Syntheses,crystal structures,and properties of Ni(II) and Co(III) complexes derived from tripod polypyridine ligands containing N7 or N6 donor set atoms

New complexes [Ni^II(pbpaen)](ClO₄)₂ (1) and [Co^III(pbpaen)](ClO₄)₃ (2) (pbpaen = N′-(pyridin-2-ylmethyl)-N,N-bis {2-[(pyridin-2-ylmethyl)amino]ethyl}ethane-1,2-diamine) have been synthesized and characterized by IR and UV–Vis spectroscopies. An X-ray structure of the nickel(II) complex shows that [Ni(pbpaen)](ClO₄)₂ (1) crystallizes in the monoclinic space group P2_1/c. The cation [Ni(pbpaen)]²⁺ is pseudo-octahedral with one of the three pyridyl nitrogen atom uncoordinated. The crystal lattice of this complex is stabilized by intra and intermolecular hydrogen bonding systems, giving one-dimensional sheets like arrays. All attempts to obtain nickel or cobalt complexes with protonated forms of the ligand resulted in isolation of only [Co^III(bpaen)](ClO₄)₃ (3) compound in which the tripod pbpaen ligand has lost one of the three pyridylmethyl groups, procuring then bpaen ligand {bpaen = N,N-bis{2-[(pyridin-2-ylmethyl)amino]ethyl}ethane-1,2-diamine}. The X-ray crystal structure reveals that the compound 3 crystallizes in the orthorhombic space group Pna2 with the Co³⁺ ion having a distorted-octahedral environment. These two ligands with strong-field N donor stabilise the +3 oxidation state of the Co center.     

Tricarbonylrhenium(I) bromide complexes with N,N′-bis[1-(4-chlorophenyl)ethylidene]ethane-1,2-diamine and N,N′-bis[1-(4-nitrophenyl)ethylidene]ethane-1,2-diamine–syntheses,structures, electrochemical and spectroscopic studies

Two rhenium(I) complexes, [Re(CO)₃Br(L ⁿ )] (n = 1, 2), (L¹= N,N′-bis[1-(4-chlorophenyl)ethylidene]ethane-1,2-diamine and L² = N,N′-bis[1-(4-nitrophenyl)ethylidene]ethane-1,2-diamine) have been synthesized and characterized by CHN analyses, ¹H NMR, IR, and UV-Vis spectroscopy. The molecular structure of [Re(CO)₃Br(L¹)] is a distorted octahedron around rhenium with one Br, facial arrangement of three CO's, and one diimine. The UV-Vis spectra of the complexes have metal-to-ligand charge transfer bands increasing in wavelength when the L² ligand is replaced by L¹, in agreement with the oxidation potential of the complexes.     

Synthesis, crystal structure and antibacterial activity of a group of mononuclear manganese(II) Schiff base complexes

Five mononuclear complexes of manganese(II) of a group of the general formula, [MnL(NCS)₂] where the Schiff base L = N,N′-bis[(pyridin-2-yl)ethylidene]ethane-1,2-diamine (L¹), (1); N,N′-bis[(pyridin-2-yl)benzylidene]ethane-1,2-diamine (L²), (2); N,N′-bis[(pyridin-2-yl)methylidene]propane-1,2-diamine (L³), (3); N,N′-bis[(pyridin-2-yl)ethylidene]propane-1,2-diamine (L⁴), (4) and N,N′-bis[(pyridin-2-yl)benzylidene]propane-1,2-diamine (L⁵), (5) have been prepared. The syntheses have been achieved by reacting manganese chloride with the corresponding tetradentate Schiff bases in presence of thiocyanate in the molar ratio of 1:1:2. The complexes have been characterized by IR spectroscopy, elemental analysis and other physicochemical studies, including crystal structure determination of 1, 2 and 4. Structural studies reveal that the complexes 1, 2 and 4 adopt highly distorted octahedral geometry. The antibacterial activity of all the complexes and their respective Schiff bases has been tested against Gram(+) and Gram(−) bacteria.     

