bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Ring‐Opening Polymerization of Hydrocarbon‐Bridged [2]Ferrocenophanes: Synthesis and Properties of Poly(ferrocenylethylene)s and Their Charge‐Transfer Polymer Salts with Tetracyanoethylene
Authors: Nelson James M. , Nguyen Paul , Petersen Ruth , Rengel Heiko , Macdonald Peter M. , Lough Alan J. , Manners Ian , Raju Nandyala P. , Greedan John E. , Barlow Stephen , O'Hare Dermot
Published: July 2007

The poly(ferrocenylethylene)s [Fe(η‐C5H3RCH2)2]n 5a and 5b (a: R = H, b: R = Me) have been prepared by thermal ring‐opening polymerization of the corresponding strained hydrocarbon‐bridged [2]ferrocenophanes [Fe(η‐C5‐H3RCH2)2] (4a and 4b). An X‐ray diffraction study of 4a indicated significant strain. Polymer 5a was crystalline and insoluble in common organic solvents and was characterized by solid‐state 13C NMR. Polymer 5b, which was soluble in organic solvents, was characterized by 1H and 13C NMR, UV/visible spectroscopy and elemental analysis. Its molecular weight distribution was bimodal (gel permeation chromatography: Mw = 9.6 × 104, Mn = 8.6 × 104 for the high molecular weight fraction, Mw = 4.8 × 103, Mn = 3.5 × 103 for the oligomeric fraction), suggesting two polymerization mechanisms. The UV/visible spectrum implied a localized structure for the polymer backbone. Cyclic voltammetry revealed that 5b undergoes two reversible oxidations in CH2Cl2 solution at–0.25 and–0.16V. The redox coupling is indicative of only a small degree of interaction between the iron centres. Thermogravimetric analysis indicated that 5a and 5b are thermally stable to ca. 300–350°C under N2. At higher temperatures they yield ferromagnetic iron carbide ceramics 6a and 6b (ca. 50% and 32%, respectively, at 600°C) together with molecular depolymerization products. The reaction of 5b with tetracyanoethylene (TCNE) yielded insoluble and soluble oxidized products 11 and 12, which differed in the degree of oligomerization of the TCNEy‐x counterions. These products were characterized by IR, elemental analysis, ESR spectroscopy, and magnetic susceptibility measurements. The last revealed the presence of significant antiferromagnetic interactions in 12.
Dendritic Bipyridine Ligands and Their Tris(Bipyridine)Ruthenium(II) Chelates—Syntheses, Absorption Spectra, and Photophysical Properties
Authors: Issberner Jörg , Vögtle Fritz , Cola Luisa De , Balzani Vincenzo
Published: July 2007

Several synthetic strategies have been explored to prepare dendrimers having the [Ru(bpy)3]2+ complex as their core (bpy = 2,2′‐bipyridine). Dendritic ligands have been synthesized by attaching branches in the 4,4′‐positions of bpy. The largest dendritic bipyridine ligand contains 54 peripherical methylester units. Four RuII dendritic complexes have been prepared. Their absorption and emission spectra are very similar to those of the unsubstituted parent RuII–bipyridine complexes. The large dendritic complexes, however, exhibit a more intense emission and a longer excited‐state lifetime than [Ru(bpy)3]2+ in aerated solutions. This is due to the shielding effect of the dendrimer branches on the Ru–bipyridine core, which limits the quenching effect of molecular oxygen. For the largest dendritic complex, which contains 54 peripherical methylester units, the excited‐state lifetime in aerated acetonitrile solution is longer than 1 μs, and the rate constant for dioxygen quenching is twelve times smaller than for [Ru(bpy)3]2+.
A Theoretical Study of the Indigoid Dyes and Their Chromophore
Authors: Serrano‐Andrés Luis , Roos Björn O.
Published: July 2007

A theoretical study of the electronic spectra of indigo, bispyrroleindigo, and the H‐chromophore, thought to be the basic structure leading to the intense absorption in the visible spectrum of the indigoid dyes, has been performed by means of the complete active space (CAS) SCF method and the multiconfigurational second‐order perturbation theory (CASPT2). The calculations include excitation energies, oscillator strengths, and transition moment directions for the valence singlet states of the molecules. The assumption that the H‐chromophore is responsible for the absorption in the visible spectrum is quantitatively revisited with the help of the modern ab initio methodologies and the main features of these molecules are theoretically analyzed, some of them for the first time.
Complexes [(P2)Rh(hfacac)] as Model Compounds for the Fragment [(P2)Rh] and as Highly Active Catalysts for CO2 Hydrogenation: The Accessible Molecular Surface (AMS) Model as an Approach to Quantifying the Intrinsic Steric Properties of Chelating Ligands in Homogeneous Catalysis
Authors: Angermund Klaus , Baumann Wolfgang , Dinjus Eckhard , Fornika Roland , Görls Helmar , Kessler Magnus , Krüger Carl , Leitner Walter , Lutz Frank
Published: July 2007

The complexes [(P2)Rh(hfacac)] 1 [P2 = R2P‐(X)‐PR2] are introduced as model compounds for the investigation of the intrinsic steric properties of the [(P2)Rh] fragment. The ligand exchange processes that occur during the syntheses of 1 from [(cod)Rh(hfacac)] and the appropriate chelating diphosphanes 3 were studied by variable‐temperature multinuclear NMR spectroscopy. The molecular structures of eight examples of 1 with systematic structural variations in 3 were determined by X‐ray crystallography. The steric repulsion of the PR2 groups within the chelating fragment was found to significantly influence the coordination geometry of [(P2)Rh], depending on the nature and length of the backbone (X). A linear correlation between the P‐Rh‐P angles in the solid state and the 103Rh chemical shifts reveals a similar geometric situation in solution. A unique molecular modeling approach was developed to define the accessible molecular surface (AMS) of the rhodium center within the flexible [(P2)Rh] fragment. The potential of this model for application in homogeneous catalysis was exemplified by the use of 1 as catalysts in a test reaction, the hydrogenation of CO2 to formic acid. Complexes 1 were found to be the most active catalyst precursors for this process in organic solvents known to date.
Self‐Assembly of Novel [2]Catenanes and [2]Pseudorotaxanes Incorporating Thiacrown Ethers or Their Acyclic Analogues
Authors: Asakawa Masumi , Ashton Peter R. , Dehaen Wim , L'abbé Gerrit , Menzer Stephan , Nouwen Jan , Raymo Françisco M. , Stoddart J. Fraser , Tolley Malcolm S. , Toppet Suzanne , White Andrew J. P. , Williams David J.
Published: July 2007

