bluuebunny/crossref_metadata_2025 huggingface dataset:
Reversal of the Selectivity Principle in Free‐Radical Addition to Alkenes
Authors: Giese Bernd , Meixner Jürgen
Published: December 2003

The selectivity of alkenes in radical reactions increases with increasing reactivity, i.e. the most selective alkenes are the most reactive ones. This result could be of interest, say in radical polymerization.
Annulenoannulenes
Authors: Nakagawa Masazumi
Published: December 2003

Annulenoannulenes formally consist of two annulenes fused together. Hitherto, almost all the known representatives of this class of compounds were the strongly dehydrogenated forms, containing a few triple bonds and several cumulated double bonds. Besides ortho‐annelated dehydroannulenoannulenes also such compounds containing bridges made up of two or four carbon atoms (“acetylene‐cumulene” annulenoannulenes) were obtained by multistep syntheses. Most dehydroannulenoannulenes are stable and form colored crystals. In addition to dehydro[4n+2]annuleno[4n+2] annulenes with 14‐, 18‐, and 22‐membered individual rings, two dehydro[4n]annuleno[4n+2]annulenes with 16‐ and 14‐, and 16‐ and 18‐membered rings have also been synthesized. Planar combinations of two [4n]‐rings of this type and size are not known.—The dehydrogentated[14]annuleno[14]annulene containing a bridge of two carbon atoms has been studied in detail; however, the problem of the induction of a diamagnetic ring current in compounds of this type has still not been completely clarified.
ω‐Formyl‐and 4‐Oxocarboxylic Acids in Blood Plasma
Authors: Pfordt Jürgen , Spiteller Gerhard
Published: December 2003

GC/MS studies on blood plasma have shown that formyl‐ and oxo‐carboxylic acids also occur in the dicarboxylic acid fraction. Molecular ions do not appear in the mass spectrum; the molecular weights were determined from the MOCH3 fragments of the esters.
A Model of Simple Liquids
Authors: Luck Werner A. P.
Published: December 2003

The intuitively clear hole defect model can be used for quantitative estimates and for understanding the properties of liquids. An ideal liquid is defined in analogy with an ideal gas and corrected for real liquids with hole defects. The good agreement permits an application of this approximation process to the understanding of some important material properties. The effective model fills a gap in the area of applied chemistry and of chemical teaching. It also leads to a correction factor for the failure of the theorem of corresponding states. The reasons for the applicability of such a simple model are demonstrated on the basis of the Lennard‐Jones potential.
A Basis for Orbital Symmetry Rules
Authors: Ross John , Whitesides George M. , Metiu Horia
Published: December 2003

The influence of molecular symmetry on reaction rates is examined with an approach in which reactions are viewed as electronic transitions between states of reacants and products (described, in turn by quasiadiabatic potential surface). The moleculer Hamiltonian is used to derive selection rules for these transitions. The complete Hamilatonian has no useful symmetery. Neglect of non‐Born‐Oppenheimer and spin‐orbit terms (and of other angular momentum coupling terms) leads to an apporixmate Hamiltonian and to selection rules which from the basis of the Woodward‐Hoffmann rules. This apporch provides an alternative to the adiabatic potantial surfaces, reaction coordinates, and transition state theory used in more familiar discussions of the Woodward‐Hoffmann rules. Further, it provides a particulary clear method for discussing violations of these symmetry rules, and for differentiating concerted and nonconcerted reactions.
Synthesis of Thymosin α1, a Polypeptide of the Thymus
Authors: Birr Christian , Stollenwerk Ulrich
Published: December 2003

For corrigendum see DOI:10.1002/anie.197904922
Triphase Catalysis [New synthetic methods (27)]
Authors: Regen Steven L.
Published: December 2003

Triphase catalysis (TC) has recently been introduced as a unique form of heterogeneous catalysis in which the catalyst and each of a pair of reactants are located in separate phases. Based on this concept, new synthetic methods have been developed for aqueous phase–organic phase reactions using a solid phase catalyst. Although it is only at an early stage of development, TC shows considerable potential for practical use. Our mechanistic understanding of these highly complex catalytic systems is at present very limited and detailed examination will be required before their relationship to phase‐transfer, micellar, and interfacial catalysis becomes clear.
Key Building Blocks of Natural Product Biosynthesis and Their Significance in Chemistry and Medicine
Authors: Franck Burchard
Published: December 2003

The principle features of the biosynthesis of natural products have been elucidated during the past thirty years by the use of isotopic methods. It was discovered that large groups of natural products originate from the same biosynthetic precursor—the key building block. The conversion of key building blocks into biologically active natural products serves as a model for the development of more efficient syntheses in chemistry. In medicine, information about key building blocks permits the elucidation and therapy of metabolic diseases.
The Chemistry of Isolated Cations
Authors: Bowen Richard D. , Williams Dudley H. , Schwarz Helmut
Published: December 2003

Organic ions decompose in the field‐free regions of a mass spectrometer after a relatively well‐defined lifetime (t ≈ 10−5s). This lifetime is very long compared with the time‐scale of molecular bond vibrations and consequently the excess internal energy (“non fixed” energy) present in the transition state for dissociation is comparable with that found in solution experiments. In general, only the energetically most favorable decay routes are able to compete. Moreover, information concerning kinetic energy release (T) accompanying unimolecular decomposition may be obtained from a consideration of the metastable peak for the process; these extremely valuable data are inaccessible to solution experiments because of the effects of collisions. The chemistry of ions may therefore be investigated conveniently by generating the ions of interest in a mass spectrometer and analyzing the reactions which occur in metastable transitions.
New Synthesis of Amino Acids from Halogenated Carboxylic Esters
Authors: Effenberger Franz , Drauz Karlheinz
Published: December 2003

