Angewandte Chemie International Edition

Cover image for Vol. 44 Issue 10

February 25, 2005

Volume 44, Issue 10

Pages 1425–1571

    1. Cover Picture: Knotting and Threading of Molecules: Chemistry and Chirality of Molecular Knots and Their Assemblies (Angew. Chem. Int. Ed. 10/2005) (page 1425)

      Oleg Lukin and Fritz Vögtle

      Article first published online: 22 FEB 2005 | DOI: 10.1002/anie.200590030

      Fantasy structures such as the heptafoil knot interlocked with seven trefoil knots shown in the cover picture represents a distant goal for template synthesis. Established template strategies for the synthesis of molecular knots (knotanes) and higher assemblies with twisted architectures can lead to such structures. More on the synthesis, functionalization, and properties of knots can be found in the Review by F. Vögtle and O. Lukin on page 1456 ff.

    2. Graphical Abstract: Angew. Chem. Int. Ed. 10/2005 (pages 1428–1436)

      Article first published online: 22 FEB 2005 | DOI: 10.1002/anie.200590031

    3. Modern Fluoroorganic Chemistry. By Peer Kirsch. (page 1439)

      G. K. Surya Prakash

      Article first published online: 22 FEB 2005 | DOI: 10.1002/anie.200485237

    4. Newton's Darkness. Two Dramatic Views. By Carl Djerassi and David Pinner. (pages 1440–1442)

      George B. Kauffman and Laurie M. Kauffman

      Article first published online: 22 FEB 2005 | DOI: 10.1002/anie.200385240

    5. Atmosphere, a Chemical Reactor—Formation Pathways of Secondary Organic Aerosols (pages 1444–1446)

      Wolfgang Schrader

      Article first published online: 22 FEB 2005 | DOI: 10.1002/anie.200461611

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      It's becoming clearer: The formation of atmospheric aerosols can have a distinct effect on the local climate and the radiation balance of the atmosphere. The first step in the formation of such particles can be explained, for example, by the formation of an intermediate complex composed of an aromatic acid and sulfuric acid (see picture), which occur as typical decomposition products in areas with high air pollution.

    6. Hetero-Aggregate Compounds of Aryl and Alkyl Lithium Reagents: A Structurally Intriguing Aspect of Organolithium Chemistry (pages 1448–1454)

      Robert A. Gossage, Johann T. B. H. Jastrzebski and Gerard van Koten

      Article first published online: 22 FEB 2005 | DOI: 10.1002/anie.200462103

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      Lithium wins on aggregate: Although often depicted as mononuclear species, organolithium compounds are in fact aggregated species and can form hetero-aggregates containing different organic groups (see structure of [(nBuLi)2(2,4,6-tBu3C6H2Li)2]; yellow Li). The aggregation behavior of organolithium compounds is presented and the significance of the formation of such aggregates on synthesis, directed ortho-metalation, and the induction and formation of chiral compounds is discussed.

    7. Knotting and Threading of Molecules: Chemistry and Chirality of Molecular Knots and Their Assemblies (pages 1456–1477)

      Oleg Lukin and Fritz Vögtle

      Article first published online: 10 FEB 2005 | DOI: 10.1002/anie.200460312

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      How and why do molecules thread or tangle? The answer is found in this Review, which covers the latest developments in templation techniques for the preparation of molecular knots (knotanes), their chiral resolution, their selective functionalization, and their further use as building blocks in the syntheses of higher assemblies (see picture).

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      High Relaxivity Confined to a Small Molecular Space: A Metallostar-Based, Potential MRI Contrast Agent (pages 1480–1484)

      João Bruno Livramento, Éva Tóth, Angélique Sour, Alain Borel, André E. Merbach and Robert Ruloff

      Article first published online: 6 DEC 2004 | DOI: 10.1002/anie.200461875

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      Good things come in small packages: For its moderate molecular weight, the metallostar complex [Fe{Gd2L(H2O)4}3]4− (see picture; L is a bipyridine–poly(aminocarboxylate) derivative) displays exceptionally high proton relaxivity, which is explained in terms of a rigid supramolecular structure, two inner-sphere water molecules with a near-optimal exchange rate, and six efficiently relaxing GdIII centers confined to a small molecular space.

