bluuebunny/crossref_metadata_2025 huggingface dataset:
Metabolism of analogs of the phytoalexin brassinin by plant pathogenic fungi
Authors: Pedras M Soledade , Okanga Francis I
Published: April 2011

he metabolism of analogs of the cruciferous phytoalexin brassinin by the phytopathogenic fungi Phoma lingam (Tode ex Fr.) "virulent" and "avirulent" groups (sexual stage Leptosphaeria maculans (Desm.) Ces. et de Not.) and Alternaria brassicae (Berk.) Sacc. is reported. It was established that each pathogen detoxified methyl tryptamine dithiocarbamate, although yielding different metabolic products. While the biotransformation by virulent P. lingam proceeded to yield methyl 3a-hydroxy-3,3a,8,8a-tetrahydropyrrolo[2,3-b]indol-1(2H)-yl carbodithioate and indole-3-acetic acid as final products, avirulent P. lingam yielded indole-3-carboxylic acid via Nb-acetyltryptamine, and A. brassicae yielded Nb-acetyltryptamine, as final products. Furthermore, to establish the importance of the dithiocarbamate group in antifungal activity against P. lingam and A. brassicae, carbamates were compared with dithiocarbamates and it was established that carbamates were devoid of antifungal activity. These products, contrary to methyl tryptamine dithiocarbamate, showed no inhibitory activity against either pathogen.Key words: Alternaria brassicae, brassinin, carbamates, detoxification, dithiocarbamates, Leptosphaeria maculans, Phoma lingam, phytoalexins.
Correlation of rates of uncatalyzed and hydroxide-ion catalyzed ketene hydration. A mechanistic application and solvent isotope effects on the uncatalyzed reaction
Authors: Andraos John , Kresge A Jerry
Published: April 2011

Rates of hydration of a number of ketenes were measured in neutral and basic solution using flash photolytic techniques, and rate constants for their uncatalyzed, kuc, and hydroxide-ion catalyzed, kHO, reactions were determined. These results, plus additional data from the literature, were found to provide the remarkably good correlation log kuc= -3.21 + 1.14 log kHO, which spans 10 orders of magnitude in reactivity and includes 31 ketenes. This good correlation implies that uncatalyzed and hydroxide-ion catalyzed ketene hydraton occur by similar reaction mechanisms, which for the hydroxide-ion catalyzed process is known to involve nucleophilic attack on the carbonyl carbon atom of the ketene. Rate constants for phenylhydroxyketene, on the other hand, do not fit this correlation, which suggests that the mechanistic assignment upon which these rate constants are based may not be correct. Solvent isotope effects on these uncatalyzed ketene hydrations are weak; most are less than kH/kD= 2. It is argued that these isotope effects are largely, if not entirely, secondary in nature and that they are consistent with both a reaction mechanism in which nucleophlic attack of a single water molecule on the ketene carbonyl carbon atom produces a zwitterionic intermediate and also a mechanism that avoids this intermediate by passing through a cyclic transition state involving several water molecules.Key words: ketene hydration, rate correlation, nucleophilic attack, solvent isotope effects, phenylhydroxyketene.
Solubility of hexachlorobenzene in organic nonelectrolyte solvents. Comparison of observed vs. predicted values based upon Mobile Order model
Authors: De Fina Karina M , Van Tiffany T , Acree, Jr. William E
Published: April 2011

Experimental solubilities are reported at 25.0°C for hexachlorobenzene dissolved in 42 different organic nonelectrolyte solvents containing ether-, chloro-, hydroxy-, ester, methyl-, and tert-butyl-functional groups. Results of these measurements are used to test the applications and limitations of expressions derived from Mobile Order model. For the 33 solvents for which predictions could be made computations show that Mobile Order model does provide fairly reasonable estimates of the saturation mole fraction solubilities. Average absolute deviation between predicted and observed values is 210%. In comparison, the average absolute deviation is 2 060% when ideal solution behavior is assumed.Key words: hexachlorobenzene solubilities, organic nonelectrolyte solvents, solubility predictions.
Studies on the synthesis of the decahydro-as-indacene ring system of (-)-spinosyn A via transannular Diels-Alder reactions of substituted (E,E,E)-cyclododeca-1,6,8-trienes
Authors: Frank Scott A , Works Andrea B , Roush William R
Published: April 2011

Stereoselective syntheses of decahydro-as-indacenes 31 and 54 are reported. The key features of our syntheses of 31 and 54 are the tandem Ireland-Claisen ring contraction of lactones 29 and 38 followed by the transannular Diels-Alder cyclization of cyclododecatrienes 30 and 35. Transition state modeling of both the transannular Diels-Alder reaction and the Ireland-Claisen ring contraction using PCModel is also described.Key words: transannular Diels-Alder reactions, tandem reactions, Claisen ring contraction, Spinosyn A, synthetic study.
Synthesis of 2,3-disubstituted norbornadienes
Authors: Tranmer Geoffrey K , Yip Carol , Handerson Sean , Jordan Robert W , Tam William
Published: April 2011

Various 2,3-disubstituted norbornadienes that can hardly be made by the traditional Diels-Alder method were synthesized by double lithium halide exchange of 2,3-dibromonorbornadiene in moderate to good yields.Key words: 2,3-disubstituted norbornadienes, Diels-Alder reaction, lithium halide exchange.
Glycosidase-catalyzed hydrolysis of 2-deoxyglucopyranosyl pyridinium salts: effect of the 2-OH group on binding and catalysis
Authors: Tanaka Kelly SE , Zhu Jiang , Huang Xicai , Lipari Francesco , Bennet Andrew J
Published: April 2011

Three 2-deoxy-α-D-glucopyranosyl pyridinium tetrafluoroborates were tested for their binding affinity to a range of α-glucosidases and α-mannosidases. The α-isoquinolinium salt (11) binds approximately 275-fold more tightly to yeast α-glucosidase than does the isomeric quinolinium salt (12). In addition, compound 11 binds to the yeast enzyme approximately two-fold tighter than the corresponding glucopyranosyl isoquinolinium salt (9). The (kcat/khyd) values for the yeast α-glucosidase-catalyzed reactions of 11 and 9 are 1.6 × 105and 2.0 × 109, respectively, when compared to the spontaneous uncatalyzed reactions. Thus, the interaction of the 2-OH group in compound 9 with the yeast enzyme's active site generates a relative transition state stabilization of about 23.5 kJ mol-1. For both compounds 11 and 12, the observed rate accelerations for the yeast α-glucosidase-catalyzed hydrolysis, relative to the spontaneous reaction in solution, (kcat/khyd) are identical within experimental error.Key words: glycosidase, inhibitor, 2-deoxyglucose, pyridinium, catalysis.
Methylamination of some 3,6-dinitro-1,8-naphthyridines with liquid methylamine  potassium permanganate
Authors: Wozniak Marian , Grzegozek Maria , Surylo Piotr
Published: April 2011