Chemically synthesized α‐amino acidsare used to fortify foodstuffs and animal feeds. The drawbacks of former syntheses are avoided in the reaction sequence(1)→(2)→(3)which leads,e.g.to lysine in an overall yield of 52% (X  Cl, Br; R1 Me, Et; M  K, Na, Li)equation image
Nickel(0)‐Induced Synthesis of Ethyllithium from Lithium, Hydrogen, and Ethylene
Authors: Jonas Klaus , Pörschke Klaus Richard
Published: December 2003

Lithium‐nickel(0) system often prove surprising: thus (COD)2Ni and Li react together in tetrahydrofuran to give (COD)2NiLi2(THF)4, which can be reduced by H2 under normal pressure to form the new “lithium hydride” (1). Unlike LiH, (1) adds to CC double bonds; it forms C2H5Li with ethylene.
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Generation of the triangulo‐Group MOV‐η‐S2 in the “Condensation” of [MoVIO2S2]2 to [MoO2S2(S2)2]2
Authors: Rittner Walter , Müller Achim , Neumann Axel , Bäther Wolfgang , Sharma Ramesh Chandra
Published: December 2003

Formation of the η‐disulfidomolybdenum(V) group by a novel intramolecular redox process has been observed on warming aqueous solutions of dithiomolybdate(VI). The structure of the anion in the orange‐red crystals of (1) was determined by X‐ray methods.
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Fully Active Insulin by Selective Formation of the Disulfide Bridges between a Sythetic A‐Chain and Natural B‐Chain
Authors: Birr Christian , Pipkorn Rüdiger
Published: December 2003

Directed formation of the three disulfide bridges in insulin is a decisive synthetic step. Only 10% of insulin is formed on random recombination of A‐ and B‐ chains (1:1). An A‐chain synthesized with selectively removable sulfur protecting groups on a polymeric carrier was allowed to react with a natural B‐chain. The yield of fully active insulin increases to 25%.
Reactions of Molybdate(VI) with Hydroxylamine and N‐Methylhydroxylamine
Authors: Wieghardt Karl , Holzbach Wolfgang , Weiss Johannes , Nuber Bernhard , Prikner Boris
Published: December 2003

Two remarkable molybdenum complexes have been isolated on recation of aqueous solutions of MoVI oxo anions with H2NOH or MeHNOH: the yellow NO complex (1) and the colorless NO‐free neutral complex (2). This shows that many yellow Mo complexes characterized only in solution pribably contain NO ligands.
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Compounds of Alkali Metal Anions
Authors: Dye James L.
Published: December 2003

Anions of sodium, potassium, rubidium, and cesium are stable both in suitable solvents and in crystalline solids. The latter can be prepared either by cooling a saturated solution or by rapid solvent evaporation. Thermodynamic arguments show that alkali metal anions can probably exist in saturated solutions of the alkali metals in any compatible solvent, but that below saturation, dissociation into the cation and solvated electrons is favored in highly polar solvents such as ammonia. The key to solvent‐free salts of the alkali metal anions is stabilization of the cation by incorporation into a suitable crown or cryptand complex. By using such complexes it also appears possible to produce “electride” salts in which the charge of the complexed cation is balanced by a trapped electron. The chemical, electrical, and optical properties of salts of the alkali metal anions and “electrides” could provide useful applications.
Formic Anhydride
Authors: Olah George A. , Vankar Yashwant D. , Arvanaghi Massoud , Sommer Jean
Published: December 2003

The parent compound of carboxylic anhydrides—formic anhydride—has now been synthesized in ethereal solution at −78° C by four different methods, and charactrized by 1H‐NMR, 13C‐NMR, and IR spectroscopy. The anhydride undergoes partial decomposition to formic acid on distillation of the solutions, even at low temperature.
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Rates of Reactive Removal of Anthropogenic Emissions in the Atmosphere
Authors: Wagner Heinz Georg , Zellner Reinhard
Published: December 2003

Anthropogenic emissions such as SO2, CO, NOx, and hydrocarbons constitute a perturbation of the natural equilibrium of the atmosphere. On a global scale, the extent of this perturbation does not significantly exceed the natural background levels as a result of direct or indirect photochemical “clean‐up” processes in the atmosphere. Regionally, however, considerably increased concentrations of these trace components may occur. They are degraded by free radical reactions having widely differing yet substance‐specific rates.
A New Bridging Mode of Carbon Disulfide in a Dinuclear Cobalt(I) Complex
Authors: Bianchini Claudio , Mealli Carlo , Meli Andrea , Orlandini Annabella , Sacconi Luigi
Published: December 2003

An unsymmetrical CS2 bridge between two Co atoms is found in the dication [(triphos)Co1(CS2)Co1(triphos)]2+. According to X‐ray structure alalysis, one Co atome is π‐bonded to a CS group while the other one forms two σ‐bonds to the two S atoms.
Crystal Structure of Na3NO4
Authors: Jansen Martin
Published: December 2003

NO is the “smallest” tetrahedral oxoanion so far, as shown by X‐ray structure analysis of painstakingly group (240 d) single crystals of Na3NO4. The NO distances (139 pm) are shorter than expected (ca. 150 pm); the shortening can only be due to polar interactions superimposed on the single bond. In this way, the bond lengths in PO, SO, or ClO could also be explained without invoking pd‐π bonding.
1,3‐Dipolar Cycloreversions
Authors: Bianchi Giorgio , De Micheli Carlo , Gandolfi Remo
Published: December 2003