Two chiral mononuclear and one-dimensional cadmium(II) complexes constructed by (1R,2R)-N1,N2-bis(pyridinylmethyl)cyclohexane-1,2-diamine derivatives: Effect of positional isomerism

Reactions of (1R,2R)-N¹,N²-bis(pyridinylmethyl)cyclohexane-1,2-diamine derivatives, (1R,2R)-2-bpcd and (1R,2R)-3-bpcd [(1R,2R)-2-bpcd = (1R,2R)-N¹,N²-bis(pyridin-2-ylmethyl)cyclohexane-1,2-diamine, (1R,2R)-3-bpcd = (1R,2R)-N¹,N²-bis(pyridin-3-ylmethyl)cyclohexane-1,2-diamine], with CdI₂ in an analogous way led to the formation of a chiral discrete mononuclear complex and a chiral one-dimensional polymeric chain, respectively, which may be attributed to the positional isomerism of the ligands. The chiral organic ligands and complexes display luminescent properties indicating that they may have a potential application as optical materials. Powder second-harmonic generation (SHG) efficiency measurement shows that the SHG efficiency of the complexes is approximately 0.3 and 0.45 times that of KDP, respectively.     

The formation of 'classical' and 'half unit' Schiff-base ligands from their components on a molybdenum(IV) centre

The in situ synthesis of the complex, (PPh₄)[Mo(CN)₃O(aceen)] (aceen = N-[1-(pyridin-2-yl)ethylidene]ethane-1,2-diamine), with a 'half unit' Schiff base ligand (with a free amino group) is described and compared with that of [Mo(CN)₂O(diaceen)]·H₂O (diaceen = N,N-bis[1-(pyridin-2-yl)ethylidene]ethane-1,2-diamine) in which a 'classical', tetradentate Schiff base ligand is formed. The mechanism of the 'half unit' and 'classical' template Schiff bases ligand formation is discussed.     

Cyclothiomethylation of aliphatic polyamines with formaldehyde and hydrogen sulfide

Cyclothiomethylation of the terminal amino groups in N-(2-aminoethyl)ethane-1,2-diamine, N,N′-bis(2-aminoethyl)ethane-1,2-diamine, and N,N′-bis(2-aminoethyl)ethane-1,1-diamine with formaldehyde and hydrogen sulfide gave the corresponding bis-1,3,5-dithiazinane derivatives. The reaction in aqueous butanol at 0°C was accompanied by intermolecular thiomethylation at the secondary amino groups with formation of previously unknown polyheterocyclic compounds containing nitrogen and sulfur atoms.     

Catalytic oxyfunctionalization of saturated hydrocarbons by non-heme oxo-bridged diiron(III) complexes: role of acetic acid on oxidation reaction

Oxo-bridged diiron(III) complexes [Fe₂O(L¹)₂(H₂O)₂](ClO₄)₄ (1) and [Fe₂O(L²)₂(H₂O)₂](ClO₄)₄ (2), where L¹ and L² are tetradentate N-donor N,N′-bis(2-pyridylmethyl)-1,2-cyclohexanediamine and N,N′-bis(2-pyridylmethyl)ethane-1,2-diamine respectively, have been isolated as synthetic models of non-heme iron oxygenases and characterized by physicochemical and spectroscopic methods. Both the complexes have been studied as catalysts for the oxyfunctionalization of saturated hydrocarbons using green hydrogen peroxide (H₂O₂) as oxidant under mild conditions. The selectivity (A/K) and regioselectivity (3°/2°) in oxidative C–H functionalization of alkanes suggests the involvement of metal-based intermediate in the oxygenation reaction. The catalytic efficiency is found to be strongly dependent on the presence of acetic acid. Remarkable increase in conversion and selectivity favoring the formation of alcohols in the oxidation of cyclohexane and cyclooctane and exclusive hydroxylation of adamantane with drastic enhancement of regioselectivity has been achieved by the addition of acetic acid in the presence of H₂O₂.

