Angewandte Chemie International Edition

Cover image for Vol. 42 Issue 37

September 29, 2003

Volume 42, Issue 37

Pages 4411–4553

    1. Cover Picture: “Cascade-Release Dendrimers” Liberate All End Groups upon a Single Triggering Event in the Dendritic Core / Self-Immolative Dendrimers (Angew. Chem. Int. Ed. 37/2003) (page 4411)

      Franciscus M. H. de Groot, Carsten Albrecht, Ralph Koekkoek, Patrick H. Beusker, Hans W. Scheeren, Roey J. Amir, Neta Pessah, Marina Shamis and Doron Shabat

      Article first published online: 25 SEP 2003 | DOI: 10.1002/anie.200390581

      Cascade-release dendrimers or self-immolative dendrimers, as shown in the cover picture, spontaneously release all the end-group molecules following a single activation event. This triggering event induces a cascade of self-eliminations which leads to complete dissociation of the dendrimer into its separate building blocks. As the research groups of both F. M. H. de Groot (on page 4490 ff) and D. Shabat (on page 4494 ff) describe, such functionally novel dendrimers open up new modes of application of dendrimers, for example, for drug delivery.

    2. Insulated Nanowire Bundles through Consecutive Template Synthesis (pages 4430–4432)

      Stefan Spange

      Article first published online: 25 SEP 2003 | DOI: 10.1002/anie.200301654

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      Conducting research and wiring zeolites: By a sol–gel process MCM-41 zeolite scaffolds are prepared, the channels of which are evenly loaded with pyrrole or thiophene template monomers. Redox-initiated polymerization leads to linking of the monomer units in the channels to form insulated potentially conducting molecular wires. These strategies increase the synthetic palette available for the targeted preparation of organic–inorganic hybrid materials.

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      The Responsibility of Scientists, a European View (pages 4434–4439)

      Richard R. Ernst

      Article first published online: 25 SEP 2003 | DOI: 10.1002/anie.200330065

      The necessity to take on more responsibility for societal matters is something scientists can no longer avoid. This essay is an appeal to researchers and teachers in academia to extend their activities to transgress their own specialist fields and to face up to the important questions of our times.

    4. Relativistic Effects in Gas-Phase Ion Chemistry: An Experimentalist's View (pages 4442–4454)

      Helmut Schwarz

      Article first published online: 25 SEP 2003 | DOI: 10.1002/anie.200300572

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      Relatively speaking: Bond energies, structural properties, and reactivity patterns of 5d transition metals are heavily affected by relativistic effects. Typical examples concern the unique ability of 5d metal cations in the electronic ground state to spontaneously dehydrogenate methane at room temperature (see scheme), and the dramatic effect of ligands on the ionization energy of gold.

    5. Chemical Safety in a Vulnerable World (pages 4456–4469)

      Sabine Gärtner, Jens Küllmer and Ulrich Schlottmann

      Article first published online: 25 SEP 2003 | DOI: 10.1002/anie.200300584

      The risks connected with chemical substances have been assessed in a number of conventions that have aimed to apply restrictions on the use of dangerous chemicals, and control of their worldwide trade. The developments in chemicals policy at the European and world level are discussed, with an insight into the interlaced structure of international cooperation that exists at both the political and the technical level.

    6. Smart Inorganic/Organic Nanocomposite Hollow Microcapsules (pages 4472–4475)

      Dmitry G. Shchukin, Gleb B. Sukhorukov and Helmuth Möhwald

      Article first published online: 1 SEP 2003 | DOI: 10.1002/anie.200352068

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      Inorganic/organic polyelectrolyte microcapsules (see diagram for synthetic approach) possess the advantages of inorganic materials (i.e., high mechanical stability) and of conventional polyelectrolyte microcapsules (i.e., the ability to control the release/uptake properties of the capsule shell by changing pH value and ionic strength). Their initial spherical shape and controlled release properties remain after drying.

