Showing papers on "Pyridine published in 1999"
TL;DR: Crystallographic studies revealed how metal ion coordination and substrate recognition direct the formation of these supramolecular assemblies, and the addition of greater amounts of pyridine N-oxide changed the curvature of the assembling surface and resulted in theformation of extended tubules.
Abstract: Amphiphilic polyhedron-shaped p-sulfonatocalix[4]arene building blocks, which have been previously shown to assemble into bilayers in an antiparallel fashion, have been assembled in a parallel alignment into spherical and helical tubular structures by the addition of pyridine N-oxide and lanthanide ions Crystallographic studies revealed how metal ion coordination and substrate recognition direct the formation of these supramolecular assemblies The addition of greater amounts of pyridine N-oxide changed the curvature of the assembling surface and resulted in the formation of extended tubules
490 citations
TL;DR: A novel combination of Pd(OAc)(2)/pyridine/MS3A catalyzes the aerobic oxidation in toluene of a variety of primary and secondary alcohols into the corresponding aldehydes and ketones in high yields.
Abstract: A novel combination of Pd(OAc)2/pyridine/MS3A catalyzes the aerobic oxidation in toluene of a variety of primary and secondary alcohols into the corresponding aldehydes and ketones in high yields. Various substituents and protecting groups are compatible with this oxidation. The ca. 2:3 ratio of O2 uptake to product yield is observed, whereas in the absence of MS3A, the ratio is ca. 1:1, suggesting the in situ formation of H2O2 and its decomposition by MS3A into water and oxygen. A catalytic cycle including the formation of a Pd(II)-alcoholate followed by β-elimination of a Pd(II)H species and a carbonyl compound and then the formation of a Pd(II)OOH species is proposed.
409 citations
TL;DR: In this article, 2.6-Di(5-alkyl-1,2,4-triazol-3-yl)-pyridine and 2,6-di(5, 6-dialkyl)-1, 2, 4, 4 triazin-3 -yl) pyridine type compounds extract Am(III) 2-bromohexanoate and nitrate from acidic solutions (≤1 M HNO3) with an appreciable efficiency and selectivity.
Abstract: 2,6-Di(5-alkyl-1,2,4-triazol-3-yl)-pyridine and 2,6-di(5,6-dialkyl-1,2,4-triazin-3-yl)pyridine type compounds extract Am(III) 2-bromohexanoate and nitrate from acidic solutions (≤1 M HNO3) with an appreciable efficiency and selectivity, yielding Am(III)/Eu(III) separation factors of ≤150.
319 citations
TL;DR: A series of zinc phenoxides of the general formula (2,6-R2C6H3O)2Zn(base)2 [R = Ph, tBu, iPr, base = Et2O, THF, or propylene carbonate] have been synthesized and characterized by X-ray crystallography as discussed by the authors.
Abstract: A series of zinc phenoxides of the general formula (2,6-R2C6H3O)2Zn(base)2 [R = Ph, tBu, iPr, base = Et2O, THF, or propylene carbonate] and (2,4,6-Me3C6H2O)2Zn(pyridine)2 have been synthesized and characterized in the solid state by X-ray crystallography. All complexes crystallized as four-coordinate monomers with highly distorted tetrahedral geometry about the zinc center. The angles between the two sterically encumbering phenoxide ligands were found to be significantly more obtuse than the corresponding angles between the two smaller neutral base ligands, having average values of 140° and 95°, respectively. In a noninteracting solvent such as benzene or methylene chloride at ambient temperature, the ancillary base ligands are extensively dissociated from the zinc center, with the degree of dissociation being dependent on the base as well as the substituents on the phenolate ligands. That is, stronger ligand binding was found in zinc centers containing electron-donating tert-butyl substituents as opposed...
293 citations
TL;DR: In this paper, the thermal stability of MCM-41 aluminosilicates is studied using 27 Al MAS NMR spectroscopy, and the tetrahedral to octahedral aluminium ratio is found to increase with higher aluminium incorporation.
245 citations
TL;DR: The scope of the Diels−Alder reaction catalyzed by bis(oxazoline) copper complexes has been investigated in this article, where the total syntheses of ent-Δ1-tetrahydrocannabinol, ent-shikimic acid, and isopulo-upone, featuring the use of this chiral catalyst in more complex Diels-Alder processes, are described.
