Angewandte Chemie International Edition in English

Cover image for Vol. 36 Issue 8

May 2, 1997

Volume 36, Issue 8

Pages 791–893

Currently known as: Angewandte Chemie International Edition

    1. Cover Picture (Angew. Chem. Int. Ed. Engl. 8/1997)

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199707891

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      The cover picture shows the structural formulas in red of citrate and a synthetic receptor that is selective for binding citrate in aqueous media. The center picture is the structure of the host–guest complex, derived by molecular mechanics, that was patterned after the crystal structure of the receptor and tricarballate. The receptor is preorganized for citrate recognition because of the alternation of steric interactions around the benzene ring. Selectivity for citrate was demonstrated in competition experiments. Further, the receptor can be used to bind citrate in juices, as is highlighted by the pictures of fruit. More on the recognition properties and synthesis of this receptor is reported by E. V Anslyn et al. on pp. 862. (Graphics developed with assistance from B. Iverson at the University of Texas at Austin.)

  1. Reviews

    1. Top of page
    2. Reviews
    3. Highlights
    4. Communications
    5. Book Reviews
    1. The Application of Analytical Methods to the Detection of Hidden Explosives and Explosive Devices (pages 800–811)

      Dr. Peter Kolla

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708001

      Chemistry for criminologists: How do analysts track down hidden explosives? When is a radio not a radio—and how can this be exposed? Why do some explosives slip through the net in spite of all the refinements of modern trace analysis? These questions highlight some of the challenges to instrumental analysis from forensic science that are of particular significance especially in the context of public safety.

    2. Compounds Containing Planar-Tetracoordinate Carbon (pages 812–827)

      Dr. Dirk Röttger and Prof. Dr. Gerhard Erker

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708121

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      Though no longer mere curiosities, compounds containing planar-tetracoordinate carbon atoms (2) are not at all common. Some of the successes from the combined endeavors of different branches of chemistry in the synthesis and understanding of this “unnatural” structural unit (with respect to the usual tetrahedral 1) are presented here. Coordination to metal atoms plays a key role in this stabilization.

  2. Highlights

    1. Top of page
    2. Reviews
    3. Highlights
    4. Communications
    5. Book Reviews
    1. Structure–Activity Relationships by NMR: A New Procedure for Drug Discovery by a Combinatorial–Rational Approach (pages 829–831)

      Prof. Dr. Horst Kessler

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708291

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      Combinatorial chemistry and rational design were elegantly combined in the “SAR (structure–activity relationship) by NMR” procedure, in which even ligands that are weakly bound to proteins could be quickly identified, optimized, and linked by rational design. The procedure is demonstrated by searching for ligands for FK binding proteins (see sketch of FK506 on the right).

    2. The First Triple Bond between Germanium and a Transition Metal (pages 831–833)

      Priv.-Doz. Dr. Ulrich Siemeling

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708311

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      “Triple bonds” is now the motto: Exceptions to the classic double bond rule were sought over many years, and these efforts were so successful that compounds with doubly bonded silicon or germanium are no longer regarded as unusual. Attention has now switched to compounds with triple bonds between the elements of higher periods. After the preparation of complexes with W[BOND]P and Mo[BOND]P triple bonds in 1995, in 1996 a compound with a Mo[BOND]Ge triple bond was synthesized; this germanetriyl complex 1 also contains the first example of a heavier homologue of a terminal alkylidyne ligand.

  3. Communications

    1. Top of page
    2. Reviews
    3. Highlights
    4. Communications
    5. Book Reviews
    1. Carbon Networks Based on Dehydrobenzoannulenes: Synthesis of Graphdiyne Substructures (pages 836–838)

      Prof. Michael M. Haley, Stephen C. Brand and Joshua J. Pak

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708361

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      Nearly 22 Å in diameter, bismacrocycle 2 is the largest known substructure of any network. This molecule and macrocycle 1 represent the first examples of subunits of graphdiyne, the most stable diacetylenic carbon allotrope comprising sp and sp2 hybridized carbons. Spectroscopic evidence suggests that the dehydro[18]annulene core of 1 and 2 retains its diatropic character.

    2. Azuliporphyrin: A Case of Borderline Porphyrinoid Aromaticity (pages 839–840)

      Prof. Timothy D. Lash and Sun T. Chaney

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708391

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      Through “electronic separation” of the seven-membered ring the formally cross-conjugated, azulene-containing macrocycle (limiting structure A) becomes a porphyrinlike species with a weak, diamagnetic ring current (limiting structure B). This aromatic character is further accentuated upon twofold protonation.

