Imine Nitrogen Atoms Research Articles

Evidence for a precursor adcomplex during the metalation of 2HTPP with iron on Ag(1 0 0)

Using X-ray photoelectron spectroscopy (XPS), we demonstrate that free-base tetraphenylporphyrin (2HTPP) on Ag(100) forms a theoretically predicted adcomplex with post-deposited iron at 100K. The formation of the adcomplex, as a precursor for metalation, can be deduced from the N 1s spectra showing clearly not-metalated 2HTPP molecules, but with strongly shifted iminic nitrogen peaks, caused by the interaction of the iminic nitrogen atoms with the Fe adatoms.

A new Salen-type azo–azomethine ligand and its Ni(II), Cu(II) and Zn(II) complexes: Synthesis, spectral characterization, crystal structure and photoluminescence studies

A novel Salen-type azo–azomethine ligand H2agen, 2,2′-{ethane-1,2-diylbis[nitrilomethylylidene]}bis{4-[ethylphenyldiazenyl]phenol}, formed by the 1:2M condensation of ethane-1,2-diamine with 5-[(4-ethylphenyl)diazenyl]-2-hydroxybenzaldehyde and its nickel(II), copper(II), and zinc(II) complexes were synthesized and characterized by the spectroscopic and analytical methods. The UV–vis spectra of the ligand were investigated in three organic solvents (DMSO, DMF and CHCl3). The ligand shows two absorption bands assigned to π–π∗ and n–π∗ transitions in the solvents used. Cu(II), and Ni(II) are tetra-coordinate binding to two phenolic oxygens and two imine nitrogens in approximate square planar geometry. Zn(II) also coordinates using the same sites like other metals but gave tetragonal configuration. Molecular structure of the Cu(II) complex [Cu(agen)] was determined by single crystal X-ray diffraction study. The X-ray data revealed that crystallographic imposed symmetry was absent for the complex molecule. In the structure, the Cu(II) ion is coordinated to two phenolate oxygen atoms and two imine nitrogen atoms of the azo-azomethine ligand with approximate square planar geometry. The ligand H2agen and its metal complexes exhibit strong blue emissions with irradiation. Fluorescence quantum yields and excited-state lifetimes for the ligand and its complexes were obtained. The H2agen ligand had a 35% quantum yield and a 3.27ns excited-state lifetime. Complexation with metal ions caused reductions in intensities and quantum yields.

Cobalt(II), copper(II), zinc(II) and palladium(II) Schiff base complexes: Synthesis, characterization and catalytic performance in selective oxidation of sulfides using hydrogen peroxide under solvent-free conditions

An asymmetric bidentate Schiff-base ligand (HL: 2-tert-butyliminomethyl-phenol) was prepared from the reaction of salicylaldehyde and tert-butylamine. Cobalt(II), copper(II), zinc(II) and Pd(II) complexes, CoL2, CuL2, ZnL2 and PdL2, were synthesized from the reaction of CoCl2·6H2O, CuCl2·2H2O, Zn(NO3)2·6H2O and PdCl2 with the bidentate Schiff base ligand HL in methanol. The ligand and its metal complexes were characterized by elemental analysis (CHN), FT-IR and UV-Vis spectroscopy. In addition, 1H and 13C NMR techniques were employed for characterization of the ligand (HL) and the diamagnetic complexes (ZnL2 and PdL2). The molecular structures of all the complexes were determined by the single crystal X-ray diffraction technique. The crystallographic data reveal that in all the complexes the metal centers are four-coordinated by two phenolate oxygen and two imine nitrogen atoms of two Schiff base ligands. The geometry around the metal center in the CoL2, CuL2 and ZnL2 complexes is a distorted tetrahedral and for PdL2 it is square-planar.The catalytic activity of these complexes has been evaluated for the selective oxidation of sulfides with the green oxidant 35% aqueous H2O2 under solvent free conditions. For all the catalysts, using optimized reaction conditions, different sulfides were converted to the corresponding sulfones. ZnL2 showed a higher catalytic performance for the oxidation of the different sulfides to the corresponding sulfones.

