Copper(II)-catalyzed ether synthesis from aliphatic alcohols and potassium organotrifluoroborate salts

[reaction: see text] A protocol for the copper(II)-catalyzed etherification of aliphatic alcohols under mild and essentially neutral conditions is described. Air- and moisture-stable potassium alkenyl- and aryltrifluoroborate salts undergo cross-coupling with a variety of aliphatic primary and secondary alcohols and phenols, and are tolerant of a range of functional groups. The optimized conditions utilize catalytic copper(II) acetate with 4-(dimethylamino)pyridine as ligand in the presence of 4 A molecular sieves under an atmosphere of oxygen.     

Copper(II) Acetate–Mediated Cross-Coupling of Phenylboronic Acids with Aryloximes: Synthesis of O-Aryloximes

A novel method for the synthesis of O-aryloxime is described. It consisted of the coupling reaction between phenylboronic acids and aryloximes in the presence of catalytic quantities of copper(II) acetate. This reaction takes place in the presence of pyridine under a mild condition (DCE, Rt, 24–36 h) with moderate yield. It represents a good alternative to known methods for O-aryloxime synthesis.     

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].     

Kupfer(II)-Komplexe von N-Benzoyl-O-methyl-N′-phenyl-isoharnstoffen

Copper(II) Complexes of N-Benzoyl-O-methyl-N′-phenyl-isoureas By reaction of N-benzoyl-N′-(p-nitro/p-bromphenyl)thioureas with copper(II)acetate-monohydrate in methanole insoluble copper(I)precipitates have been obtained, from which filtrates bis[N-benzoyl-O-methyl-N′-(p-nitrophenyl)-isoureato]copper(II) 1 and bis[N-benzoyl-O-methyl-(p-bromphenyl)-isoureato]copper(II) 2 were isolated. The moleculare structure of 1 with planar trans coordination has been determined by single crystal X-ray diffraction methods. The N-benzoyl-O-methyl- N′-(o-nitrophenyl)-isourea 3 and N-benzoyl-O-methyl-N′-(p-bromphenyl)-isourea 4 have been prepared by reaction of the corresponding N-benzoyl-N′-phenyl-thioureas with mercury(II)acetate in methanolic solution. The molecular structure of 3 has been determined by single crystal X-ray diffraction methods. The NH-tautomeric form is stabilized by a bifurcated intramolecular hydrogen bond to an oxygen atom of the o-nitro group and the benzoyl oxygen atom. XPS, NMR and mass-spectrometric investigations also confirm the structures.     

Copper-bispidine coordination chemistry: syntheses,structures, solution properties,and oxygenation reactivity

Copper(I) and copper(II) complexes of two mononucleating and four dinucleating tetradentate ligands with a bispidine backbone (2,4-substituted (2-pyridyl or 4-methyl-2-pyridyl) 3,7-diazabicyclo[3.3.1]nonanone) have been prepared and analyzed structurally, spectroscopically, and electrochemically. The structures of the copper chromophores are square pyramidal, except for two copper(I) compounds which are four-coordinate with one noncoordinated pyridine. The other copper(I) structures have the two pyridine donors, the co-ligand (NCCH(3)), and one of the tertiary amines (N3) in-plane with the copper center and the other amine (N7) coordinated axially (Cu-N3 > Cu-N7, approximately 2.25 A vs 2.20 A). The copper(II) compounds with pyridine donors have a similar structure, but the axial amine has a weaker bond to the copper(II) center (Cu-N3 < Cu-N7, approximately 2.03 A vs 2.30 A). The structures with methylated pyridine donors are also square pyramidal with the co-ligands (Cl(-) or NCCH(3)) in-plane. With NCCH(3) the same structural type as for the other copper(II) complexes is observed, and with the bulkier Cl(-) the co-ligand is trans to N7, leading to a square pyramidal structure with the pyridine donors rotated out of the basal plane and only a small difference between axial and in-plane amines (2.15, 2.12 A). These structural differences, enforced by the rigid bispidine backbone, lead to large variations in spectroscopic and electrochemical properties and reactivities. Oxygenation of the copper(I) complexes with pyridine-substituted bispidine ligands leads to relatively stable mu-peroxo-dicopper(II) complexes; with a preorganization of the dicopper chromophores, by linking the two donor sets, these peroxo compounds are stable at room temperature for up to 1 h. The stabilization of the peroxo complexes is to a large extent attributed to the square pyramidal coordination geometry with the substrate bound in the basal plane, a structural motif enforced by the rigid bispidine backbone. The stabilities and structural properties are also seen to correlate with the spectroscopic (UV-vis and Raman) and electrochemical properties.     