    3. Carbaporphyrins (pages 840–842)

      Prof. Timothy D. Lash and Michael J. Hayes

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708401

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      Excellent yields of the carbaporphyrin 1 are obtained by application of the “3 + 1” methodology for the reaction of 1,3-indenedicarboxaldehyde with a tripyrrane in the presence of 5% CF3CO2H in CH2Cl2. The related formylcarbaporphyrin 2 was prepared similarly. In contrast to earlier claims, no unusual tautomers or conformers are observed in solution.

    4. Nonenzymatic Oligomerization of Ribonucleotides on Guanosine-Rich Templates: Suppression of the Self-Pairing of Guanosine (pages 842–845)

      Dipl.-Chem. Markus Kurz, Dr. Karin Göbel, Dipl.-Chem. Christian Hartel and Prof. Dr. Michael W. Göbel

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708421

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      Acridine-labeled primers have been shown to be a very valuable tool for the study of the template-directed oligomerization of RNA (shown schematically below). Conditions for the efficient incorporation of cytidine have been established by using such compounds. The aggregation of guanosine-rich templates, which has long been considered a major obstacle for nonenzymatic replication of RNA, can thus be reduced to a minimum.

    5. Chemical Selection and Self-Assembly in a Cyclization Reaction (pages 846–848)

      Dr. Dmitry M. Rudkevich and Prof. Julius Rebek Jr.

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708461

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      Self-help: A reaction product recognizes a stable intermediate and channels its reactivity to the formation of an eleven-membered ring (see below). A template effect is proposed, which involves molecular recognition through hydrogen bonding. PFP = pentafluorophenyl.

    6. Self-Assembly and Subsequent Self-Organization of a Semiconductor Nanocrystallite Superlattice (pages 848–851)

      Lucy Cusack, Rosalba Rizza, Alexander Gorelov and Dr. Donald Fitzmaurice

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708481

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      Modified TiO2 nanocrystallites can recognize and selectively bind to each other by complementary hydrogen bonding. Subsequent self-organization yields an ordered array or semiconductor superlattice.

    7. Titanium(II)-Mediated Intramolecular Cyclizations of 2, 7- and 2, 8-Bis-Unsaturated Carbonates and Acetates: A New and Efficient Synthesis of Cycloalkanes (pages 851–853)

      Yuuki Takayama, Dr. Yuan Gao and Prof. Dr. Fumie Sato

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708511

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      An ideal supplement to Li−, Mg−, and Zn–ene reactions is provided by the cyclization of 2,7- and 2,8-dienes, -enynes, and -diynes having a leaving group at the C1 position with the TiII equivalent 1 (see below; R = R′ = alkyl, aryl). In this reaction, the alkenyltitanium intermediate is presumably formed via a bicyclic titanium compound and not via an open-chain alkenyltitanium compound.

    8. Reduction of Dicarbapentaboranes(5) to 1,2-Diborata-4-boracyclopentadienes: Antiaromatic Compounds with 4π-Electron Systems (pages 853–855)

      Markus Unverzagt, Dr. Heinz-Jürgen Winkler, Dr. Michael Brock, Dr. Matthias Hofmann, Prof. Dr. Paul von Ragué Schleyer, Prof. Dr. Werner Massa and Prof. Dr. Armin Berndt

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708531

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      Instead of tetragonal pyramids like 1, the antiaromatic 1,2-diborata-4-boracyclopentadiene five-membered rings 3 are formed on two-electron reduction of dicarbapentaboranes(5) 2.

    9. Enantiomeric Resolution of Chiral Metallobis(porphyrin)s: Studies on Rotatability of Electronically Coupled Porphyrin Ligands (pages 856–858)

      Kentaro Tashiro, Dr. Katsuaki Konishi and Prof. Takuzo Aida

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708561

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      The porphyrin–prophyrin distance and the spatial requirements of the porphyrin substituents are parameters that influence the rotatability of the ligands in metal bis(porphyrinate)s (shown on the right): the chiral cerium complexes were much easier to racemize than the zirconium complexes. The porphyrin ligands in the latter rotate in response to H+.

    10. Dynamic Kinetic Protonation of Racemic Allenylmetal Species for the Asymmetric Synthesis of Allenic Esters (pages 858–860)

      Prof. Dr. Koichi Mikami and Akihiro Yoshida

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708581

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      The selective protonation of one enantiomer in a racemic mixture of allenylmetal compounds is possible with Pd0/SmI2 and a chiral alcohol (see reaction scheme below). The products, enantiomerically pure allenic esters, are an important class of natural products and synthetic intermediates. This type of dynamic kinetic resolution by asymmetric protonation is an effective method for the asymmetric synthesis of allenes from racemic allenyl-/propargylmetal compounds.