The 1,3‐dipolar cycloreversion reaction represents a general scheme of fragmentation of pentaatomic heterocycles to produce 1,3‐dipolar systems and dipolarophiles. This review summarize cycloreversions which give rise to octet‐stabilized 1,3‐dipoles. The reaction can be either thermal or photochemical or electron impact induced. The aim of the article is to survey the published results, to emphasize the synthetic potential of this reaction, and to stimulate the study of its several not yet unambiguously defined mechanistic aspects.
Applications of SEPIL to the Solid State Defect Chemistry of Fluorites and Ultra‐trace Inorganic Analysis [New analytical methods (16)]
Authors: Wright John C. , Tallant D. R. , Gustafson F. J. , Johnston M. V. , Miller M. P. , Moore D. S. , Porter L. C. , Akse J. R.
Published: December 2003

Although it has been recognized for many years that the spectra of lanthanoid ions can provide useful information about short range phenomena in the neighborhood of these inos in a solid material, lanthanoid spectroscopy has only infrequently been used for studying complex materials because of the problem of line‐sorting the complex spectra that are obtained. The advent of convenient tuneable lasers has eliminated this problem. By selectively exciting probe ion luminescence (SEPIL), it is possible to obtain fluorescence and excitation spectra from a single kind of crystallographic environment. Two applications of this method are dicussed in this paper. The first application is the study of the defect chemistry of fluorite materials (compounds with CaF2 lattice). It is shown how this method can provide unique information about the solid state chemistry, thus clarifying many of the unexplained behaviors of this important class of material. The second application shows application shows how ultra‐trace analysis can be carried out by causing an association between an analyte ion and a fluorecent probe ion. The unique crystal field levels of a probe ion associated with a particular analyte can be selectively excited so that traces of the ion to be analyzed can be detected with very high selectivity and with very low detection limits.
Structure of the Dicyanophosphide Ion in a Crown‐Ether Sodium Salt
Authors: Sheldrick William S. , Kroner Jürgen , Zwaschka Franz , Schmidpeter Alfred
Published: December 2003

Comparably large positively and negatively charged structural units are present in the lattice of the 1:1:1: complex of NaP(CN)2, [18]crown‐6, and tetrahydrofuran: Na+/crown ether/2 THF and Na+/crown ether/2P(CN). The P(CN) ion is planar and bent; the calculated structure is essentially confirmed by X‐ray structure analysis. P/CN interaction is slight.
Directed Synthesis of the Trimeric Isoadenylate A2′p5′A2′p5′A
Authors: Engels Joachim , Krahmer Ute
Published: December 2003

New impetus for virus therapy should come from the isolation of an isoadenylate with “unnatural” 2′‐5′ linkage from interferon‐treated cells. This effector molecule, the title compound, has now been synthesized on a gram scale from inexpensive adenosine.
Determination of Morphological Properties of Swellable Solids by Size Exclusion Chromatography
Authors: Halász István , Vogtel Peter
Published: December 2003

Many technically interesting porous solids, e.g. ion exchangers or adsorbents for catalysis, are swellable polymers, i.e. the pore structure depends on the solvent medium. A method based on exclusion chromatography, permits determination of the pore size and pore size distribution in the swollen state.—Size exclusion chromatography, also referred to as gel permeation, gel filtration, or molecular sieve chromatography, is a widely employed method for the separation of dissolved substances—mostly polymer mixtures—according to their molecular size. Porous solids are used as stationary phase. Conversely, pore sizes and other structural data can be determined by exclusion chromatography. This application requires a series of standards (polymer samples) of known molecular weight. As a simple and rapid method, it has already proven valuable for such determinations in the case of rigid solids; in the case of swellable solids, this constitutes the sole method by which the pore structure can be characterized: classical methods require dry samples.
On the Symbolic Language of the Chemist
Authors: Hoppe Rudolf
Published: December 2003

Körper und Stimme verleiht die Schrift dem stummen Gedanken; Durch der Jahrhunderte Strom trägt ihn das redende Blatt.

(Friedrich von Schiller)
A Selective Pathway from Methanol to Ethylene and Propene
Authors: Wunder Friedrich August , Leupold Ernst Ingo
Published: December 2003

Assured supplies of raw materials is of topical interest in view of the threatening scarcity of petroleum. Mu‐doped aluminosilicate catalysts transform methanol into a surprisingly narrow range of products containing a large proportion of ethylene and propene. Methanol is accessible, in principle, from all carbonaceous materials via synthesis gas.
Tetraphenylcyclobutadienecycloalkenenickel(0) Complexes
Authors: Hoberg Heinz , Fröhlich Christian
Published: December 2003

Nickel(0) complexes having only one tetraphenylcyclobutadiene ligand (Ph4C4) and one cycloalkene ligand (L) are accessible with surprising ease, e.g. by prolonged stirring of the reagents given below in either at −50°C. (1a) and (1b), green crystals, only decompose at 220 and 260°C, respectively. [(1a), L = 1,5‐cyclooctadiene; (1b), L = cyclooctatetraene.]
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Developments in the Field of Inorganic Pigments
Authors: Bittler Knut , Ostertag Werner
Published: December 2003

The specific properties of inorganic pigments result from an interplay of solid‐state properties, particle size, and particle shape. However, phenomena occurring at the pigment interfaces also have implications for the use of the pigment. The interrelations for individual classes of pigments are indicated, and two selected examples, namely transparent colored pigments and magnetic pigments, are subsequently discussed with particular attention being paid to industrial developments.
Ultratrace Analysis: Determination of Cr, Fe, and Co in the ppb and ppt Range for Checking the Preparation of High‐Purity Niobium
Authors: Faix Werner G. , Krivan Viliam , Schulze Klaus
Published: December 2003

The purest niobium to be obtained so far was produced in a three‐step process from commercial pure niobium and characterized by n‐activation analysis. In order to measure the Cr, Fe, and Co content, carrier elements were added to the sample after irradiation for 42 d and surface decontamination. After chemical separation, the three elements could be determined by gamma‐ray spectrometry (detection limits 10 ppt, 1.5 ppb, and 4.0 ppt, respectively). Concentration ranges in the five samples: Cr 10—24.7 ppt, Fe 2—6.6 ppb, Co 4—19.0 ppt.
195Pt‐NMR Spectroscopy of Catalytically Active Complexes. Extremely Large Spin‐Spin Coupling between Platinum and Tin
Authors: Starzewski Karl‐H. A. Ostoja , Pregosin Paul S.
Published: December 2003

