bluuebunny/crossref_metadata_2025 huggingface dataset:
The one-electron oxidation of hydroxy(tetramesitylporphyrinato)iron(III)
Authors: Jones David H , Hinman A Scott
Published: April 2011

The oxidation of hydroxy(tetramesitylporphyrinato)Fe(III) ([Fe(tmp)]OH) has been investigated by voltammetric and spectroelectrochemical techniques in CH2Cl2 containing tetra(n-butyl)ammonium hexafluorophosphate as supporting electrolyte. In this medium, the first one-electron oxidation is reversible on the time scale of cyclic voltammetry. The UVvis spectrum, as obtained by double potential step chronoabsorptometry, indicates that the oxidation is centered at the porphyrin ring to form the corresponding π-cation radical. At longer times, or higher potentials, oxidation of [Fe(tmp)]OH leads to loss of hydroxide and formation of [Fe(tmp+)]PF6 π-cation radical. The time-dependent process is consistent with an ECE type mechanism, with the chemical step being slow conversion to neutral [Fe(tmp)]PF6. At higher potentials, the initial oxidation product loses a second electron. The overpotential dependent oxidation suggests an EEC type mechanism with the second electrochemical step being a slow heterogeneous electron transfer from the Fe-OH moiety.Key words: hydroxy(tetramesitylporphyrinato)iron(III), oxidation, electrochemistry, spectroelectrochemistry, π-cation radical.
A thermodynamic study of aqueous acetonitrile: excess chemical potentials, partial molar enthalpies, entropies and volumes, and fluctuations
Authors: Nikolova Penka V , Duff Sheldon JB , Westh Peter , Haynes Charles A , Kasahara Yasutoshi , Nishikawa Keiko , Koga Yoshikata
Published: April 2011

We measured vapour pressures of aqueous acetonitrile (abbreviated as ACN) at 6, 20, and 37°C, from which excess chemical potentials of ACN (µ EACN) were calculated. We also determined excess partial molar enthalpies of ACN (H EACN) at 6, 20, 30, 37, and 45°C. From these data, excess partial molar entropies of ACN (S EACN) were calculated at 6, 20, and 37°C. Using density data by Benson's group, excess partial molar volumes of ACN (V EACN) were evaluated. The response function data by the same group were also used to evaluate amplitude and wavelength of mean-square fluctuations in terms of volume, entropy, and cross between volume and entropy. All the above quantities and their dependence on the mol fraction of solute, i.e., the effect of additional solute on the above quantities were used to study the effect of acetonitrile on the molecular organization of H2O. It was found that acetonitrile works as a stronger structure-making solute than methanol. Rather its effect on H2O is about the same as that of propan-1-ol.Key words: aqueous acetonitrile, interaction functions, fluctuations.
An approximate ab initio method based on the DIM model
Authors: Cullen John M
Published: April 2011

Using a second quantized formulation, an approximate diatomics in molecules (DIM) theory is presented in which all three- and four-centered electronic integrals are neglected. To ameliorate the effects of this approximation, the DIM one electron operator is constructed so that the true ab initio first-order density matrix and total energy are reproduced at the HartreeFock level. The resulting model was extensively tested for a variety of basis sets for its capability of capturing both the dynamic and nondynamic components of the electron correlation energy as well as the energies of excited electronic states. A modified method in which the DIM one-electron operator is formed from the initial extended Hückel guess of the HartreeFock orbitals was also found to produce excellent results.Key words: DIM, electron correlation energy, excited states, semiempirical.
Synthesis of 5-fluoro-β-D-glucopyranosyluronic acid fluoride and its evaluation as a mechanistic probe of Escherichia coli β-glucuronidase
Authors: Wong Alexander W , He Shouming , Withers Stephen G
Published: April 2011

Synthesis of the potential mechanism-based inactivator of β-D-glucuronidases (5-fluoro-β-D-glucopyranosyluronic acid fluoride) was accomplished via a six-step process from D-glucuronic acid that involved radical bromination at C-5 and displacement of the bromide by fluoride. A key step in this process was the masking of the carboxylic acid as a phenacyl ester. This group is uniquely stable to conditions of photobromination and fluoride displacement, yet removable under very mild conditions. Incubation of the Escherichia coli β-glucuronidase with 5-fluoro-β-D-glucopyranosyluronic acid fluoride resulted in time-dependent inactivation of the enzyme through the accumulation of a covalent 5-fluoro-α-D-glucopyranosyluronic acid-enzyme. Peptic digestion of the 5-fluoro-α-D-glucopyranosyluronic acid-enzyme intermediate and subsequent analysis by liquid chromatography coupled to an electrospray ionization triple quadrupole mass spectrometer indicated the presence of a 5-fluoro-α-D-glucopyranosyluronic acid-modified peptide. This peptide was partially purified by HPLC and its sequence determined by tandem mass spectrometry in the daughter ion scan mode, permitting the identification of Glu504 as the catalytic nucleophile within the sequence ITEYGVD. This new reagent is therefore useful for the specific, mechanism-based inactivation of glycuronidases and has good potential in other studies of enzymes of this general class.Key words: β-glucuronidase, catalytic nucleophile, 5-fluoro-β-D-glucopyranosyluronic acid fluoride, electrospray MS.
Two-photon absorption of styryl-quinolinium, -pyridinium, and -barbituric acid derivatives, and intramolecular charge transfer
Authors: Wang XiaoMei , Wang Chun , Yu WenTao , Zhou YuFang , Zhao Xian , Fang Qi , Jiang MinHua
Published: April 2011