Abstract: The scope of the Diels−Alder reaction catalyzed by bis(oxazoline) copper complexes has been investigated. In particular, [Cu((S,S)-t-Bu-box)](SbF6)2 (1b) has been shown to catalyze the Diels−Alder reaction between 3-propenoyl-2-oxazolidinone (2) and a range of substituted dienes with high enantioselectivity. This cationic complex has also been employed in the catalysis of analogous intramolecular processes with good success. The total syntheses of ent-Δ1-tetrahydrocannabinol, ent-shikimic acid, and isopulo’upone, featuring the use of this chiral catalyst in more complex Diels−Alder processes, are described. Similarly, the cationic copper complex 9a, [Cu((S,S)-t-Bu-pybox)](SbF6)2, is effective in the Diels−Alder reactions of monodentate acrolein dienophiles while the closely related complex, 9d [Cu((S,S)-Bn-pybox)](SbF6)2, is the preferred Lewis acid catalyst for acrylate dienophiles in reactions with cyclopentadiene.
213 citations
TL;DR: In this article, the pyridine ring ortho positi... was methylated with a stoichiometric amount of methyl alumoxane (PMAO) in toluene.
Abstract: Reaction of {2,6-bis[2,6-(i-Pr)2PhNC(Me)]2(C5H3N)}VCl3·1.3(CH2Cl2) (1) with stoichiometric amount of methyl alumoxane (PMAO) in toluene resulted in the methylation of the pyridine ring ortho positi...
195 citations
TL;DR: The reaction between transition metal halides MX2 in an aqueous solution containing disodium terephthalate along with pyridine-based ligands gives rise to one-dimensional coordination polymers.
Abstract: The reaction between transition metal halides MX2 (where M = Co(II) and Ni(II)) in an aqueous solution containing disodium terephthalate along with pyridine-based ligands gives rise to one-dimensional coordination polymers. Both [M(terephthalate)(4-picoline)2(H2O)2]·2(4-picoline) (1) and [M(terephthalate)(pyridine)2(H2O)2]·2(pyridine)·2(H2O) (2) have been isolated. These frameworks exhibit hydrogen bond donors running along the backbone of each polymer, which gives rise to inclusion chemistry between the framework and pyridine guest molecules.
155 citations
TL;DR: In this article, a tridentate bis-amide ligand 2,6-bis[N-(phenyl)carbamoyl]pyridine (H2L), in its deprotonated form, nickel complexes in three consecutive oxidation states [Et4N]2[NiIIL2]·H2O (1), [Eit4N][NiIIIL2] ·H2
Abstract: Using a tridentate bis-amide ligand 2,6-bis[N-(phenyl)carbamoyl]pyridine (H2L), in its deprotonated form, nickel complexes in three consecutive oxidation states [Et4N]2[NiIIL2]·H2O (1), [Et4N][NiIIIL2]·H2O (2), and [NiIVL2]·0.75H2O (3) have been prepared, and 1 and 3 structurally characterized. These X-ray structures represent first crystallographically characterized NiN6 coordination sphere, with a common pyridine bis-amide ligand. Complex 1 crystallizes in the orthorhombic space group Pccn, a = 10.175(2) A, b = 20.834(3) A, c = 23.765(4) A, Z = 4, and 3 crystallizes in the monoclinic space group P21/a, a = 14.874(7) A, b = 13.300(4) A, c = 16.604(5) A, β = 99.678(3)°, Z = 4. Considerable distortion is observed with the average distances being Ni−Namide 2.131(8) A and Ni−Npy 1.994(7) A for 1 and Ni−Namide 1.946(8) A and Ni−Npy 1.846(8) A for 3. The observation of short axial M−Npy and long equatorial M−Namide bonds (tetragonally compressed octahedral geometry) is caused by the steric requirement of the l...
146 citations
TL;DR: In this paper, four kinds of new π-conjugated copolymers of electron-donating thiophene with highly electron-withdrawing pyrido[3,4-b]pyrazine derivatives have been prepared by using the Stille reaction and electrochemical oxidative polymerization in high yields.
Abstract: Four kinds of new π-conjugated copolymers of electron-donating thiophene with highly electron-withdrawing pyrido[3,4-b]pyrazine derivatives have been prepared by using the Stille reaction and electrochemical oxidative polymerization in high yields, and their optical and electrochemical properties have been compared with those of previously reported CT-type π-conjugated polymers. Chemically prepared polymers show an [η] value of about 0.3 dL g-1. The π−π* absorption bands (λmax = ca. 633 nm) of the copolymers are observed at a longer wavelength by about 30 nm than those of similar CT-type copolymers of thiophene with pyridine and quinoxaline. These UV−vis data are considered to reflect a stronger CT interaction between thiophene and pyrido[3,4-b]pyrazine, which has a higher electron-withdrawing ability than pyridine and quinoxaline. The copolymers are electrochemically active in both oxidation and reduction regions. In the reduction (n-doping) region, the copolymers show normal three couples of n-doping an...
