bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics and mechanism of covalent addition of S(IV) species to the acridinium cation
Authors: Ros Maria P. , Thomas Jesus , Crovetto Guillermo , Llor Juan
Published: May 2006

The reaction of acridine with S(IV) species (SO2•H2O, HSO3−, and SO32−) to form the adduct acridine–S(IV) has been studied spectrophotometrically throughout the pH range 2.6–8 in aqueous solutions. The observed pseudo-first-order rate constants, kobs, were determined at 25 °C and ionic strength I = 0.11 M, and the pH profile of the rate reached a maximum at pH ≈ 6.1. At constant pH the kobs values were a linear function of the total S(IV) concentration with slopes that increased significantly with pH. These data are consistent with the rate-determining attack of SO3H− and SO32− upon the C-9 of the acridinium cation. A nonlinear least-squares fitting of the experimental values to the model equation, within the overall pH region studied, yields the pH-independent rate constants k1 = 3.7 ± 0.1 and k2 = (6.24 ± 0.04) × 104 M−1 s−1 for the attack of these two species, respectively. The experimental results agree very well with the kinetic model. Due to the experimental conditions used we did not detect any possible pseudobase formation in the pH range studied. The reactivity of the S(IV) species with acridine follows the order: [Formula: see text] The value obtained for the ratio k1/k2 is similar to the results given for other addition reactions of S(IV) species to the double bond of carbonyl compounds such as benzaldehyde and formaldehyde. Key words: covalent addition, acridine, acridine – S(IV) adducts, kinetics and mechanism.
Synthesis and characterization of polymer-bound selenium coronands: enhancing the stability of reactive dications by restricting intermolecular interactions
Authors: Cordova-Reyes Ivan , Hu Hanbin , Gu Jian-Hua , Vandenhoven Elizabeth , Mohammed Ali , Holdcroft Steven , Pinto B. Mario
Published: May 2006

The stepwise synthesis of 1,5,9,13-tetraselenacyclohexadecan-3-ol 7 from the reaction of sodium propane-1,3-bisselenolate-2-ol with 4,8-diselenaundecan-1,11-di-p-toluenesulfonate 5 in THF and ethanol in 62% yield is described. Compound 5 is obtained from the corresponding diol 3, which is obtained, in turn, from the reaction of sodium propane-1,3-bisselenolate with two equivalents of 3-chloropropanol. 1,5-Diselenacyclooctan-3-ol 9 and 1,5,9,13-tetraselenacyclohexadecan-3,11-diol 10 are obtained in yields of 43% and 11%, respectively, from the one-step reaction of sodium propane-1,3-bisselenolate-2-ol with 1,3-dibromopropane. Polymers with pendant selenium coronands, 1,5-diselenacyclooctane (8Se2) and 1,5,9,13-tetraselenacyclohexadecane (16Se4), have been prepared by free radical polymerization of the corresponding selenium coronands 9 and 7, derivatized as their acryloyl esters 11 and 12. Copolymers of methyl acrylate and 3,7-diselenacyclooctyl acrylate 11 have also been prepared in analogous fashion. The polymers have been characterized by 1H and 13C NMR, IR, and UV–visible spectroscopy. The redox chemistry of polymer-bound selenium coronands in solution, and in the form of thin films coated on electrodes, has been determined by electrochemical methods. Selenium coronands attached to the polymer chain exhibit enhanced oxidative stability compared to monomeric analogues, presumably because restrictive motion of polymer-bound moieties inhibits inter- and intra-molecular degradation reactions. Electroactivity of polymer-modified electrodes is restricted to a few monolayers close to the electrode surface. Spatial separation of coronands along the chain, achieved by copolymerization with electro-inert methyl acrylate, gave copolymer-modified electrodes that possessed even greater redox stability than their corresponding homopolymers. Furthermore, by blending electro-inert poly(methyl acrylate) with electroactive selenium coronand copolymers, polymer-modified electrodes that possessed superior electrochemical stability were obtained. Key words: selenium coronands, polymers, electrochemistry, dications.
Reflections on the outer-sphere mechanism of electron transfer
Authors: Swaddle Thomas W.
Published: May 2006

The quantitative efficacy of the Stranks–Marcus–Hush theory of volumes of activation ΔV‡ for outer-sphere electron transfer between metal complexes in solution is assessed. The theory predicts ΔV‡ accurately for several couples in aqueous solution, but is satisfactory for polar nonaqueous solvents only at pressures of ca. 100 MPa and above, and accuracy is not improved when the molecular nature of the solvent is allowed for through the Mean Spherical Approximation approach. At low pressures, the calculations become numerically unstable when the isothermal compressibility of the solvent is high and its relative permittivity is low, particularly for the more highly charged couples. For aqueous systems, departures from the predicted ΔV‡ afford insights into the role of the counterions, the incursion of inner-sphere pathways, the enhanced reactivity of CoIII/II cage complexes relative to conventional chelates, and the question of "spin forbiddenness" of electron transfer processes that involve a large change in spin multiplicity. Key words: redox kinetics, inorganic reaction mechanisms, pressure effects, Marcus–Hush theory, activation volumes.
Inner-shell excitation spectroscopy of aniline, nitrobenzene, and nitroanilines
Authors: Turci Cassia C. , Urquhart Stephen G. , Hitchcock Adam P.
Published: May 2006

Oscillator strengths for C 1s, N 1s, and O 1s excitation spectra of aniline, nitrobenzene, and the isomeric nitroanilines have been derived from inner-shell electron energy loss spectroscopy recorded under low momentum transfer conditions (> 2.5 keV impact energy and small scattering angle, θ ≤ 2°). Extended Hückel Molecular Orbital (EHMO) calculations carried out within the equivalent core analogy are used to aid spectral interpretation. These spectra are used to investigate the sensitivity of core excitation spectroscopy to charge transfer interactions in aromatic molecules that have both electron-donating and electron-withdrawing substituents. Strong multielectron excitation features were not found, although these had been anticipated from photoemission studies. The C 1s → π* and N 1s (NH2) → π* spectral features of the nitroanilines are found to be strongly dependent on the substitution pattern (ortho, meta, or para). Key words: electronic structure, inner-shell excitation, nitroanilines, EHMO calculations.
Cohesive properties of metals as determined from atomic charge densities
Authors: Tal Yoram
Published: May 2006

