bluuebunny/crossref_metadata_2025 huggingface dataset:
@ TOG
Authors: Edey Katharine , Barnfield Sonia , Keay Stephen
Published: July 2007

In this issue of @TOG we start a series of web reviews on allied specialties about which we need to maintain a certain amount of knowledge when caring for women. We begin with a review of endocrinology websites. Endocrine diseases impact on many aspects of obstetric and gynaecological practice and they include diabetes, thyroid disorders, obesity and, less commonly, prolactinoma. The sites we review will, hopefully, be particularly useful for those working in infertility, reproductive endocrine or medical antenatal clinics.
Summarizing digital documents: effects of alternate or simultaneous window display
Authors: Olive Thierry , Rouet Jean‐François , François Emmanuelle , Zampa Virginie
Published: July 2007

We investigated the effect of window visibility on the computer‐based summarizing of digital documents. Two experiments studied the impact of the simultaneous or alternate display of the windows containing the notepad and source documents. In Experiment 1, the participants were asked to summarize the content of the source documents. In Experiment 2, they were required to copy out sections of the source documents. The results showed that in the alternate condition, the participants performed fewer reading and writing cycles than in the simultaneous condition. Furthermore, in the alternate condition, the writing episodes were both more numerous and more effortful, while quality of the summaries produced using the copying strategy was also affected. These experiments highlight the need for writers to be able to navigate freely and easily between the windows so that they can construct an overall mental representation of their summaries. Copyright © 2007 John Wiley & Sons, Ltd.
Environmentally friendly biocomposites based on waste of the dairy industry and poly(vinyl alcohol)
Authors: Sedlařík Vladimír , Saha Nabanita , Kuřitka Ivo , Sáha Petr
Published: July 2007

Environmentally friendly polymeric biocomposites based on whey powder, a waste material of the dairy industry, and fully or partially hydrolyzed poly (vinyl alcohol) were prepared and characterized with optical microscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, and stress–strain analysis, and their biodegradation was evaluated with the modified Zahn–Wellens method and the spectrophotometric determination of poly(vinyl alcohol). In addition, the ability of the biocomposites to absorb moisture and its consequent influence on the mechanical properties were investigated under different storage conditions. The structural differences of the two types of poly(vinyl alcohol) matrices had a significant effect on all the mentioned characteristics. Possible molecular interactions between the polymer matrix and modifier, due to hydrogen bonding, were also examined. First‐order kinetics were applied for the biodegradation data. The two‐phase character of the biodegradation was shown. The results indicated that whey powder is suitable for the modification of polymers, and this is important for the production of biodegradable polymer materials and the consequent reduction of the environmental load. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007
Spectroscopic analysis of poly(ethylene naphthalate)–poly(butylene terephthalate) blends
Authors: Jung Dylan Dae Bong , Bhattacharyya Debes , Easteal Allan J.
Published: July 2007

The characteristics of poly(butylene terephthalate) (PBT), poly(ethylene naphthalate) (PEN), and blends with 30, 40, 50, 60, and 70 wt % PEN prepared by melt‐blending were analyzed using Fourier transform infrared spectroscopy, Raman spectroscopy, X‐ray diffraction, solid‐state nuclear magnetic resonance (NMR), and X‐ray photoelectron spectroscopy. The spectroscopic analyses provide no direct evidence for the occurrence of transesterification reactions occurring during melt‐processing of the blends under the conditions that were used. The improved mechanical properties of the PBT/PEN blends are attributed to physical interactions occurring over a large interfacial area. X‐ray diffraction and high‐resolution solid‐state carbon‐13 (13C) NMR confirmed the formation of the α‐PEN phase after annealing samples at 200°C for 19 h. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007
Influence of the extrusion process on the morphology and micromechanical behavior of polystyrene‐block‐(polystyrene‐co‐butadiene)‐block‐polystyrene star block copolymer/homopolystyrene blends
Authors: Buschnakowski M. , Adhikari R. , Michler G. H. , Knoll K.
Published: July 2007

The influence of the extrusion process on the morphology and micromechanical behavior of an asymmetric polystyrene‐block‐(polystyrene‐co‐butadiene)‐block‐polystyrene (SBS) star block copolymer and its blends with general‐purpose homopolystyrene (hPS) was studied with films prepared with a single‐screw extruder. The techniques used were transmission electron microscopy and uniaxial tensile testing. Unlike the pure SBS block copolymer possessing a gyroid‐like morphology, whose deformation was found to be insensitive to the processing conditions, the mechanical properties of the blends strongly depended on the extrusion temperature as well as the apparent shear rate. The deformation micromechanism was primarily dictated by the blend morphology. The yielding and cavitation of the nanostructures were the principal deformation mechanism for the blends having a droplet‐like microphase‐separated morphology, whereas cavitation dominated for the blends containing macrophase‐separated layers of polystyrene. The mechanical properties of the blends were further examined with respect to the influence of the temperature and shear rate on the phase behavior of the blends. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007
Integrated geophysical and topographical investigation in the territory of Ancient Tarquinia (Viterbo, central Italy)
Authors: Piro S. , Peloso D. , Gabrielli R.
Published: July 2007

This paper presents the results of an ongoing study of the territory of Ancient Tarquinia (Viterbo, central Italy). The work is part of the University of Milano's ‘Tarquinia Project’, which studies the monumental area of this territory with particular emphasis on the ‘Ara della Regina’ temple site.

To enhance the knowledge of this territory, a scientific collaboration between the University of Milano (Department of Science of Antiquity) and the Institute of Technologies Applied to Cultural Heritage (ITABC‐C.N.R.) was initiated in 2000 and is still in progress. The primary objective of the study was to determine the location and degree of conservation of unknown buried structures below the sites studied, using the integration of topographical surveys, three‐dimensional laser scanner surveys of the temple and ground‐based remote sensing surveys.