A series of new chromophores, styryl-parent end-capped with various donors, and with barbituric acid, methyl-pyridinium, and methyl-quinolinium as the acceptors, have been synthesized and characterized by element analysis or X-ray diffraction. Using the Z-scan system, their two-photon absorption (TPA) cross-section values (δ) have been determined under excitation with 10 Hz, and 1064 nm, 35 ps mode-locked Nd:YAG laser pulse in DMF with do= 0.05 M. The effective δ value is as high as 10.9 × 1048 cm4 s per photon for trans-4-(4'-N,N-diphenyl amino) styryl-N-methyl quinolinium iodide (DPASQI). The δ value increases from barbituric acid- to pyridinium- to quinolinium-derivatives apparently due to the increase in both the conjugated degree and planarity; however, when the acceptor is fixed, the δ value increases from dialkyl amino groups to diphenyl amino groups even though the latter is a weaker donor than the dialkyl amino groups. Theoretical calculations confirm that the increased distortion from planarity for the barbituric acid derivative makes its δ value decrease. The relatively large δ value for quinolinium- or pyridinium-derivatives originates from larger intramolecular charge transfer, which can be characterized by the difference of dipole moment (Δµge) between the S0 and S1, and the transition dipole moment (Mee') between S1 and S2.Key words: two-photon absorption, intramolecular charge transfer, styryl-quinolinium, styryl-pyridinium, styryl-barbituric acid.
Synthesis, X-ray crystal structure, and solid-state 13C NMR study of tris(9-crown-3)triphenylene
Authors: Buchanan Gerald W , Rastegar Majid F , Yap Glenn PA
Published: April 2011

Benzo-9-crown-3 ether trimerizes in the presence of FeCl3 and aqueous H2SO4 to produce tris(9-crown-3)triphenylene in 25.4% yield. This compound crystallizes in the monoclinic P21/c space group: a = 13.759(2) Å, b = 13.318(2) Å, c = 13.399(2) Å, β = 96.883(2)°, with Z = 4. The three 9-crown-3 ether units of the trimer possess different geometries and there is substantial deviation from coplanarity in the three aromatic rings. 13C NMR chemical shifts in the solid state are consistent with this lack of symmetry and are discussed in terms of the X-ray crystal-structure data.Key words: crown ether, trimerization, stereochemistry.
The role of a hydroxycyclopentadienyl ruthenium dicarbonyl formate in formic acid reductions of carbonyl compounds catalyzed by Shvo's diruthenium catalyst
Authors: Casey Charles P , Singer Steven W , Powell Douglas R
Published: April 2011

Addition of excess HCO2H to {2,5-Ph2-3,4-Tol2(η5-C4CO)]Ru(CO)2}2 (6) at -20°C led to the formation of [2,5-Ph2-3,4-Tol2(η5-C4COH)]Ru(CO)2(η1-OCHO) (5), a proposed intermediate in catalytic transfer hydrogenations developed by Shvo. Hydroxycyclopentadienyl formate 5 undergoes rapid reversible dissociation of HCO2H at 20°C, and undergoes decarboxylation at 1°C to form a 1:10 mixture of {[2,5-Ph2-3,4-Tol2(η5-C4CO)]2H}Ru2(CO)4(µ-H) (3):[2,5-Ph2-3,4-Tol2(η5-C4COH)Ru(CO)2H] (4). 5 does not reduce PhCHO below the temperature at which 5 is converted to hydride 4. The catalytic production of benzyl alcohol from 5 and PhCHO in the presence of excess HCO2H is not accelerated by higher concentrations of PhCHO, indicating that 5 does not directly reduce PhCHO. Formate complex 5 is the precursor of hydride 4 which transfers hydrogen to PhCHO. A crucial role for the CpOH proton in the decarboxylation of 5 was indicated by the much slower decarboxylation of the methoxycyclopentadienyl analog [2,5-Ph2-3,4-Tol2(η5-C4COCH3)]Ru(CO)2(η1-OCHO) (7). A mechanism for decarboxylation of 5 is proposed which involves reversible dissociation of formic acid to form the unsaturated dienone dicarbonyl ruthenium intermediate C, followed by simultaneous transfer of hydride to ruthenium from the formic acid carbon and of proton to the carbonyl of C from the formic acid OH group.Key words: Shvo catalyst, ruthenium formate, decarboxylation.
Efficient and regioselective synthesis of bridged ring systems by domino Knoevenagel  hetero-DielsAlder reaction
Authors: Tietze Lutz F , Ott Christian , Haunert Frank
Published: April 2011

The bridged heterocycles 1012 were efficiently prepared by a domino Knoevenagel  hetero-DielsAlder reaction of N,N'-dimethylbarbituric acid 2 and the aldehydes 68 which contain an allyl moiety as dienophile. In contrast, reaction of 2 and aldehyde 5 with a dimethylallyl moiety leads to the annulated product 9. For the formation of 1012, an exo-Z-syn and for that of 9 an endo-E-syn transition structure is proposed.Key words: bridged compounds, domino reaction, DielsAlder reaction, heterocycles, Knoevenagel reaction.
Catalytic pathways in the ethanolysis of fenitrothion, an organophosphorothioate pesticide. A dichotomy in the behaviour of crown/cryptand cation complexing agents
Authors: Balakrishnan Vimal K , Dust Julian M , vanLoon Gary W , Buncel Erwin
Published: April 2011

The rates of displacement of 3-methyl-4-nitrophenoxide ion from the pesticide, fenitrothion, by alkali metal ethoxides in anhydrous ethanol were followed spectrophotometrically. Through product analysis experiments, which included 31P NMR and GC-MS, as well as spectrophotometric analysis, three reaction pathways were identified: nucleophilic attack at the phosphorus centre, attack at the aliphatic carbon, and a minor SNAr route ([Formula: see text]7%). Furthermore, a consecutive process was found to occur on the product of attack at the phosphorus centre. For purposes of kinetic treatment, the processes at the aliphatic and aromatic carbon were combined (i.e., the minor SNAr pathway was neglected), and the observed reaction rate constants were dissected into rate coefficients for nucleophilic attack at phosphorus and at aliphatic carbon. Attack at phosphorus was found to be catalyzed by the alkali metal ethoxides in the order KOEt > NaOEt > LiOEt. Catalysis arises from alkali metal ethoxide aggregates in the base solutions used (01.8 M); treatment of the system as a mixture of free ethoxide, ion-paired metal ethoxide, and metal ethoxide dimers resulted in a good fit with the kinetic data. An unexpected dichotomy in the kinetic behaviour of complexing agents (e.g., DC-18-crown-6, [2.2.2]cryptand) indicated that the dimers are more reactive than free ethoxide anions, which are in turn more reactive than ion-paired metal ethoxide. The observed relative order of reactivity is explained in the context of the Eisenman theory in which the free energy of association of the metal ion with the rate-determining transition state is largely determined by the solvent reorganization parameter. In contrast with displacement at the phosphorus centre, attack at the aliphatic carbon was not found to be catalyzed by alkali metals. In this case, the free ethoxide anion was more reactive than either the ion-paired metal ethoxide or the dimeric aggregate. The differing effects of alkali metals on the two pathways is ascribed largely to the leaving group pKa. For carbon attack, the pKa value estimated for demethyl fenitrothion, 2.15, is sufficiently low that metal ions are not required to stabilize the rate-determining transition state. In contrast, for phosphorus attack, 3-methyl-4-nitrophenoxide, with a pKa of 7.15, requires stabilization by metal ion interactions. Hence, alkali metal ions catalyze attack at phosphorus, but not attack at the carbon centres.Key words: organophosphorothioate, pesticide, fenitrothion, ethanolysis, alkali metal ethoxide, ion-pair reactivity, dimers, catalysis, competitive pathways.
Dithiophosphinates of gold (I); oxidative addition of Cl2to a neutral, dinuclear gold(I) dithiophosphinate complex, and X-ray crystal structures of [AuS2P(C2H5)2]2, [AuS2PPh2]2, Au2(CH2)2PMe2(S2PPh2), and Au2Cl2[(CH2)2PMe2][S2PPh2]
Authors: van Zyl Werner E , López-de-Luzuriaga José M , Fackler Jr. John P , Staples Richard J
Published: April 2011