A direct relation between the charge density of a free atom, ρa(r), and the cohesive energy of the corresponding metal is proposed. This relation is based on an approximation for the metallic charge density, ρm(r), that is constructed from ρa(r) through [Formula: see text] being the atomic volume of the metallic atom, and R0 the corresponding Wigner–Seitz radius. The cohesive energy Ecoh is then related to [Formula: see text] through [Formula: see text] A systematic study of 29 metallic elements including the 3d and 4d transition elements shows that the proposed relation is, in general, at least as accurate as recent ab initio results. In the same fashion, an expression for the metallic bulk modulus is derived. This expression requires, in addition to [Formula: see text], the values of ρa(R0) and its first derivative ρ′a(R0). The computed bulk moduli are, again, at least as good as the ab initio ones for the set of metallic elements studied. Key words: cohesive energies, bulk moduli, charge density, transition elements.
Applications and evaluation of IGAIM 13C and 1H chemical shift calculations for unsaturated hydrocarbons and organolithium compounds
Authors: Werstiuk Nick Henry , Ma Jiangong
Published: May 2006

Wave functions obtained at the RHF/6-31+G(d) level of theory were used with the new method IGAIM (individual gauges for atoms in molecules) developed by Keith and Bader to calculate the isotropic 13C and 1H NMR chemical shifts of a group of neutral molecules (bicyclo[3.2.1]octa-2,6-diene (1), bicyclo[3.2.1]oct-6-ene (2), bicyclo[2.2.1]hepta-2,5-diene (3), benzene (4)), carbanions (prop-2-en-1-yl (allyl) (5), bicyclo[3.2.1]octa-3,6-dien-2-yl (8)), and lithium complexes (prop-2-en-1-yllithium (6) and its dimer 7, bicyclo[3.2.1]octa-3,6-dien-2-yllithium (9)). The theoretical isotropic 13C NMR chemical shifts of the neutral molecules, relative to the calculated value for TMS(tetramethylsilane), are in excellent agreement with the experimental values, with differences between the sets of data ranging from +4.9 to −7.1 ppm. For the same group of compounds the theoretical 1H shifts are lower than the experimental values by increments ranging between 0.4 and 1.29 ppm. For allyllithium, which exists as an unsymmetrical fluxional dimer, the theoretical averaged 13C shifts are larger, 2.6 ppm for the terminal carbons and 16.7 ppm for the central carbon, than the experimental values. In the case of 8, originally considered to be a bishomoaromatic species, the theoretical 13C chemical shifts of its Li+ complex 9 differ from the experimental ones for THF-solvated 9 by values that range from +6.2 to −15.0 ppm. Yet, the relative theoretical chemical shifts — of special importance is the fact that the carbons of the vinylene bridge of this compound are unusually shielded relative to the parent diene 1 — correlate with the experimental data. The 1H chemical shifts calculated for the hydrocarbons 1, 2, 3, 4 and the lithium complexes 7 and 9 range from 0.08 to 1.38 ppm less than the experimental values. To gain information on whether variations in charge density play a significant role in determining the magnitudes of the chemical shifts, we used AIMPAC calculations to obtain the atom electron populations of diene 1, 5, 6, dimer 7, 8, and 9. We find no obvious correlation between the charges on the carbon atoms and the 13shifts for this set of compounds. Key words: IGAIM, calculations, 13C and 1H chemical shifts, unsaturated hydrocarbons, organolithium compounds.
The theory of atoms in molecules as a tool to investigate the reactivity of tetraphosphacubane
Authors: Mó O. , Yáñez M.
Published: May 2006

Bader's theory of atoms in molecules is used to rationalize the gas-phase reactivity of tetraphosphacubane vs, H+, Li+, Na+, and Be2+. For this purpose we have used MP2 densities obtained at the 6-31G(d,p) level. The characteristics of the C—P bonds of tetraphosphacubane are discussed. The Laplacian of its electron charge density shows that both phosphorus and carbon atoms are active centers for electrophilic substitutions. This is consistent with the fact that both phosphorus and carbon protonated species are minima of the potential energy surface. The strong charge redistribution associated with carbon protonation explains the enhanced stability of the carbon protonated species with respect to the phosphorus protonated one. The Laplacian field also shows the existence of a cavity inside the cage surrounded by high electronic density that can stabilize a cation of the appropriate size. Our results confirm that Li+ and Be2+ fulfil this requirement and the corresponding complexes, where the cation is located inside the cage, are minima of the corresponding potential energy surface. Na+ is far too large and a similar structure is a saddle point of the potential energy surface. Key words: atoms-in-molecules theory, tetraphosphacubane, reactivity, cationization.
Halide ion trapping of nitrenium ions formed in the Bamberger rearrangement of N-arylhydroxylamines. Lifetime of the parent phenylnitrenium ion in water
Authors: Fishbein James C. , McClelland Robert A.
Published: May 2006

The acid reactions of five arylhydroxylamines (Ar = 2,6-Me2C6H3, 2,5-Me2C6H3, 2-MeC6H4, 2-ClC6H4, and C6H5) have been studied at constant ionic strength (NaClO4) in the presence of varying amounts of NaBr and NaCl. Each system resulted in the corresponding p-aminophenol, the product of Bamberger rearrangement, as the only detectable product in the absence of halide. The addition of halide ion reduced the yield of this product, with the appearance of the corresponding p-haloaniline, o-haloaniline (where appropriate), and the parent aniline (predominantly with bromide). Rate constants for the reaction were measured in the case of the parent and 2,6-dimethyl systems and showed small decreases (chloride) or increases (bromide) with increasing halide concentration. These changes did not correlate with the change in products, implying that the rate variations were caused by specific salt effects. Product data were analyzed by a mechanism involving rate-limiting formation of the appropriate arylnitrenium ion followed by product-determining steps involving trapping by the solvent or by the added halide. The possibility that a portion of the halide-trapped products were derived from a pre-association mechanism was also included. Kinetic analyses then produced kBr:kw and kCl:kw ratios for two limiting cases, one involving pre-association with an equilibrium constant kas = 0.3, and one ignoring pre-association. From an azide:water ratio (kAz:kw) previously determined for the 2,6-dimethylphenylnitrenium, kBr was concluded to lie in the range (4–5) × 109 M−1 s−1 for all of the nitrenium ions of this study. This range for kBr then led to kw values of (1–2) × 109 s−1 (2,5-Me2), (2–3) × 109 s−1 (2-Me), and (4–8) × 109 s−1 (parent and 2-Cl), where the ranges reflect uncertainties in the exact value of kBr and in the contribution from pre-association. The lifetime of the parent phenylnitrenium ion in water at one molar ionic strength is concluded to lie in the range 125–250 ps. Key words: nitrenium ion lifetime, phenylhydroxylamine, phenylnitrenium ion, Bamberger rearrangement.
The thermolysis of ε-halodisilanes: a preference for 1,2-Si Si → O rearrangement or Si—O cleavage over Si=O bond formation
Authors: Roos Christopher , McGibbon Graham A. , Brook Michael A.
Published: May 2006