The remote sensing surveys were carried out using the ground‐penetrating radar (GPR). The analysis of the GPR time‐slice maps indicates that some structural formations and walls of the buildings are still present below the surface. The results presented and discussed in this paper demonstrate the potential of both the topographical survey combined with the three‐dimensional laser scanner survey of the monument and the remote sensing technique for understanding of the presence and the extent of buried buildings with respect to the temple area. Copyright © 2007 John Wiley & Sons, Ltd.
Aggregation Experiments on Fine Fly Ash Particles in a Gradient Magnetic Field
Authors: Li Y. W. , Zhao C. S. , Wu X. , Lu D. F.
Published: July 2007

Aggregation experiments were conducted on two kinds of fly ash particles in the size range of 0.023–9.314 μm in a gradient magnetic field produced by permanent magnetic rings. The two types of fly ash particles were obtained from Dongsheng and Datong coal combustion. The effect of particle size, total particle mass concentration, particle residence time in the magnetic field and gas velocity were examined. Experimental results showed that the removal efficiencies in a gradient magnetic field are much higher than those in a uniform magnetic field. The total and single‐sized particle removal efficiencies can be improved by increasing the total particle mass concentrations and the particle residence time in the magnetic field or reducing the gas velocity. Mid‐sized particle removal efficiencies are higher than those of the larger and smaller ones. With the increase in total particle removal efficiencies, the particle size corresponding to the maximum values of single‐sized particle removal efficiencies and the particle number median diameters both decrease. Both the single‐sized and total removal efficiencies for the particles from the Dongsheng coal combustion are higher than those from the Datong coal combustion.
Kinetic Study of Nickel Oxide Reduction by Methane
Authors: Alizadeh R. , Jamshidi E. , Ale Ebrahim H.
Published: July 2007

The reduction of the nickel oxide, NiO, by methane was investigated in this work. The thermogravimetric technique was used for the determination of kinetic parameters for the reaction. The reaction was carried out in the temperature range of 600–725 °C, at atmospheric pressure with porous pellets prepared from nickel oxide powder with a mean particle size of 0.026 μm. The conversion‐time data have been interpreted by using the grain model. Complete conversion can be achieved in 11 min at 725 °C, which is shorter than the time required by carbon, i.e., ca. 120 min at 1000 °C. This faster reduction in comparison with carbonthermal reduction is attributed to the high carbon activity in methane. For the first order reaction with respect to methane concentration, the activation energy is found to be 63.9 kcal/g mol.
NUO+, a New Species Isoelectronic to the Uranyl Dication UO
Authors: Heinemann Christoph , Schwarz Helmut
Published: July 2007

The nitridooxouranium cation NUO+ has been prepared as a new isoelectronic homologue to the uranyl dication UO+ by a sequence of ionmolecule reactions starting from the atomic uranium cation U+. Collision‐induced dissociation experiments and ligand‐exchange reactions serve to unambiguously identify the ion as a species in which the uranium cation is formally inserted in the NO molecule. New thermochemical data for NUO+ and UN+ are given, and the stability of NUO+ with respect to UO+ is investigated by means of quasi‐relativistic density‐functional calculations.
Characterisation of the Intermediate C2H4…︁Cl2 in a Gaseous Mixture of Ethene and Chlorine by Rotational Spectroscopy: A Weak π‐Type Complex
Authors: Bloemink Hannelore I. , Hinds Kelvin , Legon Anthony C. , Thorn Joanna C.
Published: July 2007

A complex of ethene and Cl2 has been characterised in the gas phase. Rotational spectra of the isotopomers C2H4…35Cl2, C2H4…35Cl37Cl and C2H4…37Cl35Cl were recorded by using a fast‐mixing nozzle in an FT microwave spectrometer. Rotational constants, centrifugal distortion constants and Cl nuclear quadrupole coupling constants. χgg (Cl) are reported in each case. The complex is of the π‐donor–acceptor type and has a C2v geometry in which Cl2 lies along the C2 axis perpendicular to the plane of the C2H4 nuclei. The binding is weak, and only small changes in the χgg (Cl) attend complex formation. A simple model attributes these changes to a transfer of around 0.02e from the inner to the outer Cl nucleus, thus confirming that the complex is of the Mulliken outer type. Similarities in the properties of C2H4… Cl2 and C2H4… HCl indicate that the angular geometry is in both cases determined mainly by the electrostatic part of the interaction. The distance from the π‐bond midpoint to Cl decreases from C2H4… HCl to C2H4… Cl2; this suggests that Cl2 is “snub‐nosed”.
Intrazeolitic Reaction between Transition Metal Ions and Open or Closed Polyamine Ligands
Authors: de Vos Dirk E. , Vanoppen Dominic L. , Li Xiao‐Yuan , Libbrecht Steven , Bruynseraede Yvan , Knops‐Gerrits Peter‐Paul , Jacobs Pierre A.
Published: July 2007

Intrazeolitic transition metals, such as Ni2+ and Co2+, were chelated by open or closed, tetra‐ or pentadentate polyamine ligands. Their coordination and redox chemistry was studied by IR‐Raman, EPR, diffuse reflectance, and magnetic techniques. For pseudo‐octahedral complexes with tetradentate ligands, the presence of the zeolite favors cis coordination over the trans form. This is explained by the very low tendency of the zeolite surface to bind as a monodentate ligand to a planar metal complex. However, if trans complexes are formed (as with Ni2+), the axial positions on the complex are available for ligand exchange. Such intracrystalline complex syntheses result in the formation of new redox solids. For example, [CoII‐(cyclam)]2+‐NaY (cyclam = 1,4,8,11‐tetraazacyclotetradecane) is a reversible, high‐affinity (p1/2<1 mbar) and high‐capacity (>90 μmol g−1) dioxygen‐sorbing material.
The Photoisomerisation Reactions of the Cluster [Os3(CO)9(μ3‐η2:η2:η2‐C6H6)] and Some of its Derivatives
Authors: Johnson Brian F. G. , Nairn Jacqueline G. M. , Brown David B. , Lewis Jack , Gallop Mark , Parker David G.
Published: July 2007