     

Synthesis,crystal structure,and antibacterial activity of mononuclear nickel(II) and cobalt(III) Schiff-base complexes

Four new mononuclear complexes, [Ni(L¹)(NCS)₂] (1), [Ni(L²)(NCS)₂] (2), [Co(L¹)(N₃)₂]ClO₄ (3), and [Co(L²)(N₃)₂]ClO₄ (4), where L¹ and L² are N,N′-bis[(pyridin-2-yl)methylidene]butane-1,4-diamine and N,N′-bis[(pyridin-2-yl)benzylidene]butane-1,4-diamine, respectively, have been prepared. The syntheses have been achieved by reaction of the respective metal perchlorate with the tetradentate Schiff bases, L¹ and L², in presence of thiocyanate (for 1 and 2) or azide (for 3 and 4). The complexes have been characterized by microanalytical, spectroscopic, single crystal X-ray diffraction and other physicochemical studies. Structural studies reveal that 1–4 are distorted octahedral geometries. The antibacterial activity of all the complexes and their constituent Schiff bases have been tested against Gram-positive and Gram-negative bacteria.     

Synthesis,characterization, and structures of copper(I) complexes with N,N′-bis[1-(4-chlorophenyl)ethylidene]ethane-1,2-diamine and N,N′-bis[1-(4-nitrophenyl)ethylidene]ethane-1,2-diamine

Two ligands, N,N′-bis[1-(4-chlorophenyl)ethylidene]ethane-1,2-diamine (L¹ ) and N,N′-bis- [1-(4-nitrophenyl)ethylidene]ethane-1,2-diamine (L² ) and their corresponding copper(I) complexes, [Cu(L ¹)₂]ClO₄ (1) and [Cu(L ²)₂]ClO₄ (2), have been synthesized and characterized by CHN analyses, ¹H-NMR, IR, and UV–Vis spectroscopy. The crystal structures of L¹ and [Cu(L ¹)₂]ClO₄ (1) were determined from single crystal X-ray diffraction. L¹ lies across a crystallographic inversion center and the C=N is approximately coplanar with the benzene ring and adopts E configuration. The coordination polyhedron about copper(I) in 1 is best described as a distorted tetrahedron. Quasireversible redox behavior is observed for the complexes.     

Reaction of thiourea with formaldehyde and simplest aliphatic diamines

N,N′-Bis(hydroxymethyl)thiourea reacted with propane-1,3-diamine at a molar ratio of 2 : 1 to give 5,5′-propane-1,3-diylbis(1,3,5-triazinane-2-thione), whereas 1,3,5,7,11,13,15,17-octaazatricyclo[15.3.1.1^7,11]-docosane-4,14-dithione was obtained in the reaction with equimolar amounts of the reactants. Tricyclic product was also formed in the three-component condensation of thiourea with formaldehyde and propane-1,3-diamine at a ratio of 1 : 3 : 1. The reactions of N,N′-bis(hydroxymethyl)thiourea with ethane-1,2-diamine (2 : 1) and of thiourea with formaldehyde and butane-1,4-diamine (1 : 2 : 1) afforded 5,5′-(ethane-1,2-diyl)bis(1,3,5-triazinane-2-thione) and 5,5′-(butane-1,4-diyl)bis(1,3,5-triazinane-2-thione), respectively.     

Heterolytic O−O Bond Cleavage Upon Single Electron Transfer to a Nonheme Fe(III)−OOH Complex

The one-electron reduction of the nonheme iron(III)-hydroperoxo complex, [Fe^III(OOH)(L₅²)]²⁺ (L₅²=N-methyl-N,N’,N’-tris(2-pyridylmethyl)ethane-1,2-diamine), carried out at −70 °C results in the release of dioxygen and in the formation of [Fe^II(OH)(L₅²)]⁺ following a bimolecular process. This reaction can be performed either with cobaltocene as chemical reductant, or electrochemically. These experimental observations are consistent with the disproportionation of the hydroperoxo group in the putative Fe^II(OOH) intermediate generated upon reduction of the Fe^III(OOH) starting complex. One plausible mechanistic scenario is that this disproportionation reaction follows an O−O heterolytic cleavage pathway via a Fe^IV-oxo species.     

