New pyridine carboxamide ligands and their complexation to copper(II). X-Ray crystal structures of mono-, di, tri- and tetranuclear copper complexes

Seven new pyridine dicarboxamide ligands H2L(1-7) have been synthesised from condensation reactions involving pyridine-2,6-dicarboxylic acid (H2dipic), pyridine-2,6-dicarbonyl dichloride or 2,6-diaminopyridine with heterocyclic amine or carboxylic acid precursors. Crystallographic analyses of N,N'-bis(2-pyridyl)pyridine-2,6-dicarboxamide monohydrate (H2L8 x H2O), N,N'-bis[2-(2-pyridyl)methyl]pyridine-2,6-dicarboxamide and N,N'-bis[2-(2-pyridyl)ethyl]pyridine-2,6-dicarboxamide monohydrate revealed extensive intramolecular hydrogen bonding interactions. 2,6-Bis(pyrazine-2-carboxamido)pyridine (H2L6) and 2,6-bis(pyridine-2-carboxamido)pyridine (H2L7) reacted with copper(II) acetate monohydrate to give tricopper(II) complexes [Cu3(L)2(mu2-OAc)2]. X-Ray crystallography confirmed deprotonation of the amidic nitrogen atoms and that the (L6,7)2- ligands and acetate anions hold three copper(II) ions in approximately linear fashion. H2L8. Reacted with copper(II) tetrakis(pyridine) perchlorate to give [Cu(L8)(OH2)]2 x 2H2O, in which (L8)2- was tridentate through the nitrogen atoms of the central pyridine ring and the deprotonated carboxamide groups at one copper centre, with one of the terminal pyridyl rings coordinating to the other copper atom in the dimer. The corresponding reaction using H2L7 gave [Cu3(L7)2(py)2][ClO4]2, which transformed during an attempted recrystallisation from ethanol under aerobic conditions to a tetracopper(II) complex [Cu4(L7)2(L7-O)2].     

Suppression of the Jahn-Teller distortion in a six-coordinate copper(II) complex by doping it into a host lattice

The electronic structures of [Cu(terpy)(2)](2+) and [Cu(bpp)(2)](2+) (bpp = 2,6-di[pyrazol-1-yl]pyridine) are different, when doped into [M(bpp)(2)][BF(4)](2) (M(2+) = Fe(2+) or Zn(2+)). The [Cu(terpy)(2)](2+) dopant is a typical pseudo-Jahn-Teller elongated copper(II) center. However, the [Cu(bpp)(2)](2+) sites show EPR spectra consistent with a tetragonally compressed {d(z(2))}(1) configuration.     

Micellar effects upon the reactions of amino acids and their derivatives with 2,6-dinitro-4-trifluoromethylbenzene sulfonate ion

In the absence of surfactants 2,6-dinitro-4-trifluoromethylbenzene sulfonate ion (1) and 2,4-dinitrofluorobenzene (DNF) have similar reactivities towards glycinate and glycylglycinate ions, but -substituents hinder reactions with 1 but not with DNF, and hydroxide ion is relatively unreactive towards 1. Cationic micelles of cetyltrimethylammonium bromide (CTABr) strongly catalyze reactions of 1 with leucinate, phenylalaninate or -phenylglycinate, but there is little catalysis of reactions of the more hydrophilic nucleophiles glycinate, and glycylglycinate ions, glycineamide and hydroxide ion, whereas the CTABr catalysis of reactions of DNF is less sensitive to the nature of the nucleophile. Rate enhancements by CTABr of the reactions of 1 are: glycinate 6(28); glycylglycinate 6(26); leucinate 93(34); phenylalaninate 740(104); -phenylglycinate 247(65); glycineamide 1(5·5); OH⁻ 3(60). (The values for DNF are in parentheses). The concentrations of CTABr necessary for catalysis of reactions of 1 are much less than for reactions of DNF. These observations suggest that 1 interacts very strongly with CTABr micelles. Added salt decreases the CTABr catalysis and anionic micelles of sodium lauryl sulfate do not affect reactions of 1 with glycinate or glycylglycinate.     