The highly efficient photoinduced isomerisation of [Os3(CO)9(μ3‐η2:η2:η2‐C6H6)] (1) to the previously characterised μ3‐benzyne complex [H2Os3(CO)9(μ3‐η2:η1:η1‐C6H4)] (2) is described. We find that for the more electron‐rich clusters [Os3(CO)9‐n(PPh3)n(μ3‐η2:η2:η2‐C6H6)] (n = 1 or 2) the efficiency of the photolytic process is improved. We suggest that photolysis generates a vacant site at osmium (mimicking the inherent coordinative unsaturation of a metal complex) and that this transformation offers a compelling model for the interconversion of associatively and dissociatively chemisorbed benzene. Moreover, we can fine‐tune our molecular “work function” (really the separation of HOMO/LUMO energies) by protonation or by phosphine substitution for CO at the metal. Thus, the cation [HOs3(CO)9(μ3‐η2:η2:η2‐C6H6)]+ does not undergo internal metalation, while photoisomerisation of the electron‐rich phosphine derivatives proceeds more readily than for 1. We find that these photolytic reactions are easily monitored by IR spectroscopy for samples suspended in polymethylmethacrylate films under ambient conditions. This method permits “matrix isolation” experiments under ideal conditions. Finally, we speculate that the mechanism of interconversion almost certainly involves the symmetric cleavage of a OsOs bond (σ‐σ* transition) to produce an extremely reactive diradical intermediate.
The Systematic Definition of Organic Reactions
Authors: Hendrickson James B. , Sander Thomas L.
Published: July 2007

A logical system is presented to describe organic reactions. It is based on the net structural change in a reaction, rather than on substructure searching. This system rigorously provides a place for any reaction. It is very simple to use by hand, but, since it is also numerical, it provides a basis for organizing and retrieving reactions in a database by computer. The effectiveness of a program, COGNOS, written to implement and test the system on a large database, lends confidence in this logic for organizing reactions.
Total Synthesis of Balanol and Designed Analogues
Authors: Nicolaou K. C. , Koide Kazunori , Bunnage Mark E.
Published: July 2007

The total synthesis of balanol, a potent protein kinase C inhibitor isolated from the fungus Verticillium balanoides, is described. The hexahydroazepine fragment was prepared from D‐serine through a sequence of reactions including the diastereoselective allylboration of a derived amino aldehyde and a base‐induced 7‐exo‐tet ring closure as key steps. The benzophenone fragment was secured through the initial coupling of the two functionalised aromatic components through an ester linkage, followed by intramolecular nucleophilic attack of an aryl lithium derivative to form the desired ketone bridge. After coupling of the two balanol domains, the adoption of benzylderived protecting groups for the latent functionalities then allowed the liberation of balanol in a single step by catalytic hydrogenolysis. Finally, the newly developed synthetic strategy was applied to the synthesis of a variety of designed balanol analogues for biological evaluation.
Synthesis of Zaragozic Acid A/Squalestatin S1
Authors: Nicolaou K. C. , Yue Eddy W. , la Greca Susan , Nadin Alan , Yang Zhen , Leresche James E. , Tsuri Tatsuo , Naniwa Yoshimitsu , de Riccardis Francesco
Published: July 2007

A novel synthetic approach to the construction of the zaragozic acids, which was used for the asymmetric synthesis of zaragozic acid A/squalestatin S1 (1), is described. Fragment 5, representing the tricarboxylic acid core portion, is assembled in three key steps: 1) Stille coupling to establish the carbon framework; 2) enantioselective dihydroxylation to introduce the absolute stereochemistry; and 3) diastereoselective dihydroxylation to complete the required carbon‐oxygen connectivity. The convergency of this synthesis is demonstrated by the dithiane addition of a variety of C 1 side chains (e.g., 78) to advanced intermediate 5. A multi‐event acid‐catalyzed rearrangement yielded the zaragozic acid core 86, which was converted to an intermediate obtained from degradation of zaragozic acid A. A second‐generation synthesis of the core of the zaragozic acids is also described. When aldehyde 90 was used instead of 5, both the yield and diastereoselectivity of the dithiane addition reaction were improved, although the degree of convergency was slightly lower.
Synthesis of (R)‐tert‐Leucinol by Classical Resolution of the Racemic Mixture
Authors: Drauz Karlheinz , Jahn Wilfried , Schwarm Michael
Published: July 2007

Optically active tert‐leucinol is an important building block in asymmetric synthesis. However, the (R) enantiomer particularly has so far remained difficult to obtain, mainly because of the laborious synthesis of the precursor amino acid, (R)‐tert‐leucine. Here we present a new, classical resolution of racemic tert‐leucinol, which allows straightforward preparation of each, but especially the (R) enantiomer, in good yields and high optical purities. The feasibility of the synthesis of useful derivatives is demonstrated by transformation into the corresponding (R)‐4‐tert‐butyl‐2‐oxazolidinone.
The Reduction of [Fe(CO)2L2X2] (L = P(OMe)3, P(OiPr)3, PEt3; X = Br, I)—From Iron(II) to Iron(0) via Stable Iron(I) Intermediates
Authors: Kandler Helmut , Gauss Christine , Bidell Wolfgang , Rosenberger Stephan , Bürgi Tobias , Eremenko Igor L. , Veghini Dario , Orama Olli , Burger Peter , Berke Heinz
Published: July 2007