A series of π electron rich macrocyclic polythioethers and their acyclic analogues have been synthesized in good yields. The association constants for the complexation of the π electron deficient bis(hexafluorophosphate) bipyridinium‐based salt, paraquat, by these macrocycles, as well as those for the complexation of corresponding acyclic compounds by the bipyridinium‐based tetracationic cyclophane, cyclobis(paraquat‐p‐phenylene), are significantly lower than those observed in the case of the “all‐oxygen” analogues. Nonetheless, yields as high as 86% were recorded in the template‐directed syntheses of [2]catenanes composed of cyclobis(paraquat‐p‐phenylene) and the macrocyclic polythioethers. Single‐crystal X‐ray crystallographic analyses of the [2]catenanes incorporating constitutionally unsymmetrical π electron rich macrocyclic polythioethers revealed that, in all cases, the dioxyaromatic units are located inside the cavity of the tetracationic cyclophane component in preference to the dithiaaromatic units. A similar selectivity was observed in solution by variable‐temperature 1H NMR spectroscopy. However, inversion of the ratio between the two translational isomers of the two [2]catenanes bearing 1,5‐dithi‐anaphthalene, as one of their π electron rich ring systems, and either 1,4‐dioxy‐benzene or 1,5‐dioxynaphthalene, as the other, occurs upon increasing the temperature from –30 to +30 πC. These [2]catenanes can be viewed as temperature‐responsive molecular switches.
A Novel Synthetic Route to Tantalum–Zinc Neophylidyne Complexes Stabilized by ortho‐Chelating Arylamine Ligands; the X‐Ray structure of [TaCl2(μ‐C6H4CH2NMe2−2)(μ‐CCMe2Ph)ZnCl(THF)]
Authors: Rietveld Marco H. P. , Lohner Pierre , Nijkamp Marije G. , Grove David M. , Veldman Nora , Spek Anthony L. , Pfeffer Michel , van Koten Gerard
Published: July 2007

A dimeric tantalum‐zinc neophylidyne complex proposed to be [{{TaCl2(μ‐CCMe2Ph)(μ‐Cl)(THF)2}{Zn(μ‐Cl)}}2](5a), which can be prepared easily on a scale of 50 mmol, is an ideal starting material for the synthesis of mono‐ and bis(ortho)‐chelated arylamine alkylidyne species such as the red Ta‐Zn neophylidyne complexes [TaCl2(μ‐C6H4CH2NMe2−2)(μ‐CCMe2Ph)ZnCl(THF)] (6) and [TaCl2‐{μ‐C6H3(CH2NMe2)2−2,6}(μ‐CCMe2Ph)ZnCl] (7), which have been isolated in high yields. Reaction of 7 with tmeda affords the Tav alkylidene complex [TaCl(=CHCMe2Ph){C6H3(CH2N(Me)CH2)−2‐CH2NMe2)‐6}] (8), which shows catalytic activity in the ring‐opening metathesis polymerization of norbornene.
Molecular Structures and Energetics of Corrole Isomers: A Comprehensive Local Density Functional Theoretical Study
Authors: Ghosh Abhik , Jynge Knut
Published: July 2007

By using geometry optimizations with local density functional theory and double‐π plus polarization basis sets, an extensive study has been carried out on the molecular structures and stabilities of free‐base and metal‐complexed corrole isomers. The optimized structures of normal metallocorroles have been found to agree well with crystallographic results. For both free‐base and metal‐complexed derivatives, the [1.1.1] ring system is found to be the most stable. The [2.0.1]‐ and [2.1.0]corrole isomers are unequivocally predicted to exist as stable materials. Of these, the [2.0.1] ring system, known as isocorrole, has been recently synthesized. Various derivatives of these two ring systems lie only about 10–20 kcal mol−1 above analogous derivatives of normal corrole. In general, the cis‐ and trans−[3.0.0]corrole derivatives are predicted to be significantly less stable than the other corrole isomers. However, the ScIII complexes of these two stereoisomeric ring systems are surprisingly stable. Direct C−α‐Cα linkages between pyrrole rings are identified as a principal source of strain in the molecular structures of corrole isomers. The N4 cores of [1.1.1]‐ and [2.0.1]corrole isomers are significantly smaller than the porphyrin core. Thus, these corrole isomers are predicted to have a strong preference for smaller metal ions such as GaIII. The [2.1.0] core is somewhat larger, as evidenced by longer metal‐nitrogen distances in [2.1.0]‐metallocorroles. These differences in core geometry account for an interesting reversal of the relative stabilities of [2.0.1]‐and [2.1.0]metallocorroles with increasing ionic radius of the complexed metal ion. Analogous to porphyrin isomer chemistry, the trans stereoisomer of [3.0.0]‐corrole is found to be more stable than the cis stereoisomer for the free‐base and for the ScIII and InIII derivatives. For the free bases of any particular isomer, the tautomers are quite similar in energy, differing by only 2–7 kcal mol−1. This, together with the presence of short, strong N‐HN hydrogen bonds, suggests that N‐H tautomerization in at least some free‐base corrole isomers should be considerably faster than that in porphyrins. Overall, it has been possible in most cases to establish a good correlation between the energetics trends and structural differences among molecules.
Formation of Hydrido–η3‐Allyl Complexes of IrIII by Sequential Olefinic CH Bond Activation and CC Coupling of Alkenyl and Olefin Ligands
Authors: Alvarado Ysaias , Boutry Olivier , Gutiérrez Enrique , Monge Angeles , Nicasio M. Carmen , Poveda Manuel L. , Pérez Pedro J. , Ruíz Caridad , Bianchini Claudio , Carmona Ernesto
Published: July 2007