    9. Oxazaborolidine-Derived Lewis Acid Assisted Lewis Acid as a Moisture-Tolerant Catalyst for Enantioselective Diels–Alder Reactions (pages 1484–1487)

      Kentaro Futatsugi and Hisashi Yamamoto

      Article first published online: 31 JAN 2005 | DOI: 10.1002/anie.200461319

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      Reactive, selective, and tough, the chiral Lewis acid generated from 1 and SnCl4 catalyzes the enantioselective Diels–Alder reactions of various classes of substrates (see scheme). The reactive species preserves its asymmetric induction ability even in the presence of a large excess of SnCl4. Importantly, this catalyst system is tolerant to a small amount of moisture, oxygen, and Lewis bases.

    10. Two-Dimensional Adatom Gas Bestowing Dynamic Heterogeneity on Surfaces (pages 1488–1491)

      Nian Lin, Dietmar Payer, Alexandre Dmitriev, Thomas Strunskus, Christof Wöll, Johannes V. Barth and Klaus Kern

      Article first published online: 28 JAN 2005 | DOI: 10.1002/anie.200461390

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      Deprotonation of the carboxy groups of 1,3,5-benzenetricarboxylic acid adsorbed on the Ag(111) surface occurs in the presence of a dilute 2D Cu adatom gas at the surface, while negligible reaction rates occur under similar conditions with Cu in the form of condensed monolayer islands. These results demonstrate that highly mobile adatoms bestow dynamic heterogeneity on materials.

    11. Motif Transition in Growth Patterns of Small to Medium-Sized Silicon Clusters (pages 1491–1494)

      Soohaeng Yoo and Xiao Cheng Zeng

      Article first published online: 26 JAN 2005 | DOI: 10.1002/anie.200461753

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      Generic structural motif: Small to medium-sized, energetically low-lying silicon clusters Sin (11<n<30) are generally prolate in shape. Starting from Si16, DFT calculations show that silicon clusters are most likely built on a generic structural motif consisting of an Si6 sixfold puckered ring subunit (dark green) and a magic-number cluster such as the Si6 tetragonal bipyramid (light green), rather than on the Si9 tricapped trigonal prism (pink).

    12. Single Protein Pores Containing Molecular Adapters at High Temperatures (pages 1495–1499)

      Xiao-feng Kang, Li-Qun Gu, Stephen Cheley and Hagan Bayley

      Article first published online: 28 JAN 2005 | DOI: 10.1002/anie.200461885

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      Bearing the heat: Current has been measured from individual protein pores at temperatures approaching 100 °C. The molecular adapter β-cyclodextrin (red) remains bound to the α-hemolysin pore at high temperatures and retains the ability to bind guest molecules (black). Recording current at high temperatures is likely to be important for the study of single-molecule chemistry and in the development of stochastic sensors.

    13. [2]Pseudorotaxanes through Second-Sphere Coordination (pages 1499–1504)

      Barry A. Blight, Kevin A. Van Noortwyk, James A. Wisner and Michael C. Jennings

      Article first published online: 31 JAN 2005 | DOI: 10.1002/anie.200462380

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      A macrocyclic tetralactam and simple trans-palladium dihalide complexes self-assemble to form [2]pseudorotaxanes. The pseudorotaxane superstructures are formed through second-sphere coordination of the metal ligands by the macrocyclic component (see picture; red: macrocycle with hydrogen atoms removed, blue: n-hexylamine, green: Cl, gray: Pd).