The formation and characterization of dinuclear gold(I) dialkyl- and diaryl-dithiophosphinate complexes of the type [AuS2PR2]2are described. The complexes are readily prepared from the reaction between a chlorogold(I) starting material and the corresponding dithiophosphinate salt. The structures of the complexes show both the absence (R = Et, 1) and presence (R = Ph, 2a) of intermolecular Au···Au interactions as confirmed by X-ray crystallographic study in the solid state. Reaction between [AuS2PPh2]2and [Au(CH2)2PMe2]2in CH2Cl2solution leads to a ligand transfer reaction to form the hetero-bridged complex [Au2{(CH2)2PMe2S2PPh2}] (3a) in high yield. Additionally, the latter complex reacts with Cl2to form the oxidative addition product [Au2Cl2{(CH2)2PMe2S2PPh2}] (4), the first gold(II) complex with a S-P-S bridging moiety. The X-ray crystal structure of both 3a and 4 exhibit rare boat conformations in the solid state, and 4 has a formal Au(II)Au(II) single bond of 2.5611(5) Å. Reaction between [AuS2PPh2]2and dppm (dppm = Ph2PCH2PPh2) leads to a sparsely soluble three-coordinate dinuclear gold(I) complex with the molecular formula [Au2{dppmS2PR2}2]n(n = 1 or [Formula: see text]) (5).Key words: dithiophosphinates, ylide, dithiols, gold-gold bond.
Mechanism of ipso aromatic substitution by reaction of aryloxy(methoxy)carbenes and diaryloxycarbenes with DMAD
Authors: Lu Xiaosong , Warkentin John
Published: April 2011

Some aryloxy(methoxy)carbenes and diaryloxycarbenes attack dimethyl acetylenedicarboxylate (DMAD) with aryl group transfer to an alkyne carbon of DMAD. In this study diaryloxycarbenes with different aryl groups that could be transferred competitively, were generated in the presence of DMAD to probe for the mechanism of that ipso aromatic substitution. It was found that a para electron-withdrawing substituent, relative to an electron-donating substituent, facilitated migration of an aryl group. Mechanisms in accord with these findings involve initial nucleophilic attack by the carbene at an alkyne carbon of DMAD. That step is followed by either nucleophilic, ipso attack on the aromatic ring or by electron transfer, from the side chain of the aromatic ring into the ring itself.Key words: aromatic substitution, diaryloxycarbene, DMAD, ipso, nucleophilic.
The reduction of oxygen and hydrogen peroxide on dinuclear ruthenium phthalocyanine electrocatalytic surfaces
Authors: Ebadi Mehrdad , Alexiou Christos , Lever A BP
Published: April 2011

The electrochemical properties of both mononuclear L2RuIIPc and dinuclear [(THF)Rupc]2species are described. The former is dominated by ring oxidation and reduction processes while the latter displays a series of metal localized processes. A Pourbaix diagram describes the various surfaces which can be generated by exposing a graphite electrode modified with [(THF)Rupc]2to aqueous buffer at different polarization over a wide range of pH. The behavior of these various surfaces towards the electrocatalytic reduction of both oxygen and hydrogen peroxide is described. Most importantly, three different regimes of hydrogen peroxide reduction are observed dependent on the nature of the modified electrode surface. At high pH the four electron reduction of oxygen to water is observed via a 2 + 2 mechanism.Key words: phthalocyanine, ruthenium, ruthenium phthalocyanine, cyclic voltammetry, suface modified electrode, Pourbaix diagram, electrocatalysis, oxygen reduction, hydrogen peroxide reduction.
Synthesis of sulfated mono- and ditertiary phosphines, complex chemistry and catalysis
Authors: Gulyás H , Dobó A , Bakos J
Published: April 2011

Cyclic and bicyclic sulfates have been prepared from commonly available alcohols. Nucleophilic cleavage of the cyclic sulfates affords a new type of water-soluble mono- and ditertiary phophines bearing -OSO3Li groups in distinguished positions in the molecular framework. Both phosphines have amphiphilic character. Reactions of the chiral 2 and the dppp analogue 5 with [Rh(COD)Cl]2 and Pt(PhCN)2Cl2 provide novel zwitterionic complexes. Rhodium complexes of 2 and 5 have been successfully applied in liquid biphasic hydroformylation of styrene and octene-1. When the rhodium complex of 5 was used as catalyst in hydroformylation of styrene, less then 4 ppm rhodium could be detected in the organic phase.Key words: cyclic sulfates, water soluble phosphines, amphiphilic character, Rh complexes, Pt complexes, hydroformylation.
Aggregation studies of benzoporphyrin derivative
Authors: Delmarre David , Hioka Noboru , Boch Ron , Sternberg Ethan , Dolphin David
Published: April 2011