Reactivity of mononuclear alkylperoxo copper(II) complex. O-O bond cleavage and C-H bond activation

A detailed reactivity study has been carried out for the first time on a new mononuclear alkylperoxo copper(II) complex, which is generated by the reaction of copper(II) complex supported by the bis(pyridylmethyl)amine tridentate ligand containing a phenyl group at the 6-position of the pyridine donor groups and cumene hydroperoxide (CmOOH) in CH3CN. The cumylperoxo copper(II) complex thus obtained has been found to undergo homolytic cleavage of the O-O bond and induce C-H bond activation of exogenous substrates, providing important insights into the catalytic mechanism of copper monooxygenases.     

Transition metal complexes of the tripodal ligand 4-(2′-pyridylmethyl)-4-azaheptane-1,7-diamine. Crystal structures of [CuLCl]ClO4 and [NiL(MeCN)2](ClO4)2

The tripodal ligand 4-(2′-pyridylmthyl)-4-azaheptane-1,7-diamine has been prepared by reaction of 2-aminemethyl pyridine with acrylonitrile, followed by the reduction of the nitrile groups. Copper(II), nickel(II), zinc(II), cobalt(III) and chromium(III) complexes of the ligand have been prepared and characterized and the crystal structures of the complexes [CuLCl]ClO₄ and [NiL(MeCN)₂](ClO₄)₂ determined. The copper complex is five coordinate with approximate square pyramidal stereochemistry with the apical position occupied by a primary amine donor. The nickel complex is octahedral with the pyridine nitrogen donor lying trans to an acetonitrile ligand.     

Optimization of a kinetic-catalytic method by use of a numerical model and the simplex method

Optimization of a kinetic-catalytic method based on a numerical model is demonstrated for the copper(II)-catalyzed decomposition of hydrogen peroxide in the presence of pyridine. The responses are calculated as initial rates of the catalytic reaction after calculating the equilibrium distributions of all species in the reaction mixture. Simulation of response surfaces as well as simplexes showed optimal concentrations for hydrogen peroxide, pyridine and pH. Experimental verifications of the simulated reaction conditions showed that the catalytic determination of copper down to 1.5 x 10^-7 M is possible.     

Monomeric and dimeric copper(II) complexes of a novel tripodal peptide ligand: structures stabilized via hydrogen bonding or ligand sharing

The novel tripodal ligand N-(bis(2-pyridyl)methyl)-2-pyridinecarboxamide (Py3AH) affords monomeric and dimeric copper(II) complexes with coordinated carboxamido nitrogens. Although many chloro-bridged dimeric copper(II) complexes are known, [Cu(Py3A)(Cl)] (1) remains monomeric and planar with a pendant pyridine and does not form either a chloro-bridged dimer or the ligand-shared dimeric complex [Cu(Py3A)(Cl)]2 (4) in solvents such as CH3CN. When 1 is dissolved in alcohols, square pyramidal alcohol adducts [Cu(Py3A)(Cl)(CH3OH)] (2) and [Cu(Py3A)(Cl)(C2H5OH)] (3) are readily formed. In 2 and 3, the ROH molecules are bound at axial site of copper(II) and the weak axial binding of the ROH molecule is strengthened by intramolecular hydrogen bonding between ROH and the pendant pyridine nitrogen. Two ligand-shared dimeric species [Cu(Py3A)(Cl)]2 (4) and [Cu(Py3A)]2(ClO4)2 (5) have also been synthesized in which the pendant pyridine of one [Cu(Py3A)] unit completes the coordination sphere of the other [Cu(Py3A)] neighbor. These ligand-shared dimers are obtained in aqueous solutions or in complete absence of chloride in the reaction mixtures.     