Tridentate complexes of 2,6-bis(4-substituted-1,2,3-triazol-1-ylmethyl)pyridine and its organic azide precursors: an application of the copper(II) acetate-accelerated azide-alkyne cycloaddition

Rapid coupling reactions between 2,6-bis(azidomethyl)pyridine and terminal alkynes in the presence of 5 mol% Cu(OAc)(2)·H(2)O without the addition of a reducing agent afford tridentate ligands for first-row transition-metal ions. The chelation between Cu(II) and alkylated nitrogen atoms of the azido groups of 2,6-bis(azidomethyl)pyridine, as observed in the solid state, is credited for the acceleration of the azide-alkyne cycloaddition reactions.     

Pyridine-substituted oligopeptides as scaffolds for the assembly of multimetallic complexes: variation of chain length

This paper presents the synthesis and characterization of pyridine-substituted artificial oligopeptides with an aminoethylglycine backbone of varying length, which are designed to act as scaffolds for the self-assembly of multimetallic structures. The identities and purities of the oligopeptides are confirmed with mass spectrometry, (1)H NMR, HPLC, and pH titrations. The acid dissociation constants for the oligopeptides were determined and were found to decrease with increasing pyridine units. Titrations of the oligopeptides with Cu(II) and Pt(II) complexes containing the tridentate ligands 2,2':6',2'-terpyridine and pyridine 2,6-dicarboxylic acid were monitored using UV-visible absorption spectroscopy and showed stoichiometric binding based on the number of pyridines on the peptide strand. Metal titrations performed using an analogous oligopeptide with methyl substituents (in place of the pyridine ligands) showed very weak or no binding. In the case of the oligopeptides containing bound Pt(terpyridine)(2+) complexes, cyclic voltammetry reveals two sequential one-electron reductions at formal potentials that do not vary as a function of oligopeptide length. The measured diffusion coefficients were measured with chronoamperometry and were found to decrease with increasing oliopeptide length.     

T-shaped cationic CuI complexes with hemilabile PNP-type ligands

The versatile coordination behavior of the PNP ligands 1A (2,6-bis[(di-tert-butylphosphino)methyl]pyridine) and 1B (2,6-bis[(diphenylphosphino)methyl]pyridine) to CuI is described, whereby a hemilabile interaction of the pyridine N-donor atom to the copper center resulted in a rare T-shaped complex with 1A, while with 1B also a tetracoordinated species could be isolated. Theoretical calculations support the weak interaction of the pyridine N donor in 1A with the Cu center.     

Bis- and tris-(methylphosphonic) acid derivatives of a 14-membered tetraazamacrocycle containing pyridine: synthesis, protonation and complexation studies

Two N-methylphosphonic acid derivatives of a 14-membered tetraazamacrocycle containing pyridine have been synthesized, H(4)L(1) and H(6)L(2). The protonation constants of these compounds and the stability constants of complexes of both ligands with Ni(2+), Cu(2+) and Zn(2+) were determined by potentiometric methods at 298 K and ionic strength 0.10 mol dm(-3) in NMe(4)NO(3). The high overall basicity of both compounds is ascribed to the presence of the phosphonate arms. (1)H and (31)P NMR spectroscopic titrations were performed to elucidate the sequence of protonation, which were complemented by conformational analysis studies. The complexes of these ligands have stability constants of the order of or higher than those formed with ligands having the same macrocyclic backbone but acetate arms. At pH = 7 the highest pM values were found for solutions containing the compound with three acetate groups, followed immediately by those of H(6)L(2), however, as expected, the increasing pH favours the complexes of ligands containing phosphonate groups. The single-crystal structure of Na(2)[Cu(HL(1))]NO(3)x8H(2)O has shown that the coordination geometry around the copper atom is a distorted square pyramid. Three nitrogen atoms of the macrocyclic backbone and one oxygen atom from one methylphosphonate arm define the basal plane, and the apical coordination is accomplished via the nitrogen atom trans to the pyridine ring of the macrocycle. To achieve this geometric arrangement, the macrocycle adopts a folded conformation. This structure seems consistent with Uv-vis-NIR spectroscopy for the Ni(2+) and the Cu(2+) complexes and with the EPR for the latter.     