Tris(trimethylsilyl)-2,2,2-trifluoroethoxysilane 6, tris(trimethylsilyl)-2-fluoroethoxysilane 7, and tris(trimethylsilyl)-2-chloroethoxysilane 8 were synthesized and characterized by 1H, 13C and 29Si NMR, IR spectroscopy, and EI and CI mass spectrometry. Thermodynamic considerations would suggest that, as a result of the driving force provided by the formation of a Si—F or Si—CI bond, the thermolyses of these compounds would lead to the formation of bis(trimethylsilyl)silanone 4. To examine this question, gas chromatography–mass spectrometry was as used a detection technique for products resulting from the high-pressure thermolyses of 6–8. The elimination of (Me3Si)3SiCl appears to be the major thermolytic pathway of decomposition for 8 at ambient or higher pressures, although it is accompanied by the formation of other products, some of which could have arisen from the addition of various halosilanes to a silanone. Neither 6 nor 7 thermolyzed cleanly; the former compound was essentially unreactive under the thermolysis temperatures used (850 °C). Of the products produced in the thermolysis of 7, no evidence for the formation of the silanone was obtained. Independently, mass spectrometry was used to study unimolecular reactions of molecular ions derived from 6–8. The major route to solitary ions appears to involve a 1,2-trimethylsilyl migration from Si to O (9 → 10) prior to decomposition, for example, of the m/z 346 parent ion in the decomposition of 6. The preparation of the ionized silanone may be a minor pathway. Some of the other fragmentation pathways for 6–8 are discussed. Key words: gas phase thermolysis, ion rearrangements, silyl group migration, silanone, halosilane.
A solid state NMR and X-ray crystallographic investigation of dynamic disorder in solid tetrahydronaphthalene derivatives
Authors: Facey Glenn A. , Connolly Terrence J. , Bensimon Corinne , Durst Tony
Published: May 2006

The solid state disorder of two tetrahydronaphthalene derivatives, N-methyl-N-methoxy-5,6,7,8-tetrahydro-1-naphthamide and 5,6,7,8-tetrahydro-1-naphthoic acid, was studied by solid state NMR and single crystal X-ray diffraction. The X-ray crystal structure of N-methyl-N-methoxy-5,6,7,8-tetrahydro-1-naphthamide was obtained at 123 K. It indicated the presence of two distinct molecular conformations. Solid state 13C CP/MAS NMR data using the dipolar dephasing technique revealed that the two conformations of the molecule are dynamically disordered, while solid state 2H NMR data, collected on a specifically deuterated analog, were used to determine the populations of each conformation as well as an apparent activation energy. Solid state NMR experiments were also used to show that 5,6,7,8-tetrahydro-1-naphthoic acid possesses the same type of dynamic disorder. Key words: deuterium NMR, solid state NMR, dynamic disorder. X-ray, tetrahydronaphthalene derivatives
Fonctionnalisation du δ-pyronène, un nouveau synthon terpénique
Authors: Quirin Marie Jeanne , Delmond Bernard , Taran Martine
Published: May 2006

δ-Pyronene, a terpenic synthon recently made industrially available from myrcene, has been characterized. It is an excellent raw material for the preparation of numerous intermediates used in the synthesis of perfumes and retinoids. Furthermore, new terpenic compounds including the cyclogeranyl skeleton have been prepared. Key words: terpenes, pyronenes, cyclogeranyl derivatives, perfumes. [Journal translation]
Total synthesis of isodeoxypodophyllotoxin using the Me3Sn radical initiated carbocyclization
Authors: Hanessian Stephen , Ninkovic Sacha
Published: May 2006

The lactone portion of the podophylotoxin framework was assembled from a free-radical carbocyclization reaction, and the target structure was constructed based on intramolecular Friedel–Crafts reaction. In addition to isodeoxypodophyllotoxin, there were formed unusual tri- and tetracyclic compounds. Key words: free-radical carbocyclization, C—Sn bond cleavage, podophyllotoxin analog.
High-pressure methods as a tool in organometallic syntheses: facilitation of oxidative addition to platinum(II)
Authors: Skauge Andrew R.L. , Shalders Richard D. , Swaddle Thomas W.
Published: May 2006

High-pressure (2 GPa) batch reactors now commercially available may offer substantial accelerations of organometallic syntheses, without resort to heating, when the activation process is multicentered or involves the generation and solvation of ions. As an example of the latter class of reactions, the kinetics of the oxidative additions of methyl and ethyl iodides (RI) to dimethyl(2,2′-bipyridine)platinum(II) in acetone have been studied over the pressure range 0–200 MPa. The volumes of activation ΔV1≠, if assumed to be constant over this range, are −11.7 ± 0.3 and −9.7 ± 0.7 cm3 mol−1, respectively, implying an acceleration of ca. 3000-fold for a batch synthesis of this sort at 2 GPa. However, a possible slight pressure dependence of ΔV1≠ may reduce this acceleration to ca. 1 000-fold. The ΔV1≠ data and the 500-fold retardation on going from R = Me to R = Et are consistent with an SN2 attack of Pt11 on the α-carbon in the alkyl iodides, forming I− and [RMe2Pt(bpy)]+. Key words: volumes of activation, high pressure, oxidative addition, platinum(II), organometallic syntheses.
The synthesis, and molecular and crystal structure of diphenyl(2-oxidonaphthylmethyl-iminoacetato)tin(IV)
Authors: Smith Frank. E. , Khoo Lian Ee , Goh Ngoh Khang , Hynes Rosemary C. , Eng George
Published: May 2006

