Angewandte Chemie International Edition

Cover image for Vol. 43 Issue 6

January 30, 2004

Volume 43, Issue 6

Pages 647–763

    1. Cover Picture: 5-Dehydro-1,3-quinodimethane: A Hydrocarbon with an Open-Shell Doublet Ground State (Angew. Chem. Int. Ed. 6/2004) (page 647)

      Lyudmila V. Slipchenko, Tamara E. Munsch, Paul G. Wenthold and Anna I. Krylov

      Version of Record online: 27 JAN 2004 | DOI: 10.1002/anie.200490009

      Contrary to the accepted guidelines for the occupancy of orbitals (such as Hund's rule or the Aufbau principle), three unpaired electrons are coupled antiferromagnetically in the 5-dehydro-m-xylylene triradical. This first example of an organic molecule with an “open-shell” doublet ground state is described by P. G. Wenthold, A. I. Krylov, and co-workers on page 742 ff. The cover pictures shows the singly occupied orbitals in the triradical and highlights the correlation between theoretical and experimental results.

    2. Novel Compounds of Elements of Group 14: Ligand-Stabilized Clusters with “Naked” Atoms (pages 664–666)

      Andreas Schnepf

      Version of Record online: 27 JAN 2004 | DOI: 10.1002/anie.200301706

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      Naked Facts: Recently, cluster compounds that contain both ligand-bound and unsubstituted atoms of Group 14 have been described. The general formula MnRm, where m<n (see picture) can be assigned to these compounds. More recent developments in this area, the bonding situation within these compounds, and their possible significance for nanotechnology are discussed.

    3. G-Quartets 40 Years Later: From 5′-GMP to Molecular Biology and Supramolecular Chemistry (pages 668–698)

      Jeffery T. Davis

      Version of Record online: 27 JAN 2004 | DOI: 10.1002/anie.200300589

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      Mononucleotides in water, lipophilic nucleosides in organic solvents, or G-rich DNA in the chromosome: Cation-templated self-assembly of guanosine gives supramolecular structures based on the G-quartet (see picture). These structures have a wide range of potential functions in areas as diverse as cancer biology, separations chemistry, and biomaterials.

    4. A Crystalline Microporous Narrow-Bandgap Semiconductor (pages 700–704)

      Anders E. C. Palmqvist, Bo B. Iversen, Ezio Zanghellini, Mårten Behm and Galen D. Stucky

      Version of Record online: 8 JAN 2004 | DOI: 10.1002/anie.200351284

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      A crystalline microporous semiconductor |(|K6(H2O)6| [Sb12O18])3| [Te36] (denoted SBC-1) has been prepared, which consists of 24-ring tubular tellurium units that host 12-ring {Sb12O18} tubular units, which in turn act as hosts for K+ ions and H2O molecules (see picture). An example of a second-order zeoate, it has a narrow bandgap of 0.25 eV and exhibits highly anisotropic electrical conductivity.

      Corrected by:

      Corrigendum: A Crystalline Microporous Narrow-Bandgap Semiconductor

      Vol. 46, Issue 5, 653, Version of Record online: 12 JAN 2007

    5. Supercritical-Fluid Processing Technique for Nanoscale Polymer Particles (pages 704–707)

      Mohammed J. Meziani, Pankaj Pathak, Razvan Hurezeanu, Mark C. Thies, Robert M. Enick and Ya-Ping Sun

      Version of Record online: 27 JAN 2004 | DOI: 10.1002/anie.200352834

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      Nanoparticles of a fluoropolymer, which is soluble in supercritical carbon dioxide, can be recovered from a liquid solvent after a rapid expansion process (see scheme). Nanoparticles with an average diameter less than 50 nm were initially obtained, however many strategies led to aggregation and the formation of agglomerates. Sodium dodecyl sulfate was found to be most effective in stabilizing the polymeric nanoparticles in aqueous suspension.