Bis(pyridylimino)isoindolato (BPI) Osmium Complexes: Structural Chemistry and Reactivity

A series of osmium complexes with monoanionic, meridionally coordinating 1,3-bis(2-pyridylimino)isoindolates (BPI) as spectator ligands has been synthesized. Reaction of the dichlorido metal precursor [OsCl2(PPh3)3] with the lithiated BPI ligand transfer reagent gave the chlorido complex [(tBu-BPIMe)Os(PPh3)2Cl] (2) which, in turn, was reacted with lithium triethylborohydride to yield the hydrido complex [(tBu-BPIMe)Os(PPh3)2H] (3). Treatment of complex 2 with thallium hexafluorophosphate under a nitrogen pressure afforded the cationic dinitrogen complex [(tBu-BPIMe)Os(PPh3)2(N2)]PF6 (4), which contains an end-on coordinated dinitrogen molecule trans to the isoindolato nitrogen atom. To synthesize the alkynyl complex [(tBu-BPIMe)Os(PPh3)2(C≡CPh)] (5), the chlorido complex 2 was treated with lithium phenylacetylide. Complex 5 was subsequently converted quantitatively by addition of one or two equivalents of HBF4 to the vinylidene complex [(tBu-BPIMe)Os(PPh3)2(═C═CHPh)]BF4 (6), and the cationic species [(H-tBu-BPIMe)Os(PPh3)2(═C═CHPh)](BF4)2 (7), respectively; the latter being formed via protonation of one imine nitrogen atom of the BPI ligand. Upon stirring, a toluene solution of the chlorido complex 2 with benzyl potassium, the four-membered metallacycle [(tBu-BPIMe)Os(PPh3)(o-C6H4PPh2)] (8) was obtained, which reacted with molecular hydrogen and phenyl acetylene to give the hydrido complex 3 and the acetylide complex 5, respectively. Stirring of 8 with methyl acetylenedicarboxylate (DMAD) yielded [(tBu-BPIMe)Os(DMAD)(o-C6H4PPh2)] (9), while treatment with carbon monoxide gave the acyl complex [(tBu-BPIMe)Os(o–C(O)-C6H4PPh2)(CO)] (10) by an insertion of CO into the osmium carbon bond.

Biosynthesis of the carbamoylated D-gulosamine moiety of streptothricins: involvement of a guanidino-N-glycosyltransferase and an N-acetyl-D-gulosamine deacetylase.

Streptothricins (STNs) are atypical aminoglycosides containing a rare carbamoylated D-gulosamine (D-GulN) moiety, and the antimicrobial activity of STNs has been exploited for crop protection. Herein, the biosynthetic pathway of the carbamoylated D-GulN moiety was delineated. An N-acetyl-D-galactosamine is first attached to the streptolidine lactam by the glycosyltransferse StnG and then epimerized to N-acetyl-D-gulosamine by the putative epimerase StnJ. After carbamoylation by the carbamoyltransferase StnQ, N-acetyl-D-GulN is deacetylated by StnI to furnish the carbamoylated D-GulN moiety. In vitro studies characterized two novel enzymes: StnG is an unprecedented GT-A fold N-glycosyltransferase that glycosylates the imine nitrogen atom of guanidine, and StnI is the first reported N-acetyl-D-GulN deacetylase.

Biosynthesis of the Carbamoylated D‐Gulosamine Moiety of Streptothricins: Involvement of a Guanidino‐N‐glycosyltransferase and an N‐Acetyl‐D‐gulosamine Deacetylase

AbstractStreptothricins (STNs) are atypical aminoglycosides containing a rare carbamoylated D‐gulosamine (D‐GulN) moiety, and the antimicrobial activity of STNs has been exploited for crop protection. Herein, the biosynthetic pathway of the carbamoylated D‐GulN moiety was delineated. An N‐acetyl‐D‐galactosamine is first attached to the streptolidine lactam by the glycosyltransferse StnG and then epimerized to N‐acetyl‐D‐gulosamine by the putative epimerase StnJ. After carbamoylation by the carbamoyltransferase StnQ, N‐acetyl‐D‐GulN is deacetylated by StnI to furnish the carbamoylated D‐GulN moiety. In vitro studies characterized two novel enzymes: StnG is an unprecedented GT‐A fold N‐glycosyltransferase that glycosylates the imine nitrogen atom of guanidine, and StnI is the first reported N‐acetyl‐D‐GulN deacetylase.