Tetraalkoxyaluminates of nickel(II), copper(II), and copper(I)

The syntheses and structural details of tetraisopropoxyaluminates and tetra-tert-butoxyaluminates of nickel(II), copper(I), and copper(II) are reported. Within the nickel series, either Ni[Al(OiPr)4]2.2HOiPr, with nickel(II) in a distorted octahedral oxygen environment, or Ni[Al(OiPr)4]2.py, with nickel(II) in a square-pyramidal O4N coordination sphere, or Ni[(iPrO)(tBuO)3Al]2, with Ni(II) in a quasi-tetrahedral oxygen coordination, has been obtained. Another isolated complex is Ni[(iPrO)3AlOAl(OiPr)3].3py (with nickel(II) being sixfold-coordinated), which may also be described as a "NiO" species trapped by two Al(OiPr)3 Lewis acid-base systems stabilized at nickel by three pyridine donors. Copper(I) compounds have been isolated in three forms: [(iPrO)4Al]Cu.2py, [(tBuO)4Al]Cu.2py, and Cu2[(tBuO)4Al]2. In all of these compounds, the aluminate moiety behaves as a bidentate unit, creating a tetrahedrally distorted N2O2 copper environment in the pyridine adducts. In the base-free copper(I) tert-butoxyaluminate, a dicopper dumbbell [Cu-Cu 2.687(1) A] is present with two oxygen contacts on each of the copper atoms. Copper(II) alkoxyaluminates have been characterized either as Cu[(tBuO)4Al]2, {Cu(iPrO)[(iPrO)4Al]}2, and Cu[(tBuO)3(iPrO)Al]2 (copper being tetracoordinated by oxygen) or as [(iPrO)4Al]2Cu.py (pentacoordinated copper similar to the nickel derivative). Finally, a copper(II) hydroxyaluminate has been isolated, displaying pentacoordinate copper (O4N coordination sphere) by dimerization, with the formula {[(tBuO)4Al]Cu(OH).py}2. The formation of all of these isolated products is not always straightforward because some of these compounds in solution are subject to decomposition or are involved in equilibria. Besides NMR [copper(I) compounds], UV absorptions and magnetic moments are used to characterize the compounds.     

Synthesis, DNA binding and cleavage activities of copper (II) thiocyanate complex with 4-(N,N-dimethylamino)pyridine and N,N-dimethylformamide

Two novel copper(II) thiocyanate complexes with 4-(N,N-dimethylamino) pyridine and N,N-dimethylformamide (1) and with 4-(N,N-dimethylamino) pyridine (2) have been synthesized and characterized. The crystal and molecular structures of complexes 1 and 2 were determined by single-crystal X-ray diffraction. Antioxidative activity tests in vitro showed that complex 1 has significant antioxidative activity against hydroxyl free radicals from the Fenton reaction and also oxygen free radicals, which is better than standard antioxidants like vitamin C and mannitol. The interaction of complex 1 with calf thymus DNA was investigated by spectroscopic, cyclic voltammetry, and viscosity measurements. Results suggest that complex 1 can bind to DNA via partial intercalation mode. Moreover, complex 1 has been found to cleavage of plasmid DNA pBR322.     

Crystal structure of nonadentate tricompartmental ligand derived from pyridine-2,6-dicarboxylic acid: Spectroscopic, electrochemical and thermal investigations of its transition metal(II) complexes

The coordinating behavior of a new dihydrazone ligand, 2,6-bis[(3-methoxysalicylidene)hydrazinocarbonyl]pyridine towards manganese(II), cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) has been described. The metal complexes were characterized by magnetic moments, conductivity measurements, spectral (IR, NMR, UV-Vis, FAB-Mass and EPR) and thermal studies. The ligand crystallizes in triclinic system, space group P-1, with α=98.491(10)°, β=110.820(10)° and γ=92.228(10)°. The cell dimensions are a=10.196(7)?, b=10.814(7)?, c=10.017(7)?, Z=2 and V=1117.4(12). IR spectral studies reveal the nonadentate behavior of the ligand. All the complexes are neutral in nature and possess six-coordinate geometry around each metal center. The X-band EPR spectra of copper(II) complex at both room temperature and liquid nitrogen temperature showed unresolved broad signals with g(iso)=2.106. Cyclic voltametric studies of copper(II) complex at different scan rates reveal that all the reaction occurring are irreversible.     