The photophysical properties of a ring B benzoporphyrin derivative 1,3-diene dimethylester were investigated in solution (waterDMSO mixtures). At low proportions of water in DMSO, the diester obeys Beer's law at all pH values and ionic strengths investigated. For solvent systems containing more than 30% water, the extent of deviation from Beer's law as a function of porphyrin concentration is attributed to formation of porphyrin dimers. Dimerization equilibrium constants (Kd) have been determined in different percentage of solvent mixtures, using absorption and fluorescence spectroscopies, and were found to exhibit a linear correlation between log (Kd) and the inverse of the dielectric constant (log (Kd) = 24.6  1060.4 × 1/εmix). This equation permits the calculation of Kd in mixtures of waterDMSO.Key words: porphyrins, dimerization, aggregation, fluorescence, benzoporphyrin derivative, photodynamic therapy, photosensitizers.
Making a 16-electron bromo (or iodo) complex of ruthenium(II) and a CF bond in one pot
Authors: Barthazy Peter , Broggini Diego , Mezzetti Antonio
Published: April 2011

The 16e bromo or iodo complexes [RuX(dppp)2]+ (dppp = 1,3-bis(diphenylphosphino)propane, X = Br (1c), I (1d)) and [RuX(dppe)2]+ (dppe = 1,2-bis(diphenylphosphino)ethane, X = Br (2c), I (2d)) have been prepared exploiting the reaction of the fluoro complexes [RuF(dppp)2]+ (1a) and [Tl(µ-F)2Ru(dppe)2]+ (3) with activated alkyl bromides or iodides. The X-ray structures of 1c, 1d, 2c, and 2d suggest that the distortion of the Y-shaped trigonal-bipyramidal structure of [MX(P∩P)2]+ is possibly related to the formation of intramolecular hydrogen bonds between the halide ligand and the ortho-hydrogen atoms of the neighbouring phenyl rings. The five-coordinate species 1c, 1d, 2c, and 2d react with H2 to form the dihydrogen complexes [RuX(η2-H2)(P∩P)2]+. The reaction of the dppp derivatives 1c and 1d with H2 (P = 1 atm, 1 atm = 101.322 kPa) is an equilibrium. Quantitative formation of [RuBr(η2-H2)(dppp)2] (4c) is obtained under H2 pressure (100 bar, 1 bar = 100 kPa), whereas the iodo analogue is not stable under analogous conditions. The less crowded dppe derivatives 2c and 2d react quantitatively with H2 under ambient pressure. The iodo and bromo derivatives [RuX(η2-H2)(P∩P)2]+ contain elongated dihydrogen ligands, as indicated by their transverse relaxation times T1 (min). The present data suggest that Cl, Br, and I have similar donor properties in these dihydrogen complexes, and that the different chemical behaviour in the Cl, Br, I series is mainly a result of steric effects.Key words: 16e complexes, ruthenium, fluoro complexes, bromo complexes, iodo complexes, dihydrogen complexes.
Synthesis and spectroscopic properties of benzo- and naphthofuryl-3-hydroxychromones
Authors: Klymchenko Andrey S , Ozturk Turan , Pivovarenko Vasyl G , Demchenko Alexander P
Published: April 2011

With the focus of designing new fluorescent probes, four new 3-hydroxy-chromone derivatives bearing benzofuran and naphthofuran groups were synthesized. They show bathochromic absorption shifts relative to 3-hydroxyflavone with the ability of retention to display the excited-state proton transfer. Disruption of the planarity by the methyl group in the furan ring leads to a decrease of both the extinction coefficient and the contribution of long wavelength absorption band, while molecules without a methyl group showed two distinct absorption bands. Shifts to longer wavelengths are also observed in fluorescent spectra, and the absence of the methyl group results in a dramatic increase of fluorescence quantum yield and lifetime. Of the extended 3-hydroxychromone derivatives, 3-hydroxy-2-naphtho[2,1-b]furan-2-yl-chromone has shown comparable, and in some cases better, absorption and fluorescence properties than the 3-hydroxychromones synthesized so far, which make it a highly promising candidate as molecular probe for analytical chemistry, biophysics, and cellular biology.Key words: benzo- and naphthofuryl-3-hydroxyflavone, synthesis, electronic spectra, fluorescence, excited state proton transfer.
Thioacetalization of aldehydes and ketones in the presence of hydroxo complexes of platinum(II): An example of Lewis acid catalytic activity
Authors: Battaglia Lorenzo , Pinna Francesco , Strukul Giorgio
Published: April 2011

The complex [(dppb)Pt(µ-OH)]2(BF4)2 displays high catalytic activity in the thioacetalization of a variety of aldehydes and ketones with mercaptoethanol under very mild conditions. The reaction rate is greatly enhanced by the addition to the reaction mixture of magnesium perchlorate as drying agent and molar turnovers as high as 9700 can be observed. The effect of different desiccating agents is also reported. The reactivity pattern observed, the similarity with other reactions and NMR spectroscopic investigations confirm the possible role of the complex as Lewis acid catalyst in promoting the reaction.Key words: thioacetalization, catalysis, aldehydes, ketones, platinum complex.
Amide directed hydrocarboxylation ofN-allylacetamide catalyzed by the aqueous Pd - tppts - Brønsted acid system (tppts = P(C6H4-m-SO3Na)3)1
Authors: Verspui Göran , Besenyei Gábor , Sheldon Roger A
Published: April 2011

The Pd - tppts - HOTs (tppts = P(C6H4-m-SO3Na)3, HOTs = p-toluenesulfonic acid) catalyzed hydrocarboxylation of N-allylacetamide in an aqueous medium afforded 4-acetamidobutyric acid and 3-acetamido-2-methylpropanoic acid under mild conditions, with a high regioselectivity towards the linear isomer. During the hydrocarboxylation an acid catalyzed hydrolysis of the amide moieties of both the substrate and the products took place, as well as the formation of acetamide and propanal, presumably via a Pd-catalyzed allylic substitution reaction of N-allylacetamide. The hydrolysis reaction was suppressed by lowering the amount of Brønsted acid cocatalyst (HOTs) or by employing a weaker Brønsted acid such as propanoic acid. The allylic substitution reaction was minimized by increasing the CO pressure but unfortunately this caused a decrease in the regioselectivity. A sudden inhibition took place after ca. 70% conversion, presumably caused by one of the side products. By increasing the tppts concentration to 13.1 mmol L-1(20 equiv per Pd) the inhibition was circumvented and a quantitative conversion of N-allylacetamide was achieved.Key words: aqueous media, olefins, palladium, hydrocarboxylation, N-allylacetamide.
Mono- and bis-(acetylacetonato) complexes of arene-ruthenium(II) and arene-osmium(II): variation of the binding mode of η1-acetylacetonate with the nature of the arene
Authors: Bennett Martin A , Mitchell Thomas R , Stevens Mark R , Willis Anthony C
Published: April 2011