The new diorganotin complex ((C6H5)2Sn(OC10H6CH=NCH2COO)) was prepared and characterized by 1H NMR, IR, elemental analysis, and a single crystal X-ray diffraction study. The crystals are monoclinic, space group P21/a with a = 16.9167(9) Å, b = 19.1276(16) Å, c = 26.538(2) Å, β = 100.534(6)°, V = 8442.5(11) Å3, Z = 16, and Dcalc = 1.574 Mg m−3. The final discrepancy factors are RF = 0.030, and RW = 0.021 for 6524 significant reflections. The tin atom has a distorted trigonal bipyramidal coordination, with no short intermolecular contacts. The two axial Sn—O bonds of 2.12 Å and 2.09 Å and the equatorial Sn—N bond of 2.14 Å are among the shortest found in related complexes. Key words: diorganotin(IV), bicycloazastannoxide, trigonal bipyramidal, antitumour.
Multinuclear NMR spectra of [Pt(L)Cl3]− (L = pyridine derivatives) complexes and crystal structure of trans-Pt(2,6-di(hydroxymethyl)pyridine)2Cl2•2H2O
Authors: , Fernande D. , Bensimon Corinne , Beauchamp André L.
Published: May 2006

Complexes of the type [Pt(L)Cl3]− (L = pyridine derivative) were synthesized and studied by 13C and 195Pt NMR spectroscopies. The 195Pt signals were observed between −1720 and −1897 ppm. No correlation between the δ(Pt) and the pKa of the protonated pyridine derivatives was found. The chemical shifts vary with the substituents on the pyridine ligand. Compounds with substituents in ortho positions were observed at lower fields, except for complexes containing hydroxy or amine groups. The latter compounds were observed at higher fields, close to the signals of the Pt-unsubstituted pyridine compound. These results were explained in terms of the solvent effect. The chemical shifts δ(C) and the coupling constants J(13C–195Pt) were measured and the results interpreted with a view of obtaining information on the nature of the Pt—N bond. The possibility of π-bonding between platinum and the pyridine ligand is examined. The conformation of the pyridine ring in relation to the platinum plane and the energies of the rotation barriers around the Pt—N bond in these types of platinum(II) complexes are briefly discussed. The crystal structure of trans-Pt(2,6-(HOCH2)2py)2Cl2•2H2O was determined by X-ray diffraction. The compound is monoclinic, C2/m, a = 7.022(6), b = 15.646(13), c = 8.344(10) Å, β = 93.35(8)°, Z = 2, R = 0.037. The platinum atom is located at the junction of the twofold axis and the mirror plane, the N atoms and the para-C atom of the pyridine ring are situated on the twofold axis, and the chloride ligands are on the mirror plane. The compound crystallizes with molecules of water, which are H-bonded to the hydroxy groups. The Pt—Cl bond distance is 2.306(2) Å, and that of the Pt—N bond is 2.041 (6) Å. The dihedral angle between the platinum and the pyridine planes is 79.8°. Key words: platinum, pyridine derivatives, NMR, crystal structure.
Synthesis of some phosphino- and arsinobenzenechromium tricarbonyl derivatives and metal carbonyl clusters
Authors: Cullen William R. , Rettig Steven J. , Zhang Hongli
Published: May 2006

The synthesis of a number of new phosphino- and arsinobenzenechromium tricarbonyl ligands ER2C6H5Cr(CO)3(ER2 = PEt2, PPri2, PBut2, PPh2, AsPh2AsMe2), ER[C6H5Cr(CO)3]2(ER = PEt, PBut, PPh, AsPh) has been achieved by reacting lithium derivatives of benzenechromium tricarbonyl with appropriate chlorphosphines or iodoarsines. The spectroscopic properties of these ligands are described. The structure of Pri2PC6H5Cr(CO)3was determined by an X-ray crystallographic study. This is the first solid state structure to be reported for a phosphinobenzenechromium tricarbonyl derivative. The structures of four metal carbonyl cluster complexes were also determined. Crystals of Pri2PC6H5Cr(CO)3(3, C15H19CrO3P) are monoclinic, space group P21/c, a = 8.150(2) Å, b = 13.490(2) Å, c = 15.125(1) Å, β = 100.19(1)°, Z = 4; those of Ru3(CO)11[PPri2C6H5Cr(CO)3] (15, C26H19CrO14PRu3) are monoclinic, space group P21/n, a = 8.565(2) Å, b = 21.808(3) Å, c = 17.167(3) Å, β = 97.41(2)°, Z = 4; those of Ru3(CO)10[PPh2C6H5Cr(CO)3]2(19, C32H15CrO14PRu3) are orthorhombic, space group Pbca, a = 17.367(4) Å, b = 24.471(5) Å, c = 16.096(3) Å, Z = 8; those of Ru3(CO)10[PPri2C6H5Cr(CO)3]2•CH2Cl2(16, C40H38Cr2O16P2Ru3•CH2Cl2) are orthorhombic, space group P21212, a = 13.832(3) Å, b = 17.558(2) Å, c = 10.144(1) Å, Z = 2; and those of Os3(CO)9[PEt2C6H5Cr(CO)3]3(26, C48H45Cr3O18Os3P3) are trigonal, space group [Formula: see text], a = 15.7558(4) Å, c = 12.662(1) Å, Z = 2. The structures were solved by the Patterson method and were refined by full-matrix least-squares procedures to R = 0.031,0.027, 0.029, 0.025, and 0.029 (Rw = 0.027, 0.024, 0.024, 0.023, and 0.025) for 2326, 4110, 3878, 3046, and 4093 reflections with I ≥ 3σ(I), respectively. Key words: metal carbonyl clusters, phosphinobenzenechromium tricarbonyl derivatives, arsinobenzenechromium tricarbonyl derivatives, crystal structures.
A pentaammineruthenium(III) dimer with the novel bridging ligand 4,4′-dicyanamidobiphenyl dianion
Authors: White Christopher A. , Bensimon Corinne , Crutchley Robert J. , Aquino Manuel A.S. , Greedan J.E.
Published: May 2006