Intramolecular charge transfer in coumarin based donor-acceptor systems: Formation of a new product through planar intermediate

Abstract Fluorescence behavior and intramolecular charge transfer (ICT) property of N,N′-dimethylamino substituted anil derivative of coumarinyl amine was studied by steady state and time-resolved fluorescence spectroscopy in combination with density functional theory calculation. Quantitative analysis of the effect of solvent hydrogen bonding on several spectral parameters was done using multiple regression analysis based on Kamlet–Taft model. The present system shows an additional long wavelength fluorescence band almost instantaneously in presence of methanol in sharp contrast to the model unsubstituted analogue. This new fluorescence band is believed to be due to the formation of a new isomer (cis-type) through a planar intermediate. While there is a substantial barrier (∼50 kJ mol−1) in the ground state, the isomerization process in the excited state in polar-protic environment proceeds very fast and believed to be catalyzed by hydrogen bond formation at the imine nitrogen atom in combination with stabilization of the resulting species through ICT.

Synthesis, structural characterization and DNA interaction of zinc complex from 2,6-diacetylpyridine dihydrazone and {4-[(2E)-2-(hydroxyimino)acetyl]phenoxy} acetic acid

A new water soluble zinc complex has been prepared and structurally characterized. The Zn(II) complex was synthesized by the reaction of 2,6-diacetylpyridine dihydrazone (dph) with {4-[(2E)-2-(hydroxyimino)acetyl]phenoxy} acetic acid (H2L) in the presence of zinc(II) acetate. Single crystal X-ray diffraction study revealed that the zinc ion is situated in distorted trigonal-bipyramidal environment where the equatorial position is occupied by the nitrogen atom of pyridine ring and the oxygen atoms of acetate groups of two oxime ligands (H2L) whereas the axial positions of the zinc complex are occupied by the imine nitrogen atoms of dph ligand. Characterization of the complex with FTIR, 1H and 13C NMR, UV–vis and elemental analysis also confirmed the proposed structure. Interaction of the Zn(II) complex with calf-thymus DNA (CT-DNA) was investigated through UV–vis spectroscopy and viscosity measurements. The results suggest that the complex preferably bind to DNA through the groove binding mode. The zinc complex cleaves plasmid pBR 322 DNA in the presence and absence of an oxidative agent (H2O2), possibly through a hydrolytic pathway which is also supported by DNA cleave experiments in the presence of different radical scavengers. The nuclease activity of the zinc complex significantly depends on concentration of the complex and incubation time both in the presence and absence of H2O2. DNA cleave activity is inhibited in the presence of methyl green indicating that the zinc complex seems to bind the major groove of DNA.

Interaction of ethylenechlorophosphite with hydroxyl-containing azomethines

The reaction of imine I with ethylenechlorophosphite II afforded cyclic phosphonate III as a mixture of diastereomers (δP 15.92, 16.13 ppm) in the 70:30 ratio. Hydrolysis of III gave aminophosphonate IV (δP 10.41 ppm). The reaction proceeded via phosphorylation of imine I at the hydroxyl group with elimination of hydrogen chloride. The latter protonated the imine nitrogen atom, increasing electrophilicity of the C=N bond. Attack of the trivalent phosphorus atom was accompanied by formation of an activated imino spirocyclic moiety which was converted into III as a result of attack of chloride anion at the carbon atom of dioxaphospholane fragment (Scheme 1).

Iridium Half-Sandwich Complexes with Di- and Tridentate Bis(pyridylimino)isoindolato Ligands: Stoichiometric and Catalytic Reactivity

A series of κ2-(N,N)-coordinated bis(2-pyridylimino)isoindolato (BPI) complexes [Cp*Ir(BPI)Cl], which possess “three-legged piano-stool” structures, with the iridium atom being coordinated by the Cp* ligand 2 × N and Cl, were prepared via deprotonation of the BPIH ligands with either potassium hydride or LDA and subsequent reaction with [Cp*IrCl2]2 in THF. Cationic complexes [Cp*Ir(BPI)]+ containing κ3-(N,N,N)-coordinated BPI ligands were prepared as well as complexes with bidentate-coordinated BPI ligands, where the chloride ligand was substituted by either neutral or anionic ligands. Substitution in the ortho-position of the PBI ligands led to the formation of cycloiridated κ3-(N,N,C) species. Upon substitution of the anionic ligand by triphenylphosphine, a product was obtained with a hitherto unobserved κ2-(N,N) coordination of oMe-BPI to the metal center via the deprotonated nitrogen atom of the isoindole unit and one of the imine nitrogen atoms of the BPI ligand. A series of (para-cymene) osmium half...

