Chemistry - A European Journal

Cover image for Vol. 10 Issue 16

August 20, 2004

Volume 10, Issue 16

Pages 3839–4094

    1. Cover Picture: A General and Versatile Approach to Thermally Generated N-Heterocyclic Carbenes (Chem. Eur. J. 16/2004) (page 3839)

      Gregory W. Nyce, Szilard Csihony, Robert M. Waymouth and James L. Hedrick

      Version of Record online: 12 AUG 2004 | DOI: 10.1002/chem.200490054

      The cover picture shows the synthesis of pentafluorobenzene adducts of N-heterocyclic carbenes (NHC), designed to undergo thermal deprotection to generate NHC. The utility of these adducts as organic catalyst precursors for living ring-opening polymerization (ROP) of lactide, condensation polymerizations and transesterification reactions is described, as well as synthons for NHC bearing organometallic complexes by J. Hedrick et al. p. 4073 ff.

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      Vibrational and Quantum-Chemical Study of Nonlinear Optical Chromophores Containing Dithienothiophene as the Electron Relay (page 3848)

      Juan Casado, Víctor Hernández, Oh-Kil Kim, Jean-Marie Lehn, Juan T. López Navarrete, Salvador Delgado Ledesma, Rocío Ponce Ortiz, Mari Carmen Ruiz Delgado, Yolanda Vida and E. Pérez-Inestrosa

      Version of Record online: 12 AUG 2004 | DOI: 10.1002/chem.200490056

    3. Spin Frustration in 2D Kagomé Lattices: A Problem for Inorganic Synthetic Chemistry (pages 3850–3859)

      Daniel G. Nocera, Bart M. Bartlett, Daniel Grohol, Dimitris Papoutsakis and Matthew P. Shores

      Version of Record online: 26 MAY 2004 | DOI: 10.1002/chem.200306074

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      The kagomé lattice presents an ideal venue to seek classical and quantum spin liquid ground states. Geometric spin frustration in a kagomé lattice may provide insight into the mechanism of scatterless hole transport in square lattices of high-Tc cuprate oxides. We have prepared jarosites, a mineralogical series of compounds, containing the kagomé lattice, in stoichiometric and single-crystal form. We present a summary of the structure (illustrated) and magnetism of pure jarosites.

    4. Interstitial Zn Atoms Do the Trick in Thermoelectric Zinc Antimonide, Zn4Sb3: A Combined Maximum Entropy Method X-ray Electron Density and Ab Initio Electronic Structure Study (pages 3861–3870)

      Fausto Cargnoni, Eiji Nishibori, Philippe Rabiller, Luca Bertini, G. Jeffrey Snyder, Mogens Christensen, Carlo Gatti and Bo Brummerstadt Iversen

      Version of Record online: 24 JUN 2004 | DOI: 10.1002/chem.200400327

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      Interstitial Zn atoms are crucial in β-Zn4Sb3, one of the most promising thermoelectric materials. They supply electrons and enhance the thermopower, besides lowering its thermal conductivity, as shown by a combined synchrotron X-ray diffraction and ab initio study. Densities of state are shown for zinc antimonide cells. Addition of interstitial Zn atoms (grey in the figure) to the 12-Zn structure yields a change from p- to n-doping. Zn12.82Sb10, with interstitial atoms in 82 % of the cells, is a p-doped semiconductor whose thermopower is very sensitive to composition and/or doping.

    5. Wedge-Shaped Molecules with a Sulfonate Group at the Tip—A New Class of Self-Assembling Amphiphiles (pages 3871–3878)

      Xiaomin Zhu, Bernd Tartsch, Uwe Beginn and Martin Möller

      Version of Record online: 24 JUN 2004 | DOI: 10.1002/chem.200400050

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      Wedge-shaped sulfonate amphiphiles self-assemble in bulk and from solution to give rodlike structures with circular cross-sections (see picture); this causes the formation of columnar mesophases, as well as gelation of the solution. Phase diagram investigations demonstrate that the transition from the gel state to the highly ordered bulk phase occurs through a lyotropic mesophase.