An extremely high coupling constant of 28954 Hz (1J(195Pt119Sn))—the highest one‐bond spin‐spin coupling yet found—has been measured for [PtCl(SnCl3)(PEt3)2]. In combination with SnCl2, platinum‐phosphane complexes are excellent homogeneous catalysts for hydrogenation and hydroformylation reactions. 195Pt‐NMR spectroscopy is extremely sensitive to changes of the coordination sphere and is therefore well suited to the study of such catalysts.
Trimethylphosphane Complexes of Nickel, Cobalt, and Iron—Model Compounds for Homogeneous Catalysis
Authors: Klein Hans‐Friedrich
Published: December 2003

One of the greatest achievements of organometallic chemistry in the last ten years has been the experimental proof that transition metal‐to‐carbon bonds are thermodynamically about as stable as those between main group elements and carbon. The present contribution demonstrates how simply constituted alkylnickel, ‐cobalt, and ‐iron complexes are obtained by means of a kinetic stabilization using suitable neutral ligands and what information these model compounds can provide with respect to the course of processes in homogeneous catalyses.
Acetaldehyde as Main Product of the Oxidation of Ethylene Oxide on a Silver Catalyst
Authors: Prauser Günther , Fischer Guillermo , Dialer Kurt
Published: December 2003

False conclusions about the relevance of a process in heterogeneously catalyzed reactions can be drawn if this process is examined in isolation. Thus ethylene is oxidized on an unmodified Ag catalyst to ethylene oxide which can undergo “after‐combustion” to CO2 and H2O. In contrast, when examined in isolation under the same conditions, ethylene oxide isomerizes to acetaldehyde. Ethylene appears to block the catalyst sites necessary for this reaction.
The Principle of Minimum Chemical Distance (PMCD)
Authors: Jochum Clemens , Gasteiger Johann , Ugi Ivar
Published: December 2003

The principle of minimum chemical distance (PMCD) allows one to formulate the isoprene rule, the conversion of tetrahydrodicyclopentadiene into adamantane, five syntheses of colchicine, and the syntheses of C16‐hexaquinacene, morphine and strychnine as optimization problems which can be solved by computers in less than a second. The principle of minimum chemical distance is based on an algebraic theory of constitutional chemistry. The PMCD, a corollary to the well known principle of minimum structure change, is a quantitative heuristic rule which serves as the foundation of the computer‐assisted combinatorial solution of a great variety of chemical problems, particularly in substructure analysis, the study of reaction mechanism, and the design of syntheses.
Absolute Configuration of the Cancerostatic S(–)‐Isophosphamide
Authors: Adamiak Dorota A. , Gdaniec Maira , Pankiewicz Krzysztof , Stec Wojciech J.
Published: December 2003

Structure/activity relations in chiral drugs can only be studied if the absolute configuration is known. The levorotatory form of the cancerostatic isophos‐phamide is shown by X‐ray structure analysis to have the S configuration.
New Dinuclear Iridium(II) Complexes Arising by Oxidative Addition of I2 to [Ir2(μ‐StBu)2 (CO)2L2]
Authors: Bonnet Jean‐Jacques , Kalck Philippe , Poilblanc René
Published: December 2003

The small family of iridium (II) complexes has increased in size. In the case of (1), L = CO and L = PMe3, the reaction shown below leads to two isomers each, which do not interconvert. The product having L = PMe2Ph has been characterized by X‐ray structure analysis.
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A Novel Proton‐Ordered, Two‐Dimensional Cross‐linking of Water Molecules in Pyridine Trihydrate
Authors: Mootz Dietrich , Wussow Hans‐Georg
Published: December 2003

The solid pyridine‐water addition compound, hitherto regarded as a dihydrate, has now been shown by a new study of the pyridine‐water melting diagram and complete X‐ray structural analysis to be the trihydrate. Typical two‐dimensional cross‐linking of the water molecules gives annelated rings; protons not involved in these rings from H bonds to pyridine.
Outer Sphere Electron Transfer Reactions: A Novel Linear Relationship between the Selectivity and the Normal Potential of the Reducing Agent
Authors: Huck Hans‐Michael , Wieghardt Karl
Published: December 2003

Interesting consequences for new theoretical models might result from the novel relationship mentioned in the title, which has been found for electron transfer between two transition metal complexes (in the encounter complex). Equation (a) is an example. Previous theories failed to predict the observed selectivity.
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Dimerization of Propylene with Catalysts Exhibiting Activities Like Highly‐Active Enzymes
Authors: Bogdanović Borislav , Spliethoff Bernd , Wilke Günther
Published: December 2003

The most active synthetic homogeneous catalysts yet obtained are solutions of EtAlCl2 and (π‐C3H5)NiBrP(C6H11)3 which effect the dimerization of propylene. The catalysts are about 1000 times as active as was determined in 1963 under unfavorable experimental conditions. The turnover number/s extrapolated to room temperature is ca. 60 000; compare 100 for hexokinase, 80 000 for catalase, and 600 000 for carboanhydrase.
Structure of [(CO)5CrNEt2]BF4, a Key Organometallic Compound; Reaction to Give the Carbene Complex (CO)5CrC(AsPh2)NEt2
Authors: Schubert Ulrich , Fischer Ernst Otto , Wittmann Dieter
Published: December 2003