    11. Hexameric Aggregates in Crystalline (Pentamethylcyclopentadienyl)gallium(I) at 200 K (pages 860–862)

      Dr. Dagmar Loos, Dr. Elke Baum, Dr. Achim Ecker, Prof. Dr. Hansgeorg Schnöckel and Prof. Anthony J. Downs

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708601

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      A hexameric cluster with only weak metal–metal bonding is found in crystalline (pentamethylcyclopentadienyl)gallium(I). A shell of η5-C5Me5 ligands encloses a near-octahedral Ga6 array with unusually long Ga…Ga distances (407.3 and 417.2 pm, see picture on the right).

    12. A Synthetic Receptor Selective for Citrate (pages 862–865)

      Dr. Axel Metzger, Dr. Vincent M. Lynch and Prof. Dr. Eric V. Anslyn

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708621

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      Applied molecular recognition—strong and selective binding of citrate in highly competitive media such as water and orange juice is reported. Five steps are enough to synthesize receptor 1 that is complementary in charge and shape of citrate. Electrostatic interactions and a network of hydrogen bonds, preorganized by steric effects, are the design principles responsible for the binding of receptor and citrate [Eq. (a)].

    13. β-Cyclodextrin-Modified Diphosphanes as Ligands for Supramolecular Rhodium Catalysts (pages 865–867)

      Prof. Dr. Manfred T. Reetz and Dr. Siegfried R. Waldvogel

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708651

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      Hydrogenation and hydroformylation occur highly selectively with rhodium complexes of β-cyclodextrin-modified phosphanes (such as 1) as catalysts. These are of interest particularly for industrial applications, in which transition-metal catalysis and phase-transfer catalysis are combined in one and the same catalyst.

    14. Relative Nucleophilicity of the Two Sulfur Atoms in 1,5-Dithioglucopyranoside (pages 868–870)

      Dr. Hideya Yuasa, Yujiro Kamata and Prof. Dr. Hironobu Hashimoto

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708681

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      First experimental evidence for a relationship between structure and the relative nucleophilicities of the sulfur atoms in dithioacetals was obtained from a systematic investigation of the electrophilic oxidation of aryl 5-thioglucopyranosides. The diminished nucleophilicity of the ring heteroatoms thus recognized in the α-anomer is rationalized by the n−σ* theory of the anomeric effect (shown schematically), but by none of the other theories.

    15. Pyranosyl-RNA Also Forms Hairpin Structures (pages 870–873)

      Dr. Ronald Micura, Dr. Martin Bolli, Dr. Norbert Windhab and Prof. Dr. Albert Eschenmoser

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708701

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      A minimum of three nucleotides in the loop are necessary for p-RNA oligomers to assume a hairpin rather than a duplex structure. Such hairpin structures form with comparable ease, as they do in RNA, in spite of the (conjectured) higher rigidity of the p-RNA backbone. Base stacking in p-RNA duplexes is interstrand rather than intrastrand; therefore, dangling bases enhance duplex stability when they are at the 2′-end (and not at the 4′-end).

    16. Composite Solids Constructed From One-Dimensional Coordination Polymer Matrices and Molybdenum Oxide Subunits: Polyoxomolybdate Clusters within [{Cu(4,4′-bpy)}4Mo8O26] and [{Ni(H2O)2(4,4′-bpy)2}2Mo8O26] and One-Dimensional Oxide Chains in [{Cu(4,4′-bpy)}4Mo15O47]·8H2O (pages 873–876)

      Douglas Hagrman, Chloe Zubeita, Dr. David J. Rose, Prof. Jon Zubieta and Dr. Robert C. Haushalter

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708731

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      Soft chemical methods were used for preparing the new class of composite materials presented here. One example is [{Cu(4,4′-bpy)}4Mo8O26] (4,4′-bpy = 4,4′-bipyridine), whose unique structure (shown on the right) consists of [Mo8O26]4− clusters embedded in a web of {Cu(4,4′-bpy)}math image one-dimensional chains.

    17. An FT–Raman Study of the Template –Framework Interaction in AlPO4-Based Molecular Sieves (pages 876–878)

      Sunil Ashtekar, Dr. Patrick J. Barrie, Mark Hargreaves and Dr. Lynn F. Gladden

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708761

      The organic template within molecular sieves may readily be studied by FT–Raman spectroscopy with virtually no interference from bands due to framework vibrations. FT-Raman spectra show that morpholine and cyclohexylamine are in the protonated form within AlPO4-based materials with the chabazite structure, while splittings of certain bands indicate specific interactions between the organic template and the framework.