138 citations
TL;DR: In this article, an extensive theoretical study of the iron(II)−bisimine pyridine based ethylene-polymerization catalysts was presented, based on density functional theory (DFT) for the generic model system 1a and a combined DFT and molecular mechanics approach for the real system 1A.
Abstract: We present an extensive theoretical study of the iron(II)−bisimine pyridine based ethylene-polymerization catalysts {[2,6-((R)NC(R‘))2−C5H3N]FeC3H7}+ (R = R‘ = H, 1a; R = 2,6-C6H4(i-Pr)2, R‘ = CH3, 1A) recently developed by the groups of Brookhart and Gibson. The study was based on density functional theory (DFT) for the “generic” model system 1a and a combined DFT and molecular mechanics approach for the “real” system 1A. It is shown that the rate-determining step for both termination and propagation in the “real” system is the capture of ethylene by 1A. The steric bulk introduced by R = 2,6-C6H4(i-Pr)2 was found to suppress ethylene capture for the termination step and increase the rate of insertion. Termination takes place on the singlet potential energy surface (PES). For propagation the singlet and triplet PES's are close in energy and spin-state change is possible. The quintet states are too high in energy to play any role in polymerization. The model system 1a was found to form an ethylene complex ...
TL;DR: The influence of a series of diamine ligands and α-amino acid ligands on the rate and enantioselectivity of the Ni2- and Cu2+-catalyzed Diels−Alder reaction between 3-phenyl-1-(2-pyridyl)-2-propen-1-ones and cyclopentadiene in water has been investigated.
Abstract: The influence of a series of diamine ligands and α-amino acid ligands on the rate and enantioselectivity of the Ni2+- and Cu2+-catalyzed Diels−Alder reaction between 3-phenyl-1-(2-pyridyl)-2-propen-1-ones and cyclopentadiene in water has been investigated. Equilibrium constants and enthalpies and entropies for binding of the dienophile to the catalyst−ligand complex as well as rate constants, activation enthalpies, and entropies for the subsequent reaction with the diene have been determined using UV−vis spectroscopy. Ligand-accelerated catalysis is observed for several aromatic α-amino acid ligands. This is likely to be a consequence of arene−arene interaction between the aromatic ring of the α-amino acid ligand and the pyridine ring of the dienophile and for which quantitative evidence is provided. The same interaction also induces up to 74% enantioselectivity in the Diels−Alder reaction. This is the first example of enantioselectivity in a Lewis-acid-catalyzed organic reaction in water. Most importantl...
TL;DR: In this article, a series of crystalline and amorphous alumino-silicates were investigated by means of temperature-programmed desorption with mass spectrometry detection (TPD-MS) and of Fourier transform infra-red (FTIR) analysis of adsorbed pyridine, in order to compare the surface concentration of acid sites potentially involved in a specific catalytic process.
TL;DR: The first terephthalato bis-tridentate bridging cadmium coordination polymer, [(TPT)(py)Cd] 1, with blue fluorescent emission, was synthesized by a hydrothermal reaction between Cd(ClO4)2· 6H2O, 1,4-dicyanobenzene and pyridine (py) as discussed by the authors.
Abstract: The first terephthalato (TPT) bis-tridentate bridging cadmium coordination polymer, [(TPT)(py)Cd] 1, with blue fluorescent emission, was synthesized by a hydrothermal reaction between Cd(ClO4)2· 6H2O, 1,4-dicyanobenzene and pyridine (py).
TL;DR: In this paper, the first examples of polymer supported aryl-heteroaryl CN crosscoupling reactions and dramatically decreased reaction times upon microwave irradiation were reported.
TL;DR: In this paper, a short synthetic approach toward a novel class of chiral nucleophilic catalysts, the dissymmetry of which stems from restricted rotation about an Ar−Ar bond, has been developed.
Abstract: A short synthetic approach toward a novel class of chiral nucleophilic catalysts, the dissymmetry of which stems from restricted rotation about an Ar−Ar bond, has been developed. The key steps of the synthesis include preparation of a nucleophilic 1-methyl-2-pyrrolino[3,2-c]pyridine core 16 by ortho-lithiation and creation of the biaryl axes via Suzuki cross-coupling reactions. Comparative HPLC studies of racemization for configurationally labile biaryls 31, 38, and 43 containing 1-methyl-2-pyrrolino[3,2-c]pyridine, 4-(dimethylamino)pyridine, and 4-(1-pyrrolidino)pyridine cores, respectively, have demonstrated that a pyrrolidino substituent ortho to the biaryl axis is optimal for slowing Ar−Ar rotation. Biaryls containing all three cores have been shown to retain DMAP-like catalytic activity in the acylation of a hindered alcohol. Biaryls 55 and 56, which are configurationally stable at ambient temperature, have also been prepared via modification of configurationally labile derivatives. Compounds 55 and ...