The bis(ethene) complex [Tp*Ir‐(C2H4)2] (1*) (Tp* = tris(3,5‐dimethyl‐1‐pyrazol‐1‐yl)hydroborato) undergoes thermal rearrangement to the hydrido–allyl complex [Tp*IrH(π3‐C3H4Me)] (6*), through the intermediacy of the hydrido–vinyl complex [Tp*IrH(C2H3)(C2H4)] (2*). The overall conversion of 1* into 6* corresponds formally to the dimerisation of ethene by an unprecedented pathway that involves sequential C–H bond activation of a coordinated olefin molecule and C–C bond formation by coupling of the resulting vinyl and ethene moieties. Similar transformations have been observed for monosubstituted olefins like propene and 1‐butene, while the internal alkene cis−2‐butene experiences allylic activation of an sp3 C–H bond, which provides an alternative route to 6*. The extension of these investigations to the analogous complexes of the unsubstituted tris(pyrazolyl)hydroborato ligand Tp is also reported. Mechanistic studies on the formation of the C–C bond by coupling of the vinyl and the olefin ligands suggest the participation of a vinylidene complex (formed by α‐H abstraction from the vinyl group), which then rearranges to an allene species. Evidence for the involvement of these and other key reaction intermediates is provided.
Synthesis and Biological Evaluation of a Backbone‐Modified Phytoalexin Elicitor
Authors: Timmers C. M. , Turner J. J. , Ward C. M. , van der Marel G. A. , Kouwijzer M. L. C. E. , Grootenhuis P. D. J. , van Boom J. H.
Published: July 2007

Two suitably protected building blocks (11 and 33) for the preparation of amide‐linked heptaglucoside mimetic 2, an analogue of the naturally occurring phytoalexin elicitor 1a, were readily accessible by glycal chemistry. Sequential elongation of terminal glucuronide 21 with laminaribiosyl hemiaminal 33 and anomeric amine 11 by EDC/HOBt‐catalyzed condensation and two‐step conversion of the C6‐OTr moiety into the corresponding carboxylate function afforded homogeneous carbopeptoid 2 in high overall yield. It was found that replacement of the acetal linkages by the more rigid amide bonds destroys the phytoalexin‐elicitor activity.
Molecular Receptors for Adenine and Guanine Employing Metal Coordination, Hydrogen‐Bonding and π‐Stacking Interactions
Authors: Kickham James E. , Loeb Stephen J. , Murphy Shannon L.
Published: July 2007

Thiacyclophane ligands 1 and 2, containing a meta‐xylyldithiaether unit, an aromatic spacing unit and a polyether chain, were prepared in good yield in a three‐step synthesis. The macrocyclic organopalladium complexes [Pd(L)‐(MeCN)][BF4] (3: L = 1; 4: L = 2) were prepared through palladation of the respective thiacyclophane ligand by reaction with [Pd(MeCN)4][BF4]2. These complexes act as metalloreceptors to aromatic amines such as p‐aminopyridine (pap), m‐aminopyridine (map) and the DNA nucleobases adenine and guanine. Binding occurs through simultaneous first‐ and second‐sphere coordination. This involves three separate interactions: first‐sphere σ donation from an aromatic N atom to the Pd centre, second‐sphere hydrogen bonds between the NH2 group and polyether O atoms, and π stacking between the electron‐poor aromatic rings of the substrate and the electron‐rich aromatic spacing units of the receptor. 1H NMR spectra exhibit chemical shift changes indicative of the H‐bonding and π‐stacking interactions in solution. X‐ray structures for thiacyclophane 1, metalloreceptor [Pd(1)(MeCN)][BF4] (3), metalloreceptor/model substrate complexes [Pd(1)(pap)][BF4 (5) and [Pd(2)‐(pap)][BF4] (7), and metalloreceptor/nucleobase complexes [Pd(1)(adenine)][BF4] (13), [Pd(2)(adenine)][BF4] (14) and [Pd(1)(guanine‐BF3)][BF4] (15b) show details of these interactions in the solid state.
The Origin of the Remarkable Regioselectivity of Fe+‐Mediated Dehydrogenation in Benzocycloalkenes
Authors: Hertwig Roland H. , Seemeyer Katrin , Schwarz Helmut , Koch Wolfram
Published: July 2007

Combined mass spectrometric experiments and density functional theory (DFT) calculations have been performed to determine the regioselectivity and uncover the origin of the CH bond activation of benzocycloalkenes by “bare” FeI cations. The hydrocarbons investigated are benzocyclohexene, ‐heptene, and ‐octene. Extensive labeling experiments demonstrate that the site of CH bond activation in the non‐aromatic ring is dependent on the ring size. The barriers for the dehydrogenation process as predicted by DFT calculations are in agreement with the experimental findings. Further, the combined experimental and theoretical approach applied in the present study allows the principles underlying the remarkable ring size dependent regioselectivity of CH bond activation in these hydrocarbons to be unraveled.
Bis(Trimethylsilyl)Ammonium Salts Obtained by Reaction of Hexamethyldisilazane with TiCl4, ZrCl4, or SnCl4
Authors: Bettenhausen Regina , Milius Wolfgang , Schnick Wolfgang
Published: July 2007

The reaction of hexamethyldisilazane with TiCl4 in CH2Cl2 leads to the formation of [(Me3SiNTiCl2)8] (3). According to the crystal structure analysis, 3 is an octameric titanium trimethylsilylimido chloride. The mechanism of the formation of 3 was studied in detail by means of time‐dependent 14N NMR spectroscopy. [(Me3Si)2NTiCl3] was identified as an intermediate during the formation of 3. Two by‐products were identified: [(NH4)2TiCl6] and the hitherto unknown bis(trimethylsilyl)ammonium salt [(Me3Si)2NH2]+[Ti2Cl9]− (5). According to the crystal structure analysis, protonation of hexamethyldisilazane to give the cation of 5 causes a significant lengthening of the Si‐N bond from 173.5 to 186 pm. Other tetravalent metal chlorides, such as ZrCl4 and SnCl4, also reacted with hexamethyldisilazane to yield bis(trimethylsilyl)ammonium salts. However, the constitution of the corresponding anions differs significantly. In the case of ZrCl4, an anionic chlorotrimethylsilylimidozirconate (6) [(Me3Si)2NH2]+2‐[{Cl3ZrCl3Zr(Cl)(NSiMe3)}2]2− was obtained, while SnCl4 reacted to give a novel spiro anion [N(SnCl3)2(SnCl2)4‐(NSiMe3)2NH)2]− together with the bis(trimethylsilyl)ammonium ion in 7; this anion is the first species containing a tetrastannylated nitrogen.
Palladacycles: Efficient New Catalysts for the Heck Vinylation of Aryl Halides
Authors: Herrmann Wolfgang A. , Brossmer Christoph , Reisinger Claus‐Peter , Riermeier Thomas H. , Öfele Karl , Beller Matthias
Published: July 2007