Models for Copper-Dioxygen Complexes: The chemistry of copper(II) with some planar tridentate nitrogen ligands

The solution chemistry of Cu(II) with a series of five planar tridentate nitrogen ligands, 2,6-bis(benzimidazol-2-yl)pyridine (bzimpy, 1 ), 2,6-bis(l-methylbenzimidazol-2-yl)pyridine (mbzimpy, 2 ) 2,6-bis(benzothiazol-2-yl) pyridine (bzthpy, 3 ), 2,6-bis(benzoxazol-2-yl)pyridine (bzoxpy, 4 ), and 2,2′, 6′, 2″-terpyridyl (terpy, 5 ) is reported. Electronic and EPR spectra are consistent with the complexes [CuL]²⁺ having essentially tetragonal structure in solution, with the fourth coordination site in the plane of the ligand occupied by solvent. bzthpy and bzoxpy show smaller ligand-field splittings than bzimpy, mbzimpy, and terpy, and are easily decomplexed from the copper. Substitution of the coordinated solvent molecule in the plane of the ligand is observed with Cl^? and OH^? (provided that the ligand has no acidic protons) for all ligands except terpy. The reaction between [Cu(mbzimpy)]²⁺ and imidazole has been studied by potentiometric titration in MeCN/H₂O 1:1 and shows strong binding of the imidazole in the plane (log K = 4.5 at 25°), and also the formation of an imidazolate-bridged dinuclear species.     

Single and double pH-driven Cu2+ translocation with molecular rearrangement in alkyne-functionalized polyamino polyamido ligands

A new series of ligands, containing one (L1H(2)-L4H(2)) or two (L5H(4)-L6H(4)) 1,4,8,11-tetraaza-5,7-dione units and functionalized with a propargyl group on the C atom between the C=O moieties, has been synthesized. Protonation constants for the ligands and formation constants of their Cu(2+) complexes have been determined in water, and the coordination geometry of the complexes existing at various pH values has been investigated by coupled pH-metric and spectrophotometric titrations. Ligands capable of simple uptake of Cu(2+) with the formation of neutral, square-planar complexes containing the -2-charged diamino-diimido donor sets and ligands containing further coordinating groups (quinoline or pyridine) capable of single and double cation translocation have been investigated. The role of the substituents on the amino groups and the structural role played by the propargyl group have been examined as regards Cu(2+) complexation and translocation. In the double-translocating ligand L6H(4), when the two Cu(2+) ions move inside the diamino-diamido donor set, the slim propargyl group allows an unprecedented folding of the whole ligand with apical coordination of one pyridine to form a five-coordinate, square-pyramidal Cu(2+) ion. The crystal and molecular structures of this unusual [L6Cu(2)] complex have been determined by X-ray diffraction. Finally, oxidation of Cu(2+) to Cu(3+) has been studied by cyclic voltammetry in water, which revealed that the redox reaction occurs only when the copper cation is within the diamino-diimido compartment. Moreover, both functionalization of the primary amines with bulky substituents and apical coordination of Cu(2+) make access to the 3+ oxidation state more difficult and disrupt the reversibility of the electrochemical process.     