The bond lengths in the carbyne complex [(CO)5CrCNEt2]BF4 suggest considerable participation of the resonance form (B). The complex is a valuable intermediate, for it affords carbene complexes even with weak nucleophiles. A new example of the utility of this approach is provided by the reaction of the intermediate with KAsPh2 to give (CO)5CrC(AsPh2)NEt2.
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A Novel SN‐Ligand: Structure of PtCl(S4N3)
Authors: Endres Helmut , Galantai Elisabeth
Published: December 2003

S4N, a new tridentate ligand with alternating S and N atoms has been obtained from S4N4. The reaction of S4N4 with cis‐tCl2(NCPh)2 leads to deep purple PtCl(S4N3) in which the terminal S atoms and the central N atom of the ligand are coordinated to the Pt atom.
Carbonates and Polycarbonates from Urea and Alcohol
Authors: Ball Peter , Füllmann Heinz , Heitz Walter
Published: December 2003

The title reaction—so convincing on paper—succeeds only in the presence of the right catalysts. Combinations of a weak Lewis acid and a Lewis base, e.g. diisobutylaluminum hydride/triphenylphosphane, accelerate formation of carbonate from carbamic esters and alcohols to such an extent that the competing elimination of isocyanic acid is suppressed.
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The Synthesis of Unusual Organic Molecules from Azoalkanes. New analytical methods (33)
Authors: Adam Waldemar , De Lucchi Ottorino
Published: December 2003

The thermal or photochemical denitrogenation of azoalkanes constitutes an effective and convenient method for the preparation of unusual organic molecules, including highly ringstrained, sterically crowded, fluxional, antiaromatic and other interesting structures. The importance of this synthetic approach is that the azo linkage serves as a means of introducing the critical (usually last) bond in the complex target molecule. This article presents a cross‐section of such elegant synthetic utilization of azoalkanes for fused‐, bridged‐ and spiro‐cyclization. Our coverage of the large body of literature has been directed by the complexity and novelty of the products. Azoalkanes are usually prepared via cycloaddition of azo dienophiles to appropriate substrates.
Oxopropenylation of Grignard Compounds with 3‐Ethoxyacroleins
Authors: Rustemeier Klaus , Breitmaier Eberhard
Published: December 2003

Aldehydes of type (3) have been synthesized from bromides R1Br via the Grignard compounds (1) and substituted 3‐ethoxyacroleins (2). This communication reports over 20 examples.
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(Trifluoromethyl)fluorogermanates
Authors: Brauer David J. , Bürger Hans , Eujen Reint
Published: December 2003

Germanates containing fluorine and trifluoromethyl ligands are generally accessible by the pathways shown below. In aqueous solution X⊖ (X = Cl, Br, I) in the starting compound can be quantitatively precipitated by Ag⊕. As expected, the ligand geometry is octahedral in the dianions, and trigonal‐bipyramidal in the monoanions.
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Synthesis of the Pentasaccharide Chain of the Forssman Antigen
Authors: Paulsen Hans , Bünsch Almuth
Published: December 2003

The current state of oligosaccharide synthesis can be demonstrated, e.g. with the Forssmann antigen. A stepwise synthesized trisaccharide is coupled with a disaccharide.
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Radical Cation Salts of Simple Arenes—A New Family of “Organic Metals”
Authors: Kröhnke Christoph , Enkelmann Volker , Wegner Gerhard
Published: December 2003

“Organic metals” from naphthalene, fluoroanthene, perylene, etc. in the form of the radical cation salts [arene2]⊙⊕X⊖ (X = PF6, AsF6, SbF6, BF4) can be generated as shiny black crystals by anodic oxidation of arenes in the presence of the anions. Species of this type were previously limited to heterocycles and compounds containing hetero atoms.
Tris(fluorosulfonyl)methane, HC(SO2F)3
Authors: Klöter Gerhard , Pritzkow Hans , Seppelt Konrad
Published: December 2003

A new strong acid, HC(SO2F)3, is reported; its acid strength lies between that of fluorosulfuric acid and nitric acid. According to X‐ray structure analysis of the K⊕ and Rb⊖ salts the CS3 skeleton is planar. The four halo compounds XC(SO2F)3.
The Pentafluoropyridine Cation C5F5N+
Authors: Züchner Klaus , Richardson Thomas J. , Glemser Oskar , Bartlett Neil
Published: December 2003

The oxidation of pentafluoropyridine to the cation has been accomplished with OAsF in SO2ClF as solvent and moderator at ‐45°C. C5F5N is the first heterocycle which could be oxidized to such a paramagnetic species.
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Influence of Ionic and Polar Solutes upon ΔG≠ and ΔV≠ of the Amide Rotation in Aqueous Solutions of Dimethylacetamide
Authors: Völkel Gerhard , Hauer Johann , Lüdemann Hans‐Dietrich
Published: December 2003

As a probe for changes in hydrate structure one can use the pressure‐dependence of the activation volume ΔV≠ for rotation of the Me2N group in dimethyl acetamide (DMA). In dilute solutions ΔV≠ for DMA is practically pressure‐independent, but is increased by ionic solutes. This could indicate an open hydrate sheath in which the rotation can take place without the water molecules in the surroundings being re‐ordered.
1,5,‐Electrocyclizations—An Important Principle of Heterocyclic Chemistry
Authors: Huisgen Rolf
Published: December 2003