3,6-Dinitro-1,8-naphthyridine and its 2-substituted derivatives are dehydro-methylaminated with the solution of potassium permanganate in liquid methylamine (LMAPP) to the corresponding mono- or mono- and bis(methylamino)-3,6-dinitro-1,8-naphthyridines. In the case of 2-chloro- and 2-methoxy-3,6-dinitro-1,8-naphthyridine the replacement of chloro and methoxy substituents by the NHCH3 group occurs as well. Quantum-chemical calculations indicate the reactions to be controlled by the interaction of the frontal molecular orbitals (FMO) of the reagents. Moreover the heats of formation of intermediary methylamino-σ-adducts and transition states are calculated for the reaction studied. The calculations show satisfactory agreement between calculated and observed results. A convenient synthesis of some 2-substituted-3,6-dinitro-1,8-naphthyridines is reported.Key words: methylaminations, calculations PM3, nitro-1,8-naphthyridines, oxidation.
A study of hydrogenation of benzhydrols in the presence of catalytic amount of triflic acid
Authors: Waterlot Christophe , Couturier Daniel , Backer Marc De , Rigo Benoît
Published: April 2011

The ionic hydrogenation of diarylcarbinols by triethylsilane, in the presence of catalytic amount of triflic acid proceeds via dibenzhydryl ethers. These ethers do not disproportionate to benzophenones and diphenylmethanes but are reduced by triethylsilane to diarylmethanes.Key words: catalytic reduction, benzhydrols, dibenzhydryl ethers, triethylsilane.
Bis(trimethylsilyl)methylamine (BSMA): tool or toy?
Authors: Picard Jean-Paul
Published: April 2011

Bis(trimethylsilyl)methylamine, BSMA, an original primary amine, was proven to be the source of a large variety of N-bis(trimethylsilyl)methylamino derivatives that otherwise have to be prepared indirectly. Because of the bulkiness of the bissilylmethyl group, regio- and stereoselectivities resulted in appropriated examples. Apart from the potential biological properties associated with the Si-C-N framework, these derivatives were powerful synthetic intermediates. Special emphasis was given to the chemistry of corresponding imines. Cleavage of SiC bonds or abstraction of the methine proton afforded α-nitrogen carbanions in very mild conditions. Application of these results to the β-lactam chemistry allowed the introduction of new synthetic methodologies in this field. It results the (Me3Si)2CH- group could now be regarded as a Me3SiCH2- or a CH3- group or a proton equivalent.Key words: bis(silyl)methylamine, preparations, reactivity, nitrogen heterocycles, α-nitrogen carbanions.
An expeditious synthesis of (±)-decahydro-5H-dipyrrolo [1,2-a:1',2'-c]pyrimidine-5-carbonitrile: a formal synthesis of (±)-tetraponerines-1, -2, -5, and -6
Authors: Plehiers M , Heilporn S , Ekelmans D , Leclercq S , Sangermano M , Braekman J C , Daloze D
Published: April 2011

A short and practical synthesis of (±)-decahydro-5H-dipyrrolo[1,2-a:1',2'-c]pyrimidine-5-carbonitrile (17), a pivotal intermediate in the synthesis of (±)-tetraponerines-1 (5), -2 (6), -5 (7), and -6 (8), in three steps and 24% overall yield, from simple and inexpensive starting materials, is reported. The key step of our synthesis is a one pot stereoselective multistep process, whereupon two molecules of Δ1-pyrroline (9) react with diethyl malonate (10) to afford the tricyclic lactam ester 13, possessing the tetraponerine skeleton. Hydrolysis of the carboethoxy group of 13 followed by decarboxylation yields lactam 15, which is converted into α-aminonitrile 17. Our fruitless efforts to transform lactam 15 into the tetraponerines through reductive alkylation are also discussed.Key words: alkaloids, tetraponerines, stereoselective synthesis, Robinson-Schöpf reaction, lactams, ants.
The reaction between hydrazines and β-dicarbonyl compounds: proposal for a mechanism
Authors: Singh Shiv P , Kumar Dalip , Batra Hitesh , Naithani Rajesh , Rozas Isabel , Elguero José
Published: April 2011

The reaction between aryl or heteroarylhydrazines with fluorinated β-diketones (CF3COCH2COR) yields a variety of 3-, 5-, and 3,5-trifluoromethylpyrazoles and 5-trifluoromethyl-5-hydroxy-Δ2-pyrazolines. Twenty-one of such compounds have been isolated and identified by 13C and 19F NMR. Together with the results from the literature they provide a comprehensive overview of the reaction. Semi-empirical calculations at the PM3 level have been used to rationalize these results. The outcome that emerges seems to be that the dehydration of a pair of 3,5-dihydroxypyrazolidines kinetically controls the isomer formed.Key words: hydrazines, 1,3-diketones, pyrazolines, pyrazoles, PM3 calculations.
Syntheses of 4-[1-(2-deoxy-β-D-ribofuranosyl)]-derivatives of 2-substituted-5-fluoroaniline: "cytosine replacement" analogs of deoxycytidine for evaluation as anticancer and antihuman immunodeficiency virus (anti-HIV) agents
Authors: Wang Zhi-Xian , Wiebe Leonard I , Clercq Erik De , Balzarini Jan , Knaus Edward E
Published: April 2011