The novel ligand 4,4′-dicyanamidobiphenyl dianion (bp2−) has been synthesized and characterized by 13C NMR spectroscopy, cyclic voltammetry, and crystallography. The crystal structure of [Ph4As]2[bp]•H2O showed that bp2− is approximately planar with a dihedral angle of 8.2° between phenyl ring planes and the cyanamide groups in an anti conformation. The water of crystallization is asymmetrically hydrogen bonded between cyanamide groups of adjacent bp2− ions. The crystal data for C62H48N4As2 + H2O are monoclinic crystal system and space group P21/c with a = 12.998(5) Å, b = 13.465(4) Å, c = 28.703(13) Å, β = 98.94(3)°, V = 4963(3) Å3 and Z = 4. The structure was refined by using 4555 reflections with I > 2.5σ(I) to an R factor of 0.058. The complex, [{(NH3)5Ru)2(μ-bp)][X]4, where X = tosylate or PF6− ions, was also synthesized and characterized by 1H NMR spectroscopy, cyclic voltammetry, spectroelectrochemistry, and temperature-dependent magnetic susceptibility measurements. From cyclic voltammetry measurements, the comproportionation constants to form the mixed-valence complex [{(NH3)5Ru)2(μ-bp)]3+ were estimated to be 4.1, 16, and 22 in water, acetonitrile, and nitromethane, respectively. The trend and magnitude of Kc suggests solvent valence trapping of a weakly coupled Class II ion. The MMCT band of the mixed-valence complex had to be deconvoluted from the low-energy LMCT band and had the following properties in acetonitrile, νmax = 8400 cm−1, εmax = 3300 M−1 cm−1, and Δν1/2 = 3300 cm−1. The weak superexchange mediating properties of bp2− compared to 1,4-dicyanamidobenzene dianion were suggested to arise from the larger barrier to the formation of the radical anion bp−. Key words: cyanamido, mixed valence, superexchange, ruthenium.
Photoinduced oxidative degradation of unsaturated M3(dppm)3CO2+ clusters (M = Pd, Pt) by chlorocarbons and chloride ion
Authors: Harvey Pierre D. , Provencher Réjean , Gagnon Jonathan , Zhang Tianle , Fortin Daniel , Hierso Karine , Drouin Marc , Socol Steve M.
Published: May 2006

Both M3(dppm)3CO2+ clusters (M = Pd, Pt) photoreact with chlorocarbons (Cl—R; R = CCl3, CHCl2, CH2Cl, C6H5, C10H15 (adamantyl)) and chloride ion (slowly) to produce the oxidized mononuclear species M(dppm)Cl2 as a sole isolated M-coordinated inorganic product. Such reactions do not proceed in the dark, except for R = CH2C6H5. Among the organic products, the coupling compound R–R (R = C6H5) is observed along with many phosphine compounds such as P(C6H5)3. In an attempt to elucidate the photoinduced mechanism at the early stage of the phototransformations, the following have been investigated: the ground state binding constants (K11 for M = Pd in methanol), the photochemical quantum yields of cluster disappearance (Φdis for M = Pd) as a function of substrates, substrate concentrations, excitation wavelengths, solvents (ethanol vs toluene), and presence of CO, and the emission lifetimes (τe for M = Pt) at 77 K as a function of substrate concentrations (CH2Cl2 and CHCl3) in ethanol and toluene. Some of the experimental conclusions have also been corroborated theoretically using density functional theory. Geometry optimization calculations have been performed for the model compounds [Formula: see text] Pd3(PH3)62+,[Formula: see text], [Formula: see text] and Pd3(PH3)6CO3+ in their ground states. Key words: atom abstraction, photochemistry, C-Cl bond, clusters, host-guest.
Synthesis and spectroscopic characterization of bis(trifluorophosphinyl)-gold(I) undecafluorodiantimonate(V) [Au(PF3)2][Sb2F11]
Authors: Bley B. , Bodenbinder M. , Balzer G. , Willner H. , Hägele G. , Mistry F. , Aubke F.
Published: May 2006

The synthesis of [Au(PF3)2][Sb2F11], the first example of a linear, thermally stable metal bis(trifluorophosphine) complex is achieved by CO substitution of [Au(CO)2][Sb2F11] by PF3. The [Au(PF3)2]+ cation can also be generated by reductive phosphorylation by an excess of PF3 in fluorosulfuric acid. Spectroscopic characterization involves 19F and 31P NMR in HSO3F and SO2 solution including spectral simulation by the WIN-DAISY method and FT-IR and Raman spectra. Spectroscopic evidence suggests that the metal–ligand bond involves predominantly σ-bonding with drastically reduced π-back-donation. Key words: gold(I) complex, linear; gold(I) PF3 complex; 31P NMR; 19F NMR; vibrational spectra.
1996 Bader Award Lecture Aminoacyl ethyl phosphates. Biomimetically activated amino acids
Authors: Kluger Ronald , Li Xianfeng , Loo Richard W.
Published: May 2006

Aminoacyl ethyl phosphates are functional analogues of aminoacyl adenylates, the activated intermediates formed by ribosomal enzymes from the reaction of amino acids with ATP. The aminoacyl ethyl phosphates are prepared by DCC-mediated coupling of a tetraalkylammonium salt of ethyl phosphate and an N-t-Boc-amino acid, followed by deprotection. The efficiency of the synthesis and the solubility properties of the product depend on the alkyl group in the ammonium counterion of the phosphate. N-Protected and free aminoacyl ethyl phosphates hydrolyze slowly ([Formula: see text] in neutral solution, 25 °C, ~100 h). These materials are potentially useful in biomimetic peptide synthesis, protein modification, and aminoacylation of RNA. Key words: amino acids, acyl phosphates, aminoacyl phosphates, biomimetic aminoacylation.
Extended chain 2,3-pyrazinedicarboxylate complexes of manganese(II) and cadmium(II); synthesis and structure and magnetic properties
Authors: Mao Long , Rettig Steven J. , Thompson Robert C. , Trotter James , Xia Shihua
Published: May 2006