The mono(acetylacetonato) complexes [MCl(O,O'-acac)(η6-arene)] (M = Ru, Os, arene = C6H6, 1,3,5-C6H3Me3, C6Me6; M = Os, arene = 1,2-C6H4Me2, 1,2,3-C6H3Me3), which are formed from [MCl2(η6-arene)]2and thallium or sodium acetylacetonate, react with thallium acetylacetonate to give bis(acetylacetonato) complexes [M(O,O'-acac)(η1-acac)(η6-arene)]. The η1-acac ligand is bound through the gamma-carbon atom for M = Ru, Os, arene = C6H6; M = Os, arene = 1,2-C6H4Me2, 1,2,3-C6H3Me3and through a keto-oxygen atom for M = Ru, Os, arene = 1,3,5-C6H3Me3, C6Me6, the difference being attributed to a combination of steric and electronic effects. Cationic ruthenium(II) derivatives [Ru(L)(O,O'-acac)(η6-arene]+(arene = C6H6, 1,3,5-C6H3Me3, C6Me6; L = DMSO, MeCN, py, PPh3) and [Ru(CO)(O,O'-acac)(η6-arene]+(arene = 1,3,5-C6H3Me3,C6Me6), and neutral osmium(II) η1-acetato derivatives [Os(η1-OAc)(O,O'-acac)(η6-arene)] (arene = C6H6, 1,2-C6H4Me2, 1,2,3-C6H3Me3, 1,3,5-C6H3Me3, C6Me6) are also described. The molecular structures of the following complexes have been determined by X-ray crystallography: [Os(O,O'-acac)(η1-C-acac)(η6-1,2-C6H4Me2)], triclinic, space group P[Formula: see text] (No. 2), a = 9.922(2), b = 9.974(2), and c = 11.001(2) Å, α = 68.33(1), β = 64.18(1), and γ = 62.38(1)°, V = 849.0(3) Å3, Z = 2; [Os(O,O'-acac)(η1-O-acac)(η6-1,3,5-C6H3Me3)], monoclinic, space group C2/c (No. 15), a = 16.032(4), b = 11.989(3), and c = 21.562(7) Å, β= 108.91(2)°, V = 3921(2) Å, Z = 8; [Os(η1-OAc)(O,O'-acac)(η6-C6H6)], triclinic, space group P[Formula: see text] (No. 2), a = 8.368(4), b = 8.402(4), and c = 11.008(4) Å, α = 71.68(3), β = 69.35(3), and γ = 69.77(3)°, V = 663.0(6) Å3, Z = 2.Key words: arene-ruthenium, arene-osmium, acetylacetone, crystal structures.
The fluxionality and crystal structures of [Fe3(CO)10L2] (L2= dppm, (Ph2P)2NH, {(EtO)2P}2O) and [Fe3(CO)9(dppm){P(OMe)3}]
Authors: Adams Harry , Agustinho Sylvana C , Chomka Krystyna , Mann Brian E , Smith Stephen , Squires Clare , Spey Sharon E
Published: April 2011

The crystal structures of [Fe3(CO)10L2] (L2= dppm, (Ph2P)2NH, {(EtO)2P}2O) and [Fe3(CO)9(dppm){P(OMe)3}] (dppm = (Ph2P)2CH2) have been determined. [Fe3(CO)10L2] (L2= dppm, (Ph2P)2NH, {(EtO)2P}2O) adopt a stereochemistry in the crystal with the bidentate ligand across an unbridged Fe-Fe edge, resulting in one phosphorus ligand being unusually in the axial position. In contrast, [Fe3(CO)9(dppm){P(OMe)3}] adopts a stereochemistry in the crystal with the bidentate ligand across the bridged Fe-Fe edge. The structures of the [Fe3(CO)10L2] (L2= dppm, (Ph2P)2NH, {(EtO)2P}2O) support the Mann concerted bridge - opening bridge - closing mechanism of carbonyl fluxionality rather than the Johnson libration mechanism. The fluxionality of the compounds in the13C NMR spectra is explained by a combination of the concerted bridge - opening bridge - closing, merry-go-round, and trigonal twist mechanisms, and ΔGvalues were determined.Key words: iron carbonyls, crystal structures,13C NMR spectroscopy, fluxionality, mechanisms.
A temperature-controlled reversible ionic liquid - water two phase - single phase protocol for hydrogenation catalysis
Authors: Dyson Paul J , Ellis David J , Welton Thomas
Published: April 2011

An ionic liquid  water system that undergoes a reversible two phase  single phase transformation dependent upon temperature has been used as a novel medium for the transition-metal-catalyzed hydrogenation of a water soluble substrate. At room temperature, the ionic liquid 1-octyl-3-methylimidizolium tetrafluoroborate, containing [Rh(η4-C7H8)(PPh3)2][BF4] catalyst, forms a separate layer to water containing 2-butyne-1,4-diol. In a stirred autoclave the mixture was pressurized with hydrogen to 60 atm (1 atm = 101.325 kPa) and heated to 80°C giving a homogeneous single phase solution. On cooling to room temperature, two phases reform, with the ionic liquid phase containing the catalyst and the aqueous phase containing a mixture of 2-butene-1,4-diol and butane-1,4-diol products that can be simply removed without catalyst contamination.Key words: ionic liquids, biphasic catalysis, hydrogenation, rhodium.
The ozonolysis of ortho-xylene and its relevance to the history of the benzene problem
Authors: Wolfe Saul , Shi Zheng
Published: April 2011