The reduction of [Fe(CO)2‐L2X2] (L = P(OMe)3X = Br (1a), I (1b); L = P(OiPr)3, X = Br (2a), I (2b); L = PEt3, X = Br (3a), I (3b)) with Zn in dioxane (1a,b‐2a,b) or PhLi in ether (3a,b) led to formation of the corresponding dicarbonyl(halo)bis(phosphorus donor)iron(I) complexes (L = P(OMe)3, X = Br (4a), I (4b); L = P(OiPr)3, X = Br (5a), I (5b); L = PEt3, X = Br (6a), I (6b)). Slightly contaminated5a,band pure6a,bwere isolated as stable crystalline blue or blue‐green complexes. Complexes4a,bwere obtained, with only minor impurities, by comproportionation of1a,band the dicarbonyl(halo)bis‐(trimethylphosphite)ferrate anions7a,band characterized in THF solution. The comproportionation products5a,b‐6a,bwere obtained in high yields by reaction of2a,b‐3a,bwith the dinitrogen complexes13‐15. Further reduction of4a,b‐6a,bor exhaustive reduction of1a,b‐3a,bwith sodium amalgam oriBuLi in THF afforded the nonisolable dicarbonyl‐(halo)bis(phosphorus donor)ferrate(o) anions (7a,b‐9a,b). The latter were characterized by acidification with trifluoroacetic acid or acetic acid yielding stable dicarbonyl (halo) hydridobis (phosphorus donor)iron(II) complexes (L = P(OMe)3, X = Br (10a), I (10b); L = P(OiPr)3, X = Br (11a), I (11b);L = PEt3, X = Br (12a), I (12b)). In the presence of N2,8awas transformed into dinitrogen complex [Fe(CO)2{P(OiPr)3}2N2] (13). With9a,bthe reaction led to formation of [Fe‐(CO)2(PEt3)2)2N2] (14) and [{Fe(CO)2‐(PEt3)2}2(μ‐N2)] (15). In solution at low temperature (−90 to 0°C), the dinitrogen complexes14and15are in equilibrium with each other. Complexes13, 14, and15were characterized by IR,1H,13C,31P, and15N NMR spectroscopy. The structures of5a, 6b, 14, and15were determined by X‐ray diffraction studies.
A Novel Low Molecular Weight Chiral Gelator for Apolar Organic Solvents
Authors: Snijder Carina S. , de Jong Johannes C. , Meetsma Auke , van Bolhuis Fré , Feringa Ben L.
Published: July 2007

The synthesis, molecular structure, and properties of a new chiral gelforming agent 1 are described. Key structural features in 1 are a γ‐alkoxybutyro‐lactone tetralin moiety and an angular phenylsulphone unit. The new low molecular weight gelator 1 can reversibly form stable gels in low concentrations (e.g., 1:800 for n‐hexane) with isopropanol and a variety of apolar organic solvents. The gels were studied with differential scanning calorimetry and a combination of electron microscopy techniques, which revealed a highly ordered three‐dimensional network of entangled fibers. X‐ray analysis showed that the aggregation of 1 leads to a helical structure in the solid state. Nonchiral analogues 2 and 3 were unable to initiate gel formation.
Synthesis and Molecular Structure of the First Neutral Transition‐Metal Complex Containing a Linear MCCCCCR2 chain
Authors: Lass Raimund W. , Steinert Paul , Wolf Justin , Werner Helmut
Published: July 2007

The reaction of [IrH2Cl(PiPr3)2] (2) with the pentadiyne derivative HCCCCCPh2OH (1) yields the five‐coordinate compound [IrH(CCCCPh2OH)Cl(PiPr3)2] (3), which photochemically rearranges to give the vinylidene‐substituted isomer trans‐[IrCl(CCH‐CCPh2OH)(PiPr3)2] (4). On treatment of 3 with pyridine, the octahedral complex [IrH (CCCCPh2OH)Cl(py)(PiPr3)2] (5) is formed. While attempts to eliminate water from 4 (or 5) failed, the reaction of 3 with one equivalent of trifluorosulfonic acid anhydride and two equivalents of triethylamine led to the formation of trans‐[IrCl(CCCCCPh2)(PiPr3)2] (6), which is the first neutral transition‐metal complex containing a C5R2 ligand. The X‐ray structural analysis of 6 reveals a perfect square‐planar coordination geometry around the metal centre and an almost linear IrC5 chain with Ir‐CC and CCC bond angles of 174–179°.
Pulled Molecular Strings and Stacked Molecular Decks: Chelate‐Ring Formation vs. Metal–Metal Bridging in Dicopper(I) Complexes of 2,2′‐Bipyrimidine with Diphosphine Ligands of Variable Polymethylene Chain Length
Authors: Schwach Manuela , Hausen H.‐D. , Kaim Wolfgang
Published: July 2007

The “self‐assembly” reaction between bischelating 2,2′‐bipyrimidine, metallic copper, Cu2+, and two equivalents of bidentate Ph2P(CH2)nPPh2 produces crystallographically characterized dinuclear complexes with a [Cu1(μ‐bpym)‐Cu1]2+ core and chelating (n = 5; type I) or bridging diphosphine ligands (n = 6, 8; type II). Structures II may be designated as “inverse cryptate” arrangements. The structural data of the solids and the spectroscopic results for the dissolved species indicate a strained configuration in the case of complex [(μ‐bpym)Cu2{μ‐Ph2P‐(CH2)n]2+ (6) with n = 6. Once the polymethylene chain length is reduced one notch further to n = 5 (5), the diphosphines can no longer bridge but help to form eight‐membered chelate rings (structure I). In this complex there is a distortion towards a trigonal‐pyramidal coordination geometry at the copper(I) centers, which is supported by the formation of an “organic sandwich” arrangement between the central bpym acceptor and two phosphino phenyl rings.
Electron‐poor 2,3‐Dihydro‐1,3‐Diborolyl Complexes of Iron and Ruthenium: Synthesis, Reactivity, and Crystal and Electronic Structures of an Iron Sandwich Complex
Authors: Hettrich Ralph , Kaschke Michael , Wadepohl Hubert , Weinmann Wolfgang , Stephan Martin , Pritzkow Hans , Siebert Walter , Hyla‐Kryspin Isabella , Gleiter Rolf
Published: July 2007