    14. Virtual Exploration of the Small-Molecule Chemical Universe below 160 Daltons (pages 1504–1508)

      Tobias Fink, Heinz Bruggesser and Jean-Louis Reymond

      Article first published online: 26 JAN 2005 | DOI: 10.1002/anie.200462457

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      Less is more: The rules of chemical bonding allow simple elements to form a multitude of different molecules, the “chemical universe”. This space is explored by constructing a database of all molecules containing up to 11 atoms, under constraints for chemical stability and synthetic feasibility. The database which contains 13.9 million compounds (see graph; coverage of property space) can be used to identify possible new drug molecules.

    15. Intramolecular C[BOND]H Activation by an Open-Shell Cobalt(III) Imido Complex (pages 1508–1510)

      Daniel T. Shay, Glenn P. A. Yap, Lev N. Zakharov, Arnold L. Rheingold and Klaus H. Theopold

      Article first published online: 3 FEB 2005 | DOI: 10.1002/anie.200462529

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      The paramagnetic CoIII imido complex 1 is stable enough to be structurally characterized by X-ray diffraction. However, in solution a primary C[BOND]H bond of the ligand is activated and gives 2, the product of formal insertion of the imido ligand into a methyl group (see scheme; Ad=adamantyl).

      Corrected by:

      Corrigendum: Intramolecular C[BOND]H Activation by an Open-Shell Cobalt(III) Imido Complex

      Vol. 45, Issue 47, 7870, Article first published online: 27 NOV 2006

    16. A Synthetic Pathway to Either Enantiomer of Merrilactone A (pages 1511–1513)

      Zhaoyang Meng and Samuel J. Danishefsky

      Article first published online: 2 FEB 2005 | DOI: 10.1002/anie.200462509

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      A route to enantioenriched merrilactone A was found via intermediate 3. A degradation pathway in which meso compound 1 is transformed into key intermediate 2 in four steps occurs with full regiocontrol and promising enantiocontrol. A key feature of this reaction sequence is the desymmetrization of 1 through an intramolecular asymmetric ring-opening reaction.

    17. Bromoallenes as Allyl Dication Equivalents in the Absence of Palladium(0): Synthesis of Bicyclic Sulfamides by Tandem Cyclization of Bromoallenes (pages 1513–1517)

      Hisao Hamaguchi, Shohei Kosaka, Hiroaki Ohno and Tetsuaki Tanaka

      Article first published online: 21 JAN 2005 | DOI: 10.1002/anie.200462557

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      Who needs a metal? A highly regioselective synthesis of cyclic sulfamides containing a bicyclo[3.3.0]octane skeleton has been developed (see scheme). The first intramolecular nucleophilic attack of the internal sulfamide nitrogen atom takes place at the central carbon atom of the allenic moiety, and is followed by a second intramolecular nucleophilic addition of the terminal sulfamide nitrogen atom to afford the bicyclic sulfamide.

    18. Synthesis of Multiwalled Carbon Nanotubes by Catalytic Combustion of Polypropylene (pages 1517–1520)

      Tao Tang, Xuecheng Chen, Xiaoyu Meng, Hui Chen and Yaping Ding

      Article first published online: 28 JAN 2005 | DOI: 10.1002/anie.200461506

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      New for old: A novel catalytic combustion method to synthesize multiwalled carbon nanotubes (MWNTs, see SEM image) in situ in high yields from polypropylene as the carbon source in the presence of an organic-modified clay and a supported nickel catalyst is reported. The method allows new high-value MWNTs to be created from used polypropylene in an energy-saving and environmentally friendly process.

    19. Counting Chromophores in Conjugated Polymers (pages 1520–1525)

      Florian Schindler, Josemon Jacob, Andrew C. Grimsdale, Ullrich Scherf, Klaus Müllen, John M. Lupton and Jochen Feldmann

      Article first published online: 31 JAN 2005 | DOI: 10.1002/anie.200461784

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      The emitting species in conjugated polymers have been studied by single-molecule spectroscopy (see picture). The number of emissive centers (chromophores) varies as a function of molecular weight and chain length. A large ladder-type undecaphenylene was used as a molecular ruler to estimate the size of chromophores in the polymer and to enable a direct assessment of the polymeric conjugation length.