The principle of orbital control of pericyclic reactions has deepened our understanding of reaction phenomena and provided an excellent classification of these one‐step processes. The electrocyclic reaction of the pentadienyl anion ⇌ cyclopentenyl anion type is relatively unimportant in all‐carbon systems and has not even been verified in the case of the parent compound. In the heterocyclic series, however, where up to five C‐atoms of the pentadienyl anion are replaced by heteroatoms, a multitude of ring closures and ring openings find their ordering principle in the mentioned electrocyclic reaction. The replacement of the carbon atoms by heteroatoms can take place isoinically, i. e., with retention of the anionic character, or isoelectronically. An isoelectronic replacement of CR2 in position 1 by NR2 OR, and or CR in position 3 by NR or O leads to a charge‐free resonance structure for the open‐chain species; the migration of the charge during the electrocyclization results in a correlation with a cyclic zwitterion. Conversely, isoelectronic exchange of CR in position 2 by NR or O produces a conjugated 1,3‐dipole, which cyclizes to a charge‐free unsaturated five‐membered ring. Twofold isoelectronic exchange allows the whole process to take place in a cation. Selected examples are to shed light on the classification and the thermodynamics of this electrocyclic reaction.
Selenium‐Catalyzed Reduction of Aromatic Nitro Compounds to Amines by CO/H2O in the Presence of Triethylamine
Authors: Miyata Toshiyuki , Kondo Kiyoshi , Murai Shinji , Hirashima Tsuneaki , Sonoda Noboru
Published: December 2003

Reductions with components of water gas (CO/H2O) can be catalyzed by selenium; thus nitroarenes are transformed in the presence of metallic selenium and triethylamine into arylamines. H2Se may plausibly be assumed as the reaction species. In a control experiment, nitrobenzene and H2Se underwent quantitative conversion (under N2) into aniline.
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Production of High Temperatures in the Chemical Laboratory: Examples of Application in Lanthanoid Oxo‐Chemistry
Authors: Müller‐Buschbaum Hanskarl
Published: December 2003

High‐temperature reactions have always been a fascinating although difficult field of experimentation for the chemist. In the case of solid‐state reactions the problems with apparatus increase exponentially with rising temperature, so that especially in this area of inorganic chemistry the modern techniques of producing high temperatures—from the solar furnace to the high‐power CO2 laser—have yielded new and interesting possibilities, particularly in the field of metastable high‐temperature compounds.
Palladium‐Catalyzed Reduction of Multiple Bonds with Mg/CH3OH
Authors: Olah George A. , Prakash G. K. Surya , Arvanaghi Massoud , Bruce Mark R.
Published: December 2003

The reduction of nonactivated multiple bonds can be carried out using magnesium/methanol, in the presence of palladium/active carbon; use of CH3O[2H] leads to deuterated compounds. In contrast to classical hydrogenation, cyclo‐propyl groups, benzyl ethers and benzyl alcohols are not attacked. Examples: 2‐Octene → octane; ethynylcyclohexane → ethylcyclohexane; 2‐cyclopropyl‐3‐buten‐2‐ol → 2‐cyclopropyl‐2‐butanol.
Topotactic Electron/Proton Transfer Reactions of Transition Metal Complexes with Columnar and Cluster Structures
Authors: Schöllhorn Robert , Wagner Klaus , Jonke Hermann
Published: December 2003

The reversible topotactic redox reactions of solids with various lattice dimensions is interesting e.g. regarding the synthesis and mode of formation of novel metastable phases at room temperature, as well as in the systematic variation of the physical properties of solids. Using the example of metal complexes with cluster and columnar structure it is established that redox reactions of this sort also occur in organic and inorganic solids having molecular lattice structures.
Novel Method for the Phase‐Transfer Catalyzed Sulfodechlorination of 1‐Chloro‐2,4‐dinitrobenzene
Authors: Gisler Markus , Zollinger Heinrich
Published: December 2003

Mild conditions and very good yields typify the sulfodechlorination of 1‐chloro‐2,4‐dinitrobenzene with potassium disulfite to 2,4‐dinitrobenzoic acid in the presence of protonated tertiary amines as phase‐transfer catalysts; the yield and above all the purity of the product depends on the chain‐length of the alkyl moiety of the amine.
Functional Groups at Concave Sites: Asymmetric Alkylation of Esters with Very High Stereoselectivity and Reversal of Configuration by Change of Solvent
Authors: Schmierer Roland , Grotemeier Gregor , Helmchen Günter , Selim Adel
Published: December 2003

An excellent asymmetric induction (enantiomeric excess >90%) is achieved in the α‐alkylation of esters of carboxylic acids and the alcohols (1) or (2) (see previous contribution). A drastic solvent effect (THF or THF‐HMPT 4:1) enables each of both enantiomers of a compound to be synthesized in high optical purity.
Darwin and Molecular Biology
Authors: Eigen Manfred
Published: December 2003

Darwin's “idea of thehe century”, the principle of selection, is as important in the age of molecular biology as it was a hundred years ago. As a natural law it is open to rigorous physical proof, if certain prerequisites are met, and to quantitative experimental test—in vitro and in vivo—under defined laboratory conditions.
Biliproteins
Authors: Scheer Hugo
Published: December 2003

Biliproteins, covalently bonded complexes of proteins and bile pigments, serve as light‐harvesting pigments in photosynthesis and light‐sensory pigments of photosynthetic organisms. Recent developments in the biochemistry and biophysics of these pigments are reviewed and an attempt is made to describe their functions of light‐harvesting and of information transduction on a molecular level.
Intramolecular Nucleophilic Addition in a Thiolatobridged “Crown‐like” Iridium Complex
Authors: Devillers Jean , de Montauzon Dominique , Poilblanc René
Published: December 2003

An iridium complex exhibiting several unusual properties, the title compound (2), is formed on reaction of (1) with an excess of hexafluoro‐2‐butyne at −196 °C. X‐ray structure analysis confirms the six‐membered ring of three S‐, two IrII‐atoms and one IrI‐atom, the different bonding of the alkane ligands, and the coordination of a S atom.
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Reactions of Carbon Suboxide with Rhodium(I) Complexes
Authors: Paiaro Gastone , Pandolfo Luciano
Published: December 2003