    6. A Three-Dimensional Ferrimagnet Composed of Mixed-Valence Mn4 Clusters Linked by an {Mn[N(CN)2]6}4− Unit (pages 707–711)

      Hitoshi Miyasaka, Kazuya Nakata, Ken-ichi Sugiura, Masahiro Yamashita and Rodolphe Clérac

      Version of Record online: 27 JAN 2004 | DOI: 10.1002/anie.200353093

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      A ferrimagnet with a 3D molecular network (depicted) has been synthesized and characterized. The compound is composed of units of mixed-valence Mn4 clusters, a unit that is well known for its single-molecule magnet properties, and MnII paramagnetic units. Both building blocks are linked by a dicyanamide bridging ligand to form a covalently bonded three-dimensional network. The compound becomes a ferrimagnet at 4.1 K that exhibits a spin-flip phenomenon under the influence of a magnetic field.

    7. Catalytic Generation of Indium Hydride in a Highly Diastereoselective Reductive Aldol Reaction (pages 711–714)

      Ikuya Shibata, Hirofumi Kato, Tatsuya Ishida, Makoto Yasuda and Akio Baba

      Version of Record online: 27 JAN 2004 | DOI: 10.1002/anie.200352738

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      A one-pot synthesis of β-hydroxyketones has been achieved by the reductive aldol reaction of enones and aldehydes in the presence of Et3SiH and a catalytic amount of InBr3 (see scheme). The reaction is highly diastereoselective and no reduction of the starting aldehydes occurs. This method is superior to conventional reductive aldol reactions in terms of applicability to a wide range of enones and aldehydes.

    8. The Circumambulation of a Phosphirane: Taking 9-Phenyl-9-phosphabicyclo[6.1.0]nona-2,4,6-triene for a “Walk” (pages 714–717)

      Rosa E. Bulo, Helen Jansen, Andreas W. Ehlers, Fransiscus J. J. de Kanter, Marius Schakel, Martin Lutz, Anthony L. Spek and Koop Lammertsma

      Version of Record online: 27 JAN 2004 | DOI: 10.1002/anie.200351855

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      Walking rings: At room temperature, the P-R entity of a bicyclic phosphirane (see picture) “walks” along the perimeter of the larger ring. Although this concerted rearrangement is similar to that of its hydrocarbon analogue, the additional 1,5-sigmatropic shift follows a different mechanism.

    9. Synthesis of Thermoresponsive Polyurethane from 2-Methylaziridine and Supercritical Carbon Dioxide (pages 717–719)

      Osamu Ihata, Yoshihito Kayaki and Takao Ikariya

      Version of Record online: 27 JAN 2004 | DOI: 10.1002/anie.200352215

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      Under pressure: Temperature-dependent optical transmission in aqueous solution is exhibited by polyurethanes that are obtained by copolymerization of 2-methylaziridine and supercritical CO2 (scCO2; see scheme). The transmittance drops sharply at the lower critical solution temperature (LCST). The molecular weight, content of urethane linkages, and LCST value of the polyurethanes are controllable simply by changing the CO2 pressure.

    10. Tandem 1,4-Addition/Enantioselective Protonation Catalyzed by Rhodium Complexes: Efficient Access to α-Amino Acids (pages 719–723)

      Laure Navarre, Sylvain Darses and Jean-Pierre Genet

      Version of Record online: 27 JAN 2004 | DOI: 10.1002/anie.200352518

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      Conjugate addition of potassium trifluoro(organo)borates 2 (R=aryl, alkenyl) to 2-acetamidoacrylate 1 mediated by a chiral rhodium catalyst and with in situ enantioselective protonation afforded a variety of α-amino acids 3 with high yields and ee values up to 90 % (see scheme, cod=cycloocta-1,5-diene, binap=2,2′-bis(diphenylphosphanyl)-1,1′-binaphthyl). Among the tested chiral ligands and proton sources, binap in combination with 2-methoxyphenol (guaiacol), an inexpensive and nontoxic phenol, afforded the highest asymmetric inductions.