A group of 4-[1-(2-deoxy-β-D-ribofuranosyl)]-derivatives of 5-fluoroaniline possessing a variety of aryl C-2 substituents (6a R = H, 6b R = F, 6c R = Me) were synthesized. Accordingly, a Heck-type coupling reaction of the 4-iodoaniline derivatives (13ac) with the bis(tert-butyldimethylsilyl)glycal (11) in the presence of Pd(OAc)2 and Ph3As, followed by removal of the tert-butyldimethylsilyl protection groups using n-Bu4N+F-, yielded the corresponding 4-(β-D-glycero-pentofuran-3-ulos-1-yl)aniline derivatives (14ac) having a C-3 C=O in the sugar ring. Reduction of the C-3 C=O compounds (14ac) using NaB(OAc)3H afforded the target 4-[1-(2-deoxy-β-D-ribofuranosyl)]-derivatives of the respective 2-substituted-5-fluoroaniline (6ac). The deoxycytidine mimic, 3-fluoro-4-[1-(2-deoxy-β-D-ribofuranosyl)]aniline (6a), in which the cytosine ring of deoxycytidine is replaced by a 4-(3-fluoroaniline) ring system, was inactive as an anticancer agent against a variety of tumor cell lines, and as an antihuman immunodeficiency virus (HIV-1, HIV-2) agent. The failure of this unnatural deoxycytidine mimic (6a) to exhibit anticancer-antiviral activity may be due to its inability to undergo phosphorylation by host cell- and virus-induced kinases.Key words: fluoroanilines, deoxycytidine mimics, anticancer-antihuman immunodeficiency virus (HIV) evaluation.
Densities, refractive indices and excess properties of mixing of the n-octanol + 1,4-dioxane + 2-butanol ternary system at 298.15 K
Authors: Camacho Alberto G , Postigo Miguel A , Pedrosa Graciela C , Acevedo Inés L , Katz Miguel
Published: April 2011

Excess molar volumes and excess refractive indices of the n-octanol + 1,4-dioxane + 2-butanol system and the three corresponding binary mixtures have been determined at 298.15 K by measuring densities and refractive indices. Different expressions exist in the literature to predict these excess properties from binary data. An estimation of excess molar volumes is also evaluated using a modified Heller equation which depends on the refractive indices of the mixtures. A comparison of the predictions of different methods with the experimental values of the physical properties has been made.Key words: excess molar volumes, densities, refractive indices, n-octanol, 1,4-dioxane, 2-butanol, ternary system.
Thermodynamics of mixtures with strongly negative deviations from Raoult's law. Part 3. Application of the DISQUAC model to mixtures of triethylamine with alkanols. Comparison with Dortmund UNIFAC and ERAS results
Authors: González Juan Antonio , de la Fuente Isaias Garcia , Cobos Jose Carlos
Published: April 2011

Binary mixtures of triethylamine (TEA) and alkanols have been investigated in the framework of DISQUAC. The systems are built by three contacts: aliphatichydroxyl, aliphaticnitrogen, and hydroxylnitrogen. The corresponding interaction parameters are reported and discussed. The former are avalilable in the literature but were modified (particularly the third dispersive (DIS) and quasichemical (QUAC) interchange coefficients) for sec- and tert-alkanols + n-alkanes using recent data on excess heat capacities at constant pressure (CEP) for systems of these alkanols with n-heptane. The interaction parameters for aliphatic-nitrogen contacts are purely dispersive. The structure dependence of the DIS and QUAC interchange coefficients of the hydroxyl-nitrogen contacts in 1-alkanols + TEA systems is similar to that found in other solutions previously investigated. The QUAC interchange coefficients remain constant from ethanol and are also valid for 2-alkanols and tert-butanol. Methanol behaves differently. A short discussion in terms of effective dipole moments is also included. DISQUAC represents well the thermodynamic properties examined: vapor-liquid equilibria (VLE), molar excess Gibbs energies (GE) and molar excess enthalpies (HE). DISQUAC provides better results than the Dortmund version of UNIFAC using the published geometrical and interaction parameters. ERAS parameters for 1-alkanols + TEA systems are also reported. Interactions between unlike molecules are stronger for solutions with methanol or ethanol. DISQUAC improves ERAS results on HE, while both models give similar results for GE. However, ERAS needs an specific parameter, with unknown temperature-dependence, to describe properly GE. The main advantage of ERAS is its ability to provide information on VE. Its main limitation is that can be only applied to those systems where association is expected. DISQUAC, a purely physical model, can be applied to any type of binary mixture, as it is followed from this and previous studies.Key words: theory, liquids, associated, thermodynamics, group contributions.
Synthesis, spectroscopic characterization and structural studies of organotin monothiocarbonates. Crystal structures of Ph3Sn[SCO2Me] and Ph3Sn[SCO2(i-Pr)]
Authors: Drake John E , Yang Jincai
Published: April 2011

O-alkyl monothiocarbonate (monoxanthate) derivatives of tin were obtained by the reaction of a sodium salt of the monothiocarbonic acid with an organotin chloride to give Ph3Sn[SCO2R], Ph2Sn[SCO2R]2, and Me3Sn[SCO2R], where R = Me and i-Pr. The compounds have been characterized by infrared, Raman, 1H NMR, and 13C NMR spectroscopy, as well as mass spectrometry, and in two cases by X-ray crystallography. Ph3Sn[SCO2Me] (1) and Ph3Sn[SCO2(i-Pr)] (2), crystallize in the triclinic space group P[Formula: see text] (no. 2) with cell parameters a = 10.218(4), b = 10.568(6), c = 9.366(7) Å, α = 106.73(5), β = 96.99(5), γ = 85.55(4)°, V = 960(1) Å3, and Z = 2 for 1; and a = 14.793(2), b = 17.856(3), c = 9.813(3) Å, α = 103.86(5), β = 98.36(5), γ = 106.85(4)°, V = 2343(1) Å3, and Z = 2 for 2. The latter has two molecules in the asymmetric unit. The immediate environment about tin in both 1 and 2 is that of the expected distorted tetrahedron. However, the orientation of the monothiocarbonate group is such that there is an Sn-O intramolecular interaction of 3.040(8) for 1 and 3.05(2) Å on average for 2. Thus, the considerable distortion is consistent with a tendency to form a five-coordinate, trigonal bipyramidal species with one of the O-Sn-C angles approaching 180o (153.4(4) for 1 and an average of 157.1(6) for 2). Estimations of the Pauling partial bond orders suggest this weak Sn-O interaction is slightly stronger than the corresponding Ge-O interaction in the analogous germanium derivative, Ph3Ge[SCO2Me].Key words: structure, tin, methyl, phenyl, isopropyl, monothiocarbonates.
Solvation thermodynamics of cyclohexane
Authors: Graziano Giuseppe
Published: April 2011