    7. Intermediates Released from a Polyether-Producing Polyketide Synthase Provide Insight into the Mechanism of Oxidative Cyclization (pages 4475–4478)

      Zoë A. Hughes-Thomas, Christian B. W. Stark, Ines U. Böhm, James Staunton and Peter F. Leadlay

      Article first published online: 25 SEP 2003 | DOI: 10.1002/anie.200351375

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      Stereochemistry resolved: The introduction of hybrid polyketide synthases in Streptomyces cinnamonensis has shown that the E forms of a tetraketide and pentaketide are intermediates in the biosynthesis of the antibiotic ionophore monensin A (see structure). Furthermore, the trans double bond present in these intermediates has been identified as one of the targets for the epoxidase that initiates oxidative cyclization.

    8. Detection of Ligands from a Dynamic Combinatorial Library by X-ray Crystallography (pages 4479–4482)

      Miles S. Congreve, Deborah J. Davis, Lindsay Devine, Cesare Granata, Marc O′Reilly, Paul G. Wyatt and Harren Jhoti

      Article first published online: 25 SEP 2003 | DOI: 10.1002/anie.200351951

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      A dynamic combinatorial library of ligands derived from hydrazines A and isatins B was assembled in the presence of crystals of the target protein, cyclin-dependent kinase 2 (CDK2). Unambiguous detection of potent ligands, formed as part of the library, was successfully achieved by X-ray crystallographic analysis.

    9. A Nanoscopic Molecular Cadmium Phosphonate Wrapped in a Hydrocarbon Sheath (pages 4482–4485)

      Ganapathi Anantharaman, Mrinalini G. Walawalkar, Ramaswamy Murugavel, Bunkóczi Gábor, Regine Herbst–Irmer, Marc Baldus, Brigitta Angerstein and Herbert W. Roesky

      Article first published online: 25 SEP 2003 | DOI: 10.1002/anie.200352133

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      The molecular cadmium phosphonate [(MeCd)10{(thf)Cd}4Cd64-O)23-OH)2(tBuPO3)12] (see picture) is unlike all other such Cd compounds, which are polymeric or layered structures. It contains a 68-atom inorganic hollow skeleton made up of twenty cadmium (green), twelve phosphorus (purple), and thirty-six oxygen atoms (red), held together internally by pairs of oxo and hydroxo groups.

    10. A Pair of Remarkably Stable Mononuclear Chromium(III) and Chromium(IV) Hydrides (pages 4486–4489)

      Alexander C. Filippou, Sven Schneider and Gregor Schnakenburg

      Article first published online: 25 SEP 2003 | DOI: 10.1002/anie.200352177

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      Often regarded as rare and unstable species, mononuclear CrIII and CrIV hydrides (2 and 3, respectively; see scheme) have been prepared by various methods, and their interplay is illustrated by various reactions. The electronic structures of the hydrides were elucidated by utilizing several theoretical methods.

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      “Cascade-Release Dendrimers” Liberate All End Groups upon a Single Triggering Event in the Dendritic Core (pages 4490–4494)

      Franciscus M. H. de Groot, Carsten Albrecht, Ralph Koekkoek, Patrick H. Beusker and Hans W. Scheeren

      Article first published online: 1 SEP 2003 | DOI: 10.1002/anie.200351942

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      A single triggering event in the core of a dendrimer composed of two or more generations of multiple-release monomeric building blocks can induce the release of all end groups at the termini of the dendrimer (see schematic representation). Such multiple-release systems could find application, for example, in the field of (targeted) drug delivery, where a disease- or organ-specific activation event could trigger simultaneous release of multiple biologically active molecules.

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      Self-Immolative Dendrimers (pages 4494–4499)

      Roey J. Amir, Neta Pessah, Marina Shamis and Doron Shabat

      Article first published online: 8 SEP 2003 | DOI: 10.1002/anie.200351962

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      Docking the tails: The triggering of a single cleavage at the core of a new class of dendrimers (see, for example, the second generation dendron) results in a spontaneous chain fragmentation and the release all of the tail (reporter) units. Such dendrimers may be applied as a general platform for prodrugs or sensor molecules for enzymatic activity.