A spectrochemical walk: single-site perturbation within a series of six-coordinate ferrous complexes

A series of ferrous complexes with the pentadentate ligand 2,6-(bis-(bis-2-pyridyl)methoxymethane)pyridine (PY5) was prepared and examined. PY5 binds ferrous iron in a square-pyramidal geometry, leaving a single coordination site accessible for complexation of a wide range of monodentate exogenous ligands: [Fe(II)(PY5)(X)](n+), X = MeOH, H(2)O, MeCN, pyridine, Cl-, OBz-, N(3)-, MeO-, PhO-, and CN-. The spin-states of these ferrous complexes are extremely sensitive to the nature of the single exogenous ligand; the spectroscopic and structural properties correlate with their high-spin (hs) or low-spin (ls) electronic ground state. Systematic metrical trends within six crystallographic structures clearly indicate a preferred conformational binding mode of the PY5 ligand. The relative binding affinities of the exogenous ligands in MeOH indicate that exogenous ligand charge is the primary determinant of the binding affinity; the [Fe(II)(PY5)](2+) unit preferentially binds anionic ligands over neutral ligands. At parity of charge, strong-field ligands are preferentially bound over weak-field ligands. In MeOH, the pK(a) of the exogenously ligated MeOH in [Fe(PY5)(MeOH)](2+) (9.1) limits the scope of exogenous ligands, as strongly basic ligands preferentially deprotonate [Fe(PY5)(MeOH)](2+) to yield [Fe(PY5)(OMe)](1+) rather than ligate to the ferrous center. Exogenous ligation by a strongly basic ligand, however, can be achieved in polar aprotic solvents.     

Complexes of 2,6-bis[N-(2'-pyridylmethyl)carbamyl]pyridine: formation of mononuclear complexes, and self-assembly of double helical dinuclear and tetranuclear copper(II) and trinuclear nickel(II) complexes

The potentially pentadentate ligand 2,6-bis[N-(2'-pyridylmethyl)carbamyl]pyridine (H2L1), readily prepared from reaction of a diester of pyridine-2,6-dicarboxylic acid (H2dipic) and 2-aminomethylpyridine (ampy), shows limited tendency to form 1:1 M:L complexes with labile metal ions, although [CuL1] and [NiL1] were observed as minor species, the latter characterized by a crystal structure analysis. A mononuclear complex formed with inert Co(III) was characterized by a crystal structure as the neutral 1:2 complex [Co(L1)(HL1)] with two ligands acting as tridentate ligands, one coordinated by the central pyridine and its two flanking deprotonated amido groups, and the other by the central pyridine, one amido and one terminal pyridine group, with the remaining poorly coordinating protonated amide remaining unbound along with other terminal pyridine groups. Fe(III) is known to form a symmetrical 1:2 complex, but that complex is anionic due to binding of all four deprotonated amido groups; the unsymmetrical neutral Co(III) complex converts into a symmetrical anionic species only on heating for hours in aqueous base in the presence of activated carbon. The most remarkable tendency of H2L1, however, is towards the formation of robust double helical complexes: a dinuclear Cu(II) complex [Cu2L1(2)] forms, as well as a trinuclear Ni(II) complex [Ni(3)(L1)2(OAc)2(MeOH)2]. Moreover, in the presence of added H2dipic, the tetranuclear complex [Cu4(L1)2(dipic)2(OH2)2] is obtained. All helical complexes have been characterized by X-ray crystal structure analyses, and all crystals feature a racemic mixture of left- and right-handed double helices stabilized by inter-ligand pi-stacking (inter-ring distances of 3.2-3.8 A) of ligands which each span several metal ions. Using the chelating ligand pentane-2,4-dione (acac), each of the two pairs of adjacent monodentate ligands in [Ni3(L1)2(OAc)2(OH2)2] have been shown to be available for substitution without destroying the helical structure, to form [Ni3(L1)2(acac)2], also characterized by a crystal structure.     

Micropatterning of metallopolymers: syntheses of back-to-back coupled octylated 2,6-bis(pyrazolyl)pyridine ligands and their solution-processable coordination polymers

This paper presents a 10-step synthetic route for the preparation of a series of new back-to-back coupled 2,6-bis(pyrazol-1-yl)pyridine (bpp) ligands (L0-L3) decorated with tetraoctyl chains. Ligand L1 self-assembles with Zn(2+) ion to form a highly soluble metallo-supramolecular polymer 1 with M(n) ～ 9600 g/mol. To demonstrate the processability of polymer 1, by following a "top-down" approach periodic one-dimensional fluorescent microstripes were fabricated on a silica substrate.     