The decomposition of carbon suboxide in the presence of two rhodium(I)‐complexes leads to CO and C2O. With (PPh3)3RhCl, (1) and polymeric C2O are formed, with [(C8H14)2RhCl]2 the polymers (2) and cyclooctene. Pyridine can “dissolve” the Cl‐bridge in (2); a dimer is formed.
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A Novel Carbonyldiniobium Complex with Hydrogen Bridge
Authors: Herrmann Wolfgang A. , Biersack Helmut , Ziegler Manfred L. , Wülknitz Peter
Published: December 2003

The first homodinuclear carbonyl compound, the hydrido complex (3), was obtained in a light‐induced reaction from the newly accessible (1) and (2). The (η5‐C5H5)2Nb(CO)3‐ and (η5‐C5H5)Nb(CO)‐fragments are coupled by a slightly bent H‐bridge.
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Photoelectron Spectra and Molecular Properties: Real‐Time Gas Analysis in Flow Systems
Authors: Bock Hans , Solouki Bahman
Published: December 2003

For the analysis and optimization of numerous gas phase reactions in flow‐systems, photoelectron spectroscopy has proven most valuable. This real‐time measuring probe allows one to determine—with millimol quantities and within a few hours—the temperatures for different decomposition channels. Simultaneously, main products are characterized and, if need be, their yield can be improved. By careful performance of the experiment, short‐lived and/or reactive molecules such as P2, thioformaldehyde or silabenzene can be detected. PE‐spectroscopic gas analysis is of particular advantage in the search for heterogeneous catalysts; they can be tested within a day using gas mixtures of varying composition over the temperature range from 300 K to 1300 K. In addition, PE‐spectrometers are well‐suited for on‐line connection to computers; portable instruments for laboratory use are under development.
Charge‐Transfer Interactions between the Ligands of a Ternary ATP‐Cu2+‐Phenanthroline Complex
Authors: Sheldrick William S.
Published: December 2003

The first elucidation of the structure of a metal complex of ATP has been carried out on [Cu(ATP)(phen)]2·7H2O. This complex could be isolated at pH = 2.8. The two independent Cu atoms exhibit highly distorted octahedral coordination: The two N atoms of the phenanthroline and two phosphate O atoms are equatorial ligands, two further phosphate O atoms are axial. Complexes of this type are interesting as models of ternary enzyme‐M2+‐ATP complexes which participate in enzymatic phosphate transfer.
Nitrogen Dioxide and the Isoelectronic COOH Group as 5‐Electron Donors in Carbonylmetal Complexes; Preparation and Characterization of the First “Metallacarboxylic Acid”
Authors: Balbach Barbara K. , Helus Frantisek , Oberdorfer Franz , Ziegler Manfred L.
Published: December 2003

No ReRe bonds, but NO2 and COOH as 5‐electron donors characterize the novel trinuclear complexes (1) and (2). They are formed along with other complexes in the photolysis of Re2(CO)10 in the presence of NO and cyclo‐octatetraene. The complexes (1) and (2) contain a Re(CO)4C(O)Re(CO)4NO and CO ring, respectively, with an Re(CO5)O‐group on the N or C atom.
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The Kinetics of Intramolecular Reactions from Relaxation Time Measurements
Authors: Lambert Joseph B. , Nienhuis Ronald J. , Keepers Joe W.
Published: December 2003

Analysis of spin‐lattice relaxation (T1) provides alternatives to the standard line shape procedures for the investigation of intramolecular reactions; furthermore it expands the NMR range at both the high and the low energy barrier limits. Dipole‐dipole‐ and quadrupole‐relaxation times are sensitive to very rapid processes such as methyl rotation. Analysis of relaxation in the rotating frame(T1ρ) provides kinetics for many sorts of processes, particularly those in the dynamic range that is too rapid for line shape methods. Saturation transfer and the coalescence of relaxation times at high temperatures can be used to measure high energy barriers. The scope and limitations of these methods are described.
Benzvalene—Properties and Synthetic Potential
Authors: Christl Manfred
Published: December 2003

Today, thanks to the versatile synthesis developed by Katz et al., benzvalene is not only the most extensively studied valence isomer of benezene but also one of the most easily synthesized bicyclo[1.1.0]butane derivatives. The double bond in this highly strained hydrocarbon is particulary reactive owing to interactions between the σ system and the double bond. Benzvalene is one of the most reactive olefins toward electron deficient substrates. Furthermore, the compound is bifunctional, since after addition to the π system the ring strain of the σ system provides the driving force for rearrangement or further addition reactions. This paper summarizes the spectroscopic properties and the reactivity of benzvalene. In order to demonstrate the importance of benzvalene and its derivatives as building blocks in organic synthesis the chemistry of compounds arising from benzvalene is also discussed. The article concludes with a summary of substituted benzvalenes.
Non‐planar Double Bonds and Increased Reactivity in Olefins with Low Strain
Authors: Burkert Ulrich
Published: December 2003

Norbornene and norbornadiene contain non‐planar double bonds; these findings from ab initio calculations have now been confirmed by force field calculations (molecular mechanics). If the non‐planarity of the double bonds in the two compounds mentioned is explained in terms of torsional strain, then the same effect can be predicted for other cyclic olefins, inter alia, for cyclopentene.
Trimethylsilylaluminium Compounds as Catalyst Components in the Polymerization of Ethene
Authors: Rösch Lutz , Altnau Gerald
Published: December 2003

Can the alkylaluminum compound in Ziegler‐Natta catalysts be replaced by asi lylaluminum compound? TiCl4/Al(SiMe3)3·Et2O (5:2), for example, has proven to be a suitable catalyst for the polymerization of ethylene. This is the first catalyst in which no transition metal‐carbon but a transition metal‐silicon bond might be present, at least in the first polymerization step.
Mass Spectrometry of Negative Ions
Authors: Budzikiewicz Herbert
Published: December 2003