The addition product of sodium hydride and the 2,3‐dihydro‐1,3‐diborole (CiPr)2(BEt)2CHMe (3c) reacted with [{(C5Me5)FeCl}x] to produce the green sandwich complex [(C5Me5)Fe{n5‐(CiPr)2(BEt)2CMe}] (2 c), which formally contains 16 valence electrons (VE). Complex 2c has unexpected structural properties in the solid state: the 1,3‐diborolyl ring is extremely folded (41°), and the Fe–C2 distance is short (1.90 Å). Analogously, violet Ru complexes 4a,c,d were obtained from 3a,c, NaH or tBuLi, and [{(C5Me5)RuCl}4]. With the less bulky heterocycles 3 b,e the new 30 VE triple‐decker complexes [(C5Me5)Ru{μ,n5‐(CR1)2(BR2)2CMe}RuH(C5Me5)] (5b,e) were formed, which contain a Ru–H bond. Cyclic voltammetric studies revealed the existence of stable anions 2c‐ and 4d‐ formed by reversible one‐electron reduction at –1.26 and –1.40 V, respectively (vs. SCE). The red‐brown anions were further characterized by ESR spectroscopy following stepwise reduction of the neutral species with potassium in THF. Addition of CO to 4a and 4d led to formation of the monocarbonyl complexes [(C5Me5)Ru(CO){n5‐(CR1)2‐(BR2)2CMe}] (6a,d), and 6d was characterized by X‐ray structure analysis. The heterocycle in 6d is less folded (19°) than in 2 c. Its CO ligand causes a 28.5° tilt of the cyclic ligands. Reaction of CO with 2 c yielded a red product of unknown structure. The electronic structure of 2 was studied by EH‐MO theory, which revealed a unique bonding in the sandwich. The s̀ electron density of the B–C bonds participates in the bonding to the iron atom; this demonstrates that the number of bonding electrons is the same as in ferrocene. Thus, the complexes 2 actually have 18 VE.
C‐Disaccharides of Ketoses
Authors: Streicher Hansjörg , Geyer Armin , Schmidt Richard R.
Published: July 2007

Reaction of gluconolactone2with allylmagnesium bromide at low temperatures afforded ketopyranose3, which could easily be converted into open‐chain ketoses (R)‐6and (S)‐6. Their reaction with lithioacetylide9afforded propargylic alcohol derivatives (R)‐10and (S)‐10, which could not be cyclized directly to the desiredC‐ketosides. They were converted by standard procedures into (R)‐14and (S)‐14and then into dicobalthexacarbonyl complexes (R)‐16and (S)‐16. A facile acid‐catalyzed ring closure gave the desiredC‐ketosides (R)‐18α/βand (S)‐18α/β, respectively, in different ratios. In order to demonstrate that removal of the protective groups and hydrogenation of the CC triple bond proceed smoothly, (R)‐18α was transformed into the deprotected target molecule (R)‐1α. For the assignment of the new chiral centers at C‐2/2′ and at C‐8, (S)‐18α was transformed into azido derivative (S)‐22α, which underwent intramolecular cycloaddition to afford the spiro derivative (S)‐25α. Because of the conformational constraints in this molecule, unequivocal configurational assignment was possible with the help of NMR data.
The Pagodane → Dodecahedrane Concept–Shorter Routes, Higher Yields
Authors: Bertau Martin , Leonhardt Jürgen , Weiler Andreas , Weber Klaus , Prinzbach Horst
Published: July 2007

Two variants of the “SN2 route” from pagodanes (A, B) to functionalized dodecahedranes (D, F) and particularly dodecahedradienes (E) offer considerable improvements in the number of operations (from nine to five to three) and yields (e.g., for diesterFfrom 55–65 to 70–75 to 85–91%). Key steps are the regio‐ and stereospecific introduction of four to six bromine substituents into dimethyl pagodane‐4‐syn,9‐syn‐dicarboxylate (1 b) and a highly complex (thirteen bond‐breaking/bond‐forming events in four participating structures). yet very convenient (one‐pot operation) and extremely efficient (nearly quantitative) transformation of secopagodane to bissecododecahedradiene with complete stereocontrol in transannular CH2functionalizations. The prohibitively low kinetic acidity of “caged” hydrogens has so far only been overcome with the recently reported P2F reagent (Schwesinger). Further improvement of the overall economy of the pagodane → dodecahedrane scheme has been achieved by efficiently channeling a byproduct of the pagodane synthesis (ca. 10%) back into the SN2 track.
Permethyltitanocene Derivatives with Naked Chalcogen Ligands: Synthesis of [(Cp*2Ti)2(μ‐E)] and [Cp*2Ti(μ2‐E2)] and the Role of the Terminal Chalcogenides [Cp*2Ti(E)] in Their Interconversion (E = Se, Te)
Authors: Piers Warren E. , Ziegler Tom , Fischer Jason M. , Macgillivray Leonard R. , Zaworotko Michael J.
Published: July 2007

Permethyltitanocene hydride, [Cp*2TiH], reacts with elemental selenium or tellurium to give the products [(Cp*2Ti)2(μ‐E)] (E = Se, 1a Te, 1b), [Cp*2Ti(μ2‐E2)] (E = Se, 2a; Te, 2b) and [Cp*2Ti(μ2‐Se3)] (3), depending on the equivalency of the chalcogen employed. Dinuclear compounds 1 are paramagnetic and have D2d (idealized) structures, as shown by X‐ray structural analysis of μ‐telluride 1b; they may be converted to diamagnetic dichalcogenides 2 through further reaction with the appropriate chalcogen. Derivatives 2 are monomeric in the solid state, as shown by X‐ray structural analysis of ditelluride 2b, and in solution, as demonstrated by multinuclear NMR spectroscopy. Combination of diselenide 2a and ditelluride 2b results in partial redistribution to the mixed species [Cp*2Ti(μ2‐SeTe)], suggesting dimeric structures of formula [Cp*2Ti(μ‐E‐E)2 TiCp*2] may be accessible in solution. The dichalcogenides and the triselenide may be converted back to complexes 1 by treatment with a chalcogen‐abstracting agent. The possible involvement of monomeric terminal chalcogenides [Cp*2Ti(E)] in the interconversion of 1 and 2 was probed experimentally and computationally by means of Density Functional Theory calculations on [Cp2M(E)] (M = Ti, E = O, S, Se, Te; M = Zr, E = O, Te). Several unsuccessful attempts to generate and trap [Cp*2Ti(Te)] are described. The results of these studies suggest that [Cp*2Ti(Te)] has a very weak Ti–Te bond and a readily accessible triplet excited state. These factors, along with the small size of titanium, render this member of the [Cp*2M(E)] family of complexes difficult to trap with Lewis bases, in contrast to many other congeners in the series of Group 4 terminal chalcogenides.
Triazidogallium and Derivatives: New Precursors to Thin Films and Nanoparticles of GaN
Authors: Fischer Roland A. , Miehr Alexander , Herdtweck Eberhardt , Mattner Michael R. , Ambacher Oliver , Metzger Thomas , Born Eberhard , Weinkauf Sevil , Pulham Colin R. , Parsons Simon
Published: July 2007