Bis(oxazoline) Lewis acid catalyzed aldol reactions of pyridine N-oxide aldehydes--synthesis of optically active 2-(1-hydroxyalkyl)pyridine derivatives: development, scope, and total synthesis of an indolizine alkaloid

A new, short, and simplified procedure for the synthesis of optically active pyridine derivatives from pro-chiral pyridine-N-oxides is presented. The catalytic and asymmetric Mukaiyama aldol reaction between ketene silyl acetals and 1-oxypyridine-2-carbaldehyde derivatives catalyzed by chiral copper(II)-bis(oxazoline) complexes gave optically active 2-(hydroxyalkyl)- and 2-(anti-1,2-dihydroxyalkyl)pyridine derivatives in good yields and diastereoselectivities, and in excellent enantioselectivities-up to 99 % enantiomeric excess. As a synthetic application of the developed method, a full account for the asymmetric total synthesis of a nonnatural indolizine alkaloid is provided.     

Anion and symmetry effects on the electron spin resonance spectra of copper complexes. Part III

ESR spectra of calcium copper acetate hexahydrate and tetra-(6-aminohexanoic acid) copper(II) diperchlorate have been recorded for solutions in methanol, ethanol, dimethylformamide and pyridine at 295 and 77 K. The coordination around the Cu(II) ion in both there complexes is of dodecahedral symmetry, comprising both an elongated and a compressed tetrahedron of oxygen atoms. The spin-Hamiltonian parameters of the complexes in ethanol, methanol and dimethylformamide, obtained after fitting the spectra to an axially-symmetric spin-Hamiltonian, indicate an effectively flattened tetrahedron alone. In contrast, the spectra recorded for solutions in pyridine indicate octahedral coordination caused by substitution of the oxygen atoms by pyridine.     

Flow injection fluorimetric determination of thiamine and copper based on the formation of thiochrome

The reaction, involving the oxidation of thiamine by copper(II) in basic solutions to fluorescent thiochrome, has been adapted to the determination of thiamine by flow-injection analysis. Linear calibration graphs are obtained between 0.30 and 6.02 mug/ml with a sampling rate of 50 samples/hr and a relative standard deviation of 0.53%. This reaction has also been adapted to the determination of copper(II) over the range 0.5-5.0 mug/ml. The applicability of both methods for determination of thiamine and copper is demonstrated by investigating the effect of potential interferences and by the analysis of real samples (pharmaceuticals for thiamine and ores and alloys for copper).     

Evidence of zinc superoxide formation in the gas phase: comparisons in behaviour between ligated Zn(I/II) and Cu(I/II) with regard to the attachment of O2 or H2O

Singly and doubly charged atomic ions of zinc and copper have been complexed with pyridine and held in an ion trap. Complexes involving Zn(II) and Cu(I) (3d(10)) display a strong tendency to bind with H(2)O, whilst the Zn(I) (3d(10)4s(1)) complexes exhibit a strong preference for the attachment of O(2). DFT calculations show that this latter result can be interpreted as internal oxidation leading to the formation of superoxide complexes, [Zn(II)O(2)(-)](pyridine)(n), in the gas phase. The calculations also show that the oxidation of Zn(I) to form Zn(II)O(2)(-) is promoted by a mixing of the occupied 4s and vacant 4p orbitals on the metal cation, and that this process is facilitated by the presence of the pyridine ligands.     

Analytical reactions of 5-amino-orotic acid

The potential of 5-amino-orotic acid (AOA) for spectrophotometric determination of metal ions is explored. Only the reactions with copper(II), cobalt(II) and osmium(VIII) are sensitive and suitable for this purpose. Ternary complexes of copper(II) formed with AOA and ammonia or pyridine can also be used for photometric determination of the metal and given better sensitivity and selectivity than the binary complex. Optimum conditions for determination of all the three metal ions have been established.     

Asymmetric Henry reaction catalyzed by a chiral Cu(II) complex: a facile enantioselective synthesis of (S)-2-nitro-1-arylethanols

A catalytic asymmetric Henry reaction has been developed using a novel chiral Cu(II) complex derived from (R)-2-(diphenylmethanol)-l-(2-pyridylmethyl)pyrrolidine and copper(II) acetate in ethanol under mild conditions. The corresponding chiral 2-nitro-1-arylethanol derivatives were obtained in high yields with moderate to good enantiomeric excess (up to 86% ee). The results indicate that the coordination of a metal atom to the nitrogen of the pyridine ring is essential in determining the stereochemistry of the process.     