Self-assembly of chelating, bridging N, N, N donor ligands and Cu(I), Cu(II), Cd(II), Hg(II): Molecular box versus coordination polymer

Three flexible chelating and bridging ligands, (E)-N-(pyridin-2-ylmethylene)-1-(pyridin-3-yl)methanamine (L1), 1-(pyridine-2-yl)-N-(pyridin-3-ylmethyl)methanamine (L1′), (E)-N-(pyridin-2-ylmethylene)-1-(pyridin-4-yl)methanamine (L2), have been synthesized. The reaction of these ligands with various metal salts yielded a series of compounds, namely [Cu2(L1)(PPh3)2I2]2 (1), [Cu2(L2)(PPh3)2I2]n (2), [CuL1(NO3)2]2 (3), [ZnL1(NO3)2]2 (4), [CdL1(NO3)2]2 [(5), [CdL1′ (NO3)2]2 (6) and [HgL1Cl2]n (7). The compounds were characterized by elemental analysis, spectroscopic methods (IR, UV–Vis) and X-ray crystallography. X-ray structural analysis of compound 1 reveals the formation of a centrosymmetric tetranuclear compound. The repeat unit of coordination polymer 2 comprises a Cu2I2 unit with a triphenyl phosphane substituent on Cu1 linked to an adjacent Cu2I2 unit by the ligand L2 that acts as a bridge. Compounds 3, 4, 5 and 6 exhibit a common metallo-cyclophane [M2(L)2(NO3)4] skeleton. Two M2+ cations are linked by two L1 ligands and these ligands chelate to each metal atom through the imine nitrogen (or amine nitrogen) atoms and the nitrogen atom of the 2-pyridyl ring, and bind to the other metal atom of the pair via the nitrogen atoms of the 3-pyridyl rings. Structural studies of 7 revealed the formation of a coordination polymer in which the polymer chain propagates in helical spirals along a twofold screw axis parallel to b. The metal coordination geometries and coordination of the nitrato anions to the metals are noted and discussed.

Hydrogen capture by porphyrins at the TiO2(110) surface.

Metal-free porphyrin molecules adsorb on the rutile TiO2(110) surface with their pyrrolic nitrogen atoms atop the O-bridge rows, whereas the iminic nitrogen atoms capture two additional hydrogen atoms. Hydrogenation occurs spontaneously at room temperature, irrespective of the distance of the polypyrrolic macrocycle from the surface, as varied by changing the porphyrin functionalization.

Copper(II) and nickel(II) complexes with two new bis(thiosemicarbazone) ligands: Synthesis, characterization, X-ray crystal structures and their electrochemistry behavior

Two new bis(thiosemicarbazone) ligands 2-[1-(2-{3-[2-({2-[(4-chloroanilino)carbothioyl]hydrazono}methyl)phenoxy]propoxy}phenyl)methylidene]-N1-(4-chlorophenyl)-1-hydrazinecarbothiamide (H2L1) and 2-[1-(2-{3-[2-({2-[(4-chloroanilino)carbothioyl]hydrazono}methyl)phenoxy]-2-hydroxypropoxy}phenyl)methylidene]-N1-(4-chlorophenyl)-1-hydrazinecarbothiamide (H3L2) were synthesized and characterized by FT-IR spectroscopy, 1H NMR spectroscopy and elemental analysis. Their nickel(II) and copper(II) complexes were prepared and characterized by UV–Vis spectroscopy, FT-IR spectroscopy, elemental analysis and single-crystal X-ray diffraction. Both ligands lose hydrazinic hydrogen atoms upon coordination and act as dianionic tetradentate donors. In [NiL1]·EtOH and [CuL1]·MeOH complexes metal centers are coordinated by two imine nitrogen atoms and two sulfur atoms with a distorted square planar coordination geometry. The geometrical distortion from square planar in the copper complex is greater than in the nickel complex. Cyclic voltammetry studies of Cu(II) and Ni(II) complexes in DMF show that all complexes able to stabilize low oxidation states of Cu(I) and Ni(I).