Using B3LYP density functional theory in conjunction with the 6-311++G** basis set, the relative rates of the initial rate-determining attack of ozone upon the carboncarbon bonds of o-xylene are found to be 4,5- [Formula: see text] 3,4- > 2,3- > 1,2-. With the assumption that the final products glyoxal (G), methylglyoxal (M), and dimethylglyoxal (D) are determined by the site of the initial attack, and taking statistical factors into account, the ratio G:M:D is calculated to be 3:2:1. This is close to the value found experimentally, and identical to the result predicted by the contention that two nearly equivalent KekuléPauling valence bond (resonance) structures of o-xylene exist and each localized carboncarbon double bond of these structures is oxidized at the same rate. Although Frontier Molecular Orbital theory also predicts a 3:2:1 ratio of G:M:D, this theory incorrectly predicts that the initial attack of ozone will take place at the 1,2- and 4,5- bonds, with 1,2-attack slightly preferred. These results are discussed in relation to a recent historical analysis of the benzene problem, and it is concluded that since the products of ozonolysis of o-xylene are determined by the relative energies of the transition states leading to the four possible primary ozonides, these transition states should be the focus of theory.Key words: Kekulé structure, resonance, frontier orbital theory, density functional theory, kinetics.
Electrical conductivity, speeds of sound, and viscosity of aqueous ammonium nitrate solutions
Authors: Wahab Abdul , Mahiuddin Sekh
Published: April 2011

Density, electrical conductivity, speeds of sound, and viscosity of aqueous ammonium nitrate solutions were measured as functions of concentration (m, mol kg1) (0.1599 [Formula: see text] m [Formula: see text] 20.42) and temperature (T, K) (273.15 [Formula: see text] T [Formula: see text] 323.15). Experimental values are consistent with the reported data. Variation of isotherms of electrical conductivity, isentropic compressibility, and structural relaxation time with concentration evoke structural information on the ion solvation in aqueous ammonium nitrate solution at different concentration regions. The primary hydration numbers of ammonium nitrate were estimated at a particular concentration at which the isentropic compressibility isotherms converge. The existence of free hydrated ions, resulting from strong ion solvent interactions in dilute to 9.1 mol kg1, the solvent-separated ion-pairs resulting from the relative competition between the ionsolvent and the ionion interactions in 9.1 to 12.0 mol kg1, and the solvent-shared ion-pairs beyond 12.0 mol kg1 resulting from a decrease in the number of solvent molecules, govern the transport process.Key words: electrical conductivity, speeds of sound, viscosity, ammonium nitrate, hydration number.
Tetrazole ethers from lignin model phenols: synthesis, crystal structures, and photostability
Authors: Lu Andy Z , Hu Thomas Q , Osmond David A , Patrick Brian O , James Brian R
Published: April 2011

The phenolic OH moiety in lignin is one of the key functional groups responsible for the photo-induced yellowing of mechanical wood pulps and papers. To evaluate new protective groups for the stabilization of lignin phenols, the model compounds, 2-methoxy-4-propylphenol (1) and 4-hydroxy-3-methoxyacetophenone (2) were reacted with 5-chloro-1-phenyl-1H-tetrazole to give the corresponding tetrazole ethers 1' and 2', respectively, that were then studied for their photostability. The synthesis of these ethers was more efficient than that of alkyl ethers because of less hydrolysis of the alkylating agent under the reaction conditions. Compounds 1' and 2' were fully characterized, including X-ray crystal structure analyses. Crystals of 1' and 2' were monoclinic of space groups P21/c and P21/a, respectively. For 1': a = 9.8679(6), b = 16.708(1), c = 10.2841(6) Å, β = 109.732(5)°, Z = 4. For 2': a = 7.7212(2), b = 27.350(5), c = 14.569(3) Å, β = 101.30(2)°, Z = 8. The structures were solved by direct methods and refined by full-matrix least-squares procedures to R = 0.039 (Rw = 0.046) for 2029 reflections with I [Formula: see text] 3σ(I) (for 1'), and to R = 0.055 (Rw = 0.073) for 3634 reflections with I [Formula: see text] 3σ(I) (for 2'). Compound 2' was much more photostable than the precursor phenol on exposure to strong fluorescent light, while 1' was only slightly more stable than the precursor phenol.Key words: alkylation, ethers, lignin model compounds, methylation, phenols, yellowing inhibition.
Synthesis of trichiliasterones A and B  16-Ketosteroids isolated from Trichilia hirta and Trichilia americana
Authors: Hantos Susanne M , Tripathy Sasmita , Alibhai Najma , Durst Tony
Published: April 2011

The syntheses of trichiliasterone A (3β-hydroxypregnan-2,16-dione) and trichiliasterone B (2-hydroxyandrost-1,4-diene-3,16-dione) have been carried out starting from isoandrosterone and testosterone acetate, respectively. In each synthesis the functionality in the D ring was installed prior to working on ring A. In the case of trichiliasterone A, the D ring chemistry involved a Wittig reaction to generate the 17-methylene group, followed by SeO2 oxidation to give an α,β-unsaturated ketone. Reaction with lithium dimethyl cuprate gave the required 17-ethyl-16-keto functionality. A 2,3-epoxy enol acetate served as the key intermediate for the generation of the 2-keto-3-hydroxy functions in ring A. The transposition of the keto function from C-16 to C-17 in the synthesis of trichiliasterone B was accomplished via oxymercurationdemercuration of the Δ1617 double bond followed by oxidation. The hydroxyl group at C-2 and the additional ring A unsaturation were introduced by lead tetra-acetate treatment of the 3-keto-4-enone function and subsequent air oxidation.Key words: 16-ketosteroids, plant steroids, Trichilia hirta, trichiliasterones.
Organometallic reactions in aqueous media  Antimony-mediated allylation of carbonyl compounds and the nature of allylstibine intermediates
Authors: Li Lian-Hai , Chan Tak Hang
Published: April 2011

Commercial antimony metal, in aqueous 1 M H(D)Cl solution, reacts with allyl bromide and aldehydes to give the corresponding homoallylic alcohols in good yield. The reaction proceeds through the formation of allylstibine intermediates. The structures of the allylstibine intermediates are likely to be allylstibine dibromide and diallylstibine bromide.Key words: allylation reaction, aqueous organometallic reactions, homoallylic alcohols, allylstibine dibromide, diallylstibine bromide.
Isomerization of (Z)-alkenylsilanes to (E)-isomers with hydrosilane and RhI(PPh3)3
Authors: Mori Atsunori , Takahisa Eisuke , Nishihara Yasushi , Hiyama Tamejiro
Published: April 2011