    11. A Peptide Flavoprotein Mimic: Flavin Recognition and Redox Potential Modulation in Water by a Designed β Hairpin (pages 724–727)

      Sara M. Butterfield, Catherine M. Goodman, Vincent M. Rotello and Marcey L. Waters

      Version of Record online: 27 JAN 2004 | DOI: 10.1002/anie.200352527

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      Pinning down flavoproteins: A designed β-hairpin peptide binds flavin mononucleotide (FMN) in water through noncovalent interactions involving Trp and Lys residues on one face of the β hairpin (see model). Reduction of FMN is disfavored in the complex as a result of favorable π–π stacking interactions between Trp side chains and the oxidized flavin ring. This system mimicks the function of naturally occurring flavoproteins.

    12. Synthesis and Incorporation of the First Polyketide Synthase Free Intermediate in Monocerin Biosynthesis (pages 727–730)

      Lorraine C. Axford, Thomas J. Simpson and Christine L. Willis

      Version of Record online: 27 JAN 2004 | DOI: 10.1002/anie.200352652

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      Enzyme essential: Feeding studies with Dreschlera ravenelii show that labeled dihydroisocoumarin 1 is metabolized into monocerin (2) in exceptionally high levels. These results provide evidence for the role of 1 as the first enzyme-free intermediate in the monocerin biosynthesis pathway and, thus, as the final product of the polyketide synthase (PKS) catalyzed part of the pathway. Compound 1 may therefore be of use in further studies to isolate and sequence the monocerin PKS gene.

    13. Oxidative Polymerization of 2,6-Dimethylphenol To Form Poly(2,6-dimethyl-1,4-phenyleneoxide) in Water (pages 730–733)

      Kei Saito, Takahiro Tago, Toru Masuyama and Hiroyuki Nishide

      Version of Record online: 27 JAN 2004 | DOI: 10.1002/anie.200352764

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      Green polymerization: The simple stirring of 2,6-dimethylphenol with an excess of oxidant or a catalytic amount of a copper complex in an alkaline aqueous solution yields poly(2,6-dimethyl-1,4-phenyleneoxide), a commercially important polymer (see scheme). The formed polymer was easily separated as an off-white powder by filtration.

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      Electrochemical Preparation of Silicon and Its Alloys from Solid Oxides in Molten Calcium Chloride (pages 733–736)

      Xianbo Jin, Pei Gao, Dihua Wang, Xiaohong Hu and George Z. Chen

      Version of Record online: 27 JAN 2004 | DOI: 10.1002/anie.200352786

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      Electroreduction, or electrodeoxidation, of pelleted SiO2 powder (left image) or its mixture with other metal oxide powders in molten CaCl2 produces pure Si powder (right image), or the respective silicon alloy powder. Being advantageous by simplicity and resulting in less CO2 emission, the electrochemical approach has an energy consumption that is below 13 kWh (kg of Si)−1.

    15. Synthesis of a Delocalized Azepinium Ion and Investigation of Its Electrophilic Character (pages 736–738)

      Kyosuke Satake, Yasuhiro Kubota, Christopher E. J. Cordonier, Hideki Okamoto and Masaru Kimura

      Version of Record online: 27 JAN 2004 | DOI: 10.1002/anie.200352794

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      An isolated example: The first π-delocalized azepinium ions 2 were generated from 2H-azepines 1 and fully characterized by NMR spectroscopy. The stability of the ions was investigated by ab initio calculations. Reaction with nucleophiles led to further support of the characterization of the ions by the selective formation of 2-substituted 2H-azepines.

    16. Stereoselective Total Synthesis of (+)-Norrisolide (pages 739–742)

      Thomas P. Brady, Sun Hee Kim, Ke Wen and Emmanuel A. Theodorakis

      Version of Record online: 27 JAN 2004 | DOI: 10.1002/anie.200352868

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      In a convergent approach to the marine natural product (+)-norrisolide (1) the two bicyclic ring systems are coupled through the C9[BOND]C10 bond to assemble the carbon framework in a late stage of the synthesis. Other highlights of the synthetic strategy include the formation of the unusual fused γ-lactone–γ-lactol motif of 1 through a sequence of oxidation reactions.