The synthesis and properties of [Ga(N3)3]∞ (1) and the related derivatives [(Do)nGa(N3)3] (2a‐d: Do = THF, NEt3, NMe3, quinuclidine, n = 1; 2e: Do = pyridine; n = 3), Li[(CH3)Ga(N3)3] (3), [(N3)2Ga{(CH2)3NMe2}] (4), [Cp(CO)2‐Fe‐Ga(N3)2(py)] (5), and [(CO)4Co‐Ga(N3)2(NMe3)] (6) are reported. Compounds 2e and 4 were characterized by single‐crystal X‐ray diffraction. The deposition of polycrystalline GaN thin films from 2a‐e by solution methods (spin‐on pyrolysis) and the solid‐state pyrolysis of 1 to give GaN nanoparticles are described.
A Paradigm Case for the Merging of Glycal and Enzymatic Assembly Methods in Glycoconjugate Synthesis: A Highly Efficient Chemo‐Enzymatic Synthesis of GM3
Authors: Liu Kevin K.‐C. , Danishefsky Samuel J.
Published: July 2007

A concise, regio‐ and stereoselective synthesis of the ganglioside GM3 has been achieved. Use of an α‐1,2‐oxirane derived from lactal facilitated installation of the anomeric β‐ceramide side chain. Introduction of the sialic acid residue at C3, of the lactose was accomplished regiospecifically by enzymatically mediated sialyl transfer from CMP‐Neu‐5‐Ac.
Photochemistry of N‐Phthaloylcysteine Derivatives: Multiplicity‐Directed Regioselective CH Activation
Authors: Griesbeck Axel G. , Hirt Joachim , Peters Karl , Peters Eva‐Maria , von Schnering Hans Georg
Published: July 2007

The photochemistry of the methyl esters of N‐phthaloylcysteine derivatives 1b–5b was studied. The results are remarkable, because they prove a pronounced, multiplicity‐controlled regioselectivity of the initial CH activation step. From substrates 1b–4b the benzazepine‐1,5‐dione 6 was produced exclusively by the singlet path. The formation of compound 6 is initiated by a γ‐H abstraction; this was demonstrated by deuterium labeling experiments. The penicillamine derivative 5b was unreactive in the singlet manifold. From substrates 1b–3b and 5b the thiazinoisoindoles 7–9 and 11 were produced exclusively by the triplet path. The sterically hindered S‐isopropylcysteine derivative 4b also furnished this product type (10) as a proportion of the products in the singlet manifold. These annulation products result from a primary photoinduced electron‐transfer (PET) step followed by heterolytic ϵ‐H activation. The mechanistic scenario was elucidated by quenching and sensitization experiments. An interplay of CH activation steps and electron back‐transfer is probably responsible for this type of spin selectivity.
Concave Hydrocarbons
Authors: Gross Jens , Harder Gabriele , Siepen Astrid , Harren Jörg , Vögtle Fritz , Stephan Holger , Gloe Karsten , Ahlers Benedikt , Cammann Karl , Rissanen Kari
Published: July 2007

Concave hydrocarbons, such as 1 (C36H36), 4 (C60H60), 5 (C54H48), and 6 (C60H52), represent three‐dimensionally clamped analogues of π‐prismands. They encapsulate small metal ions and accomplish metal‐ion extraction from aqueous solution. Their remarkable selectivity allows applications such as incorporation in ion‐selective electrodes. The synthetic route is based on well‐established cyclophane methodology and, thus, offers a general approach to a whole family of concave hydrocarbons.
Heterocyclic Carbenes: A High‐Yielding Synthesis of Novel, Functionalized N‐Heterocyclic Carbenes in Liquid Ammonia
Authors: Herrmann Wolfgang A. , Köcher Christian , Gooßen Lukas J. , Artus Georg R. J.
Published: July 2007

To date the only free carbenes of the imidazoline‐2‐ylidene type to have been described in the literature are those bearing simple hydrocarbon or haloalkyl and ‐aryl substituents. We report here a novel, versatile and high‐yielding method for the synthesis of N‐heterocyclic carbenes in a mixture of liquid ammonia and aprotic organic solvents. Deprotonation of the imidazolium precursor salts proceeds under mild conditions within a few minutes at temperatures below –30°C, and side reactions are thus avoided. The imidazolium salts are much more soluble in organic solvents if liquid ammonia is added. Furthermore, the acidity of the C‐2 protons appears to be enhanced by hydrogen bonding. Not only are the known free ylidenes conveniently and quantitatively accessible by this procedure, but also novel functionalized derivatives that are not accessible by known procedures. Imidazoline‐2‐ylidenes with linear, branched, cyclic, heteroatom‐substituted (O, N, P) and chiral hydrocarbon residues are accessible through the novel route. Stable carbene‐metal “adducts” are conveniently obtained by treating the free carbenes with chloro‐ or acetato‐bridged dinuclear metal complexes, or by displacement of coordinated ligands such as carbon monoxide, THF or acetonitrile by the free carbenes. The syntheses of novel imidazolium salts. N‐heterocyclic carbenes and carbene adducts of RuII, RHI, W0 and sulfur are reported, and the structures of five products analysed by single‐crystal X‐ray diffraction. N‐Heterocyclic carbenes bearing functionalized side chains are important because a number of these complexes show excellent activity in catalytic reactions. They do not show the typical reactivity of metal‐carbon “double bonds” and are remarkably stable both thermally and chemically. For a number of reasons, they are best viewed as donor adducts of the highly Lewis basic imidazoline‐2‐ylidene ligands and the Lewis acidic organometallic fragments. The new synthetic procedure reported here makes N‐heterocylic carbenes a generally accessible class of useful ligands in coordination chemistry and catalysis.
Synthesis, Structure, and Reactions of the First Rotational Isomers of Stable Thiobenzaldehydes, 2,4,6‐Tris[bis(trimethylsilyl)methyl]thiobenzaldehydes
Authors: Takeda Nobuhiro , Tokitoh Norihiro , Okazaki Renji
Published: July 2007