A turn-on fluorescence chemosensor for Al3+, F− and CN− ions, and its application in cell imaging

A chemosensor 3-[(2-hydroxybenzylidene)-amino]-1H-pyridin-2-one (HL) for multi-ions was synthesized and characterized by single-crystal X-ray diffraction. HL is a turn-on fluorescence chemosensor for Al3+, F−, and CN− ions in DMSO. F− and CN− anions could be further distinguished by the ratiometric absorption spectrometry method. Job plot and 1H NMR data showed that the binding stoichiometries of HL with Al3+, F−, or CN− all were 1:1. Further observations of 1H NMR titration and ESI-MS showed that the possible fluorescent species of Al3+ with HL was [AlL(OH)(DMSO)2]+ in DMSO. The spectroscopic observations of the Al(III) complex showed that the two oxygen atoms and one imine nitrogen atom of HL were coordinated to the Al(III) ion. While the crystal structure of the Ni(II)-L complex confirmed the tridentate coordination mode of HL in the complexes. The experimental results revealed that HL and F− ion formed hydrogen bond in DMSO, while CN− attacked the carbon atom at –CN of HL to undergo a nucleophilic addition. The theoretical calculations confirmed that HL showed very weak fluorescence because of the excited-state intramolecular proton transfer (ESIPT). The turn-on sensing of HL to Al3+, F−, and CN− ions arose from the inhibition of ESIPT. MTT tests showed that HL was low toxic to cells. Also, HL could probe intracellular Al3+ and F− ions by bioimaging.

Unsymmetrical Schiff base (ON) ligand on complexation with some transition metal ions: Synthesis, spectral characterization, antibacterial, fluorescence and thermal studies

A series of eight metal Schiff base complexes were synthesized by the thermal reaction of Cu(II), Ni(II), Fe(III), Co(II), Zn(II), Hg(II), La(III) or Sm(III) with a Schiff base “L” produced by the condensation of furfuraldehyde and 1,2-diaminobenzene. These compounds were characterized by elemental analysis, UV–Vis, FT-IR, molar conductance, mass spectrometry, thermal and fluorescence studies. The studies suggested the coordination of the ligand L to metal through azomethine imine nitrogen and furan oxygen atoms of Schiff base moiety. Thermogravimetric (TG/DTG) analyses data were studied and indicated high stability for all complexes and suggested the presence of lattice and/or coordinated water molecules in the complexes. Coats–Redfern method has been used to calculate the kinetic and thermodynamic parameters of the metal complexes. The spectral and thermal analysis reveal that all complexes have octahedral geometry except Cu(II) and Ni(II) complexes which can attain a square planner arrangements. The ligand and its complexes exhibited intraligand (π–π∗) fluorescence and can potentially serve as photoactive materials. Both the ligand and its complexes have been screened for antibacterial activities.

β-Diketimine appended periodic mesoporous organosilica as a scaffold for immobilization of palladium acetate: An efficient green catalyst for Wacker type reaction

A series of β-diketimine appended periodic mesoporous organosilicas (PMOs) were prepared and characterized. These PMOs were found to be an excellent scaffold for the immobilization of palladium acetate [Pd(OAc)2] through the complexation between Pd(OAc)2 and iminic nitrogen atoms of β-diketiminate, leading to the formation of efficient heterogeneous catalysts (Pd/PMOs) for the oxidation of styrene. Catalytic evaluations show that, in liquid phase using H2O2 as oxidant, Pd/PMOs could promote styrene to undergo Wacker type reaction with a high selectivity of up to 100% toward the formation of acetophenone, a useful chemical with high demand in the global market. The novel solid catalyst offers a good catalytic recyclability with consistently high catalytic activity. In addition, it was experimentally demonstrated that H2O2 plays an important role to prevent unwanted catalyst deactivation. Thus, the current work presents a convenient approach for the direct production of acetophenone from styrene.