Fluorescent Type II Materials from Naphthylmethyl Polyamine Precursors

Speciation studies in aqueous solution on the interaction of Cu²⁺ and Zn²⁺ with a series of polyaminic ligands N-naphthalen-1-ylmethyl-N′-{2-[(naphthalen-1-ylmethyl)-amino]-ethyl}-ethane-1,2-diamine (Ll), N-naphthalen-1-ylmethyl-N′-(2-{2-[(naphthalen-1-ylmethyl)-amino]-ethylamino}-ethyl)-ethane-1,2-diamine (L2) and N-naphthalen-1-ylmethyl-N′-[2-(2-{2-[(naphthalen-1-ylmethyl)-amino]-ethylamino}-ethylamino)-ethyl]-ethane-1,2-diamine (L3) containing two naphthylmethyl groups at their termini and N ¹-(2-{2-[(naphthalen-1-ylmethyl)-amino]-ethylamino}-ethyl)-ethane-1,2-diamine (L4) containing just one naphthylmethyl group have been carried out at 298.1 K in 0.15 mol dm^?3 NaCl. In the case of the tetraamines L2 and L4, their coordination capabilities towards Cd²⁺, Ni²⁺, Co²⁺ and Pb²⁺ have also been considered. The stability constants follow the general Irving-Williams sequence. The steady-state fluorescence emission studies on the interaction with metal ions show that while Cu²⁺ produces a chelation enhancement of the quenching (CHEQ), the interaction with Zn²⁺ leads to a chelation enhancement of the fluorescence (CHEF). Finally, ligands L1, L2 and L3 have been successfully covalently attached to silica surfaces and some preliminary results of their emissive properties are given.     

Coordination compounds of cobalt,nickel, copper,and zinc with N 1,N 2-bis(pyridin-2-ylmethylidene)benzene-1,2-diamine and its derivatives

o-Phenylenediamine reacts with 2-formyl-, 2-acetyl-, or 2-benzoylpyridine in ethanol in the presence of cobalt, nickel, copper, or zinc chlorides to form monomeric complexes ML^1–3Cl₂·nH₂O {M = Co, Ni, Cu, Zn; L¹ = N ¹,N ²-bis(pyridin-2-ymethylidene)benzene-1,2-diamine, L² = N ¹,N ²-bis(pyridin-2-ylethylidene) benzene-1,2-diamine, L³ = N ¹,N ²-bis[phenyl(pyridin-2-yl)methylidene]benzene-1,2-diamine; n = 0–3}. The condensation products (L¹–L³) act in the complexes as tetradentate N,N,N,N-ligands. Thermolysis of the complexes occurs in two stages: dehydration (70–95°C) and complete degradation (320–450°C). At concentrations of 10^?5–10^?7 M, the complexes inhibit in vitro growth and proliferation of HL-60 human promyelocytic leukemia cells.     

Iron-Catalyzed Highly Enantioselective cis-Dihydroxylation of Trisubstituted Alkenes with Aqueous H2O2

Reliable methods for enantioselective cis-dihydroxylation of trisubstituted alkenes are scarce. The iron(II) complex cis-α-[Fe^II(2-Me₂-BQPN)(OTf)₂], which bears a tetradentate N₄ ligand (Me₂-BQPN=(R,R)-N,N′-dimethyl-N,N′-bis(2-methylquinolin-8-yl)-1,2-diphenylethane-1,2-diamine), was prepared and characterized. With this complex as the catalyst, a broad range of trisubstituted electron-deficient alkenes were efficiently oxidized to chiral cis-diols in yields of up to 98 % and up to 99.9 % ee when using hydrogen peroxide (H₂O₂) as oxidant under mild conditions. Experimental studies (including ¹⁸O-labeling, ESI-MS, NMR, EPR, and UV/Vis analyses) and DFT calculations were performed to gain mechanistic insight, which suggested possible involvement of a chiral cis-Fe^V(O)₂ reaction intermediate as an active oxidant. This cis-[Fe^II(chiral N₄ ligand)]²⁺/H₂O₂ method could be a viable green alternative/complement to the existing OsO₄-based methods for asymmetric alkene dihydroxylation reactions.     