TL;DR: In this article, the crystal structure of an infinite inorganic chain consisting of MnII and an N-centered tripodal ligand N,N-(2-pyridylmethyl)[(1-methylimidazol-2-yl)-methyl] is presented.
Abstract: The crystal structure of an infinite inorganic chain consisting of MnII and an N-centered tripodal ligand N,N-(2-pyridylmethyl)[(1-methylimidazol-2-yl)-methyl]glycinate is presented. It exhibits a chiral helical structure with a pitch of two monomeric units (each monomeric unit containing one Mn atom). Each manganese is connected to its neighbor through a carboxylate bridge in a syn-anti geometry. Around each manganese center, two carboxylates bind in a cis geometry. This peculiar bridging geometry (syn-anticis) provides a broken-line chain, running in a zig-zag manner along the b axis of the P21 space group. The magnetic properties have been investigated. They show a pseudo-2D magnetic structure, with one major pathway along the chain and an inter-chain minor one. The intrachain coupling is a weak antiferromagnetic interaction (J/k = -0.25). This low value is entirely consistent with the geometry of the bridge. The interchain coupling is a weaker antiferromagnetic coupling (J'/k = -0.11) and could be mediated through π-π interactions between pyridine and imidazole from two adjacent helixes.
TL;DR: In this article, a 2-phosphorylation of 1-alkyl substituted imidazoles with P(III) halides in pyridine was shown to proceed at the 3-N atom of the heteroaryl ring and was followed by triethylamine-in-duced migration of the phosphorus group to the 2-C atom.
Abstract: Phosphorylation of 1-alkyl substituted imidazoles and benzimidazoles with P(III) halides in pyridine was shown to proceed at the 3-N atom of the heteroaryl ring and was followed by triethylamine-in- duced migration of the phosphorus group to the 2-C atom. Preparative methods were developed for the syn- thesis of a range of 2-phosphorylated derivatives of the indicated imidazoles. The latter were found to undergo alkylation either at P(III) or 3-N centers, depending on the alkylating agent. q 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 585-597, 1999
TL;DR: The reactions of 1 and 4 with dihydrogen provide a model for possible mechanisms of H(2) activation by metal-sulfide hydrodesulfurization catalysts and a four-center mechanism for this exchange is proposed.
TL;DR: In this paper, the nine-nuclear cluster Ni9(HOOCCMe3)4(μ4-ΟΗ)3(μ3-OH)3 (OOCCme3)12 (1) with pyridine results in the binuclear species Py4Ni2(OOCCME3)2(μ-OOCCM3) 2 (μ-OH2)2 (2)
Abstract: Reaction of the nine-nuclear cluster Ni9(HOOCCMe3)4(μ4-ΟΗ)3(μ3-OH)3 (OOCCMe3)12 (1) with pyridine results in the binuclear species Py4Ni2(OOCCMe3)2(μ-OOCCMe3)2(μ-OH2) (2). Thermolysis of 2 at 100−140 °C in toluene or xylene leads to complex Py2Ni2(HOOCCMe3)2(OOCCMe3)2(μ-OOCCMe3)2(μ-OH2) (3). This complex can be converted back in 2 by the reaction of 3 with 2 equiv of pyridine. Thermolysis of solid 3 in vacuo at 170 °C gives the binuclear tetra-bridged trimethylacetate Py2Ni2(μ-OOCCMe3)4 (4) which can be reverted in 3 by reaction with 1 equiv of H2O and 2 equiv of HOOCCMe3. Compound 4 might be also prepared by the reaction of the complexs L2Ni2(μ-OOCCMe3)4 (L = 2,3-lutidine (5), Et3N (6)) with pyridine at 40−80 °C in hexane or benzene solution. Complexes 5 and 6 are formed in an one-step reaction by interaction of complex 1 and ligand L. Complex Dipy2Ni2(OOCCMe3)2(μ-OOCCMe3)2(μ-OH2) (7), an isoelectronic analogue of complex 2, was prepared by reacting 1 with Dipy. Thermolysis of solid 7 at 170 °C in vacuo ...
TL;DR: In this paper, the trans-Pt(Ypy)2X2 complex was studied by spectroscopic methods, especially by multinuclear NMR spectroscopy, and the results showed that the iodo ligand has the greatest trans influence.