    20. Catalytic Asymmetric Addition of β-Ketoesters to Various Imines by Using Chiral Palladium Complexes (pages 1525–1529)

      Yoshitaka Hamashima, Naoki Sasamoto, Daido Hotta, Hidenori Somei, Natsuko Umebayashi and Mikiko Sodeoka

      Article first published online: 31 JAN 2005 | DOI: 10.1002/anie.200462202

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      A highly enantioselective Mannich-type reaction of β-ketoesters was developed using a catalytic amount of the Pd–aqua complexes 1 (see scheme; PG=protecting group). A variety of imines derived from glyoxylate, as well as simple aromatic and α,β-unsaturated aldehydes were successfully used. The corresponding Mannich adducts were obtained in high yield with excellent enantioselectivity.

    21. A Purine-like Nickel(II) Base Pair for DNA (pages 1529–1532)

      Christopher Switzer, Surajit Sinha, Paul H. Kim and Benjamin D. Heuberger

      Article first published online: 28 JAN 2005 | DOI: 10.1002/anie.200462047

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      Metal in the middle: A metallo base pair incorporating 6-pyridylpurine (Purp) was synthesized and characterized. PurP binds nickel(II) preferentially over other divalent ions and yields a base pair that is more stable than natural Watson–Crick pairs with high mismatch selectivity. Computational studies support a dimensional resemblance between PurP⋅Ni2+⋅PurP (see structure) and natural base pairs.

    22. Tetramic Acid Antibiotics: Stereoselective Synthesis of Streptolic Acid and Tirandalydigin (pages 1532–1536)

      Yasuhiro Iwata, Naomi Maekawara, Keiji Tanino and Masaaki Miyashita

      Article first published online: 28 JAN 2005 | DOI: 10.1002/anie.200462300

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      A new and promising methodology for the synthesis of the tetramic acid family of antibiotics was developed. The first synthesis of N-2,4-dimethoxybenzyl tirandalydigin (1), as well as a synthesis of streptolic acid (2), was achieved in a highly stereoselective manner.

    23. A Biomimetic Model of the Electron Transfer between P680 and the TyrZ–His190 Pair of PSII (pages 1536–1540)

      Fabien Lachaud, Annamaria Quaranta, Yann Pellegrin, Pierre Dorlet, Marie-France Charlot, Sun Un, Winfried Leibl and Ally Aukauloo

      Article first published online: 28 JAN 2005 | DOI: 10.1002/anie.200461948

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      Artificial photosynthesis: The first photoelectron trade between P680 and the TyrZ–His190 pair of Photosystem II was modeled by a ruthenium(II) trisbipyridine type complex that contains a phenol hydrogen atom bonded to an imidazole group. The photogenerated phenoxyl radical has been characterized. This opens up the way for a more complete biomimetic model of Photosystem II.

    24. C[BOND]H Activation of Alkanes and Arenes Catalyzed by an O-Donor Bis(tropolonato)iridium(III) Complex (pages 1540–1543)

      Gaurav Bhalla and Roy A. Periana

      Article first published online: 26 JAN 2005 | DOI: 10.1002/anie.200462065

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      Stable and swift: The title complex is stable to air and water under thermal conditions. It efficiently activates the C[BOND]H bonds of alkanes and arenes at rates 50 times higher than does the only previously reported O-donor IrIII complex (see picture).

    25. The Direct Catalytic Enantioselective Synthesis of Protected Aryl β-Hydroxy-α-Amino Acids (pages 1543–1545)

      Michael C. Willis, Gary A. Cutting, Vincent J.-D. Piccio, Matthew J. Durbin and Matthew P. John

      Article first published online: 28 JAN 2005 | DOI: 10.1002/anie.200462125

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      The combination of three reagents—a tridentate pybox ligand (pybox=pyridine bis(oxazoline)), magnesium perchlorate, and Hünig base (iPr2EtN)—allows the catalytic generation of a chiral glycine enolate from 1 that undergoes highly enantioselective addition to a range of aryl aldehydes 2. The protected aryl β-hydroxy-α-amino acid products obtained include a protected version of one of the aryl serine units present in the glycopeptide antibiotic vancomycin.