Cyclopalladated complexes of the general formula [Pd2(μ‐L)2(PC)2] (L = bridging ligand, e.g. OAc, Cl, Br, I; PC = cyclometallated P donor, e.g. o‐CH2C6H4P(o‐Tol)2 or o‐CH2C6H2(CH3)2‐P(Mes)2) are highly efficient catalysts for the Heck vinylation of aryl halides. The isolated complexes are easily accessible from palladium(II) acetate by spontaneous metallation of ortho‐methyl‐substituted arylphosphines. They display improved activity and stability compared to conventional catalyst mixtures (e.g. [Pd(OAc)2] +nPPh3), and also exhibit a higher stability towards air than conventional Pd0‐based systems (e.g. [Pd(PPh3)4]). Turnover numbers (TON) of up to 1000000 and turnover frequencies (TOF) in the range of 5000‐20000 are achieved in catalytic coupling reactions of aryl bromides. Even technically interesting aryl chlorides undergo the Heck reaction (TON = 600‐40000) if promoting salts are added to the catalyst ((NBu4)Br, LiBr). The new structural type for catalysts is compared to palladacycles formed in situ from mixtures of [Pd(OAc)2] + P(o‐tolyl)3 and the established [Pd(OAc)2] + nPPh3 system. The scope of the new CC coupling catalysts is outlined for the vinylation of aryl halides by the use of different mono‐ and disubstituted olefins. Mechanistic consequences for the Heck reaction in general are discussed.
Stereoselective Synthesis of (S)‐3,4‐Methylenedioxyamphetamines from (R)‐Cyanohydrins
Authors: Effenberger Franz , Jäger Jürgen
Published: July 2007

A stereoselective synthesis of (S)‐3,4‐methylenedioxyamphetamines (S)‐7, which are highly interesting as psychoactive compounds, is described. Starting from readily available (R)‐cyanohydrins (R)‐2 the 2‐amino‐1‐aryl alcohols (1R,2S)‐4 were obtained with high diastereoselectivity by addition of Grignard reagents to the O‐protected cyanohydrins (R)‐3, transimination of the addition products A with primary amines, and hydrogenation of the imino intermediates B with NaBH4. For the hydrogenation of the benzylic hydroxyl group in the 1,2‐amino alcohols (1R,2S)‐4 a new, very efficient method was developed. The optically pure amphetamines (S)‐7 were obtained under very mild conditions by catalytic hydrogenation of the oxazolidinones (4S,5R)‐6, which were readily available by phosgenation of the amino alcohols (1R,2S)‐4.
From Dendrimers to Knedel‐like Structures
Authors: Wooley Karen L.
Published: July 2007

Shell‐crosslinked knedels are nanometer‐sized (5–200 nm diameters), amphiphilic core‐shell spheres that are prepared by the self‐assembly of amphiphilic block copolymers into polymer micelles, followed by crosslinking of side chain functionalities along the block composing the shell of the polymer micelles. Such structures resemble dendrimers in the basic structural components, and have the advantages of a rapid synthetic approach and the production of larger and broader size ranges.
Theory of the d10–d10 Closed‐Shell Attraction: 1. Dimers Near Equilibrium
Authors: Pyykkö Pekka , Runeberg Nino , Mendizabal Fernando
Published: July 2007

We study the dependence of the aurophilic attraction (AuI–AuI) in perpendicular model systems of the type [(ClAuPH3)2] on the ab initio method, basis set and different pseudopotentials used, and on relativity. The effects of varying the „halogen”︁ (X = F, H, Cl, Me, Br, ‐C≡CH, I), the „phosphine”︁ (L = PH3, PMe3, ‐N≡CH) and the metal (M = Cu, Ag, Au) on the M–M′ interaction of the [(XML)2] dimer are also studied. The depth of the interaction potential increases with the softness of the group X. It decreases by 27% for M = Au, X = Cl and L = PH3 if relativistic effects are omitted at fixed geometry.
Theory of the d10–d10 Closed‐Shell Attraction: 2. Long‐Distance Behaviour and Nonadditive Effects in Dimers and Trimers of Type [(x‐Au‐L)n] (n = 2, 3; X = Cl, I, H; L = PH3, PMe3, ‐N≡CH)
Authors: Pyykkö Pekka , Mendizabal Fernando
Published: July 2007

We study the nature of the aurophilic attraction (AuI–AuI) at its long‐range limit for the model systems [(X‐Au‐L)n] (n = 2, 3; X = Cl, I, L = PH3, PMe3; X = H, L = ‐N≡CH) at the ab initio MP2 and Hartree‐Fock levels. The nature of the interactions and nonadditive effects at various orientations are related to simple electrostatic induction and dispersion expressions involving the individual properties of each monomer.
Strong Binding of Alkylguanidinium Ions by Molecular Tweezers: An Artificial Selective Arginine Receptor Molecule with a Biomimetic Recognition Pattern
Authors: Schrader Thomas
Published: July 2007

Bisphosphonates 2 and 3 represent the first artificial receptor molecules for alkylguanidinium ions. They bind to the guanidinium moiety by forming a 1:1 chelate complex, stabilized by a planar network of electrostatic interactions and hydrogen bonds. This hydrogen bonding configuration is identical to the „arginine fork”︁ postulated by Frankel as a key element in RNA–protein recognition of the AIDS virus. Our guanidinium–bisphosphonate complexes thus constitute the first synthetic model for this important biological interaction and demonstrate that the high binding energy can be a driving force for a conformational change in the receptor (induced fit, e.g., in the RNA). Although binding of monosubstituted alkylguanidines is generally strong (Ka ≈ 10 000 in DMSO), molecular tweezer 3 recognizes N‐ and C‐amide‐protected arginine derivatives especially well (Ka ≈ 300 000 in DMSO), because an additional hydrogen bond is formed between the amide and the phosphonate. Since 3 does not bind amines effectively, it is highly selective for arginine, even in the presence of lysine or other amino acids. For di‐, tri‐, and tetrasubstituted guanidines the association constant remains low (Ka⩽1000 in DMSO) reflecting the increase in the steric bulk of the guest.
The Nature of the Metal—Silicon Bond in [M(SiR3)H3(PPh3)3] (M = Ru, Os) And the Crystal Structure of [Os{Si(N‐pyrrolyl)3}H3(PPh3)3]
Authors: Hübler Klaus , Hübler Ute , Roper Warren R. , Schwerdtfeger Peter , James Wright L.
Published: July 2007