    13. Conductive Organic Plastic Crystals Based on Pyrazolium Imides (pages 4499–4501)

      Yaser Abu-Lebdeh, Pierre-Jean Alarco and Michel Armand

      Article first published online: 25 SEP 2003 | DOI: 10.1002/anie.200250706

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      Plastic batteries: Pyrazolium trifluoromethanesulfonimide 1 displays a single plastic crystalline phase (20–65 °C). When doped with a lithium salt (2 mol %), solid-state conductivity values above 10−4 S cm−1 at 55 °C are measured. The superior properties of these materials make them candidates for a new generation of lithium batteries.

    14. Growth of Large Diamond Crystals by Reduction of Magnesium Carbonate with Metallic Sodium (pages 4501–4503)

      Zhengsong Lou, Qianwang Chen, Wei Wang, Yitai Qian and Yufeng Zhang

      Article first published online: 25 SEP 2003 | DOI: 10.1002/anie.200351478

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      Diamonds in the rough: Crystals as large as 510 μm in diameter were formed at a temperature as low as 500 °C by the reduction of magnesium carbonate with metallic sodium (see picture). The product mixture was found to contain cubic diamonds by X-ray diffraction and micro-Raman spectrum analysis. The yield of diamond is about 6.6 % with respect to carbonate carbon. Magnesium carbonate is nontoxic, cheap, and abundant, and the temperature of this process is much lower than that of traditional methods. Therefore, the results of these studies could be applied in the production of industrial low-cost diamonds.

    15. Anilines Made Easily: From Aldehydes to Tri-, Tetra-, and Pentasubstituted Anilines in Two Steps (pages 4503–4507)

      Helfried Neumann, Axel Jacobi von Wangelin, Stefan Klaus, Dirk Strübing, Dirk Gördes and Matthias Beller

      Article first published online: 25 SEP 2003 | DOI: 10.1002/anie.200351484

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      Easy as one, two, three. Highly substituted anilines are accessible with unprecedented efficiency from the three-component-coupling reaction of O-benzyl carbamate, aldehydes, and dienophiles followed by a new domino aromatization/deprotection reaction involving transfer hydrogenation (see scheme). EWG: electron-withdrawing group.

    16. Chromium(V) and Chromium(VI) Nitrido Complexes of Tris(pentafluorophenyl)corrole (pages 4507–4510)

      Galina Golubkov and Zeev Gross

      Article first published online: 25 SEP 2003 | DOI: 10.1002/anie.200351793

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      Nitrogen-atom transfer from a (nitrido)manganese(V) complex to a CrIII complex of the 5,10,15-tris(pentafluorophenyl)corrole trianion gave the stable CrV nitrido complex 1 (Ar=C6F5). In contrast, treatment of the same CrIII starting material with ammonia/sodium hypochlorite gave the CrVI analogue of 1.

    17. The Boratacyclooctatetraene Ligand: An Isoelectronic Trianionic Analogue of the Cyclooctatetraene Dianion (pages 4510–4514)

      Xiangdong Fang, David Woodmansee, Xianhui Bu and Guillermo C. Bazan

      Article first published online: 25 SEP 2003 | DOI: 10.1002/anie.200351911

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      Expanding the ring: Acetylene inserts into one of the intracyclic B[BOND]C bonds of [(C5H5B[BOND]Me)2Ti(CO)] (1) to yield [(C7H7B[BOND]Me)(C5H5B[BOND]Me)Ti], which contains the formally trianionic methylboratacyclooctatetraene ligand and a boratabenzene ligand. Similarly, the reaction of 1 with trimethylsilylacetylene produces [(2-SiMe3[BOND]C7H6B[BOND]Me)(C5H5B[BOND]Me)Ti] (2), in which the trimethylsilyl group occupies the sterically more encumbering site adjacent to boron (Cα; see picture). The regiochemistry of 2 indicates that the transmetallation step may be viewed as an electrophilic attack of boron on the metal coordinated acetylene ligand.