    18. Studies of the First S-Position Isomer of Bis(ethylenedithio)tetrathiafulvalene (pages 878–881)

      Dr. Piétrick Hudhomme, Dr. Philippe Blanchard, Dr. Marc Sallé, Soazig Le Moustarder, Prof. Amédée Riou, Prof. Michel Jubault, Prof. Alain Gorgues and Prof. Guy Duguay

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708781

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      Worthwhile goals for the synthesis of conducting materials are compounds 1–3, which contain the tetrathiafulvalene (TTF) framework. Compound 1 and a bis(methylsulfanyl) analogue have now been synthesized. Their oxidation behavior resembles that of the title compound, whose cation-radical salts are superconductors. The TTF core of these systems is essentially planar, and the outer sulfur atoms play a role in the crystallographic network.

    19. A Spiroindolinopyran with Switchable Optical Activity (pages 881–883)

      Dr. Lutz Eggers and Prof. Volker Buss

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708811

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      Photochemical switching between the diastereomeric spiropyrans [equilibrium (1)] surprisingly does not lead to a decay of the optical activity. This behavior can be attributed to the asymmetric induction by the stereogenic center C3. If the room-temperature equilibrium concentrations of the diastereomers are frozen below −40°C, irradiation with UV light displaces the equilibrium, thus causing information to be stored. The chiroptical properties enable subsequent reading of the data.

    20. The Redox Potential of Selenocystine in Unconstrained Cyclic Peptides (pages 883–885)

      Dipl.-Chem. Dörthe Besse, Dr. Frank Siedler, Dipl. Chem. Tammo Diercks, Prof. Dr. Horst Kessler and Prof. Dr. Luis Moroder

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708831

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      A much lower redox potential than that of the mixed Sec,Cys-peptide and particularly of the related Cys,Cys-peptide is a feature of the cyclic selenocystine-peptide (Sec,Sec-peptide). These findings that were obtained with appropriately modified glutaredoxin-octapeptides at pH 7 [Eq. (1); X = S, Se; DTT = dithiothreitol], open interesting new approaches for the design of productive intermediates in the oxidative folding of synthetic peptides and recombinant proteins. Moreover, such seleno derivatives may represent useful heavy metal analogs for X-ray structure analysis.

    21. Absolute Configuration of Bromochlorofluoromethane from Experimental and Ab Initio Theoretical Vibrational Raman Optical Activity (pages 885–887)

      Dr. Jeanne Costante, Dr. Lutz Hecht, Prof. Dr. Prasad L. Polavarapu, Prof. Dr. André Collet and Prof. Dr. Laurence D. Barron

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708851

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      After more than 100 years, the absolute configurations of the dextro- and levorotatory enantiomers of bromochlorofluoromethane 1, one of the simplest chiral molecules, have now been determined. Comparison of the measured Raman optical activity spectrum (in the range of vibrational modes) of an enantiomerically enriched sample of 1 with the calculated spectra allow the assignments (S)-(+) and R-(−) to be made.

    22. The First Transition Metal Complex of a Silaborane (pages 888–890)

      Dr. Lars Wesemann, Dipl.-Chem. Yves Ramjoie, Dipl.-Chem. Beate Ganter and Prof. Dr. Bernd Wrackmeyer

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708881

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      An unprecedented structural motif for metallaboranes is exhibited by the anion [{HFe(MeSiB10H10)}2]2− (see picture), which was isolated as the {nBu4N}2 salt in 63% yield from the reaction of deprotonated sila-nido-undecaborate and FeBr2.

    23. Helical, Polymeric Chains in Crystalline Gallaborane [GaBH6]n at 110 K (pages 890–891)

      Prof. Anthony J. Downs, Dr. Simon Parsons, Dr. Colin R. Pulham and Dr. Philip F. Souter

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199708901

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      Distorted tetrahedral GaH4 and tetrahedral BH4 moieties are the building blocks of the helical, polymeric chains formed by gallaborane at 110 K (schematically shown on the right). There are two distinct types of BH4 groups: one is involved in Ga(μ-H)2B coordination and the other in unusual monohydrogen bridging of two adjacent GaH2 units. The structure invites comparison with those of other main group hydrides.

  4. Book Reviews

    1. Top of page
    2. Reviews
    3. Highlights
    4. Communications
    5. Book Reviews