The compounds [M(SiR3)H3(PPh3)3] (1: M = Ru, R = 1 ‐ NC4H4 = pyr; 2a‐c: M = Os, R = pyr, Et, Ph) are prepared through reaction of either [RuH2(PPh3)4] or [OsH4(PPh3)3] with the appropriate silane HSiR3 (3a‐c: R = pyr, Et, Ph). The X‐ray structure analysis of compound 2 a and ab initio calculations on the model compounds [Os(SiR3)H3(PH3)3] (4a‐c: R = H, NH2, pyr) reveal a trigonal distortion along the Os‐Si axis from an idealised tetrahedral geometry for the central OsSiP3 heavy‐atom skeleton. The structure can be described as two face‐shared octahedra, one based on osmium (OsH3P3) and the other based on silicon (SiH3N3). Studies of the bonding situation in 2 a reveal that the N‐pyrrolyl substituents have a marked shortening effect on the osmium‐silicon distance (229.3(3) pm) and that each of the three hydride ligands participates in partial three‐centre bonding involving osmium, silicon and hydrogen. 1H, 13C, 29Si and 31P NMR spectra were used to determine the solution structures of complexes 1 and 2 a.
Carbohydrate‐Modified Metal Carbenes: Synthesis And First Applications
Authors: Heinz Dötz Karl , Ehlenz Richard
Published: July 2007

Carbohydrate‐modified carbene complexes can be synthesised by combining a sugar electrophile with a metalate nucleophile or vice versa. Acyclic sugar skeletons adopt conformations that are controlled by the minimisation of 1,3‐interactions and are not significantly affected by the incorporation of a metal fragment. Thus, the latter can be used exclusively for reactivity tuning. Sugar carbene complexes undergo regio‐ and stereoselective ligand‐ and metal‐centred reactions such as C2‐homologisation and benzannulation.
Intermediates in the Catalytic Dehydrogenative Coupling of Arylgermanes
Authors: Bender John E. , Litz Kyle E. , Giarikos Dimitrios , Wells Norman J. , Banaszak Holl Mark M. , Kampf Jeff W.
Published: July 2007

The use of a new electron‐withdrawing germane, H2Ge[3,5‐(CF3)2C6H3]2 (3), has facilitated the isolation and characterization of three new complexes implicated in the dehydrogenative coupling of bisarylgermanes by Pt0‐phos‐phane complexes. The intermediates include a digermyl species, trans‐[(Et3P)2Pt{GeH(Ar)2}2] (7), a bound digermane showing the first stage of Ge‐Ge catenation, cis‐[(Et3P)2Pt(H){Ge(Ar)2‐GeH(Ar)2}] (8), and the Ge‐H activated form of this product, [(Et3P)2HPtGe(Ar)2‐Ge(Ar)2PtH(PEt3)2] (6). Complexes such as 6 and 8 have not previously been isolated as intermediates in dehydrogenative coupling reactions. An X‐ray crystal structure was determined for complex 6, confirming the cis geometry of the hydrogen and germanium ligands; this provides yet another example of the stability of germyl hydrides towards reductive elimination. A similar cis geometry was observed for complex 8. Performing the dehydrogenative coupling reaction under a CO2 atmosphere failed to yield any products containing trapped germylene species.
Biomimetic Crystallization of Calcium Carbonate Polymorphs by Means of Collagenous Matrices
Authors: Falini Giuseppe , Fermani Simona , Gazzano Massimo , Ripamonti Alberto
Published: July 2007

Crosslinked gelatin films with entrapped poly‐L‐aspartate were used to induce the crystallization of calcite and aragonite polymorphs. Calcite with high degrees of isomorphous substitution (up to 12mol% magnesium) has been obtained. The morphology and layered organization of magnesium calcite crystals grown inside the crosslinked gelatin films with entrapped poly‐L‐aspartate resemble some structural features of radial calcitic ooids. The concentration of entrapped poly‐L‐aspartate and the uniaxial deformation of the films control the growth of aragonite aggregates inside the films. Such aggregates grown inside uniaxially deformed films consist of parallel rods with an architectural assembly similar to that found in some marine organisms. The crystals' aggregation and the control of calcium carbonate polymorphism are related to the modelling of the nucleation sites by poly‐L‐aspartate structure and concentration, local supersaturation and microenvironment shape. The results indicate that the collagenous matrices with entrapped polyelectrolytes are versatile systems which can contribute to the elucidation of strategies for biomimetic materials chemistry.
A Quintupled Superstructure of the KHg2 Type Realized for the New Stannide EuAuSn
Authors: Pöttgen Rainer , Hoffmann Rolf‐Dieter , Müllmann Ralf , Mosel Bernd D. , Kotzyba Gunter
Published: July 2007

The title compound was prepared from the elements by reaction in a sealed tantalum tube at 1320 K followed by slow cooling to 970 K. EuAuSn crystallizes with a pronounced subcell of space group Imma (KHg2 type). Additional very weak reflections required a quintupled b axis. The superstructure was refined from single‐crystal four‐circle diffractometer data (Imm 2, a = 479.1(1) pm, b = 3833.6(5) pm, c = 820.1(1) pm, Z = 20, wR2 = 0.0834, 3675 F2 values and 94 variables). Six crystallographically different europium sites occur in the superstructure. Each europium site has an ordered near‐neighbour environment of six gold and six tin atoms in the form of two tilted hexagons. Magnetic susceptibility measurements show Curie‐Weiss behaviour above 50 K with an experimental magnetic moment of 7.6(1) μB/Eu, indicating divalent europium. EuAuSn orders antiferromagnetically at about 12 K and undergoes a metamagnetic transition at a critical field of 2.0(2) T. Electrical conductivity measurements show metallic behaviour with a room temperature value of 260 μΩcm. 151Eu and 119Sn Mössbauer spectroscopic experiments are compatible with divalent europium and show complex magnetic hyperfine field splitting at low temperature.
2,3,7,8,12,13,17,18‐Octafluoro‐5,10,15,20‐Tetraphenylporphyrin: First Synthesis and X‐Ray Crystal Structure of the ZnII Complex
Authors: Leroy Jacques , Bondon Arnaud , Toupet Loïc , Rolando Christian
Published: July 2007