The solvation thermodynamics of cyclohexane in pure liquid phase and in water is analyzed by means of the theoretical approach developed by Lee. The sum of the work of cavity creation and the dispersive solutesolvent interaction energy reproduces well the experimental Gibbs energy values over the whole temperature range 5100°C. This implies that the purely structural solvent reorganization is an exactly compensating process in both liquids. The dispersive solutesolvent interaction energy is larger in magnitude in cyclohexane than in water, whereas the work of cavity creation is larger in water than in cyclohexane. Therefore, both terms contrast the transfer of cyclohexane from pure liquid phase to water, determining its hydrophobicity. This mechanism qualitatively corresponds to that operative in the case of benzene.Key words: hydrophobicity, cavity creation, excluded volume, dispersive interactions, enthalpyentropy compensation.
Synthesis, characterization, and CN bond cleavage of tungsten(VI)arylimido-calix[4]arene complexes
Authors: Brown Martyn , Jablonski Chet
Published: April 2011

The tetradentate, partially flattened cone tungsten(VI) imido-calix[4]arene derivative [W(NC6H5)(t-BucalixH)]+Cl, (4), is formed in good yield from reaction of p-tert-butyl-calix[4]arene (t-BucalixH4), and W(NC6H5)Cl4. A reaction mechanism involving a putative, bidentate calixarene intermediate W(NC6H5)(t-BucalixH2)Cl2 (3), which partitions by reversible cleavage of the imido group to give the known tetradentate calixarene complex W(t-Bucalix)Cl2 (2), and elimination of HCl to form the thermodynamic imido product 4 is proposed. A series of iso structural [W(NAr)(t-BucalixH)]+Cl (Ar = C6H5 or o,m,p-C6H4CH3) imido derivatives (47), which adopt a partially flattened cone conformation in solution has been prepared by reaction of dichloride 2 with H2NAr (Ar = C6H5, o,m,p-C6H4CH3). Reaction of W(t-Bucalix)Cl2 with aliphatic amines affords a red product formulated as the nitrido complex, 9, which results from facile cleavage of the imido CN bond.Key words: calix[4]arene complex, imido complex, nitrido complex, CN bond cleavage, conformation, metallocalixarene.
Geminal bis(hypersilyl) compounds  the synthesis and structure of bis[tris(trimethylsilyl)silyl]silanes
Authors: Gross Thoralf , Reinke Helmut , Oehme Hartmut
Published: April 2011

Protodesilylation of diphenylsilane with trifluoromethanesulfonic acid and subsequent reaction of the obtained bis(trifluoromethanesulfonyloxy)silane with tris(trimethylsilyl)silyllithium (1) (molar ratio 1:2) afforded bis[tris(trimethylsilyl)silyl]silane (8). Methyl-bis[tris(trimethylsilyl)silyl]silane (3) and phenyl-bis[tris(trimethylsilyl)silyl]silane (10) were obtained by coupling reactions of 1 with MeHSiCl2 or PhHSiCl2, respectively, (2:1). By treatment with HCBr3, the H-silanes 3, 8, and10 were converted into the bromosilanes [(Me3Si)3Si]2SiR1R2 (9: R1 = R2 = Br; 11: R1 = Me, R2 = Br; 12: R1 = Ph, R2 = Br). X-ray crystal structure analyses, performed for 3, 10 and 12, confirmed the expected distortions of the molecular skeletons of the compounds. Thus, e.g., in 10, the spatial demand of the two extended hemispherical hypersilyl groups forces a widening of the Si-Si-Si angle at the central Si atom to a value of 128.3°.Key words: silanes, sterically congested, bis(hypersilyl)silanes, hypersilylsilanes, bis(hypersilyl)germanes, tris(trimethylsilyl)silylsilanes.
AIM study on the transferability of the oxygen atom in linear ethers
Authors: Vila Antonio , Carballo Enrique , Mosquera Ricardo A
Published: April 2011

The integrated values of the electron population, electron energy, nucleuselectron potential energy interaction, dipole moment and volume of the oxygen atoms, and the main properties of the OC bond critical points, were determined by employing the theory of atoms in molecules and 6-31++G**//6-31G* wave functions for a series of 25 unbranched alkyl monoethers. These results were used to assess the degree of approximate transferability of the oxygen atom along this series in terms of the particular alkyl radicals bonded to it. It has been found that a set of six different oxygen atoms is necessary to classify all the computed values. It can be established that the oxygen atoms bonded to propyl and larger radicals can be treated, in practice, as a transferable fragment, while those bonded to at least one smaller radical are specific. Though the total HF energy and the available experimental heats of formation are well fitted by a traditional additivity scheme that distinguishes only among O, CH2, and CH3 units, it has been found that the energy properties are influenced by the size of the molecule.Key words: transferability, AIM theory, ethers.
Anhydrous perchlorato complexes of palladium(II): Pd(ClO4)2, (ClO2)2Pd(ClO4)4, and (NO2)2Pd(ClO4)4. Syntheses and structural analyses
Authors: Cunin Frédérique , Favier Frédéric , Pascal Jean Louis
Published: April 2011

Chlorine trioxide (Cl2O6) reacts with PdCl2 to yield "ClO2Pd(ClO4)3" which is, in fact, an equimolar mixture of Pd(ClO4)2 and (ClO2)2Pd(ClO4)4. The chloryl salt decomposes under vacuum to give Pd(ClO4)2. (NO2)2Pd(ClO4)4· 0.5 NO2ClO4 is prepared using Pd(NO3)2·0.5 (H2O, HNO3) as the starting salt. Excess NO2ClO4 sublimes easily and pure (NO2)2Pd(ClO4)4 is obtained. Pd(ClO4)2 and (NO2)2Pd(ClO4)4 crystallize poorly; however, a P21/m space group is proposed for the latter. A complete assignment of vibrational modes, and DFT calculations, show that Pd(ClO4)2 is monomeric with chelating bidentate [ClO4] groups and Pd is in a square planar environment. In nitryl and chloryl salts, individual anions (Pd(ClO4)2-4), where unidentate [ClO4] groups interact partially with the cation or the Pd core, were characterized.Key words: palladium(II), chlorine trioxide, perchlorato complexes, chelating bidentate, vibrational spectroscopy, DFT calculations, powder X-ray diffraction.
Binap and MeO-Biphep complexes of Ru(II). Dicationic ligands as 6e donors. Unexpected cyclometallation in connection with PC bond breaking
Authors: den Reijer Carolien J , Dotta Pascal , Pregosin Paul S , Albinati Alberto
Published: April 2011