    26. Enantioselective Protonation of Silyl Enolates Catalyzed by a Binap⋅AgF Complex (pages 1546–1548)

      Akira Yanagisawa, Taichiro Touge and Takayoshi Arai

      Article first published online: 11 JAN 2005 | DOI: 10.1002/anie.200462325

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      Silver lining: A catalytic enantioselective protonation of trimethylsilyl enolates uses a binap/silver(I) fluoride complex as a chiral catalyst in a mixture of dichloromethane and methanol (see scheme). Various ketones with tertiary asymmetric carbon centers at the α position can be prepared with high enantioselectivities.

    27. Powerful Chiral Phase-Transfer Catalysts for the Asymmetric Synthesis of α-Alkyl- and α,α-Dialkyl-α-amino Acids (pages 1549–1551)

      Masanori Kitamura, Seiji Shirakawa and Keiji Maruoka

      Article first published online: 31 JAN 2005 | DOI: 10.1002/anie.200462257

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      The catalytic performance of the chiral phase-transfer catalyst 1 (0.1–0.01 mol %) in the asymmetric alkylation of protected glycine and alanine derivatives exceeds that of existing catalysts. The reaction is used in the enantioselective synthesis of structurally diverse natural and non-natural α-alkyl and α,α-dialkyl-α-amino acids.

    28. Novel Strategy for the Synthesis of the Butenolide Moiety of Peridinin (pages 1553–1557)

      Thomas Olpp and Reinhard Brückner

      Article first published online: 28 JAN 2005 | DOI: 10.1002/anie.200460259

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      Tartaric acid is the starting point for the stereoselective synthesis of the butenolide unit (see scheme)in peridinin, a marine carotenoid. Key steps were the desymmetrization of tartaric acid bis(Weinreb amide), an E-selective olefination by Ando-type bromophosphonates, and an anti-selective Mitsunobu elimination (for establishing the C1′[DOUBLE BOND]Cγ bond).

    29. Gadolinium Nitride Gd3N in Carbon Cages: The Influence of Cluster Size and Bond Strength (pages 1557–1560)

      Matthias Krause and Lothar Dunsch

      Article first published online: 26 JAN 2005 | DOI: 10.1002/anie.200461441

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      Extra filling: A covalent gadolinium nitride is prepared and encapsulated as a Gd3N cluster in fullerene cages ranging in size from C80 to C88. The most abundant structure, Gd3N@C80 (I) (see figure; gray C, red Gd), is a large-energy-gap material based on an icosahedral cage. Gd3N is the largest rare-earth nitride cluster to be caged in a fullerene to date. This compound has potential application as an effective contrast agent in magnetic resonance imaging.

    30. Reversible Cross-Linking of Hyperbranched Polymers: A Strategy for the Combinatorial Decoration of Multivalent Scaffolds (pages 1560–1563)

      Michael Barth, Rainer Fischer, Roland Brock and Jörg Rademann

      Article first published online: 2 FEB 2005 | DOI: 10.1002/anie.200460559

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      All decked out: Peptide-decorated dendritic polymers were synthesized on macroscopic polymer resins and then released by cleaving the reversible cross-linkers (see scheme). The released multivalent structures entered cells efficiently at low concentrations by endocytosis.

    31. Complete Self-Assembly of Discrete Supramolecular Dendrimers (pages 1564–1567)

      Alexander Franz, Walter Bauer and Andreas Hirsch

      Article first published online: 28 JAN 2005 | DOI: 10.1002/anie.200462104

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      Simply mixing a core (black) with defined amounts of branching units (red) and end caps (blue) leads to programmed complete self-assembly of supramolecular dendrimers through complimentary and multiple hydrogen bonding.

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      Preview: Angew. Chem. Int. Ed. 10/2005 (page 1571)

      Article first published online: 22 FEB 2005 | DOI: 10.1002/anie.200590032

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