes 1-4 and 6, the metal ions are coordinated in a distorted-octahedral fashion; the four terminal pyridines of PY5 occupy the equatorial sites while the axial positions are occupied by the bridging pyridine of PY5 and a chloride anion. Major distortions from an ideal octahedral geometry arise from displacement of the metal atom from the equatorial plane toward the chloride ligand and from differences in pyridine-metal-pyridine bond angles. The series of complexes shows that M(II) ions are consistently accommodated in the ligand by displacement of the metal ion from the PY5 pocket, a tilting of the axial pyridine subunit, and nonsymmetrical pyridine subunit ligation in the equatorial plane. The displacement from the ligand pocket increases with the ionic radius of M(II). The axial pyridine tilt, however, is approximately the same for all complexes and appears to be independent of the electronic ground state of M(II). In complex 5, the Cu(II) ion is coordinated by only four of the five pyridine subunits of the ligand, resulting in a square-pyramidal complex. The overall structural similarity of 5 with the other complexes reflects the strong tendency of PY5 to enforce a distorted-octahedral coordination geometry. Complexes 1-6 are further characterized in terms of solution magnetic susceptibility, electrochemical behavior, and optical properties. These show the high-spin nature of the complexes and the anticipated stabilization of the divalent oxidation state.     

Synthesis of transition metal complexes containing a Schiff base ligand derived from 1,10-phenanthroline-2,9-dicarboxaldehyde and 2-aminobenzenethiol

The synthesis of a new Schiff base containing 1,10-phenanthroline-2,9-dicarboxaldehyde and 2-aminobenzenethiol subunits is described. The reaction of 1,10-phenanthroline-2,9-dicarboxaldehyde with 2-aminobenzenethiol leads to the isolation of 2,9-bis(2-benzothiazolinyl)-1,10-phenanthroline (I) which undergoes rearrangement when reacted with cobalt, nickel, copper or zinc ions to produce complexes of the tautomeric Schiff base 2,9-bis[2-(2-mercaptophenyl)-2-azaethene]-1,10-phenanthroline (L). The [Cu(L)ClO₄][ClO₄] and [M(L)X₂] complexes (where M = Co(II), Ni(II) and Zn(II) and X = Br) were characterized by physical and spectroscopic measurements which indicated that the ligand is acting probably as a tetradentate N₄ chelating agent.     

The structure of a novel Schiff base mixed ligand complex for simulating superoxide dismutase

Summary A novel copper(II) complex of mixed ligands 2-acetylpyridine and N-ethylene(2-acetylpyridineimine) has been prepared by condensation and its crystal structure determined by XRD. The central copper(II) atom of the complex anion is coordinated to one oxygen of 2-acetylpyridine and four nitrogen atoms of the Schiff base in a distorted square pyramidal geometry. It has a similar coordination geometry to that found in Cu/Zn-SOD.     

White phosphorus as a ligand for the coinage metals

Reaction of equimolar quantities of MX (M = Au, Cu, X = Cl; M = Ag, X = OTf) and GaCl(3) in CH(2)Cl(2) with P(4) leads to phosphorus ligating a cationic coinage metal centre. For Cu and Ag, ion-contacted coordination polymers are formed; for Au, an ion-separated complex is observed that features the [Au(η(2)-P(4))(2)](+) cation, which is the first homoleptic Au-P(4) complex to be characterised in the condensed phase.     

A macrocycle/molecular-clip complex that functions as a quadruply controllable molecular switch

Herein, we report the synthesis of a molecular clip with TTF side-walls and its binding behavior towards electron-deficient guests, namely the formation of macrocycle/molecular-clip supramolecular complexes in solution. Four different sets of external stimuli--the K(+)/[2.2.2]cryptand, NH(4) (+)/Et(3)N and (p-BrPh)(3)NSbCl(6)/Zn pairs, and heating/cooling cycles-control the movement of this molecular switch between its threaded and unthreaded states and provide color changes that are observable by the naked eye. This macrocycle/molecular-clip complex system can be considered not only as a quadruple-use molecular switch, but can also be operated by three of these stimuli as a three-input molecular NOR-functioning logic gate that may be monitored by UV-visible spectroscopy.     