A series of cationic and dicationic Ru-arene complexes with Binap (1a) and MeO-Biphep (1b) have been prepared. 13C NMR studies are shown to be useful in connection with recognising the 6e-bonding mode of 1a and 1b in the dications [Ru(1a or 1b)(η6-arene)](SbF6)2 (8,9). Reaction of 8,9 with: (a) (Bu4N)(Ph3SiF2) leads to a cyclometallated product which arises via PC bond breaking and PF bond making; (b) methanol provides a straightforward synthesis of the corresponding hydrides. 13C NMR p-cymene chemical shifts are reported.Key words: PC bond cleavage, 6e donors, cyclometallation, hydrides, 13C NMR.
Phase behaviours and conductivity study of water/CPC/alkan-1-ol (C4and C5)/1-hexane water/oil microemulsions with reference to their structure and related thermodynamics
Authors: Moulik S P , Aylward Wanda M , Palepu R
Published: April 2011

The microemulsion forming systems of water/cetylpyridinium chloride/butan-1-ol/n-hexane, and water/cetylpyridinium chloride/pentan-1-ol/n-hexane have been studied with respect to their phase behaviours and percolation of conductance to derive information on their droplet physicochemical characteristics (dimension, interfacial area and composition, and number density). This was carried out at different water contents at specific ratios of surfactant and cosurfactant and at various temperatures. From the information collected, the energetics of the transfer of the alkanol (butan-1-ol and pentan-1-ol) from the continuous oil-phase to the interfacial region (the interphase) have been estimated. At the conductance percolation threshold, the droplets cluster or associate, can be considered to form a pseudophase similar to surfactants forming micelles. Based on this concept, the energetics of the clustering process have been evaluated, and the results are discussed in comparison with other recently studied systems.Key words: energetics of clustering, percolation, phase diagrams, microemulsions and thermodynamics of transfer.
Synthetic and solution calorimetric investigations of chelating phosphine ligands in Ru(allyl)2(PP) complexes (PP = diphosphine)
Authors: Smith, Jr. Dale C , Cadoret Jérémie , Jafarpour Laleh , Stevens Edwin D , Nolan Steven P
Published: April 2011

Reaction enthalpies of (COD)Ru(allyl)2 (COD = η4-1,5-cyclooctadiene; allyl = 2-methylpropenyl) with a series of bidentate phosphines (dppm, dppf, dppe, dppb, dppp, depe, dmpe) have been measured by anaerobic solution calorimetry. The relative stability of the resulting complexes is strongly influenced by the electronic donor properties of the bidentate phosphine ligand. Reactions involving ligands that are better σP) donors result in higher enthalpy values and, therefore, more thermodynamically stable complexes. Additionally, the synthesis and characterization of two new ruthenium allyl complexes Ru(allyl)2(dppf) (3) and Ru(allyl)2(depe) (8) and the X-ray crystal structure of 3 are reported.Key words: ruthenium, allyl, solution calorimetry, thermodynamics, X-ray structure.
The photochemistry of the 4-cyanobenzoic acid esters of trans- and cis-2-phenylcyclohexanol
Authors: Pincock J A , Rifai S , Stefanova R
Published: April 2011

Irradiation of trans-2-phenylcyclohexyl 4-cyanobenzoate (4) in methanol results in formation of the 1-phenylcyclohexene and 4-cyanobenzoic acid as the major products. The mechanism proposed for this example of the Norrish Type II-like reaction, normally inefficient for the π,π* state of esters, begins with intramolecular electron transfer in the excited singlet state. The next step, intramolecular proton transfer, is highly exergonic as a result of the increased acidity of the benzylic hydrogen of the radical cation and the increased basicity of the carbonyl oxygen of the radical anion. The final step is cleavage of the 1,4-biradical. This mechanism is proposed on the basis of product studies, absorption spectra, fluorescence spectra, oxidation and reduction potentials, and nanosecond laser flash photolysis spectra. The stereochemical requirements for the process have also been examined using solution NMR, the X-ray structure, and MM3 calculations. The stereoisomer, cis-2-phenylcyclohexyl 4-cyanobenzoate (5), undergoes cis to trans isomerization before photofragmentation. Photolysis of the cis isomer in methanol-OD demonstrated that the cis to trans isomerization occurred by inversion at C1.Key words : Norrish Type II, aromatic esters, intramolecular electron transfer.
Synthesis of new substituted dihydroheptalene derivatives: SiO2- and base-catalyzed rearrangement of dimethyl trans-3,8-dihydroheptalene-3,8-dicarboxylate
Authors: Saraçoglu Nurullah , Menzek Abdullah , Kinal Armagan , Balci Metin
Published: April 2011

Dimethyl trans-3,8-dihydroheptalene-3,8-dicarboxylate (trans-3) isomerizes to dimethyl cis-3,8-dihydroheptalene-3,8-dicarboxylate (cis-3) upon treatment with SiO2. On the other hand, base-catalyzed reaction of trans-3 undergoes a direct 1,3-intramolecular proton shift to give 6 at room temperature in 5 min. Prolonged reaction time formed isomers 7 and 8 in a ratio of 4:1. AM1 calculations indicate that the isomer 8, which is formed as minor product, has a lower heat of formation (99.34 kcal mol1) than that of the major isomer 7 (92.05 kcal mol1). However, when a similar reaction was performed at 100°C, the thermodynamically more stable isomer 8 was formed as the major product. Furthermore, cycloaddition reactions of these new dihydroheptalene derivatives 6 and 7 with different dienophiles have been studied. The mechanism has been discussed.Key words: dihydroheptalene, cycloaddition, 1,3-hydrogen shift, cycloheptatrienenorcaradiene equilibrium.
Structure and redox kinetics of nickel(II) tetraazamacrocycles containing pendant carboxylate groups
Authors: Haines Robert Ivor , Hutchings Dean Reginald , Lucas Rhonda Jane , Miller David
Published: April 2011