Comparative study of NS(2)(S-aryl) pyridine-based dithia-containing ligands with different substituent groups. Reactivity toward Cu(II) and Ru(II)

Ligands LX of the type NS(2) with S-aryl substituents which incorporate the unit 2,6-bis(thiomethyl)pyridine modified with functional groups bonded to the aromatic moieties, either on the phenyl or on the pyridine, are produced. Electron-withdrawing groups, 3-chloro and 4-nitro, that reduce the pyridine basicity have been introduced. Methoxy or methoxycarbonyl substituents have been incorporated on the thiophenyl moieties. The comparative results from the reaction of these ligands with Cu(ClO(4))(2).6H(2)O and [RuCl(2)(PPh(3))(3)] have revealed that their coordination capacity has not been greatly modified as a result of the introduced groups. Complexes of general formulas [Cu(LX)][ClO(4)](2), except for L5, and [RuCl(2)(LX)(PPh(3))], have been obtained, respectively. The electronic characteristics of these complexes have been studied by cyclic voltammetry experiments. The structures of 2,6-bis[(2'-methoxycarbonyl)phenylthio-methyl]-4-nitropyridine (L5) and [RuCl(2)(L5)(PPh(3))].2CCl(4) have been characterized by single-crystal X-ray diffraction methods.     

A series of trinuclear Cu(II)Ln(III)Cu(II) complexes derived from 2,6-Di(acetoacetyl)pyridine: synthesis, structure, and magnetism

A series of trinuclear Cu(II)Ln(III)Cu(II) complexes with the bridging ligand 2,6-di(acetoacetyl)pyridine have been prepared by one-pot reaction with Cu(NO(3))(2).3H(2)O and Ln(NO(3))(3).nH(2)O in methanol. X-ray crystallographic studies for all the complexes indicate that two L(2)(-) ligands selectively sandwich two Cu(II) ions with the 1,3-diketonate entities and one Ln(III) ion with the 2,6-acetylpyridine entity to form a trinuclear CuLnCu core bridged by the enolate oxygen atoms. Cryomagnetic properties of the complexes are studied with respect to the electronic structure of the Ln ion.     

Interactions of pyridinecarboxylic acid chelators with brain metal ions: Cu(II), Zn(II), and Al(III)

Abstract  

The interactions of Cu(II), Zn(II), and Al(III) with 1,6-dimethyl-4-hydroxy-3-pyridinecarboxylic acid (DQ716) and 2,6-dimethyl-3-hydroxy-4-pyridinecarboxylic acid (DT726), possible chelating agents in Alzheimer’s disease, were investigated in aqueous solution. The proton dissociation constants of the ligands, the stability constants, and the coordination modes of the metal complexes formed were determined by pH-potentiometric, UV–vis spectrophotometric, and ¹H NMR methods. The nitrogen of the pyridine ring changes the proton affinity of the carboxylate and phenolate moieties and these pyridine derivatives form stronger complexes with Cu(II), Zn(II), and Al(III) than salicylic acid. Interactions of the ligands with human serum albumin as their potential transporter in blood were investigated at physiological pH through ultrafiltration by UV–vis and fluorescence spectroscopy.     

Asymmetric catalysis,part 91: Enantioselective monophenylation ofcis-1,2-cyclopentanediol with triphenylbismuth diacetate and chiral copper(II) complexes as catalysts

Summary The monophenylation ofcis-1,2-cyclopentanediol with triphenylbismuth diacetate in the presence of chiral Cu(II) complexes as catalysts gavecis-2-hydroxy-1-phenoxy-cyclopentane with enantiomeric excesses up to 38%. The optically active ligands used were triamine derivatives of 2,6-bis(aminomethyl)pyridine and diamine derivatives of 2-(aminomethyl)pyridine. Selectivity in the monophenylation occurred only in the presence of the latter as auxiliary ligands.