    6. Self-Assembly of Small Peptidomimetic Cyclophanes (pages 3879–3890)

      Jorge Becerril, M. Isabel Burguete, Beatriu Escuder, Francisco Galindo, Raquel Gavara, Juan F. Miravet, Santiago V. Luis and Gabriel Peris

      Version of Record online: 24 JUN 2004 | DOI: 10.1002/chem.200400031

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      To gel or to crystallize, that's the question! Small peptidomimetic cyclophanes self-assemble through hydrogen bonds (see picture), and several factors such as slight structural differences, changes in solvent and cooling rate have been found to determine their final supramolecular architecture.

    7. An Industrially Viable Catalyst System for Palladium-Catalyzed Telomerizations of 1,3-Butadiene with Alcohols (pages 3891–3900)

      Ralf Jackstell, Surendra Harkal, Haijun Jiao, Anke Spannenberg, Cornelia Borgmann, Dirk Röttger, Franz Nierlich, Mark Elliot, Stuart Niven, Kingsley Cavell, Oscar Navarro, Mihai S. Viciu, Steven P. Nolan and Matthias Beller

      Version of Record online: 21 JUN 2004 | DOI: 10.1002/chem.200400182

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      Unprecedented catalyst productivities (TON >1 500 000) and activities (TOF = 100 000 h−1) are observed in the presence of an excess of imidazolium salts in the highly efficient palladium-catalyzed telomerization reactions of 1,3-butadiene with alcohols with monocarbene–palladium complexes (see picture).

    8. PKU-5: An Aluminoborate with Novel Octahedral Framework Topology (pages 3901–3906)

      Jing Ju, Tao Yang, Guobao Li, Fuhui Liao, Yingxia Wang, Liping You and Jianhua Lin

      Version of Record online: 21 JUN 2004 | DOI: 10.1002/chem.200400066

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      Interconnecting octahedra: A primary octahedron-based framework topology was found in an aluminoborate Al4B6O15 (PKU-5). The octahedra are all triangularly three-connected to the neighboring octahedra that form a novel octahedral framework with the chiral (10,3)-a topology (illustrated here).

    9. Donor–Acceptor Polymers: A Conjugated Oligo(p-Phenylene Vinylene) Main Chain with Dangling Perylene Bisimides (pages 3907–3918)

      Edda E. Neuteboom, Paul A. van Hal and René A. J. Janssen

      Version of Record online: 24 JUN 2004 | DOI: 10.1002/chem.200400097

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      Subpicosecond photoinduced electron transfer occurs in new donor–acceptor copolymers consisting of oligo(p-phenylene vinylene) donor segments alternating with phenylenes carrying dangling perylene bisimide acceptors (see picture). UV/Visible and circular dichroism spectroscopy indicate that the donor and acceptor chromophores organize in a preferred helical orientation with respect to each other.

    10. Solvation of Uranyl(II), Europium(III) and Europium(II) Cations in “Basic” Room-Temperature Ionic Liquids: A Theoretical Study (pages 3919–3930)

      Alain Chaumont and Georges Wipff

      Version of Record online: 24 JUN 2004 | DOI: 10.1002/chem.200400207

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      Solvation by ionic liquids: A molecular dynamics study of the UO22+, Eu3+, and Eu2+ ions in “basic” (Lewis acidity) room-temperature ionic liquids (RTILs) composed of the EMI+ cation and a mixture of AlCl4 and Cl ions, reveals the importance of “solvation forces” on the stability of [UO2Cl4]2− (shown here), [EuIIICl6]3−, and [EuIICl6]4− species in equilibrium with less halogenated complexes. In the presence of a small amounts of water, europium(III) forms [EuCl3(OH2)4] and [EuCl4(OH2)3] complexes.