    18. One-Step Stereocontrol of Three Contiguous Stereogenic Centers in Acyclic Systems: The Tuning Effect of an Additive in a Tandem Asymmetric Michael Addition and Meerwein–Ponndorf–Verley Reduction (pages 4515–4517)

      Kiyoharu Nishide, Minoru Ozeki, Hideaki Kunishige, Yukihiro Shigeta, Pranab K. Patra, Yuri Hagimoto and Manabu Node

      Article first published online: 25 SEP 2003 | DOI: 10.1002/anie.200351915

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      A domino addition–reduction sequence to construct three contiguous stereogenic centers with a high level of diastereoselectivity makes use of the chiral camphor-derived thiol 1 in a Michael addition to acyclic α,β-disubstituted α,β-unsaturated ketones 2 (see scheme). The effect of additives was investigated, and it was also shown that compounds 3 are suitable precursors to 1,3-hydroxythiols of type 4. R1=aryl, R2=alkyl, R3=alkyl or phenyl.

    19. Thermally Induced Stoichiometric and Catalytic O-Atom Transfer by a Non-Heme Iron(III)–Nitro Complex: First Example of Reversible {Fe–NO}7[LEFT RIGHT ARROW]FeIII-NO2 Transformation in the Presence of Dioxygen (pages 4517–4521)

      Apurba K. Patra, Raman K. Afshar, John M. Rowland, Marilyn M. Olmstead and Pradip K. Mascharak

      Article first published online: 25 SEP 2003 | DOI: 10.1002/anie.200352070

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      The non-heme iron(III) complex [(PaPy3)Fe(NO2)](ClO4) (1) transfers oxygen in the temperature range 45–65 °C to PPh3 to afford OPPh3 in MeCN. The product, [(PaPy3)Fe(NO)](ClO4), a {Fe-NO}7 species, reverts rapidly back to 1 in the presence of dioxygen, thus making the system catalytic (see scheme). Formation of an oxo-bridged species terminates the oxo-transfer process (PaPy3H=N-[N,N-bis(2-pyridylmethyl)aminoethyl]-2-pyridinecarboxamide).

    20. Enantioselective Conjugate Radical Addition to β-Acyloxy Acrylate Acceptors: An Approach to Acetate Aldol-Type Products (pages 4521–4523)

      Mukund P. Sibi, Jake Zimmerman and Tara Rheault

      Article first published online: 8 SEP 2003 | DOI: 10.1002/anie.200352096

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      An unusual bond-construction strategy based on conjugate radical additions leads to acetate aldol-like products with high enantioselectivity (see scheme). Unlike their ionic counterparts, the enantioselective nucleophilic radical addition to β-acyloxyenoates proceeds without elimination and occurs by an Si-face radical addition to an s-cis conformer of the substrate (as shown).

    21. Highly Active Catalysts in Alkene Metathesis: First Observed Transformation of Allenylidene into Indenylidene via Alkenylcarbyne—Ruthenium Species (pages 4524–4527)

      Ricardo Castarlenas and Pierre H. Dixneuf

      Article first published online: 25 SEP 2003 | DOI: 10.1002/anie.200352108

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      A cat. for all seasons: The transformation of the allenylidene-ruthenium complexes [RuCl(η6-arene)([DOUBLE BOND]C[DOUBLE BOND]C[DOUBLE BOND]CR2)(PRequation image)][CF3SO3] into indenylidene species [RuCl(η6-arene)(indenylidene)(PRequation image)][CF3SO3]2 by the simple protonation with CF3SO3H and formation of an alkenylcarbyne intermediate (see picture; arene=p-cymene) is observed by low temperature NMR experiments. The new in situ generated 18 electron ionic indenylidene species are highly active in the polymerization of cyclooctene and cyclopentene, ring-closing metathesis of dienes and enynes, and the acyclic diene metathesis of decadiene, thus making it a catalyst for all seasons.

    22. Supramolecular Adducts between Poly-L-arginine and [TmIIIdotp]: A Route to Sensitivity-Enhanced Magnetic Resonance Imaging–Chemical Exchange Saturation Transfer Agents (pages 4527–4529)

      Silvio Aime, Daniela Delli Castelli and Enzo Terreno

      Article first published online: 25 SEP 2003 | DOI: 10.1002/anie.200352132

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      Markedly improved sensitivity is achieved in a contrast agent through formation of a supramolecular adduct between a diamagnetic system endowed with a high number of exchangeable protons (poly-L-arginine) and a paramagnetic shift reagent ([Tm(Hdotp)]4−). The increase in the chemical shift separation between the two exchanging proton pools, induced by the shift reagent, allows irradiation of the mobile guanidine protons of the polymer, thus resulting in a very efficient saturation transfer (see graph).