Isomerization of (E)-2-phenylethenylsilanes to the (Z)-isomers is found to easily take place at 60°C within 1 h using 20100 mol% of a hydrosilane and 0.1 mol% of RhI(PPh3)3 and is understood in terms of insertion of alkenylsilanes to hydridorhodium followed by β-hydride elimination.Key words: hydrosilylation, isomerization, RhI(PPh3)3, alkenylsilane, hydrosilane.
An 1H and 13C NMR conformational study of 2-(benzotriazol-1-yl)-substituted tetrahydropyrans
Authors: Katritzky Alan R , Akhmedov Novruz G , Denisenko Sergey N , Perumal Subbu
Published: April 2011

Proton and carbon NMR signals for 2-(benzotriazol-1-yl)tetrahydropyrans are assigned on the basis of spin decoupling, H,H-COSY, HETCOR, and nuclear Overhauser enhancement experiments. Conformational preferences are deduced. It was found that 2-(benzotriazol-1-yl) substituents: (i) prefer the equatorial orientation; and (ii) display a rotameric preference to minimize the electronic repulsion and (or) steric interaction.Key words: anomeric, NMR, tetrahydropyrans.
Synthesis, characterization, and application in asymmetric catalysis of dendrimers containing chiral ferrocenyl diphosphines
Authors: Köllner Christoph , Togni Antonio
Published: April 2011

Starting from the functionalized Josiphos derivatives (R)-1-[(S)-2-(diphenylphosphino)-1'-(dimethyl-3''-aminopropylsilyl)-ferrocenyl]ethyldicyclohexylphosphine ((R)-(S)-3), (R)-1-[(S)-2-(diphenylphosphino)-1'-(hydroxy methyl) ferrocenyl]ethyldicyclohexylphosphine ((R)-(S)-4), and (R)-1-[(S)-2-(diphenylphosphino)-1'-(3''-hydroxy propyl)ferrocenyl]ethyldicyclohexylphosphine ((R)-(S)-5), a series of dendrimers containing up to sixteen ferrocenyl diphosphine units were prepared. Dendrimer cores are based on benzene 1,3,5-tricarboxylic acid and 1,3,5,7-adaman tanetetracarboxylic acid, with 5-substituted isophthalic acid derivatives constituting the branching units. The dendrimers have been used in three different asymmetric catalytic reactions: Rh-catalyzed hydrogenation of dimethyl itaconate, Pd-catalyzed allylic substitution, and Rh-catalyzed hydroboration of styrene with catecholborane. In all three reactions the selectivity obtained with the dendrimers was very similar to the one obtained with the parent ligand Josiphos.Key words: dendrimer, asymmetric catalysis, ferrocenyl ligands, hydrogenation.
Spectroscopic studies of the electrophilic activation of amides with triflic anhydride and pyridine
Authors: Charette André B , Grenon Michel
Published: April 2011

The reaction of amides with trifluoromethanesulfonic (triflic) anhydride in the presence of pyridine was thoroughly investigated by NMR spectroscopic techniques. Different pyridinium intermediates were generated from secondary amides, tertiary amides with enolizable protons, and tertiary amides lacking enolizable protons. It was found that the actual triflating reagent is N-(trifluoromethylsulfonyl)pyridinium triflate 11 which is formed by the initial reaction of triflic anhydride with pyridine. The alcoholysis of these intermediates yields O-alkyliminium ethers which can then be easily hydrolyzed under mild acidic conditions to the corresponding esters.Key Words: amides, triflic anhydride, pyridinium intermediates, NMR study.
Studies on enolate chemistry of 8-thiabicyclo[3.2.1]- octan-3-one: enantioselective deprotonation and synthesis of sulfur analogs of tropane alkaloids
Authors: Majewski Marek , DeCaire Marc , Nowak Pawel , Wang Fan
Published: April 2011

Enantioselective deprotonation of 8-thiabicyclo[3.2.1]octan-3-one (1) with chiral lithium amides, followed by reactions with electrophiles affords sulfur analogs of tropane alkaloids of pyranotropane family. Thus, deprotonation of 1 with (S)-N-(diphenyl)methyl-1-phenylethylamine (11d), followed by the reaction of the resulting nonracemic enolate with benzaldehyde gives the corresponding aldol product as one diastereoisomer (exo, threo) and in high enanatiomeric purity (95% ee). Trimethylsilyl chloride, acetic anhydride, and acyl cyanides react readily with the lithium enolate to give the corresponding derivatives of 1, however common alkylating agents fail to provide C-alkylated products. The reaction with acyl cyanides derived from α,β-unsaturated carboxylic acids (e.g., cinnamoyl cyanide) can be utilized in synthesis of thia-analogs of tropane alkaloids physoperuvine and isobellendine (13, 15).Key words: enantioselective deprotonation, tropane alkaloids.
Synthesis, characterization, and thermodynamics of tertiary phosphine cobalt(III) Schiff-base complexes
Authors: Asadi Mozaffar , Sarvestani Ali Hossein
Published: April 2011

[Co(5-nitroSalen)(PBu3)]ClO4·H2O and [Co(Salpd)(PBu3)]ClO4·H2O were synthesized and characterized. The stability constants and the thermodynamic parameters were measured spectrophotometrically for 1:1 adduct formation of [CoL(PBu3)]ClO4·H2O, (L = Salen, 5-nitroSalen, Salpd), and [Co(Salen)(PMe2Ph)]ClO4·H2O as acceptors with P(OR)3, (R = Me, Et, i-Pr) as donors, in acetonitrile solvent and in constant ionic strength (I = 0.01 M) and at various temperatures. The trend of the reactivity of cobalt(III) Schiff-base complexes with PBu3 axial ligand toward a given donor is as follows: 5-nitroSalen > Salen > Salpd.Also, the following reactivity trend of the donors toward a given cobalt(III) Schiff-base complex is in the operation: P(O-i-Pr)3 > P(OEt)3 > P(OMe)3.Key words: cobalt(III) Schiff-base complexes, thermodynamic parameters, trialkylphosphite, adduct complexes, stability constants.
Solubility predictions for crystalline nonelectrolyte solutes dissolved in organic solvents based upon the Abraham general solvation model
Authors: Acree, Jr. William E , Abraham Michael H
Published: April 2011