Trigonal planar copper(I) complex: synthesis, structure, and spectra of a redox pair of novel copper(II/I) complexes of tridentate bis(benzimidazol-2'-yl) ligand framework as models for electron-transfer copper proteins

The copper(II) and copper(I) complexes of the chelating ligands 2,6-bis(benzimidazol-2'-ylthiomethyl)pyridine (bbtmp) and N,N-bis(benzimidazol-2'-ylthioethyl)methylamine (bbtma) have been isolated and characterized by electronic and EPR spectra. The molecular structures of a redox pair of Cu(II/I) complexes, viz., [Cu(bbtmp)(NO(3))]NO(3), 1, and [Cu(bbtmp)]NO(3), 2, and of [Cu(bbtmp)Cl], 3, have been determined by single-crystal X-ray crystallography. The cation of the green complex [Cu(bbtmp)(NO(3))]NO(3) possesses an almost perfectly square planar coordination geometry in which the corners are occupied by the pyridine and two benzimidazole nitrogen atoms of the bbtmp ligand and an oxygen atom of the nitrate ion. The light-yellow complex [Cu(bbtmp)]NO(3) contains copper(I) with trigonal planar coordination geometry constituted by the pyridine and two benzimidazole nitrogen atoms of the bbtmp ligand. In the yellow chloride complex [Cu(bbtmp)Cl] the asymmetric unit consists of two complex molecules that are crystallographically independent. The coordination geometry of copper(I) in these molecules, in contrast to the nitrate, is tetrahedral, with pyridine and two benzimidazole nitrogen atoms of bbtmp ligand and the chloride ion occupying the apexes. The above coordination structures are unusual in that the thioether sulfurs are not engaged in coordination and the presence of two seven-membered chelate rings facilitates strong coordination of the benzimidazole nitrogens and discourage any distortion in Cu(II) coordination geometry. The solid-state coordination geometries are retained even in solution, as revealed by electronic, EPR, and (1)H NMR spectra. The electrochemical behavior of the present and other similar CuN(3) complexes has been examined, and the thermodynamic aspects of the electrode process are correlated to the stereochemical reorganizations accompanying the redox changes. The influence of coordinated pyridine and amine nitrogen atoms on the spectral and electrochemical properties has been discussed.     

Binuclear copper(II) oxidation products from copper(I) complexes with tridentate ligands. Magnetostructural characterization

The bis-pyridine tridentate ligands (6-R-2-pyridylmethyl)-(2-pyridylmethyl) benzylamine (RDPMA, where R = CH(3), CF(3)), (6-R-2-pyridylmethyl)-(2-pyridylethyl) benzylamine (RPMPEA, where R = CH(3), CF(3)), and the bidentate ligand di-benzyl-(6-methyl-2-pyridylmethyl)amine (BiBzMePMA) have been synthesized and their copper(I) complexes oxidized in a methanol solution to afford self-assembled bis-micro-methoxo-binuclear copper(II) complexes (1, 2, 4, 6) or hydroxo- binuclear copper(II) complexes (3). Oxidation of the nonsubstituted DPMA (R = H) in dichloromethane gives a chloride-bridged complex (5). The crystal structures for [Cu(MeDPMA)(MeO)](2)(ClO(4))(2) (1), [Cu(RPMPEA)(MeO)](2)(ClO(4))(2) (for 2, R= Me, and for 4, R = CF(3)), [Cu(BiBzMePMA)(MeO)](2)(ClO(4))(2) (6), [Cu(FDPMA)(OH)](2)(ClO(4))(2) (3), and [Cu(DPMA)(Cl)](2)(ClO(4))(2) (5) have been determined, and their variable-temperature magnetic susceptibility has been measured in the temperature range of 10-300 K. The copper coordination geometries are best described as square pyramidal, except for 6, which is square planar, because of the lack of one pyridine ring in the bidentate ligand. In 1-4 and 6, the basal plane is formed by two pyridine N atoms and two O atoms from the bridging methoxo or hydroxo groups, whereas in 5, the bridging Cl atoms occupy axial-equatorial sites. Magnetic susceptibility measurements show that the Cu atoms are strongly coupled antiferromagnetically in the bis-methoxo complexes 1, 2, 4, and 6, with -2J > 600 cm(-)(1), whereas for the hydroxo complex 3, -2J = 195 cm(-)(1) and the chloride-bridged complex 5 shows a weak ferromagnetic coupling, with 2J = 21 cm(-)(1) (2J is an indicator of the magnetic interaction between the Cu centers).