Synthesis, characterization, crystal structure determination, thermal study and catalytic activity of a new oxidovanadium Schiff base complex

A new bidentate ON Schiff base ligand of HL (HL=5-nitro-2-hydroxybenzyl-2-furylmethyl) imine), was synthesized by simple condensation reaction of 5-nitro-2-hydroxybenzaldehyde and 2-furfurylamine. Then by reaction of a methanolic solutions of the HL and VO(acac)2 in the ratio of 2:1, a new oxidovanadium(IV) Schiff base complex of VOL2 was synthesized. The Schiff base ligand and its vanadyl Schiff base complex were characterized by FT-IR, UV–vis spectra and CHN analysis. Single crystals suitable for X-ray analysis were obtained in DMSO as a VOL2(DMSO) complex. The crystal structure of the VOL2(DMSO) was determined by the single-crystal X-ray analysis. The coordination geometry around the vanadium center can be described as a distorted octahedron formed by two phenolato oxygen and two imine nitrogen atoms of the two Schiff base ligands in the equatorial position, the oxygen atom of DMSO and the oxido ion coordinated in the axial position. Thermogravimetric analysis of the VOL2 showed that the formation of mixed vanadium oxides at 450 ˚C. In addition, decomposition of the vanadyl Schiff base complex (VOL2) in air at 660°C resulted in the formation of the V2O5 nano particles with the average size of 52nm. The catalytic activity of the VOL2 complex was evaluated in the epoxidation of cyclooctene (90% conversion and 100% epoxide) and oxidation of methyl phenyl sulfide (100% conversion and 100% sulfoxide).

Syntheses, characterizations and biological activities of two Cu(II) complexes with acylhydrazone ligand bearing pyrrole unit

Two novel Cu(II) complexes, [Cu(L)2(CH3OH)]·CH3OH (1) and [Cu(L)(DMF)Cl] (2) based on HL (where HL=2-ethoxycarbonyl-5-formyl-3,4-dimethylpyrrole 4-hydroxylbenzoylhydrazone) were synthesized and characterized by X-ray diffraction analyses. The results show that in each complex, the acylhydrazone ligand is deprotonated and coordinated to the copper(II) ion via enolizated oxygen and imine nitrogen atoms. The central metal ion possesses a distorted square pyramidal and a square-planar coordination geometry in complexes 1 and 2, respectively. In addition, complex 2 shows obvious inhibitory effect to bacterial strains Staphylococcus aureus and Salmonella typhimurium, and complex 1 has excellent antitumor activity towards Hepatocellular carcinoma (Hep G2) cells (IC50=2.0μM).

Coverage- and temperature-dependent metalation and dehydrogenation of tetraphenylporphyrin on Cu(111).

Using temperature-programmed desorption, supported by X-ray photoelectron spectroscopy and scanning tunneling microscopy, a comprehensive overview of the main reactions of 5,10,15,20-tetraphenyl-21H,23H-porphyrin (2HTPP) on Cu(111) as a function of coverage and temperature is obtained. Three reactions were identified: metalation with Cu substrate atoms, stepwise partial dehydrogenation, and finally complete dehydrogenation. At low coverage the reactions are independent of coverage, but at higher coverage metalation becomes faster and partial dehydrogenation slower. This behavior is explained by a weaker interaction between the iminic nitrogen atoms and the Cu(111) surface in the high-coverage checkerboard structure, leading to faster metalation, and the stabilizing effect of T-type interactions in the CuTPP islands formed at high coverage after metalation, leading to slower dehydrogenation. Based on the amount of hydrogen released and the appearance in STM, a structure of the partially dehydrogenated molecule is suggested.

Sensing of Zn²⁺ ion by N-furfurylsalicylaldimine based on CHEF process.

The recognition ability of N-Furfurylsalicylaldimine (HL) toward various cations (Pb(2+), Hg(2+), Ba(2+), Cd(2+), Ag(+), Zn(2+), Cu(2+), Ni(2+), Co(2+), K(+), Sr(2+), and Na(+)) has been studied by UV-Vis and fluorescence spectroscopy. The compound showed highly selective fluorescence signaling behaviour for Zn(2+) ions in methanol-water medium based on CHEF process and is capable of distinguishing Zn(2+) from Cd(2+) ion. From single crystal X-ray analysis it is revealed that a Zn(2+) ion binds two ligand molecules through imine nitrogen and phenolate oxygen atom.