2,3,7,8,12,13,17,18‐Octafluoro‐5,10,15,20‐tetraphenylporphyrin has been prepared from 3,4‐difluoropyrrole and benzaldehyde under Lindsey conditions. An X‐ray crystal structure study of its ZnII complex has shown that the macrocycle core is nonplanar, a result in apparent contradiction with a blue‐shifted UV/Vis spectrum. The results reported here demonstrate that a wide range of β‐octafluoro‐meso‐arylated porphyrins, a new class of highly electron‐deficient ligands, are potentially accessible from 3,4‐difluoropyrrole, thus opening the door to, inter alia, efficient and robust oxidation catalysts.
Total Synthesis of Oxazole‐ and Cyclopropane‐Containing Epothilone A Analogues by the Olefin Metathesis Approach
Authors: Nicolaou K. C. , Vallberg Hans , King N. Paul , Roschangar Frank , He Yun , Vourloumis Dionisios , Nicolaou Christopher G.
Published: July 2007

For structure‐activity relationship studies, two series of epothilone A (1) analogues have been designed and synthesized, one containing an oxazole moiety instead of the thiazole heterocycle and the other containing a spirocyclopropane moiety in place of the gem‐dimethyl group at position C‐4 (4,4‐ethano‐epothilones). The olefin metathesis strategy in solution was utilized for the chemical synthesis of these compounds starting with key building blocks 7–9 for the oxazole series (compounds 2, 14–18, 21–26) and building blocks 8, 30, and 31 for the 4,4‐ethano series (compounds 3,39–43, 46–51). The convergent strategy towards the designed epothilone A series involved a) an aldol condensation reaction, b) an esterification reaction, c) an olefin metathesis reaction catalyzed by [RuCl2(=CHPh)‐(PCy3)2], and d) epoxidation of the macrocycle double bond.
Total Synthesis of Oxazole‐ and Cyclopropane‐Containing Epothilone B Analogues by the Macrolactonization Approach
Authors: Nicolaou K. C. , Sarabia Francisco , Finlay M. Ray V. , Ninkovic Sacha , King N. Paul , Vourloumis Dionisios , He Yun
Published: July 2007

In order to probe structure‐activity relationships in the epothilone area, two series of epothilone B analogues have been designed and synthesized. The first series containing an oxazole moiety in place of a thiazole on the side chain was constructed by utilizing key intermediates 7–9 or 10, 12, and 13 (Scheme 1), whereas the second series containing an ethano group instead of the gem‐dimethyl group at position 4 was synthesized from fragments 42 and 43. A Yamaguchi‐type macrolactonization reaction was used to construct the macrocycle from a secoacid, which was assembled, in both cases, by means of a) an aldol reaction, b) an Enders alkylation, and c) a Wittig‐type reaction. This convergent strategy provided access to oxazole analogues 2,4,29–32 and 4,4‐ethano derivatives 3,40,60–63 for biological studies.
Enantioselective Cathodic Reduction of 4‐Methylcoumarin: Dependence of Selectivity on Reaction Conditions and Investigation of the Mechanism
Authors: Nielsen Merete Folmer , Batanero Belen , Löhl Thorsten , Schäfer Hans J. , Würthwein Ernst‐Ulrich , Fröhlich Roland
Published: July 2007

The cathodic reduction of 4‐methylcoumarin (1) in acidic methanol/water in the presence of yohimbine leads to formation of a mixture of the hydrogenation product 4‐methyl‐3,4‐dihydrocoumarin (2), with an enantiomeric excess (ee) of (R)‐2of 0–67%, and the hydrodimer3. The relative yields of2and3and theeeof2depend on a number of experimental parameters such as pH, supporting electrolyte, working potential, and the concentrations of substrate and yohimbine, as demonstrated by a series of preparative‐scale experiments. In addition, a series of voltammetric and kinetic measurements were carried out to investigate the influence of the individual experimental parameters. Three mechanistic possibilities have been examined, and by combination of the analytical data with the results of the preparative experiments, a single model is put forward which is in accord with the available results. The main features of the mechanistic model can be summarized as follows: 1) under acidic conditions (pH 2–3) the electroactive species is a complex between1and H3O+, the reduction of which leads to an enolic radical; 2) this radical is not reduced at the working potential but tautomerizes into the more easily reduced keto radical or dimerizes; 3) the keto radical is reduced and further protonated; 4) the function of the yohimbineH+is to catalyze the tautomerization and enantioselectively protonate the final carbanion. Additionally, we conclude that the concentration of yohimbine in the immediate vicinity of the electrode is considerably higher than its stoichiometric concentration. Quantum chemical calculations demonstrate thatsiprotonation of the intermediate anion by yohimbineH+to give (R)‐2is energetically favored.
Rapid Coupling of Methyl Iodide with Aryltributylstannanes Mediated by Palladium(0) Complexes: A General Protocol for the Synthesis of 11CH3‐Labeled PET Tracers
Authors: Suzuki Masaaki , Doi Hisashi , Björkman Margareta , Andersson Yvonne , Långström Bengt , Watanabe Yasuyoshi , Noyori Ryoji
Published: July 2007