    23. [tBuLi⋅(−)-Sparteine]: Molecular Structure of the First Monomeric Butyllithium Compound (pages 4531–4533)

      Carsten Strohmann, Timo Seibel and Katja Strohfeldt

      Article first published online: 25 SEP 2003 | DOI: 10.1002/anie.200351308

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      A chiral butyllithium reagent: Monomeric [tBuLi⋅(−)-sparteine] crystallizes from a solution in n-pentane on cooling. At the lithium center of the compound a formally free coordination site with a chiral environment is formed through angular distortion of the tert-butyl group (see structure).

    24. Stepwise Solid-Phase Synthesis of Di- and Trinuclear Metal Complexes (pages 4533–4536)

      Katja Heinze and Juan D. Bueno Toro

      Article first published online: 25 SEP 2003 | DOI: 10.1002/anie.200351849

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      Step by step: Oligonuclear organometallic complexes are constructed in a stepwise manner on insoluble polymeric matrices and directly characterized on the support (see scheme). Liberation under mild conditions yields the corresponding soluble oligonuclear complexes.

    25. Bond-Stretch Isomerism: Trapped Isomeric Structures of Hexacoordinate Copper(II) Bispidine Chromophores along a Jahn–Teller Active Vibrational Coordinate (pages 4536–4540)

      Peter Comba, Andreas Hauser, Marion Kerscher and Hans Pritzkow

      Article first published online: 8 SEP 2003 | DOI: 10.1002/anie.200351900

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      The long and the short of it: Copper(II) complexes of the pentadentate bispidine ligands exist in two isomeric forms (see structure) with bond-length differences up to 0.5 Å. The stabilization of either isomer may be achieved by a variation of the substituent at N7.

    26. Aqueous Chemistry of Titanium(II) Species (pages 4540–4542)

      Ulrich Kölle and Philipp Kölle

      Article first published online: 25 SEP 2003 | DOI: 10.1002/anie.200351280

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      Wetting the appetite for TiIIchemistry: Titanium metal is dissolved by aqueous acids in the presence of fluoride ions. The resulting green solution does not contain TiIII but a mixture of TiII and TiIV complexes. The presence of a d2 TiII species is confirmed by UV/Vis spectroscopy. A mixed-valent solid, TiII(TiIVF6)(H2O)4, can be isolated from the solution and its structure parameters determined by powder diffraction (see picture, TiIV red, TiII blue).

    27. Knotaxanes—Rotaxanes with Knots as Stoppers (pages 4542–4545)

      Oleg Lukin, Takateru Kubota, Yoshio Okamoto, Frauke Schelhase, Albena Yoneva, Walter M. Müller, Ute Müller and Fritz Vögtle

      Article first published online: 25 SEP 2003 | DOI: 10.1002/anie.200351981

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      Get knotted: Molecular knots have been used as stoppers in the assembly of “knotaxanes”, a new family of topologically chiral rotaxanes (see picture). Two knotaxanes were separated into enantiomers using HPLC with a chiral stationary phase and characterized by measuring their CD spectra. The chirality designation of these topological species is reminiscent of the Fischer projections of open-chain sugar acids.

    28. Conformative Coupling of Two Conformational Molecular Switches (pages 4546–4549)

      Michael Karle, Dirk Bockelmann, Dirk Schumann, Christian Griesinger and Ulrich Koert

      Article first published online: 25 SEP 2003 | DOI: 10.1002/anie.200352130

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      Passing on information. Two conformational switches, decalin units, were coupled to a 14-membered bislactam ring (see formula, TBDPS=tert-butyldiphenylsilyl). Removal of a bisacetal clamp on the left side of the molecule resulted in a double ring-flip of the left decalin unit. Conformational coupling through the bislactam unit led to a double ring-flip in the right decalin unit.

    29. Preview: Angew. Chem. Int. Ed. 37/2003 (page 4553)

      Article first published online: 25 SEP 2003 | DOI: 10.1002/anie.200390585