    11. New 2,2′-Substituted 4,4′-Dimethoxy-6,6′-dimethyl[1,1′-biphenyls], Inducing a Strong Helical Twisting Power in Liquid Crystals (pages 3931–3935)

      Richard Holzwarth, Richard Bartsch, Zoubair Cherkaoui and Guy Solladié

      Version of Record online: 21 JUN 2004 | DOI: 10.1002/chem.200400035

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      Helical twist: We report in this paper the synthesis of 2,2′-, 4,4′-, 6,6′-substituted biphenyls (two examples of which are illustrated here) inducing a strong helical twisting power in nematic phases.

    12. Copper-Free Monomeric and Dendritic Palladium Catalysts for the Sonogashira Reaction: Substituent Effects, Synthetic Applications, and the Recovery and Re-Use of the Catalysts (pages 3936–3944)

      Karine Heuzé, Denise Méry, Dominique Gauss, Jean-Claude Blais and Didier Astruc

      Version of Record online: 24 JUN 2004 | DOI: 10.1002/chem.200400150

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      The copper-free Sonogashira reaction was catalyzed by monomeric and recoverable dendritic PdII complexes containing a bidentate phosphine (the benzyl group in the monomers models the dendritic branch; see scheme: Cat=DAB-dendr-[N(CH2PR2)2Pd(OAc)2]x, x=4, 8, 16; R=Cy, tBu). The kinetics, which were investigated by means of GPC, confirmed the dramatic influence of the diphosphine substituents (tBu versus Cy). The catalytic efficiency decreases as the dendrimer generation increases.

    13. Stereoselective Synthesis of trans-threo-trans-Oligopyrrolidines: Potential Agents for RNA Cleavage (pages 3945–3962)

      Hans-Dieter Arndt, Rüdiger Welz, Sabine Müller, Burkhart Ziemer and Ulrich Koert

      Version of Record online: 28 JUN 2004 | DOI: 10.1002/chem.200400181

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      A promising class of novel RNA-binding agents has been developed by using bis- and terpyrrolidines with 2,5′-threo-trans configurations. The compounds such as depicted were synthesized stereoselectively and tested for RNA cleavage.

    14. Two 3D Supramolecular Polymers Constructed from an Amino Acid and a High-Nuclear Ln6Cu24 Cluster Node (pages 3963–3969)

      Jian-Jun Zhang, Tian-Lu Sheng, Sheng-Min Hu, Sheng-Qing Xia, Guido Leibeling, Franc Meyer, Zhi-Yong Fu, Ling Chen, Rui-Biao Fu and Xin-Tao Wu

      Version of Record online: 28 JUN 2004 | DOI: 10.1002/chem.200400018

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      The first successful attempt to construct 3D supramolecular frameworks with high-nuclear 3d–4f heterometallic clusters as a node is reported. The two polymers obtained 1 and 2 utilize Ln6Cu24 octahedral clusters as nodes and trans-Cu(amino acid)2 groups as bridges (see figure).

    15. Synthesis and Reactivity of the Monomeric Late-Transition-Metal Parent Amido Complex [Ir(Cp*)(PMe3)(Ph)(NH2)] (pages 3970–3978)

      Daniela Rais and Robert G. Bergman

      Version of Record online: 28 JUN 2004 | DOI: 10.1002/chem.200400151

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      Improved synthesis of [Ir(Cp*)(PMe3)(Ph)(NH2)] by deprotonation of the corresponding ammonia complex has produced the uncontaminated amide, which deprotonates weak acids, reacts with electrophiles yielding insertion products, and, in the presence of 2,6-dimethylphenyl isocyanide, unexpectedly forms the η4-tetramethylfulvene complex [(η4-C5Me4CH2)Ir(PMe3)(Ph)(CNC6H3-2,6-(CH3)2] (see scheme).

    16. Silsesquioxane Models for Silica Surface Silanol Sites with Adjacent Siloxide Functionalites and Olefin Polymerization Catalysts Thereof (pages 3979–3990)

      Robbert Duchateau, Tessa W. Dijkstra, Rutger A. van Santen and Glenn P. A. Yap

      Version of Record online: 28 JUN 2004 | DOI: 10.1002/chem.200400206

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      Incompletely condensed silsesquioxanes containing a siloxane ring of variable size and a neighboring silanol mimic silica surface silanol sites with adjacent siloxide functionalities. Hydrogen bridging between the silanol and the siloxane ring affects the silanol's acidity. Interaction of the siloxide oxygens with the metal site such as depicted in corresponding cationic titanasilsesquioxane species significantly influences the acivity and stability of these olefin polymerization catalysts.