Manganese and cadmium complexes of singly and doubly deprotonated 2,3-pyrazinedicarboxylic acid (pyzdcH2) have been prepared and studied. Crystal data: [H3O]2χ[Mn(pyzdc)2]x, 1, monoclinic, C2/c (no. 15), a = 14.472(1) Å, b = 8.475(2) Å, c = 13.0771(9) Å, β = 114.753(4)°,Z = 4; [H3O]2x[Cd(pyzdc)2]x, 2, monoclinic, C2/c (no. 15),a = 14.4857(9) Å, b = 8.502(1) Å, c = 14.9803(7) Å, β = 126.951(2)°, Z = 4; [Mn(pyzdc)(H2O)2]x•2xH2O, 3, monoclinic, P21/c (no. 14), a = 6.5523(7) Å, b = 7.6702(7) Å, c = 20.5815(6) Å, β = 93.605(5)°, Z = 4; [Cd(pyzdc)(H2O)3]x•xH2O,4, monoclinic, Cc (no. 9), a = 6.088(1) Å, b = 11.5410(9) Å, c = 15.0624(7) Å, β = 96.532(8)°, Z = 4. The structures were solved by Patterson (1,4) or direct (2,3) methods and were refined by full-matrix least-squares procedures to R = 0.036, 0.025, 0.034, and 0.022 (Rw = 0.032, 0.025, 0.036, and 0.023) for 2825, 4961, 1672, and 2641 reflections with I ≥ 3σ(F2), respectively. The structures of 1 and 2 consist of extended anionic chains of metal ions that are linked by double-bridging pyzdc2−groups, with electrical neutrality maintained by the presence of H3O+ cations in the lattice. In 3 double chains of manganese ions are cross-linked by pyzdc2− ligands forming a "ladder-like" motif. The structure of 4 consists of extended chains of cadmium ions in which single pyzdc2− groups bridge metal centres. Magnetic susceptibility studies indicate, at most, only weak antiferromagnetic exchange in 1 but moderately strong antiferromagnetic interactions in 3, mediated by bridging carboxylate groups (J = −0.27 cm−1). Key words: extended chains, manganese, cadmium, 2,3-pyrazinedicarboxylates, X-ray structures, antiferromagnetism.
Synthesis of chemically and functionally diverse scaffolds from pentaerythritol
Authors: Hanessian Stephen , Prabhanjan Hubli , Qiu Dongxu , Nambiar Sudhir
Published: May 2006

not available
Use of aldolases in the synthesis of non-carbohydrate natural products. Stereoselective synthesis of aspicilin C-3—C-9 fragment
Authors: Chênevert Robert , Lavoie Michèle , Dasser Mohammed
Published: May 2006

The C-3—C-9 main fragment of aspicilin was prepared via a fructose 1,6-diphosphate aldolase reaction. The same fragment was also synthesized by chemical transformation starting from D-arabinose. Key words: aldolase, aspicilin, arabinose, synthesis.
Kinetic isotope effects from reactions of muonium atoms in water with various ketones, and acetaldehyde: contrasts with hydrogen atoms
Authors: Stadlbauer John M. , Venkateswaran Krishnan , Walker David C.
Published: May 2006

This paper presents data showing that in dilute aqueous solutions of butanone, 3-pentanone, cyclohexanone, di-tert-butyl ketone, and acetaldehyde the addition reaction of muonium atoms occurs with a rate constant close to 1 × 108 M−1 s−1. The same value was obtained previously for acetone. Thus the reaction rate is virtually independent of the group attached to the C=O, be it a methyl, methylene, tert-butyl, or even a hydrogen atom. This is in sharp contrast to the reactivity of ordinary 1H atoms, whose rate constants are much slower and dependent on adjacent groups. In fact muonium and 1H react by different mechanisms, to form different products, so their rate ratio represents a complex kinetic isotope effect. Keywords: kinetic isotope effects, muonium atoms, muon spin rotation, ketones, hydrogen atom reactions.
On sodium clusters in C60 fullerides
Authors: Apostol M. , Rachdi F. , Goze C. , Hajji L.
Published: May 2006

Sodium (Na) clusters in octahedral cages of Na-intercalated fullerides Na6C60 and Na11C60 are studied within a Thomas–Fermi model. It is shown that the tetrahedral Na4 cluster in Na6C60 has an electric charge ~ +2.7 (in electron charge units), while the body-centered cubic Na9 cluster in Na11C60 is almost electrically neutral. Keywords: sodium clusters, alkali fullerides, Thomas–Fermi theory, ionization charge.
Micellar catalysis of organic reactions. Part 37. A comparison of the catalysis of ester and amide hydrolysis by copper-containing micelles
Authors: Broxton Trevor J. , Nasser Abdulla
Published: May 2006

The hydrolysis of a number of nitroactivated esters and amides has been studied in the presence of copper-containing metallomicelles at neutral pH. The relative rates of hydrolysis in the pure metallomicelle and in co-micelles with either cetyltrimethylammonium bromide (ctab) or Triton X-100 depends on the hydrophobicity of the substrate and whether it is completely solubilized by the copper micelle. Thus it depends on the concentration of the copper micelle. At low concentrations of copper micelle (0.2 mM) where the substrate is incompletely solubilized, the reaction is faster when 2 mM ctab is added. At higher concentrations (>0.6 mM) where the substrate may be almost completely solubilized by the copper micelle, the reaction is slower when 2 mM ctab is added. For ester hydrolysis the presence of either a carboxylic acid group or a heterocyclic nitrogen atom close to the reaction centre resulted in much larger catalysis by the metallomicelle than for model compounds without these additional groups. It is postulated that these groups coordinate with the metal ion and thus present the reaction centre close to a metal-bound hydroxyl resulting in a significant increase in the rate of bond formation, which is the rate-determining step for ester hydrolysis. For amide hydrolysis the presence of a carboxyl group ortho to the reaction centre did not lead to larger catalysis by the copper micelle than for the compound without this group. This difference is attributed to the different rate-determining steps for amide and for ester hydrolysis. Keywords: metallomicelles, ester and amide hydrolysis.
The design of radical clocks to probe the reactivity of the intermediates in arylmethyl ester photochemistry
Authors: Nevill S.M. , Pincock J.A.
Published: May 2006