The nickel(II) complex of the deprotonated pendant-arm macrocycle 5,12-dimethyl-7,14-diphenyl-1,4,8,11-tetraazacyclotetradecane-4,11-diacetate (L2)2has been structurally characterized by X-ray crystallography. The Ni(II)L2complex crystallizes in the monoclinic system, space group P21/c, with a = 12.981(8), b = 16.474(6), c = 14.262(7) Å and β = 98.81(4)°. The complex shows a distorted cis-geometry about the metal centre, the macrocyclic ligand being folded about a N-Ni-N axis, with the pendant arms coordinated cis to one another. The Ni(II)L1(where (L1)2is meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane-4,11-diacetate) and Ni(II)L2complexes undergo reversible one-electron oxidation, with redox potentials of 0.717 and 0.766 V (vs. S.H.E.), respectively. Chemical oxidation of the complexes by peroxodisulfate obey overall second-order rate laws. Enthalpies and entropies of activation for Ni(II)L1are 38 ± 3 kJ mol1and -106 ± 9 J K1mol-1; and for Ni(II)L2the corresponding values are 41 ± 5 kJ mol1and 126 ± 15 J K-1mol-1. Outer-sphere oxidation of Ni(II)L1by bis-(triazacyclononane)nickel(III) ([Ni(III)(tacn)2]3+) has been studied, and a self-exchange rate constant for the [Ni(II)L1]0/+system has been estimated at 55 mol1dm3s1.Key words: peroxodisulfate, nickel(II), dicarboxylato-pendant arm macrocycles, bis-(triazacyclononane)nickel(III), self-exchange rate.
Studies on transition-metal nitrido and oxo complexes. Part 20. Oxoruthenates and oxo-osmates in oxidation catalysis; cis-[Os(OH)2O4]2- as a catalytic oxidant for primary amines and for alcohols
Authors: Griffith William P , Suriaatmaja Maria
Published: April 2011

cis-[Os(OH)2O4]2 with [Fe(CN)6]3 and other co-oxidants has been studied as a catalytic reagent for the oxidative dehydrogenation of primary aromatic and aliphatic amines to nitriles, the oxidation of primary alcohols to carboxylic acids and of secondary alcohols to ketones. Electronic and Raman spectroscopy have been used to elucidate the nature of the oxoruthenates and oxo-osmates present in a number of reported organic oxidations catalyzed by ruthenium and osmium species.Key words: oxidation catalysis, ruthenium, osmium, amine dehydrogenation, alcohol oxidation.
Precipitation from alkaline aqueous aluminosilicate solutions
Authors: North Michael R , Fleischer M Alejandra , Swaddle Thomas W
Published: April 2011

The longevity of metastable, highly alkaline Na and K aluminosilicate solutions has been examined over a wide range of Si/Al concentration ratios R (0.04 [Formula: see text] R [Formula: see text] 20) at 24°C and, in selected cases, at 50 and 75°C. In general, the longest solution lifetimes (tppt) (several weeks) were found at 24°C and for the highest alkalinities and (or) large R, but long tppt were also found for R = 1.0 at the lower alkalinities. Solution lifetimes generally shortened when the temperature was raised, but the opposite effect was observed with the smaller Al concentrations when 2 [Formula: see text] R [Formula: see text] 6. These results are interpreted in terms of the requirement for =Si-OH groups for precipitate growth by condensation and of the relatively high solubility (few nuclei for gel growth) of the aluminosilicate solutes when R = 1.0.Key Words: aluminosilicates, precipitation kinetics, aluminates, aqueous silicates, gelation, Bayer process, zeolite synthesis.
Pressure effects and solvent dynamics in the electrochemical kinetics of the tris(hexafluoroacetylacetonato)ruthenium(III)/(II) couple in nonaqueous solvents
Authors: Zhou Jinkui , Swaddle Thomas W
Published: April 2011

Rate constants and reactant diffusion coefficients for the Ru(hfac)30/ electrode reaction have been measured at 25°C as functions of pressure (0-200 MPa) in acetone, acetonitrile, methanol, and propylene carbonate. In sharp contrast to the negative volumes of activation ΔVex found for the corresponding bimolecular self-exchange reaction in organic solvents, the volumes of activation ΔVel for the electrode reaction are markedly positive, ranging from 8 to 12 cm3 mol1. The volumes of activation ΔVdiff for reactant diffusion (which can be equated to the volume of activation ΔVvisc for viscous flow) range from 12 to 19 cm3 mol1. For the Debye solvents acetonitrile and acetone at least, ΔVel is given within the experimental uncertainty by ΔVdiff + (ΔVex/2). In this relation, the numerical value of ΔVdiff represents indirectly the dominant contribution of solvent dynamics (solvent friction) to ΔVel, and ΔVex/2 represents the pressure dependence of the free-energy barrier height for the electrode reaction. It is proposed that solvent friction is important in nonaqueous electrode processes but not in the corresponding bimolecular self-exchange reactions because the free-energy activation barrier is twice as high in the latter.Key words: electrode reaction kinetics, solvent dynamics, electron transfer mechanisms, pressure effects, volume of activation.
Octaarylethynyl and octaarylbutadiynyl phthalocyanines
Authors: Leznoff Clifford C , Suchozak Bohdan
Published: April 2011

4,5-Diphenylethynylphthalonitrile, 4,5-di(p-tert-butylphenylethynyl)phthalonitrile, 4,5-di(p-neopentoxyphenylethynyl)phthalonitrile, and 4,5-di(p-neopentoxyphenyl-1,3-butadiynyl)phthalonitrile were prepared via 4,5-diiodophthalonitrile and the appropriate alkyne in palladium-catalyzed coupling reactions. Condensation of the above alkynylphthalonitriles with lithium 1-octanolate in 1-octanol afforded the desired polyalkynylphthalocyanines, but only 2,3,9,10,16,17,22,23-octa (p-neopentoxyphenylethynyl)phthalocyanine and 2,3,9,10,16,17, 22,23-octa (p-neopentoxyphenylbutadnyl)phthalocyanine were soluble enough to be suitably characterized.Key words: phthalocyanines, phenylacetylenes, 1-phenyl-1,3-butadiynes.
Formation of heterocyclic arylboronates by thermally induced 1,4-aryl migration in diarylboron chelates of C-(1-hydroxyalkyl)nitrones. Crystal and molecular structures of some of the rearrangement products and of one of the educts
Authors: Kliegel Wolfgang , Lubkowitz Gottfried , Pokriefke Jens O , Rettig Steven J , Trotter James
Published: April 2011