The reaction of methyl iodide and (excess) aryltributylstannane to give a methylarene has been studied with the focus on the realization of rapid coupling for incorporation of short‐lived radionuclides into bioactive organic compounds. The coupling of methyl iodide with tributylphenylstannane (40 equiv) is accomplished in >90% yield within 5 min at 60°C with a tri‐o‐tolylphosphine‐bound, coordinatively unsaturated Pd0 complex together with a CuI salt and K2CO3 in DMF. This protocol is applicable to a variety of homo‐ and heteroaromatic tin compounds, to give the corresponding methylated derivatives. The effects of the tri‐o‐tolylphosphine ligand, a Cu(I) salt, and DMF are discussed. This new protocol provides a firm chemical basis for the synthesis of 11CH3‐incorporated PET tracers.
Topologic Equivalents of Coronands, Cryptands and Their Inclusion Complexes: Synthesis, Structure and Properties of {2}‐Metallacryptands and {2}‐Metallacryptates
Authors: Saalfrank Rolf W. , Dresel Andreas , Seitz Verena , Trummer Stefan , Hampel Frank , Teichert Markus , Stalke Dietmar , Stadler Christian , Daub Jörg , Schünemann Volker , Trautwein Alfred X.
Published: July 2007

The synthesis and structural characterisation of two dinuclear iron(III) complexes are reported. The compounds of general structure [Fe2L] [8; L1 = dianion of 2,2′‐dicyano‐2,2′‐isophthaloyldi(isopropyldicarboxylate)] and [K ⊂ Fe2L]+ (PF6)‐ [10; L2 = dianion of 1,1′‐(2,6‐pyridylene)bis‐1,3‐(4‐dimethyl)‐pentanedione] are formed by the deprotonation of ligands 7 and 9 with triethylamine and potassium hydride respectively, followed by addition of iron(III) chloride and work up with water or aqueous potassium hexafluorophosphate. X‐ray crystallographic studies reveal that 8 is a racemic mixture composed of triple helicates with (Δ,Δ)‐fac and (Δ,Δ)‐fac configuration at the two iron bridgeheads. In contrast to racemic 8, the two iron centres in the meso‐10 [(Δ,Δ)‐fac] have opposite configuration. Investigations of the redox‐active iron centres in {2}‐metallacryptand 8 and {2}‐metallacryptate 10 by cyclic voltammetry show slightly different behaviour. The peaks for the two consecutive reductions of the two iron centres of 8 can hardly be resolved, whereas 10 shows two well‐separated peaks. Mössbauer measurements were performed on 8 and 10 between 4.2 and 300 K, with and without a field applied perpendicular or parallel to the γ‐beam. All zero‐field and 20 mT spectra exhibit a broad and unresolved absorption pattern. Application of 5.3 T at 4.2 K results in well‐resolved magnetic hyperfine patterns which are practically the same for 8 and 10.
Differential, age‐dependent MEK‐ERK and PI3K‐Akt activation by insulin acting as a survival factor during embryonic retinal development
Authors: Chavarría Teresa , Valenciano Ana I. , Mayordomo Raquel , Egea Joaquim , Comella Joan X. , Hallböök Finn , de Pablo Flora , de la Rosa Enrique J.
Published: July 2007

Programmed cell death is a genuine developmental process of the nervous system, affecting not only projecting neurons but also proliferative neuroepithelial cells and young neuroblasts. The embryonic chick retina has been employed to correlate in vivo and in vitro studies on cell death regulation. We characterize here the role of two major signaling pathways, PI3K‐Akt and MEK‐ERK, in controlled retinal organotypic cultures from embryonic day 5 (E5) and E9, when cell death preferentially affects proliferating neuroepithelial cells and ganglion cell neurons, respectively. The relative density of programmed cell death in vivo was much higher in the proliferative and early neurogenic stages of retinal development (E3–E5) than during neuronal maturation and synaptogenesis (E8–E19). In organotypic cultures from E5 and E9 retinas, insulin, as the only growth factor added, was able to completely prevent cell death induced by growth factor deprivation. Insulin activated both the PI3K‐Akt and the MEK‐ERK pathways. Insulin survival effect, however, was differentially blocked at the two stages. At E5, the effect was blocked by MEK inhibitors, whereas at E9 it was blocked by PI3K inhibitors. The cells which were found to be dependent on insulin activation of the MEK‐ERK pathway at E5 were mostly proliferative neuroepithelial cells. These observations support a remarkable specificity in the regulation of early neural cell death. © 2007 Wiley Periodicals, Inc. Develop Neurobiol 67:1777–1788, 2007
Summary of ‘School‐based secondary prevention programmes for preventing violence’
Authors: Milne Andrea
Published: July 2007

This is a summary of a Cochrane review, published in this issue of EBCH, first published as: Mytton J, DiGuiseppi C, Gough D, Taylor R, Logan S. School‐based secondary prevention programmes for preventing violence. Cochrane Database of Systematic Reviews 2006, Issue 3. Art. No.: CD004606. DOI: 10.1002/14651858.CD004606.pub2.

Further information for this Cochrane review is available in this issue of EBCH in the accompanying Commentary and Characteristics and Key Findings Tables articles. Copyright © 2007 John Wiley & Sons, Ltd.
Summary of ‘Nitric oxide for respiratory failure in infants born at or near term’
Authors: Milne Andrea
Published: July 2007

This is a summary of a Cochrane review, published in this issue of EBCH, first published as: Finer NN, Barrington KJ. Nitric oxide for respiratory failure in infants born at or near term. Cochrane Database of Systematic Reviews 2006, Issue 4. Art. No.: CD000399. DOI: 10.1002/14651858.CD000399.pub2.

Further information for this Cochrane review is available in this issue of EBCH in the accompanying Commentary and Characteristics and Key Findings Tables articles. Copyright © 2007 John Wiley & Sons, Ltd.
Summary of ‘Systemic antibiotics versus topical treatments for chronically discharging ears with underlying eardrum perforations’
Authors: Milne Andrea
Published: July 2007

This is a summary of a Cochrane review, published in this issue of EBCH, first published as: Macfadyen CA, Acuin JM, Gamble C. Systemic antibiotics versus topical treatments for chronically discharging ears with underlying eardrum perforations. Cochrane Database of Systematic Reviews 2006, Issue 1. Art. No.: CD005608. DOI: 10.1002/14651858.CD005608.

Further information for this Cochrane review is available in this issue of EBCH in the accompanying Commentary and Characteristics and Key Findings Tables articles. Copyright © 2007 John Wiley & Sons, Ltd.
Commentary on ‘School‐based secondary prevention programmes for preventing violence’
Authors: LeBlanc John , Cameron Paula
Published: July 2007

This is a commentary on a Cochrane review, published in this issue of EBCH, first published as: Mytton J, DiGuiseppi C, Gough D, Taylor R, Logan S. School‐based secondary prevention programmes for preventing violence. Cochrane Database of Systematic Reviews 2006, Issue 3. Art. No.: CD004606. DOI: 10.1002/14651858.CD004606.pub2.