The photochemistry in methanol of the esters 1–6was examined. These reactions normally proceed through radical pairs that result from homolytic cleavage of the carbon–oxygen bond in the excited singlet state. Each of the esters was designed to probe the intervention and reactivity of the substituted arylmethyl radical by incorporating a potential radical clock at the carbon of the reactive bond. For esters 1–5, the products isolated indicated that the radical clock was not reactive enough to compete with the very rapid alternate processes of the radical pair, namely, electron transfer to form the corresponding ion pair and decarboxylation of the phenylacyloxy radical (k = 4.6 × 109 s−1). Ester 6, which incorporates the extremely rapid fluorenylcyclopropylcarbinyl clock, showed very unusual reactivity. On thermal solvolysis in methanol, 6 rearranged quantitatively to the ester 20. No methyl ethers were detected. In contrast, photolysis of 6 in benzene resulted in an alternate rearrangement to the cyclobutyl ester, 22, resulting from the aryl version of the cyclopropyl-π-methane photochemical rearrangement. No ester cleavage occurred on excitation. A rationale for the latter conversion was based on stereoelectronic arguments provided by a crystal structure of 6. Keywords: photochemistry of arylmethyl esters, radical clocks.
Determination of the absolute configuration of the fragments composing the phytotoxin phomalide
Authors: Pedras M. Soledade C.
Published: May 2006

The absolute configurations of the residues constituting phomalide (1) were determined on the products resulting from acidic hydrolysis. The configurations of the amino acids Val and Leu were determined as (S) and (R), respectively, by chiral GC analysis (Chirasil-Val capillary column), employing N-trifluoroacetyl (TFA) amino acid methyl ester derivatives. The configurations of the hydroxy acids O-Phe and O-Leu were determined as (S) by 1H NMR of the Mosher's esters of the isopropyl ester derivatives. The method described allowed for the unambiguous assignment of the absolute configuration of the α-amino and α-hydroxy acid residues composing phomalide (1). Keywords: absolute configuration, depsipeptide, Mosher's ester.
Synthesis and characterization of 4-alkenyl and 4,4′-dialkenyl-2,2′-bipyridyl ligands bearing π-donor substituents
Authors: Bourgault Manuel , Renouard Thierry , Lognoné Barbara , Mountassir Chakour , Bozec Hubert Le
Published: May 2006

The synthesis of a new series of π-donor mono-and disubstituted vinyl bipyridines (donor = 4-R2N-C6H4-; 4-RO-C6H4-; (C5H5)Fe(C5H4-); (C5H5)Ru(C5H4-)) has been achieved by reaction of the mono- and dilithio species of 4,4′-dimethyl-2,2′-bipyridine and the monolithic species of 4-nonyl-4′-methyl-2,2′-bipyridine with the appropriate aldehydes. Their 1H NMR and UV–visible characterizations are reported. Keywords: 2,2′-bipyridines, π-donor substituents, UV–visible, 1H NMR, nonlinear optics.
Quantitative description of analyte migration behavior based on the dynamic complexation model in capillary electrophoresis
Authors: Peng Xuejun , Bebault Gwendolyn M. , Chen David D.Y. , Sacks Stephen L.
Published: May 2006

A theory based on dynamic complexation is used to describe analyte migration behavior in capillary electrophoresis (CE). This theory is based on a one-phase system, instead of the commonly accepted two-phase system. The migration behavior of an analyte is described by three parameters (the electrophoretic mobility of the free analyte, the electrophoretic mobility of the analyte–additive complex, and the equilibrium constant (formation constant) that determines the fractions of the free analyte and the complex at a certain additive concentration). Varying the additive concentration shifts the equilibrium and changes the viscosity of the background electrolyte. Viscosity correction is crucial in interpreting the observed migration behavior of analytes. While electroosmotic flow in a capillary often varies from one capillary to another, the viscosity of a buffer is characteristic of the buffer composition and is constant for each buffer. The electrophoretic mobility of a certain species and the equilibrium constant are intrinsic properties and are less sensitive to changes in the environment. Understanding these relationships is indispensable in CE method development and method validation. A universal resolution equation is proposed, with a separation factor that has taken both the electrophoretic mobilities and equilibria into consideration. This resolution equation gives clear guidance for the optimization of CE separations. A group of nucleosides and their phosphates are used as analytes, and β-cyclodextrin is used as the additive in the model system studied in this paper. Both the observed analyte migration behavior and the resolution of analytes agree well with this theory. Keywords: dynamic complexation capillary electrophoresis, nucleoside and nucleotide separation, capacity factor, resolution equation, viscosity correction.
Electrochemical investigation of some potential antibacterials, II
Authors: Jain Rajeev , Padmaja P. , Gupta Seema
Published: May 2006

The electrochemical behaviour of 2-(4′-sulphonamoyl)hydrazonobutyrate-1,3-diones and sulphonamoylazoaminobenzenes has been studied over a wide range of pH at dropping mercury as well as glassy carbon electrodes. Both types of compounds exhibited a 4e− reduction reaction at both electrodes. At pH > 4.5, 2-(4′-sulphonamoyl)hydrazonobutyrate-1,3-diones exhibited a 2e− reduction wave at higher potentials. Both compounds undergo a 2e− oxidation reaction. On the basis of polarography, linear and cyclic voltammetry, controlled potential electrolysis, coulometry, and spectral analysis, a detailed mechanism has been postulated for the reduction as well as the oxidation. Keywords: electrochemistry, sulphonamides, polarography, cyclic voltammetry, coulometry.
C3 Symmetric oxazolinyl ligand as catalyst in the enantioselective addition of diethylzinc to aldehydes
Authors: Chan T.H. , Zheng G.Z.
Published: May 2006