TL;DR: In this paper, three different heterocyclic amine additives, pyridine, 3-cyanopyridine and pyrazole, were compared in the methyltrioxorhenium (MTO) catalyzed epoxidation of olefins using aqueous hydrogen peroxide.
TL;DR: In this article, femtosecond transient absorption (population and anisotropy) spectroscopy was combined with ab initio electronic structure methods to study excited-state deactivation pathways of the pyridine molecule in liquid solutions.
Abstract: In this work, we combined femtosecond transient absorption (population and anisotropy) spectroscopy with ab initio electronic structure methods to study excited-state deactivation pathways of the pyridine molecule in liquid solutions. Studies of the effects of excitation energy, deuteration and substitution, solvent polarity and viscosity, and protonation of pyridine were performed. The experiments reveal the dynamics of S_1(nπ^*) and S_2(ππ^*) excited states of pyridine. The photoexcitation of the S_2(ππ^*) state leads to formation of the prefulvenic form of pyridine, a valence isomer, in ∼2.2 ps, while nonradiative deactivation of the S_1(nπ^*) state occurs in 9−23 ps and is to a large extent due to intersystem crossing. Using ab initio methods at the CASSCF and time-dependent DFT levels, we calculated the potential energy surfaces of the ground and S_2(ππ^*) states. A conical intersection was found responsible for the ultrafast deactivation of the pyridine molecule.
TL;DR: In this paper, a concise total synthesis of phomazarin is detailed enlisting a heterocyclic azadiene inverse electron demand Diels−Alder reaction (1,2,4-triazine → pyridine) for preparation of the fully substituted and appropriately functionalized pyrinyidine C-ring.
Abstract: A concise total synthesis of phomazarin (1) is detailed enlisting a heterocyclic azadiene inverse electron demand Diels−Alder reaction (1,2,4-triazine → pyridine) for preparation of the fully substituted and appropriately functionalized pyridine C-ring. Thus, [4 + 2] cycloaddition (85%) of triethyl 1,2,4-triazine-3,5,6-tricarboxylate (2) with trimethoxyethylene (3) followed by conversion of the cycloadduct 11 to the cyclic anhydride 13 provided the phomazarin C-ring with the three carboxylates suitably differentiated. Linkage of the A- and C-rings through selective nucleophilic addition of the aryllithium reagent 9 to the least hindered anhydride carbonyl of 13 followed by Friedel−Crafts closure of the B-ring provided the fully functionalized phomazarin skeleton. The successful structural correlation of synthetic 1 with natural material and its derivatives confirmed the latest structural assignment for the natural product.
TL;DR: In this article, the reaction of [RuCl 2 ( p -cymene)] 2 with the tridentate N - N ′- N ligands, 2,6-pyridyl-diimines, led to substitution of p -cyclohexene.
Abstract: Reaction of [RuCl 2 ( p -cymene)] 2 with the tridentate N - N ′- N ligands, 2,6-pyridyl-diimines, led to substitution of p -cymene. The resulting complexes, believed to be coordinatively unsaturated, exhibit efficient activity for the epoxidation of cyclohexene in the presence of iodosobenzene (PhIO): the complexes formed initially take up donor molecules such as acetonitrile to achieve hexacoordination. The molecular structure for one of these, (acetonitrile){2,6-bis[1-(4-methoxyphenylimino)ethyl]pyridine}dichlororuthenium(II), 2 , has been determined by X-ray diffraction. The immediate coordination sphere is a distorted octahedron with trans chloride atoms and a short Ru–N(py) (1.906 A) bond.
TL;DR: In this article, various bromopyridines were converted to corresponding pyridylmagnesium chlorides at room temperature by treatment with iPrMgCl and the resulting Grignard reagents were quenched by various electrophiles.
Patent•
13 Sep 1999TL;DR: In this article, the substitutions of formula (I) in which the substituents are as defined in claim 1 are suitable for use as herbicides, and they are defined as follows:
Abstract: Compounds of formula (I) in which the substituents are as defined in claim 1 are suitable for use as herbicides.
TL;DR: The solid acidity of 12-tungstophosphoric acid (H 3 PW) has been measured using slurry calorimetry in cyclohexane with pyridine as the probe as mentioned in this paper.
TL;DR: A range of mostly new oxovanadium(IV) complexes are described in this paper, which contain coordinated Schiff bases, made from natural amino acids (glycine, alanine, valine, leucine, isoleucine and methionine, phenylalanine, threonine, aspartic acid, and histidine) and salicylaldehyde or such derivatives as 3-, 4-, or 5-methoxy-salicyl-aldehyde.