Complexation studies of Mn2+, Zn2+ and Cd2+ ions with a series of tetradentate (N4) Schiff base ligands containing pyridine moiety in acetonitrile and nitromethane solutions by a competitive NMR technique using 7Li nucleus as a probe

Lithium-7 NMR spectroscopy was used to investigate the stoichiometry and stability of a Li⁺ complex with N¹,N²-bis(pyridin-2-ylmethylene)ethane-1,2-diamine (L¹), N¹,N³-bis(pyridin-2-ylmethylene)propane-1,3-diamine (L²) and N¹,N⁴-bis(pyridin-2-ylmethylene) butane-1,4-diamine (L³) in acetonitrile (AN) and nitromethane (NM) solutions. A competitive ⁷Li NMR method was also employed to probe the complexation of Mn²⁺, Cd²⁺ and Zn²⁺ ions with L¹, L² and L³ in the same solvents. The formation constants of the resulting complexes were evaluated from computer fitting of the mole ratio data to an equation that relates the observed chemical shifts to the formation constant. In both solvents, the stability of the resulting 1:1 complexes were found to vary in the order Zn²⁺>Cd²⁺>Mn²⁺>Li⁺. In addition, the stability of M–L complexes of M²⁺ with the Schiff base ligands found to vary in the order M²⁺–L¹ > M²⁺–L² > M²⁺–L³.     

Complexation of N4-Tetradentate Ligands with Nd(III) and Am(III)

To improve understanding of aza-complexants in trivalent actinide?Clanthanide separations, a series of tetradentate N-donor ligands have been synthesized and their complexation of americium(III) and neodymium(III) investigated by UV?Cvisible spectrophotometry in methanolic solutions. The six pyridine/alkyl amine/imine ligands are N,N??-bis(2-methylpyridyl)-1,2-diaminoethane, N,N??-bis(2-methylpyridyl)-1,3-diaminopropane, trans-N,N-bis(2-pyridylmethyl)-1,2-diaminocyclohexane (BPMDAC), N,N??-bis(2-pyridylmethyl)piperazine, N,N??-bis-[pyridin-2-ylmethylene]ethane-1,2-diamine, and trans-N,N-bis-([pyridin-2-ylmethylene]-cyclohexane-1,2-diamine. Each ligand has two pyridine groups and two aliphatic amine/imine N-donor atoms arranged with different degrees of preorganization and structural backbone rigidity. Conditional stability constants for the complexes of Am(III) and Nd(III) by these ligands establish the selectivity patterns. The overall selectivity of Am(III) over Nd(III) is similar to that reported for the terdentate bis(dialkyltriazinyl)pyridine molecules. The cyclohexane amine derivative (BPMDAC) is the strongest complexant and shows the highest selectivity for Am(III) over Nd(III) while the imines appear to prefer a bridging arrangement between two cations. These results suggest that this series of ligands could be employed to develop an enhanced actinide(III)?Clanthanide(III) separation system.     

Cation Coordination of Bisamidopyridine-derived Receptors as Investigated in the Solid-state and in Solution

A bisamidopyridine-type receptor, N,N′-bis(6-methyl-2-pyridyl)pyridine-2,6-dicarboxamide (1), and its Co^III complex were prepared and their X-ray structures were compared to those of N,N′-diphenylpyridine-2,6-dicarboxamide (2) and Co^III(2)². Introduction of the two additional coordinative groups resulted in second-order interactions between the central ion and the nitrogen atoms of the terminal pyridine moieties in the crystalline state. Solution studies in acetonitrile revealed the importance of these interactions for the ligand's metal ion recognition ability. Whereas 2 only binds to Pb^II and Cu^II, 1 yields complexes with a majority of the heavy and transition metal ions studied, Co^II, Ni^II, Cu^II, Zn^II, Fe^III, Fe^II, Hg^II, and Pb^II, respectively. The cation binding properties in solution were investigated by absorption spectroscopy and in the case of 1–M^II/III, the formation of two spectroscopically distinguishable types of complexes was found. Protonation experiments and theoretical considerations helped to gain further insight into possible modes of coordination in solution.     