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Asymmetrische Katalysen, 91. Mitt.: Enantioselektive Monophenylierung voncis-1,2-Cyclopentandiol mit Triphenylwismutdiacetat und chiralen Kupfer(II)-Komplexen als Katalysatoren

Zusammenfassung Die Monophenylierung voncis-1,2-Cyclopentandiol mit Triphenylwismutdiacetat in Gegenwart chiraler Cu(II)-Komplexe als Katalysatoren ergabcis-2-Hydroxy-1-phenoxy-cyclopentan mit Enantiomerenüberschüssen von bis zu 38%. Die eingesetzten optisch aktiven Liganden waren Triamin-Derivate von 2,6-bis(Aminomethyl)pyridin und Diamin-Derivate von 2-(Aminomethyl)pyridin. Selektivität bei der Monophenylierung war nur in Gegenwart letzterer als Auxiliar-Liganden zu beobachten.

     

Asymmetric cyclopropanation catalyzed by C2-symmetric bis-(ephedrine)-Cu(II) complexes

The asymmetric cyclopropanation of styrene with alkyl diazoacetate was performed with a series of Cu(II) complexes of novel chiral ligands, which were derived from substitution of 1,3-dibromopropane, 1,2-dibromoethane, α,α′-dibromo-m-xylene and 2,6–bis(bromomethyl)pyridine with 1R, 2S-(−)-ephedrine. These prepared catalysts shown to be highly active in the enantioselective cyclopropanation with ee higher than 89% under the optimal conditions.     

A novel 2,6-dicarbonylpyridine-based fluorescent chemosensor for Co2+ with high selectivity and sensitivity

A novel fluorescence chemosensor based on 2,6-dicarbonylpyridine was designed and synthesized and its photophysical properties were characterized. Upon coordination of Co(2+) by the central 2,6-dicarbonylpyridinyl functional group, the chemosensor 2,6-bis(4-diphenylamino-styrylcarbonyl)pyridine (PhPy) showed nearly complete fluorescence quenching, while no fluorescence response was seen towards other competing cations. The experimental results show the chemosensor is highly selective and sensitive towards Co(2+) in the presence of competing ions, even in the ppb range. Job plot analysis was carried out and the results suggested that the binding of PhPy and Co(2+) was probably a 2?:?1 stoichiometry.     

Synthesis, structure and heterogeneous catalytic activities of Cu-containing polymeric compounds: anion effect and comparison of homogeneous vs. heterogeneous catalytic activity

The structures of new polymeric compounds containing Cu(II) ions and btp (2,6-bis(N'-1,2,4-triazolyl)pyridine) ligands have been determined. The btp ligands bridge Cu(II) ions to form double zigzag chains, [Cu(ClO4)2(btp)2] 3 with perchlorate anions, and form single zigzag chains, [Cu(btp)(H2O)4](SO4).2H2O 4 with sulfate anions. The polymeric compound 3 was found to effectively catalyze the epoxide ring-opening reaction with methanol, while polymeric compound 4 was almost inactive with epoxides under the same conditions. The polymeric compound 3 showed an efficient catalytic activity and regioselective reactivity in the ring opening of epoxides and allowed reuse without a significant loss of activity through three runs with epoxides.     

Binuclear and polynuclear transition metal complexes with macrocyclic ligands. 5. Novel complexes of asymmetric polydentate macrocyclic Schiff bases. Step-by-step synthesis

Reactions of 2,6-bis(3-aminopropylaminocarbonyl)pyridine (1) with 4-tert-butyl-2,6-diformylphenol and 2,5-diformylpyrrole in the presence of Ba(ClO₄)₂ in EtOH afford barium complexes with asymmetric macrocyclic Schiff bases as soft and hard ligands. The reaction of compound 1 with Cu(OCOCMe₃)₂ involves closure of a tetrahydropyrimidine ring to give a mononuclear complex, which was structurally characterized by X-ray diffraction analysis.