The first rotational isomers of thiobenzaldehydes, TbtCHS (2a and 2b; Tbt = 2,4,6‐tris[bis(trimethylsilyl)methyl]phenyl), were synthesized and isolated as stable crystalline compounds by the desulfurization of the corresponding overcrowded cyclic polysulfides TbtCHSn (n = 5 or 8) with phosphine reagents. The molecular structures of 2a and 2b in the solid state, determined by X‐ray crystallographic analysis, differed in their conformations, which were essentially identical with those in solution as revealed by 1H{1H} nuclear Overhauser effect (NOE) experiments. The isomeric thiobenzaldehydes 2a and 2b were found to undergo thermal interconversion. A kinetic study of this process gave reasonable kinetic and thermodynamic parameters for conformational isomerizations of this type. Interesting differences in reactivity among the two isomers 2a,b and 2,4,6‐tri‐tert‐butylthiobenzaldehyde (1) were shown in the reactions with hydrazine and m‐chloroperoxybenzoic acid.
The Thiazole Ylide: A Frequently Invoked Intermediate Is a Stable Species in the Gas Phase
Authors: McGibbon Graham A. , Hrušák Jan , Lavorato David J. , Schwarz Helmut , Terlouw Johan K.
Published: July 2007

The 1, 2‐hydrogen shift isomers of neutral (singlet and triplet) thiazole (1) and its radical cation have been investigated by a combination of mass spectro‐metric experiments and hybrid density functional theory calculations. The latter were used to probe the structures and stabilities of selected C3H3NS and C3H3NS.+ isomers and transition state structures. Although 3H‐thiazole‐2‐ylidene (2) is less stable than 1, by 31.5 kcalmol−1, it is expected to be capable of independent existence, since the 1, 2‐hydrogen shift from carbon to nitrogen involves a very large energy barrier of 72.4 kcalmol−1. The other 1, 2‐hydrogen shift reaction from C(2) leads not to the expected cyclic 1H‐thiazole‐2‐ylidene structure (3), which is apparently unstable, but rather to the ring‐opened species HSCHCHNC (4), which is 34.5 kcalmol−1 higher in energy than 1. The barrier in this case is lower but still large (54.9 kcalmol−1). The triplet ground states of 1, 2 and 4 are considerably destabilised (69.5, 63.2 and 58.7 kcalmol−1) relative to their singlet states. Interestingly, in addition to 2.+ and 4.+, the cyclic radical cation 3.+ is predicted to be stable although it is substantially higher in energy than ionised thiazole 1.+ (by 53.9 kcalmol−1), whereas 2.+ and 4.+ are much closer in energy (only 10.2 and 27.0 kcalmol−1 higher, respectively). Dissuading 2.+ and 3.+ from isomerising to 1.+ are energy barriers of 52.6 and 15.3 kcalmol−1, respectively. Experimentally, dissociative ionisation of 2‐acetylthiazole enabled the generation of 2.+, which could be differentiated from 1.+ by collisional activation mass spectrometry. Reduction of the ylide ion 2.+ in neutralisation‐reionisation mass spectrometry experiments yielded the corresponding neutral molecule 2. This direct observation of a thiazolium ylide provides support for postulates of such species as discrete intermediates in a variety of biochemical transformations.
Edge‐sharing SiN4 Tetrahedra in the Highly Condensed Nitridosilicate BaSi7N10
Authors: Huppertz Hubert , Schnick Wolfgang
Published: July 2007

The novel nitridosilicate BaSi7N10 was obtained by the reaction of barium metal with Si(NH)2 in a special high‐frequency furnace at 1650 °C. The single‐crystal structure determination (a = 687.29(3), b = 671.29(3), c = 963.28(4) pm, β = 106.269(3)°, PC, Z = 2, R1 = 0.0497, wR2 = 0.0924) reveals a network structure of connected SiN4 tetrahedra. BaSi7N10 is the first nitridosilicate with both corner and edge‐sharing SiN4 tetrahedra. Unlike the situation in normal oxosilicates, vertex‐sharing of SiN4 tetrahedra is not exclusively favored over edge‐sharing. With a Si:N molar ratio of 7:10, BaSi7N10 is the most highly condensed multinary nitridosilicate known and has almost the same degree of condensation as binary Si3N4.
On the Role of Structural Zinc in Bis(Cysteinyl) Protein Sequences
Authors: Meißner Axel , Haehnel Wolfgang , Vahrenkamp Heinrich
Published: July 2007

Besides its functional role in many hydrolytic metalloenzymes, zinc acts as a structural component by being attached to bis(cysteinyl) protein sequences in some of the same enzymes, and in other metalloproteins and zinc fingers, and by being an essential constituent in metallothioneins. It is not always obvious whether the zinc‐binding proteins are pre‐organized for the incorporation of the metal or whether the zinc ion provides the structurizing power and stability for the observed peptide conformations. We have addressed the coordination chemistry aspects of this question by synthesizing zinc complexes of small model peptides and by determining their structures in solution by 2D NMR spectroscopy. The peptides chosen were of the terminally protected bis(cysteinyl) type: Cys‐Cys, Cys‐Gly‐Cys, Cys‐Phe‐Cys, and Cys‐Gly‐Ile‐Cys. The zinc ions fold these peptides into structures that can be superimposed on those of the natural proteins.
Phenoxyl Radical Complexes of Gallium, Scandium, Iron and Manganese
Authors: Adam Britta , Bill Eckhard , Bothe Eberhard , Goerdt Beatrix , Haselhorst Gabriele , Hildenbrand Knut , Sokolowski Achim , Steenken Steen , Weyhermüller Thomas , Wieghardt Karl
Published: July 2007