Synthesis, structural, thermal studies and biological activity of a tridentate Schiff base ligand and their transition metal complexes

Schiff base (L) ligand is prepared via condensation of pyridine-2,6-dicarboxaldehyde with -2-aminopyridine. The ligand and its metal complexes are characterized based on elemental analysis, mass, IR, solid reflectance, magnetic moment, molar conductance, and thermal analyses (TG, DTG and DTA). The molar conductance reveals that all the metal chelates are non-electrolytes. IR spectra shows that L ligand behaves as neutral tridentate ligand and bind to the metal ions via the two azomethine N and pyridine N. From the magnetic and solid reflectance spectra, it is found that the geometrical structures of these complexes are octahedral (Cr(III), Fe(III), Co(II), Ni(II), Cu(II), and Th(IV)) and tetrahedral (Mn(II), Cd(II), Zn(II), and UO2(II)). The thermal behaviour of these chelates shows that the hydrated complexes losses water molecules of hydration in the first step followed immediately by decomposition of the anions and ligand molecules in the subsequent steps. The activation thermodynamic parameters, such as, E*, ΔH*, ΔS* and ΔG* are calculated from the DTG curves using Coats-Redfern method. The synthesized ligand, in comparison to their metal complexes also was screened for its antibacterial activity against bacterial species, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus pyogones and Fungi (Candida). The activity data shows that the metal complexes to be more potent/antibacterial than the parent Schiff base ligand against one or more bacterial species.     

Bimetallic complexes of a potentially pentadentate,acyclic, symmetrical compartmental Schiff base ligand that provides suitable topology for an exogenous bridge

The binucleating ligand LH₃, 2,6-diformyl-p-cresol-bis(phenylthioacetyldrazone), a Schiff base condensation product of 2,6-diformyl-p-cresol and phenylthioacetyldrazide forms complexes of the [M₂ClL] type with Co^II, Ni^II and Cu^II ions, which were characterized by elemental analysis, magnetic susceptibility, electronic spectra, molar conductance, i.r., n.m.r., e.p.r., t.g. and FAB mass spectral measurements. Sub-normal magnetic moments indicate the operation of antiferromagnetic coupling between the metal centres. The ligand and its copper complex show a pronounced fungistatic activity.     

A novel bioactive tyramine derived Schiff base and its transition metal complexes as selective DNA binding agents

A novel tyramine derived Schiff base, 3-4-dimethoxybenzylidene-4-aminoantipyrinyl-4-aminoethylphenol(L) and a series of its transition metal complexes of the type, ML2Cl2 where, M=Cu(II), Ni(II), Co(II) and Zn(II) have been designed and synthesized. Their structural features and other properties were deduced from the elemental analysis, magnetic susceptibility and molar conductivity as well as from mass, IR, UV-vis, 1H NMR and EPR spectral studies. The binding properties of these complexes with calf thymus DNA (CT-DNA) were investigated using electronic absorption spectroscopy, viscosity measurement, cyclic voltammetry and molecular docking analysis. The results reveal that the metal(II) complexes interact with DNA through minor groove binding. The interaction has also been investigated by gel electrophoresis. Interestingly, it was found that all the complexes could cleave the circular plasmid pUC19 super coiled (SC) DNA efficiently in the presence of AH2 (ascorbic acid). The complexes showed enhanced antifungal and antibacterial activities compared to the free ligand.     

Renewable vegetable raw materials as a base for preparing versatile functional nanocomposites

A power-saving technology was developed for preparing functional nanocomposites from renewable vegetable raw materials and nanosized elements.     

A new vanadium Schiff base complex as catalyst for oxidation of alcohols

The monoanionic bidentate Schiff base, N-(phenolyl)-benzaldimine (HL), has been employed to synthesize a new vanadium(IV) complex of general composition [VO(L)₂] (where L?=?O,?N donor of Schiff base). The ligand and complex have been fully characterized by elemental analyses, molar conductance data, FT-IR, ¹H- and ¹³C-NMR, and UV-Vis spectroscopies. Oxidation of alcohols to their corresponding aldehydes and ketones was conducted by this complex catalyst using Oxone as oxidant under biphasic reaction conditions (CH₂Cl₂/H₂O) and tetra-n-butylammonium bromide as phase transfer agent under air at room temperature.