The C3 symmetric oxazolinyl ligand 1 has been synthesized. Compound 1 catalyzed the addition of diethylzinc to aromatic aldehydes to give secondary alcohols with high enantiomeric excesses (up to 90%). Keywords: diethylzinc, enantioselective synthesis, C3 symmetric ligands, enantioselective addition reactions, oxazolinyl ligands.
Synthetic studies on clerodane diterpenoids. The total synthesis of (±)-2-oxo-5α,8α-13,14,15,16-tetranorclerod-3-en-12-oic acid
Authors: Liu Hsing-Jang , Shia Kak-Shan , Han Yongxin , Sun Daqing , Wang Yu
Published: May 2006

A general synthetic approach to diterpenoids of the cis-clerodane family has been developed, leading to the first total synthesis, in racemic form, of 2-oxo-5α,8α-13,14,15,16-tetranorclerod-3-en-12-oic acid (2). The key operation involved is the face-selective Diels–Alder reaction of dienone ester 10 with trans-piperylene, giving rise to adduct 11 containing the decalin nucleus and correct stereogenic centers common to many cis-clerodane diterpenoids. Keywords: cis-clerodanes, general synthetic approach, total synthesis, face-selective Diels–Alder reaction.
Synthesis of 10-methyl-Δ4-octalins by Diels–Alder reactions of 2H-thiopyran surrogates for 1-ethenyl-2-methylcyclohexene
Authors: Ward Dale E. , Gai Yuanzhu
Published: May 2006

Diels–Alder reactions of 1-ethenyl-2-methylcyclohexene derivatives could be a versatile route to a variety of natural product skeletons that possess a 10-methyldecalin substructure with additional substitution at C-8 and C-9. These dienes are unreactive due (in part) to the presence of the vinyl methyl group, which destabilizes the necessary s-cis conformation. The use of 2H-thiopyran diene surrogates for 1-ethenyl-2-methylcyclohexene is investigated. The desired Diels–Alder adducts were not obtained by reaction of 6,7,8,8a-tetrahydro-5,5-dimethyl-3-tris(1-methylethyl)silyloxy-1H-2-benzothiopyran (7c) or 1,5,7,8-tetrahydrospiro[6H-2-benzothiopyran-6,2′-[1,3]dioxolane] (17) with N-phenylmaleimide. Reactions of 3-[2-(2-methyl-1,3-dioxolan-2-yl)ethyl]-4-[(tris(1-methylethyl)silyl)oxy]-2H-thiopyran (19) with maleimide, N-methylmaleimide, and N-phenylmaleimide under thermal conditions and with N-methylmaleimide, N-phenylmaleimide, 3-(propenoyl)-2-oxazolidinone, and methyl acrylate under Lewis acid mediated conditions (EtAlCl2, TiCl4) gave Diels–Alder adducts in moderate to good yields. In each case, those adducts were readily converted into products that are synthetically equivalent to Diels–Alder adducts of 17 with the same dienophiles. Desulfurization of those products gives 10-methyl-Δ4-octalins (2,3,4,4a,5,6,7,8-octahydro-4a-methylnapthalenes) that are synthetically equivalent to hypothetical Diels–Alder adducts of 1-ethenyl-2-methylcyclohexene-5-one. Keywords: Diels–Alder, 2H-thiopyran, cis-substituted 1,3-diene surrogate, 1-ethenyl-2-methylcyclohexene, octahydro-4a-methylnapthalene derivatives.
Synthesis of 1-N-hydroxyhydantoin 5-phosphates as potential fungicides
Authors: Hanessian Stephen , Yang Rui-Yang , Sancéau Jean-Yves
Published: May 2006

Two hydantoin analogs were synthesized utilizing an organometallic allylation reaction in aqueous solution as a key step. One of the derivatives showed weak fungicidal activity. Keywords: hydantoin, fungicide, phosphate.
The biosynthesis of the new tremulane sesquiterpenes isolated from Phellinustremulae
Authors: Cruz Elizabete R.
Published: May 2006

The tremulane sesquiterpenes isolated from the wood-rotting fungus Phellinustremulae are irregular isoprenoids derived from the cyclization and rearrangement of farnesyl pyrophosphate (FPP). The most interesting feature in the formation of the tremulane skeleton seems to involve the migration of a methyl group from one of the isoprene units. To investigate the biosynthetic origin of this unique sesquiterpene skeleton, labelling experiments were carried out by adding 13C-labelled sodium acetate to liquid cultures of Phellinustremulae. The labelling pattern was determined by 13C NMR spectral analysis of labelled tremulenediol A, which was purified as its di-p-bromobenzoate. A possible route to the tremulane skeleton, which accounts for the observed labelling pattern, proceeds from FPP, via humulene. The stereochemical course of the tremulane biosynthesis is discussed. Keywords: fungal metabolites, aspen, perhydroazulene sesquiterpenes, labelling experiments.
Synthesis of the fatty acid of pramanicin
Authors: Cow Christopher , Valentini David , Harrison Paul
Published: May 2006

The natural product tetradec-2-enoic acid-4,5-epoxide (2), which is also a component of the antibiotic pramanicin (1), was prepared in racemic form by a glycoluril-template directed approach. Two sequential additions of acetate units to decanoic acid are effected by intramolecular condensations on the template, mimicking the proposed biosynthetic pathway to 1. Cleavage of the grown trans,trans-tetradeca-2,4-dienoyl chain from the template and epoxidation yields 2. The reaction sequence illustrates the applicability of this biomimetic approach to total synthesis of natural products. Keywords: pramanicin, biomimetic, glycoluril, template.
Isolation and structure of spongilipid from the Republic of Singapore marine porifera Spongiacf. hispida
Authors: Pettit George R. , Bond Timothy J. , Herald Delbert L. , Penny Martin , Doubek Dennis L. , Williams Michael D. , Pettit Robin K. , Hooper John N.A.
Published: May 2006

Cell growth inhibitory (P388 lymphocytic leukemia) fractions from the purple marine sponge Spongiacf. hispida were employed to uncover a new biologically active monogalactosyl monoglyceride designated spongilipid (5a). The structure and absolute configuration of spongilipid was established by X-ray crystallography. Spongilipid specifically inhibited growth of the fecal opportunist Enterococcusfaecalis. Keywords: marine sponge, Spongiahispida, spongilipid.