    17. The Effect of Fluorination: A Crystallographic and Computational Study of Mesogenic Alkyl 4-[2-(Perfluorooctyl)ethoxy]benzoates (pages 3991–3999)

      Megumi Yano, Tetsuya Taketsugu, Kayako Hori, Hiroaki Okamoto and Shunsuke Takenaka

      Version of Record online: 28 JUN 2004 | DOI: 10.1002/chem.200400123

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      Chain interactions: The systematic change of crystal structures in the series of alkyl 4-[2-(perfluorooctyl)ethoxy]benzoates (F8-n), as illustrated here, is discussed in relation to their mesophase behavior and intermolecular interactions. Computational studies show weaker interactions between the perfluoroalkyl chains than between other moieties.

    18. Poly(phenylacetylene)s Bearing a Peptide Pendant: Helical Conformational Changes of the Polymer Backbone Stimulated by the Pendant Conformational Change (pages 4000–4010)

      Katsuhiro Maeda, Nobuto Kamiya and Eiji Yashima

      Version of Record online: 30 JUN 2004 | DOI: 10.1002/chem.200400315

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      Optically active, cis-transoid poly(phenylacetylene) derivatives bearing a poly(γ-benzyl-L-glutamate) or poly(L-glutamic acid) chain as the pendant were prepared, and the main chain conformational changes in solution induced by a helix–coil transition of the pendant polypeptides (see figure) were investigated using circular dichroism (CD) and absorption spectroscopies.

    19. Staudinger Reaction at in-Bridgehead Positions of Phosphorus Macrobicyclic Compounds (pages 4011–4016)

      Ingmar Bauer, Margit Gruner, Sigrid Goutal and Wolf D. Habicher

      Version of Record online: 30 JUN 2004 | DOI: 10.1002/chem.200400204

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      Phosphorus bicycles! The first introduction of large groups at in-bridgehead positions of macrobicyclic compounds (an example of which is illustrated here) has been achieved in in,in- and in,out-phosphites by means of the Staudinger reaction with a phosphoryl azide. This opens the way for specific modification of the inside of cage compounds with respect to applications as ligands for metal cations and as hosts for the molecular recognition of neutral substrates.

    20. Stabilizing or Destabilizing Oligodeoxynucleotide Duplexes Containing Single 2′-Deoxyuridine Residues with 5-Alkynyl Substituents (pages 4017–4028)

      Thomas Kottysch, Carolin Ahlborn, Frank Brotzel and Clemens Richert

      Version of Record online: 30 JUN 2004 | DOI: 10.1002/chem.200306044

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      Tuning duplex stability: Oligonucleotides have been prepared with 5-alkynyl substituents at a 2′-deoxyuridine residue (see structure) by on-support Sonogashira coupling. The substituents either stabilize or destabilize the duplex, as monitored from the UV melting point. The ability to tune the melting point of a DNA dodecamer duplex with a single side chain may prove useful when developing DNA sequences for biomedical applications.

    21. 103Rh NMR Chemical Shifts in Organometallic Complexes: A Combined Experimental and Density Functional Study (pages 4029–4040)

      Laura Orian, Annalisa Bisello, Saverio Santi, Alberto Ceccon and Giacomo Saielli

      Version of Record online: 30 JUN 2004 | DOI: 10.1002/chem.200305671

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      Chemical shifts of rhodium in mono- and bimetallic complexes have been measured and calculated, resulting in a good correlation between experimental and theoretical values (see diagram). The effect of the ancillary ligands and HOMO–LUMO gap on the chemical shift has been rationalised by means of density functional theory calculations.