Synthesis of heterocyclic arylboronates has been carried out by thermally induced rearrangement of diarylboron chelates of C-(1-hydroxyalkyl)nitrones. The structures have been determined from spectroscopic data and from X-ray analyses. Thermoanalytical and time-dependent NMR measurements give information on the nature of the isomerization reaction. Crystal data (at 293 K for 2j, 180 K for the others): 1m, monoclinic, P21/n, a = 14.059(3), b = 12.5531(13), c = 14.8531(6) Å, β = 95.8067(12)°, Z = 4; 2j, triclinic, [Formula: see text]1, a = 10.4729(11), b = 13.5896(11), c = 9.5803(7) Å, α = 104.764(6), β = 103.279(7), γ = 107.278(7)°, Z = 2; 2m, monoclinic, P21/n, a = 14.9442(13), b = 11.990(2), c = 16.0613(4) Å, β = 114.0153(7)°, Z = 4; 9, monoclinic, P21/n, a = 11.123(2), b = 18.433(3), c = 13.4852(4) Å, β = 108.2075(7)°, Z = 4. The structures were solved by direct methods and refined by full-matrix least-squares procedures to R(F, I [Formula: see text] 3σ(I)) = 0.036, 0.052, 0.043, and 0.040, respectively, for AFC6 data for 2j and CCD data for 1m, 2m, and 9. All four molecules contain six-membered OBONCC rings, with an approximately planar ON=CC segment in the educt 1m and approximately planar OBOC segments in the rearrangement products. A probable transition state geometry is derived for the isomerization process.Key words: diarylboron chelates, C-(1-hydroxyalkyl)nitrones, heterocyclic arylboronates, organoboron compounds, rearrangement, crystal structures.
Studies on the synthesis and properties of bischelating dioxotetraamine macrocycle, its metal complexes and thermodynamic stability in aqueous solution
Authors: Su Xun-Cheng , Zhou Zhi-Fen , Lin Hua-Kuan , Zhu Shou-Rong , Sun Hong-Wei , Zhao Guang-Hua , Chen Yun-Ti
Published: April 2011

A new route to obtain C-functionalized dioxotetraamine, in which two independent chelating groups 8-quinolinol and dioxotetraamine are included, is described. In addition, two trinuclear metal complexes are synthesized and fully characterized. The thermodynamic properties of the ligand and its respective metal complex were investigated by a potentiometric titration method. Coupled with UV spectra, the difference in affinities for copper ion between dioxotetraamine and 8-quinolinol in the new ligand are investigated and the results show that 8-quinolinol is a stronger donor group than the dioxotetraamine macrocycle in an aqueous solution. Over pH 3~11, 8-quinolinol interacts 100% with the copper ions while dioxotetraamine is only partially coordinated.Key words: macrocycle, dioxotetraamine, 8-quinolinol, copper ion, stability constants.
Potentiometric titration study of two novel polydenate ligands and investigations of their complexes
Authors: Cao Dengke , Lin Hua-Kuan , Zhou Zhi-Fen , Zhu Shou-Rong , Su Xun-Cheng , Chen Yun-Ti
Published: April 2011

Two novel linear polyamine ligands, N,N'-bis-(2-(N''-2-hydroxyl-5-bromobenzyl)aminoethyl) malondiamide (L1) and N,N'-bis-(3-(N''-2-hydroxyl-5-bromobenzyl)aminopropyl) malondiamide (L2), have been synthesized and fully characterized by elemental analysis (1H NMR and IR spectroscopy) (Fig. 1). The binding ability of ligands L1 and L2 to metal ions such as Cu(II), Zn(II), Co(II), Mn(II), Mg(II), and Ca(II) has been investigated by the potentiometric method in 1,4-dioxanewater (v/v = 15:100) and KNO3 (0.1 mol dm3) at 25.0°C. In view of the linear structures of L1 and L2, binuclear metal complexes can be formed in solution by controlling Cu(II)-5-substituted o-phenanthroline (Rphen, R = CH3, H, Cl, NO2):L to a 2:1 molar ratio, whereas the mononuclear metal complexes form at molar ratio M(II):L of 1:1, where M(II) is Cu(II), Zn(II), Co(II), Mn(II), Mg(II), and Ca(II). The stability constants of metal complexes have been determined and further discussed. In addition, two manganic complexes have been synthesized and IR and electronic spectra showed their coordination nature.Key words: linear polyamine ligand, 5-substituted o-phenanthroline, mononuclear and binuclear metal complex, stability, spectrum.
Addition of bridging-hydrosulfido ligands in diiridium complex to acrylonitrile. Synthesis of diiridium cyanoethylthiolato complexes and RuIr2 sulfido-cyanoethylthiolato cluster
Authors: Takagi Fusao , Seino Hidetake , Mizobe Yasushi , Hidai Masanobu
Published: April 2011

Treatment of [Cp*Ir(µ-SH)3IrCp*]Cl (Cp* = η5-C5Me5) with acrylonitrile and NEt3 in MeCN or ClCH2CH2Cl gave [Cp*Ir(µ-SCH2CH2CN)3IrCp*]+, [Cp*Ir(µ-S)(µ-SCH2CH2CN)2IrCp*] (3), or [Cp*Ir(µ-SCH2CH2CN)2(µ-SCH2CH2Cl)IrCp*]+, depending upon the conditions employed. From the reaction of 3 with [(Cp*Ru)4(µ-Cl)4], a sulfido-thiolato cluster [Cp*3RuIr2(µ3-S)(µ-SCH2CH2CN)2Cl] was obtained.Key words: diiridium complex, thiolate, sulfide, ruthenium, cluster.
Adsorption of etioporphyrin and Ni-etioporphyrin on a fractal silica
Authors: Hill Josephine Mary , Ng Flora TT
Published: April 2011