The hexadentate macrocyclic ligands 1,4,7‐tris(3,5‐dimethyl‐2‐hydroxybenzyl)‐1,4,7‐triazacyclononane (LH3), 1,4,7‐tris(3,5‐di‐tert‐butyl‐2‐hydroxybenzyl)‐1,4,7‐triazacyclononane (LBuH3) and 1,4,7‐tris(3‐tert‐butyl‐5‐methoxy‐2‐hydroxybenzyl)‐1,4,7‐triazacyclononane (L‐H3) form very stable octahedral neutral complexes LMIIIwith trivalent (or tetravalent) metal ions (GaIII, ScIII, FeIII, MnIII, MnIV). The following complexes have been synthesized: [LBuM], where M = Ga (1), Sc (2), Fe (3); [LBuMnIV]PF6(4′); [LM], where M = Ga (1 a), Sc (2 a), Fe (3 a); [LMnIV]PF6(4 a'); [LM], where M = Sc (2 b), Fe (3 b), MnIII(4 b); [LMnIV]2(ClO4)3(H3O)(H2O)3(4 b'). An electrochemical study has shown that complexes1, 2, 3, 1 a, 2 aand3 aeach display three reversible, ligand‐centred, one‐electron oxidation steps. The salts [LFeIII]ClO4and [LGaIII]ClO4, have been isolated as stable crystalline materials. Electronic and EPR spectra prove that these oxidations produce species containing one, two or three coordinated phenoxyl radicals. The Mössbauer spectra of3 aand [3 a]+show conclusively that both compounds contain high‐spin iron(III) central ions. Temperature‐dependent magnetic susceptibility measurements reveal that3 ahas anS= 5/2 and [3a]+anS= 2 ground state. The latter is attained through intramolecular antiferromagnetic exchange coupling between a high‐spin iron(III) (S1= 5/2) and a phenoxyl radical (S2= 1/2) (H= ‐ 2JS1S2;J= ‐ 80 cm−1). The manganese complexes undergo metal‐ and ligand‐centred redox processes, which were elucidated by spectroelectrochemistry; a phenoxyl radical MnIVcomplex [MnIVL]2+is accessible.
Chain Conformation and Metal…Metal Contacts in Dimers and Stacks of d8‐ML4Complexes: Electronic Effects
Authors: Aullón Gabriel , Alvarez Santiago
Published: July 2007

A qualitative theoretical study is presented of the ligand effects on the strength of the M…︁M nonbonded interaction in dimers and stacks of8‐ML4chains. It is found that π‐acidic ligands enhance and π‐basic ligands weaken the M…︁M bonding interaction. A large amount of structural data can be rationalized with the help of a simple orbital model. Other features of the crystal structures of such compounds are correctly accounted for by semiempirical molecular orbital and electronic band calculations (extended Hückel level). Electronic effects control the deviation from linearity of stacks of complexes with mixed ligands, whereas coupled electronic and steric effects determine the conformational preference. The predictive capability of theoretical band calculations is found to be good.
Absolute Asymmetric Synthesis from Achiral Molecules in the Chiral Crystalline Environment
Authors: Sakamoto Masami
Published: July 2007

The current status of absolute asymmetric synthesis in a chiral crystalline environment has been reviewed. A number of topochemically controlled four‐center type photocycloadditions are described for a series of unsymmetrically substituted diolefin crystals and CT crystals. This concept has been applied to intramolecular photoreactions, and several successful absolute asymmetric syntheses have been achieved, involving Norrish Type II reaction, di‐π‐methane rearrangement, electrocyclization, thietane formation, oxetane formation, hydrogen abstraction by thiocarbonyl and alkenyl groups, and radical‐pair intermediates.
The Structure of α‐Gallium and Its Relationship to Deltahedral Clusters
Authors: Häuermann Ulrich , Lidin Sven , Simak Sergei I. , Abrikosov Igor A.
Published: July 2007

We present idealised geometrical models for the α‐Ga and β‐Ga structures based on two differently distorted, corrugated 36 nets. We investigated the structural stability of two sets of two‐dimensional and three‐dimensional model structures consisting of these corrugated nets as a function of the net puckering. We used the simple tight‐binding (TB) Hückel model with the structural energy difference theorem and the advanced full‐potential linear muffin‐tin orbital (FP‐LMTO) method in the framework of local‐density functional theory. Both methods show the existence of an optimum puckering angle that corresponds well to the situation in the experimental α‐Ga structure. The geometrical model of the α‐Ga structure follows the building principle of terminally coordinated deltahedral clusters, extended to two‐dimensional structures. The chemical bonding in α‐Ga is interpreted in terms of multicentre bonding within the corrugated 36 nets and two‐electron–two‐centre bonds connecting these nets.
Peptide Nucleic Acids with a Conformationally Constrained Chiral Cyclohexyl‐Derived Backbone
Authors: Lagriffoule Pierre , Eriksson Magdalena , Jensen Kristine Kilså , Nielsen Peter E. , Wittung Pernilla , Nordén Bengt , Buchardt Ole
Published: July 2007

Peptide nucleic acid (PNA) is an achiral nucleic acid mimic with a backbone consisting of partly flexible aminoethyl glycine units. By replacing the aminoethyl portion of the backbone by an amino cyclohexyl moiety, either in the (S, S) or the (R, R) configuration, we have synthesized conformationally constrained PNA residues. PNA oligomers containing (S, S)‐cyclohexyl residues were able to form hybrid complexes with DNA or RNA, with little effect on the thermal stability (Tm = 1°C per (S, S) unit, depending on their number and the sequence). In contrast, incorporation of the (R, R) isomer resulted in a drastic decrease in the stability of the PNA‐DNA (or RNA) complex (Tm = −8°C per (R, R) unit). In PNA‐PNA duplexes, however, the (R, R)‐ and (S, S)‐cyclohexyl residues only exerted a minor effect on the stability, and the complexes formed with the two isomers are of opposite handedness, as evidenced from circular dichroism spectroscopy. In some cases the introduction of a single (S, S) residue in a PNA 15‐mer improves its sequence specificity for DNA or RNA. From the thermal stabilities and molecular modeling based on the solution structure of a PNA‐DNA duplex determined by NMR techniques, we conclude that the right‐handed helix can accommodate the (S, S) isomer more easily than the (R, R) isomer. Thermodynamic measurements of H and S upon PNA‐DNA duplex formation show that the introduction of an (S, S)‐cyclohexyl unit in the PNA does indeed decrease the entropy loss, indicating a more conformationally constrained structure. However, the more favorable entropic contribution is balanced by a reduced enthalpic gain, indicating that the structure constrained by the cyclohexyl group is not so well suited for DNA hybridization.