The Abraham general solvation model is used to predict the saturation solubility of crystalline nonelectrolyte solutes in organic solvents. The derived equations take the form of log (CS/CW) = c + rR2+ sπ2H+ aΣα2H+ bΣβ2H+ vVxand log (CS/CG) = c + rR2+ sπ2H+ aΣα2H+ bΣβ2H+ l log L(16)where CSand CWrefer to the solute solubility in the organic solvent and water, respectively, CGis a gas-phase concentration, R2is the solute's excess molar refraction, Vxis McGowan volume of the solute, Σα2Hand Σβ2Hare measures of the solute's hydrogen-bond acidity and hydrogen-bond basicity, π2Hdenotes the solute's dipolarity and (or) polarizability descriptor, and log L(16)is the solute's gas-phase dimensionless Ostwald partition coefficient into hexadecane at 298 K. The remaining symbols in the above expressions are known equation coefficients, which have been determined previously for a large number of gassolvent and watersolvent systems. Computations show that the Abraham general solvation model predicts the observed solubility behavior of anthracene, phenanthrene, and hexachlorobenzene to within an average absolute deviation of about ±35%.Key words: solubility predictions, organic solvents, nonelectrolyte solutes, partition coefficients.
Geometric and solvent effects on intramolecular phenolic hydrogen abstraction by carbonyl n,π* and π,π* triplets
Authors: Lathioor Edward C , Leigh William J
Published: April 2011

The photochemistry of a series of alkoxyacetophenone, -benzophenone, and -indanone derivatives, which contain a remote phenolic group linked to the ketone by a para,para'- or meta,meta'-oxyethyl spacer, has been studied in acetonitrile and dichloromethane solutions using laser flash photolysis techniques. The corresponding methoxy-substituted compounds and, in the case of the alkoxyindanones, derivatives bearing just a remote phenyl substituent, have also been examined. The triplet lifetimes of the phenolic compounds are determined by the rates of intramolecular abstraction of the remote phenolic hydrogen, and depend on the solvent, the geometry of attachment and the configuration of the lowest triplet state. In contrast to the large (>500-fold) difference in lifetime of the para,para'- and meta,meta'-alkoxyacetophenone derivatives, both of which have lowest π,π* triplet states, smaller differences are observed for the alkoxyindanone (lowest charge transfer triplet, ~twofold difference) and alkoxybenzophenone (lowest n,π* triplet, ~18-fold difference) derivatives in acetonitrile solution. The triplet lifetimes of the acetophenone and benzophenone are significantly shorter in dichloromethane than in acetonitrile, consistent with the intermediacy of a hydrogen-bonded triplet exciplex in the reaction. This is not the case with the para,para'-indanone derivative, sugesting that hydrogen abstraction in this compound is dominated by a mechanism involving initial charge transfer rather than hydrogen bonding. This is most likely due to orientational constraints that prevent the remote phenolic -O-H group from adopting a coplanar arrangement with the n-orbitals of the carbonyl group.Key words: photochemistry, aromatic ketone, phenol, triplet, intramolecular, quenching, hydrogen abstraction, phenoxyl radical, kinetics, kinetic isotope effect, laser flash photolysis.
Quasiclassical trajectory studies on the gas-phase BrO self-reaction
Authors: Papayannis Demetrios K , Kosmas Agnie M
Published: April 2011

The effect of initial vibrational energy and the mode of disposal of available energy into products for the disproportionation reaction between BrO radicals are studied using the quasiclassical trajectory (QCT) technique. The calculations are performed on an analytical potential enegy surface based on ab initio results reported for the three isomeric forms of (BrO)2 system. The results indicate a mild dependence on reactant vibrational energy, which is discussed in terms of the mechanistic aspects of the reaction. The study of the distribution of total accessible energy among products indicates a different mode of energy disposal in each path and hence important differences on the mechanism by which each channel takes place.
MONOREG  an expert system for structural elucidation of monoterpenes
Authors: Ferreira Marcelo J , Rodrigues Gilberto V , Emerenciano Vicente P
Published: April 2011

This paper describes a new expert system denominated MONOREG for structural determination of monoterpenes. This system is composed of five programs capable of performing 13C NMR spectra data analyses and analyses of systematic data from living organisms. At the end of this procedure, it shows the likely skeletons of the compound in question as well as the substructures compatible with the 13C NMR data. The system was tested on the skeleton elucidation of 40 monoterpenes from a wide variety of structure types and exhibited excellent results in the skeleton prediction process.
The mechanism and kinetics of the HCO + HONO → HCHO + NO2 reaction — A DFT study
Authors: Sun Xiaomin , Cai Zhengting , Feng Dachang , Bian Wenshang , Qiao Qing'an , Wang Wenxing
Published: April 2011

The hydrogen-transfer reaction of HCO + HNO2 → HCHO + NO2 has been studied using both the density function theory (DFT) and high-level ab initio method. Three complete reaction paths have been located for the transfer reaction. Geometry optimization and frequency calculation have been performed at the B3LYP/6-311++G** level. QCISD(T) and G3B3 methods have been used to verify the single-point energy. On the basis of the ab initio data, the rate constants have been deduced over a temperature range of 300–3000 K using the transition-state theory and canonical variational transition-state theory with small-curvature tunneling effect. The calculated rate constants have been compared with the previous reported values.Key words: density function theory, reaction mechanism, variational transition-state theory, rate constant.
Structures of the 2:1 adducts of benzyne with 2-methylanisole and benzene
Authors: Bender Christopher O , Boeré René T , Dibble Peter W , McKay Ryan T
Published: April 2011

The 2:1 adduct of benzyne with 2-methylanisole is shown to have the bisbenzotricyclic structure 6,6a,11,11a-tetrahydro-5-methoxy-6-methyl-5,6,11-metheno-5H-benzo[a]fluorene by a single-crystal X-ray diffraction study (C20H18O: Pca21, a = 15.0497(17), b = 9.87783(11), c = 9.6846(11); Z = 4; 1672 data points, R1 = 0.0325). This structure is compared to an unpublished crystal structure of the parent hydrocarbon 6,6a,11,11a-tetrahydro-5,6,11-metheno-5H-benzo[a]fluorene, C18H14. Both structures have also been computed by DFT methods at the B3LYP/6-311(d,p) level of theory. Bond distances and angles between the solid-state measurements and gas-phase calculations are found to agree well; average deviations are well below 1%. The 1H NMR spectra show surprisingly small 3JHH couplings in the central tricyclic cage, but can be assigned using 2D spectroscopy.Key words: Hydrocarbon cages, strained rings, cyclopropane, X-ray crystallography, NMR.