“It appears that negative ion mass spectra measured with a commercial instrument and the electron energies used (20–70 eV) are not suitable either for molecular weight or for structure determination—”. This was the conclusion of a paper appearing in 1965 which expressed the then almost universal opinion on the importance of negative ion mass spectrometry in the structure analysis of organic compounds[8]. The fact that quinones and aromatic nitro compounds were exceptions to this rule was rather taken as substantiation of this opinion. The potential value of the work originating from the laboratories of Manfred von Ardenne was first realized with the development of chemical ionization. This technique gave a firm foundation to negative ion spectrometry in the area where it is complementary to that of positive ions.
Experimental Evidence for the [H2SSH2]∔ Radical Cation in Solution
Authors: Chaudhri Shamim A. , Asmus Klaus‐Dieter
Published: December 2003

Pulse radiolysis of an aqueous H2S‐solution leads to formation of the radical cation [H2SSH2]∔ This species, which absorbs at 370 nm, has a three‐electron SS bond in which two electrons form a σ‐bond; the third electron resides in an antibonding σast;‐orbital.
Synthesis of a Novel Amphoteric Polyelectrolyte by Polymerization of 6‐Amino‐2,4‐hexadienoic Acid in Layer Perovskites
Authors: Tieke Bernd , Wegner Gerhard
Published: December 2003

The topochemically controlled polymerization of 6‐amino‐2,4‐hexadienoic acid in complexes with CdCl2, MnCl2 and FeCl2 is initiated by UV or 60Co‐γ‐radiation. Tacticity of the polymer, slight structural changes during transition from the monomer to polymer and control of reactivity by the type of ion in the matrix render the proposed course of reaction likely. The liberated amphoteric polyelectrolyte could be suitable as a polymeric complexing agent.
[(η5‐CH3C5H4)Mn(CO)2Hg]4, a Compound with an Mn4Hg4 Eight‐Membered Ring and Additional Hg—Hg Bonds
Authors: Gäde Wolfgang , Weiss Erwin
Published: December 2003

The complex (1) contains both a four‐ and an eight‐membered ring of metal atoms. The four Hg atoms are almost coplanar, and the short Hg—Hg bond length indicates that an interaction occurs between these atoms. The four Hg atoms form an eight‐membered ring with the four Mn atoms, in which the MnHgMn groups enclose a notably small angle of 157.2°.
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Experimental Electron Density Determination of a Dimetallacyclopropane‐Type μ‐Methylene Complex
Authors: Clemente Dore Augusto , Rees Bernard , Bandoli Giuliano , Biagini Marina Cingi , Reiter Barbara , Herrmann Wolfgang A.
Published: December 2003

A considerable negative charge on the bridge carbon atom in the dimanganacyclopropane complex (1) has been demonstrated by determination of the electron density. This finding is in agreement with the result of detailed MO calculations. No accumulation of charge density was found between the two Mn atoms, although according to MO calculations direct metal‐metal bonding is present. It must be assumed that there is inadequate overlap of the corresponding metal orbitals.
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Pyramidal Carbocations
Authors: Schwarz Helmut
Published: December 2003

Pyramidal cations are discussed with reference to their role as the connecting link between organic and inorganic chemistry. The electronic structure of these ions is treated with respect to their physical and chemical properties, namely charge distribution, geometry, and quenching reactions with nucleophiles. The chemistry in the gas phase of certain carbenium ions, in particular the scrambling of carbon atoms, is readily explicable by invoking transition states or intermediates of pyramidal structure. Moreover, the behavior of unimolecular processes can be understood in terms of transition states in which a hydrogen molecule is positioned as a “side‐on” or an “end‐on” ligand.
Physical Methods for the Microanalysis of Solids—General Significance, Recent Developments, and Limitations
Authors: Grasserbauer Manfred
Published: December 2003

The characterization of solid systems by physical methods (“physical analysis”) is one of the most important future‐orientated areas of analytical chemistry. Important developments are the increase of the informational content of analytical signals by application of mathematical methods, the investigation of extremely small amounts (microanalysis), as well as concentrations (trace analysis). New developments in analytical methodology and strategy in micro and surface analysis permit, for example, the direct identification of compounds in individual phases in the solid state, the quantitative elemental analysis of aerosol particles in the submicrometer region (identification of asbestos fibers), and highly sensitive distribution analysis of trace elements in semiconductors. Important technological‐scientific problems can be explained in this way.
[Fe3S(S2C10H12)3]2−: The First Synthetic Trinuclear Iron‐Sulfur Cluster Compound
Authors: Henkel Gerald , Tremel Wolfgang , Krebs Bernt
Published: December 2003

In the first model for trinuclear iron‐sulfur centers in recently discovered proteins—namely, the central FeS7 moiety in [(C2H5)4N][Fe3S7C30H36]·CH3OH—the Fe atoms from a completely bonded triangle and are each surrounded by a tetrahedron of S atoms which is somewhat distorted from idealized symmetry and consists of an inorganic S atom above the center of the metal triangle and three mercapto S atoms, two of which form slightly asymmetric bridges to neighboring Fe atoms.
Di‐ tert‐butylthia‐ and ‐selenadiphosphirane
Authors: Baudler Marianne , Suchomel Horst , Fürstenberg Gabriele , Schings Ulrike
Published: December 2003

For corrigendum see DOI:10.1002/anie.198200861
Stabilization of Diphosphorus Tetrabromide as the Bis(pentacarbonylchromium) Complex
Authors: Hinke Axel , Kuchen Wilhelm , Kutter Jürgen
Published: December 2003

The hitherto unknown P2Br4 has been stabilized as ligand for the first time, namely in the bis(pentacarbonylchromium) Complex (1). (1) is formed, inter alia, on reaction of (CO)5Cr. THF with PBr3, and of (2) with HBr. Evidence of the formation of free P2Br4 was also obtained.
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