    22. Electron Delocalization and Electrostatic Repulsion at the Origin of the Strong Spin Coupling in Mixed-Valence Keggin Polyoxometalates: Ab Initio Calculations of the One- and Two-Electron Processes (pages 4041–4053)

      Nicolas Suaud, Alejandro Gaita-Ariño, Juan Modesto Clemente-Juan and Eugenio Coronado

      Version of Record online: 30 JUN 2004 | DOI: 10.1002/chem.200305628

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      A general theoretical procedure to treat the problem of electron delocalization and magnetic interactions in high-nuclearity mixed valence clusters based on polyoxometalates. The main interactions between the delocalized electrons of mixed-valence polyoxometalate anions (see for example figure) are extracted from valence spectroscopy ab initio calculations on embedded fragments. Electron transfer, magnetic coupling and exchange transfer parameters between nearest and next-nearest-neighbor metal ions, as well as the value of the electrostatic repulsion between pairs of metal ions are determined.

    23. Unprecedented Polymerization of ε-Caprolactone Initiated by a Single-Site Lanthanide Borohydride Complex, [Sm(η-C5Me5)2(BH4)(thf)]: Mechanistic Insights (pages 4054–4062)

      Isabelle Palard, Alain Soum and Sophie M. Guillaume

      Version of Record online: 5 JUL 2004 | DOI: 10.1002/chem.200400319

      Controlled ring-opening polymerization of ε-caprolactone (ε-CL) has been achieved by using [Sm(Cp*)2(BH4)(thf)] (1) (Cp* = η-C5Me5). The single-site initiator 1, which produces α,ω-dihydroxytelechelic poly(ε-caprolactone) displaying relatively narrow polydispersity indices (<1.3) within a short period of time (30 min), allows a better understanding of the polymerization mechanism.

    24. Generating and Dimerizing the Transient 16-Electron Phosphinidene Complex [Cp*Ir[DOUBLE BOND]PAr]: A Theoretical and Experimental Study (pages 4063–4072)

      Arjan T. Termaten, Tom Nijbacker, Andreas W. Ehlers, Marius Schakel, Martin Lutz, Anthony L. Spek, Michael L. McKee and Koop Lammertsma

      Version of Record online: 5 JUL 2004 | DOI: 10.1002/chem.200400080

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      Dehydrohalogenation of [Cp*IrCl2(PH2Ar)] in CH2Cl2 results in novel fused-ring systems, dimeric [{Cp*Ir[DOUBLE BOND]PAr}2] being the likely intermediate (see scheme). Intramolecular C[BOND]H bond activation induced by steric factors is considered to be the driving force for this irreversible formation.

    25. A General and Versatile Approach to Thermally Generated N-Heterocyclic Carbenes (pages 4073–4079)

      Gregory W. Nyce, Szilard Csihony, Robert M. Waymouth and James L. Hedrick

      Version of Record online: 19 JUL 2004 | DOI: 10.1002/chem.200400196

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      Simplified approach toN-heterocyclic carbenes: Pentafluorobenzene adducts of N-heterocyclic carbenes (NHC), designed to undergo thermal deprotection to generate NHC, were prepared. Their utility was demonstrated in organic catalysis for lactide polymerization and transesterification reactions, as well as synthons for NHC bearing organometallic complexes (see scheme).

    26. Effect of Conformational Changes on a One-Electron Reduction Process: Evidence of a One-Electron P[BOND]P Bond Formation in a Bis(phosphinine) (pages 4080–4090)

      Sylvie Choua, Cosmina Dutan, Laurent Cataldo, Théo Berclaz, Michel Geoffroy, Nicolas Mézailles, Audrey Moores, Louis Ricard and Pascal Le Floch

      Version of Record online: 5 JUL 2004 | DOI: 10.1002/chem.200400073

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      The cryptand factor: Reaction of 1 on an alkali metal mirror leads to the formation of a radical anion that is localized on only one phosphinine ring. In the presence of cryptand the formation of tight ion pairs is prevented, and reduction of 1 leads to the formation of a one-electron P[BOND]P bond.

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      Preview: Chem. Eur. J. 16/2004 (page 4094)

      Version of Record online: 12 AUG 2004 | DOI: 10.1002/chem.200490057