Synthesis and Characterization of Two vic-Dioximes Containing the 1,3-Dioxolane Ring and 1,4-Diaminobutane and Their Cobalt(II), Nickel(II), Copper(II) and Zinc(II) Metal Complexes

Two new vic-dioxime ligands, (E,E)-N-{4-[(1,4-dioxaspiro[4.4]non-2-ylmethyl)amino]butyl}-N-hydroxy-2-(hydroxyimino)ethanimidamide (L¹H₂) and (E,E)-N-{4-[(1,4-dioxaspiro[4.5]dec-2-ylmethyl)amino]butyl}-N-hydroxy-2-(hydroxyimino)ethanimidamide (L²H₂) containing two different heteroatoms (N,O) have been prepared from anti-chloroglyoxime, N-(1,4-dioxaspiro[4.4]non-2-ylmethyl)butane-1,4-diamine (3) and N-(1,4-dioxaspiro[4.5]dec-2-ylmethyl)butane-1,4-diamine (4). Co^II, Ni^II and Cu^II complexes of the ligands have a metal:ligand ratio of 1:2 and the ligands coordinate through the two N atoms, as do most of the vic-dioximes. However, Zn^II complexes of the ligands have a metal:ligand ratio of 1:1 and the ligands are coordinated only by the N, O atoms of the vic-dioximes. In the Co^II complexes two water molecules, and in the Zn^II complexes a chloride ion and a water molecule, are also coordinated to the metal ion. The structures of the compounds were determined by a combination of elemental analysis, magnetic moments, molar conductances, thermogravimetric analysis (t.g.a.) and spectroscopic (u.v.–vis., i.r., ¹H- and ¹³C-n.m.r.) data.     

Synthesis,crystal structures,and catalytic properties of phenoxo-bridged dinuclear manganese(III) complexes with bis-Schiff bases

Two structurally similar centrosymmetric phenoxo-bridged dinuclear manganese(III) complexes, [Mn₂(L¹)₂(N₃)₂] (1) and [Mn₂(L²)₂(NCS)₂] (2), were prepared from the tetradentate bis-Schiff base ligands, N,N’-bis(salicylidene)propane-1,2-diamine (H₂L¹) and N,N’-bis(salicylidene)ethane-1,2-diamine (H₂L²), respectively, in the presence of pseudohalides. The complexes have been characterized by FTIR, elemental analyses, and molar conductivity. Structures of the complexes have been confirmed by single-crystal X-ray determination. The bis-Schiff base ligands coordinate with Mn through their phenolate oxygen and imino nitrogen. Each Mn is an octahedral. The complexes showed that they exhibit high activity in catalytic olefin oxidation.     

Allgemeiner Zugang zu Polyaminen mit Ethan-1,2-diamin-Einheiten: Synthese von nicht natürlich vorkommenden homologen und isomeren N1,4-Di(4-cumaroyl)sperminen

█tl="American"█The synthesis of the three N,N′-di(4-coumaroyl)tetramines, i.e., of (E,E)-N-{3-[(2-aminoethyl)amino]propyl}-3,3′-bis(4-hydroxyphenyl)-N,N′-(ethane-1,2-diyl)bis[prop-2-enamide] ( 1a ), (E,E)-N-{4-[(2-aminoethyl)amino]butyl}-3,3′-bis(4-hydroxyphenyl)-N,N′-(ethane-1,2-diyl)bis[prop-2-enamide] ( 1b ), and (E,E)-N-{6-[(2-aminoethyl)amino]hexyl}-3,3′-bis(4-hydroxyphenyl)-N,N′-(ethane-1,2-diyl)bis[prop-2-enamide] ( 1c ), is described. It proceeds through stepwise construction of the symmetric polyamine backbone including protection and deprotection steps of the amino functions. Their behavior on TLC in comparison with that of 1,4-di(4-coumaroyl)spermine (=(E,E)-N-{4-[(3-aminopropyl)amino]butyl}-3,3′-bis(4-hydroxyphenyl)-N,N′-(propane-1,3-diyl)bis[prop-2-enamide]; 2 ) is discussed.