Further information for this Cochrane review is available in this issue of EBCH in the accompanying EBCH Summary and Characteristics and Key Findings Tables articles. Copyright © 2007 John Wiley & Sons, Ltd.
Tips and tricks for understanding and using SR results. No. 6: development of a search strategy
Authors: Lundh Andreas , Kremer Leontien C. M. , Leclercq Edith
Published: July 2007

This sixth article in the series ‘Tips and tricks for understanding and using SR results’ is, like the previous ones, aimed at helping the readers to understand the results of systematic reviews and to use these results in clinical practice. Earlier articles in the Tips and Tricks section of this journal have addressed the sources of evidence, i.e. the bibliographic databases where primary studies for a Cochrane systematic review may be identified. This article will focus on how reviewers actually search an electronic bibliographic database for studies to go into Cochrane systematic reviews. The information summarized in this article is based on earlier papers, the Cochrane Handbook and the authors' experience in evidence‐based medicine and searching medical databases (1–9). Copyright © 2007 John Wiley & Sons, Ltd.
Characteristics and key findings for ‘School‐based secondary prevention programmes for preventing violence’
Authors: van Dalen Elvira , Offringa Martin , Kremer Leontien
Published: July 2007

These are the characteristics and key findings for a Cochrane review, published in this issue of EBCH, first published as: Mytton J, DiGuiseppi C, Gough D, Taylor R, Logan S. School‐based secondary prevention programmes for preventing violence. Cochrane Database of Systematic Reviews 2006, Issue 3. Art. No.: CD004606. DOI: 10.1002/14 651 858.CD004606.pub2.

Further information for this Cochrane review is available in this issue of EBCH in the accompanying EBCH Summary and Commentary articles. Copyright © 2007 John Wiley & Sons, Ltd.
Characteristics and key findings for ‘Antibiotics for the prevention of acute and chronic suppurative otitis media in children’
Authors: van Dalen Elvira , Offringa Martin , Kremer Leontien
Published: July 2007

These are the characteristics and key findings for a Cochrane review, published in this issue of EBCH, first published as: Leach AJ, Morris PS. Antibiotics for the prevention of acute and chronic suppurative otitis media in children. Cochrane Database of Systematic Reviews 2006, Issue 4. Art. No.: CD004401. DOI: 10.1002/14 651 858.CD004401.pub2.

Further information for this Cochrane review is available in this issue of EBCH in the accompanying EBCH Summary and Commentary articles. Copyright © 2007 John Wiley & Sons, Ltd.
Characteristics and key findings for ‘Nitric oxide for respiratory failure in infants born at or near term’
Authors: van Dalen Elvira , Offringa Martin , Kremer Leontien
Published: July 2007

These are the characteristics and key findings for a Cochrane review, published in this issue of EBCH, first published as: Finer NN, Barrington KJ. Nitric oxide for respiratory failure in infants born at or near term. Cochrane Database of Systematic Reviews 2006, Issue 4. Art. No.: CD000399. DOI: 10.1002/14 651 858.CD000399.pub2.

Further information for this Cochrane review is available in this issue of EBCH in the accompanying EBCH Summary and Commentary articles. Copyright © 2007 John Wiley & Sons, Ltd.
Use of Voltammetry to Monitor O2 Using Au/Hg Electrodes and to Control Physical Sensors on an Unattended Observatory in the Delaware Bay
Authors: Moore Tommy S. , Nuzzio Donald B. , Deering Timothy W. , Taillefert Martial , Luther George W.
Published: July 2007

A voltammetric analyzer was used to control an observatory mooring in the Delaware Bay at the same time oxygen data were collected with solid‐state gold‐amalgam (Au/Hg) electrodes. Oxygen, temperature and salinity data were collected for 8 days and sent wirelessly back to the shore‐based laboratory. Observed oxygen saturations ranged from 70 to 171%, with a mean of 107%. The highest oxygen concentrations were observed when there were low tides during the solar maximum, indicating higher rates of production within the Delaware Bay than in coastal Atlantic Ocean waters which passed the mooring at high tides, as expected based on previous shipboard studies. Lower percent saturations indicated respiration, the decomposition of organic matter by oxygen, as the dominant process and corresponded to night periods. Upon recovery the electrodes were free of bio‐fouling. This study demonstrates that voltammetric techniques and equipment can be used in observatory and mooring systems.
Single Polypyrrole Nanowire Ammonia Gas Sensor
Authors: Hernandez Sandra C. , Chaudhuri Debangshu , Chen Wilfred , Myung Nosang V. , Mulchandani Ashok
Published: July 2007

We report the synthesis, electrical characterization and ammonia gas sensing with single nanowire of conducting polypyrrole. Three hundred nanometer in diameter and 50 to 60 μm long polypyrrole nanowires were synthesized by chemical polymerization inside SiO2 coated alumina membranes. Temperature dependent electrical resistance studies established that the chemically synthesized nanowires were more ordered compared to electrochemically synthesized nanowires. We further demonstrated that gas sensors based on single polypyrrole nanowire exhibited good sensitivity towards ammonia, and provided a reliable detection at concentration as low as approximately 40 ppm.
The conformational equilibrium of [2.2]paracyclophanes in solution
Authors: Ernst Ludger
Published: July 2007

A conformational equilibrium exists in solution between two skew forms (s+ and s−) of [2.2]paracyclophane (1a). The vicinal coupling constants in the 1H‐NMR spectra of the bridge protons in the six ar‐monosubstituted derivatives 1b–1g (RCN, NO, Br, CH3, CHO, and NO2) indicate an increasing shift of the equilibrium towards one side in the order mentioned. The s+ form (positive CCCC torsional angles of the bridges) is favored in the (S) enantiomer. MM2(91) and MM3(89) molecular mechanics computations suggest that this is largely caused by increasing unfavorable nonbonded interactions in the s− conformer between the substituent and the syn proton on the ortho bridge carbon atom. Thus the „effective size”︁ of the substituent increases from 1b towards 1g.