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      5-Dehydro-1,3-quinodimethane: A Hydrocarbon with an Open-Shell Doublet Ground State (pages 742–745)

      Lyudmila V. Slipchenko, Tamara E. Munsch, Paul G. Wenthold and Anna I. Krylov

      Version of Record online: 8 JAN 2004 | DOI: 10.1002/anie.200352990

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      Theory predicts an open-shell doublet ground state for the 5-dehydro-1,3-quinodimethane triradical (see picture), with three low-spin coupled electrons in three singly occupied molecular orbitals. The bond dissociation enthalpy for formation of the triradical from meta-xylylene, measured by MS indicates an interaction of (1±4) kcal mol−1 between the unpaired electrons in the σ and π systems in the triradical.

    18. The Direct Synthesis of a Silene–Organometallic Complex (pages 745–748)

      Dmitry Bravo-Zhivotovskii, Hanan Peleg-Vasserman, Monica Kosa, Gregory Molev, Mark Botoshanskii and Yitzhak Apeloig

      Version of Record online: 8 JAN 2004 | DOI: 10.1002/anie.200353048

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      σ or π? The direct synthesis and the molecular and electronic structures of a novel η2-silene platinum complex, 1, is reported (see scheme). The nature of bonding in 1 was studied by using geometrical and electronic structure criteria, and the results suggested that 1 is best described as an hybrid between a π complex and a σ-cyclopropane structure with a more dominant π-complex character than in a related disilene complex.

    19. High-Throughput Synthesis of Phosphonate-Based Inorganic–Organic Hybrid Compounds under Hydrothermal Conditions (pages 749–752)

      Norbert Stock and Thomas Bein

      Version of Record online: 27 JAN 2004 | DOI: 10.1002/anie.200351718

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      A new phase in combinatorial chemistry: High-throughput methods for hydrothermal reactions including automated solid-dosing and pH-measurement capabilities have been applied to the synthesis of five novel zinc phosphonocarboxylates and seven novel metal tetraphosphonates. This automated combinatorial synthesis and characterization method allows a large parameter space to be explored rapidly (see phase diagram) and has great potential for materials science.

    20. High-Throughput Method for the Impedance Spectroscopic Characterization of Resistive Gas Sensors (pages 752–754)

      Andreas Frantzen, Jens Scheidtmann, Gerald Frenzer, Wilhelm F. Maier, Jörg Jockel, Thomas Brinz, Daniel Sanders and Ulrich Simon

      Version of Record online: 27 JAN 2004 | DOI: 10.1002/anie.200352424

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      A combinatorial work flow for the rapid synthesis and testing of thick oxide films for the development of new gas sensors with improved sensitivity and selectivity involves the synthesis and deposition of mixed-oxide films of variable composition. The library is based on the sol–gel synthesis of mixed oxides on an array of 8×8 interdigitated electrodes. For the characterization of the sensor arrays, test gas sequences and sensor temperatures were varied.

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      Superphenalene-Based Columnar Liquid Crystals (pages 755–758)

      Željko Tomović, Mark D. Watson and Klaus Müllen

      Version of Record online: 8 JAN 2004 | DOI: 10.1002/anie.200352855

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      Liquid crystals from large graphitic segments: Discotic compounds based on substituted superphenalenes were prepared by a surprisingly simple synthesis and processed to give soft and highly soluble columnar liquid-crystalline materials. The regiospecific synthesis leads to compounds with pinwheel-type C3 symmetry.

    22. Preview: Angew. Chem. Int. Ed. 6/2004 (page 763)

      Version of Record online: 27 JAN 2004 | DOI: 10.1002/anie.200490012