Metal compounds are contaminants in heavy oil and must be removed using hydrodemetallization catalysts. To optimize the structure of hydrodemetallization catalysts it is useful to know the effective size of the metal compounds. To this end, fractal geometry has been used to determine the relationship between monolayer coverage and adsorbate size for silica by adsorbing a series of alcohols at 298 K. It was found that the silica had a fractal dimension of 2.923. Etioporphyrin and Ni-etioporphyrin were then adsorbed on the silica and their effective areas determined based on this fractal dimension. Cross-sectional areas of 4.58 and 14.8 nm2 were determined for etioporphyrin and Ni-etioporphyrin, respectively. The areas are larger than those determined by X-ray methods and likely reflect the fact that the porphyrins are solvated with solvent (cyclohexane) molecules.
Stereochemistry at carbon upon protonolysis of a late transition metal-alkyl bond: a reaction of relevance to catalytic enantioselective hydrogenation of olefins
Authors: Wiles Jason A , Bergens Steven H , Young, Jr Victor G
Published: April 2011

Reaction of [Ru((R)-BINAP)(H)(MeCN)n(acetone)3n](BF4) (where n = 03) (2) with 1 equiv of the olefin substrate methyl α-acetamidoacrylate (MAA) in acetone at room temperature immediately generated a mixture (72:28) of two diastereomers of the complex [Ru((R)-BINAP)(MeCN)(MAA(H))](BF4) (3). The olefinhydride insertion reaction between 2 and MAA to generate 3 was regioselective, with transfer of the hydride to the β-olefinic carbon and transfer of ruthenium to the α-carbon in both diastereomers of 3. The two diastereomers of 3 differ by the absolute configuration at the α-carbon of MAA(H) ((SCα)-3 and (RCα)-3). The absolute configuration of the major ((SCα)-3) diastereomer was determined by X-ray diffraction in conjunction with NMR spectroscopic data. Protonolysis of the rutheniumcarbon bond in 3 and in the methyl α-acetamidocinnamate (MAC) analog ([Ru((R)-BINAP)(MeCN)((S)- MAC(H))](BF4) ((SCα)-4)) by addition of 2 equiv HBF4·Et2O in CH2Cl2 at room temperature was not stereospecific and did not occur with β-hydride elimination from the methyl or benzyl groups.Key words: ruthenium, BINAP, enantioselective, hydrogenation, catalysis.
Reactions of SO2 with trans-Ir(CO)(Cl)(TPPTS)2 in water
Authors: Bowden Allen A , Atwood Jim D
Published: April 2011

Reaction of SO2 with trans-Ir(CO)(Cl)(TPPTS)2 in water mirrors the nature of SO2 dissolved in water. At low pH (pH = 1) where SO2 exists as the hydrated species SO2·H2O, only Ir(CO)(Cl)(SO2)(TPPTS)2 forms. At higher pH (pH = 6) where HSO3 dominates, no SO2 complex is observed and a hydride, Ir(CO)(Cl)(H)(OH)(TPPTS)2, is the primary product. A mixture of SO2 and O2 does not lead to an iridium sulfate or show any evidence of the dioxygen adduct upon reaction in water with trans-Ir(CO)(Cl)(TPPTS)2, in contrast to the analogous reaction in organic solvents. In water, only the SO2 complex, Ir(CO)(Cl)(SO2)(TPPTS)2, is observed prior to decomposition. The contrasts to the PPh3 analogues in organic solvents provide further insight to water as a solvent for organometallic complexes.Key words: iridium(I), sulfur dioxide, water soluble, TPPTS.
Demethoxylation and hydroxylation of methoxy- and hydroxybenzoic acids by OH-radicals. Processes of potential importance for food irradiation
Authors: Gaisberger Birgit , Solar Sonja
Published: April 2011

The hydroxylation process for methoxy- and hydroxy-benzoic acids (MBA, HBA) induced by γ-radiation is compared. 2-, 3-, and 4-methoxybenzoic acid as well as 3-hydroxybenzoic acid have been irradiated in N2O and aerated solutions up to 1.5 kGy. The products were analyzed by HPLC. The results for 2- and 4-HBA have been taken from literature data. The OH·-adduct distribution is generally the same for the hydroxy- as well as for the methoxy-benzoic acid isomers. With both 4-HBA and 4-MBA more than 65% C3-adducts and about 15% C4-adducts are formed, which could be proved by their reactions with K3Fe(CN)6. Oxidation of the nonipso-adducts of 3-HBA and 3-MBA results in 84 and 87% of the corresponding phenols. Whereas in N2O-saturated solutions only part of the OH·-radicals leads to substrate decomposition, in the presence of air, the degradation of both kinds of compounds is equivalent to [OH·]. The nonipso OH·-adducts of the HBAs are converted into 6877% hydroxylation products. With the MBAs, the hydroxylation process is [Formula: see text] 10%. This is attributed to different decay pathways of the peroxyl radicals, intermediates formed by O2 addition to the OH·-adducts. The hydroxyperoxycyclohexadienyl radicals of the HBAs decay mainly by HO2· elimination to the corresponding phenols, those of the MBAs decay predominantly by fragmentation of the benzene ring, yielding to nonidentified aliphatic products. The replacement of -OCH3 by -OH is practically not influenced by the presence of oxygen, it increases in the sequence 3-MBA < 4-MBA < 2-MBA. For 2-MBA, yields of more than 15% are obtained. Both processes, hydroxylation as well as demethoxylation, might be of importance for the recognition of radiolytical changes in foodstuff.Key words: γ-radiolysis, methoxybenzoic acids, hydroxybenzoic acids, phenolic acids, food components, reaction mechanisms, product analysis, HPLC analysis.
2000 Alfred Bader Award LectureIn the footsteps of Pasteur: asymmetric induction in the photochemistry of crystalline ammonium carboxylate salts
Authors: Scheffer John R
Published: April 2011

This review describes the development of a new, synthetically useful method of asymmetric synthesis in organic photochemistry. Similar in many ways to the Pasteur procedure for resolving racemic carboxylic acids and organic amines, the method relies on the use of crystalline organic salts in which the enantioselectivity of a photochemical reaction of an achiral organic ion (for example, a carboxylate anion) is governed in the solid state by the presence of an optically pure counterion (for example, an optically active ammonium ion). Such optically pure counterions are termed ionic chiral auxiliaries. Salts containing ionic chiral auxiliaries are required to crystallize in chiral space groups, which provide the asymmetric environment necessary for chiral induction. Using this methodology, we have obtained near-quantitative optical yields in a wide variety of photochemical reactions.Key words: photochemistry, solid state, chiral auxiliaries, asymmetric synthesis, crystal structurereactivity relationships.