Angewandte Chemie International Edition in English

Cover image for Vol. 31 Issue 9

September 1992

Volume 31, Issue 9

Pages 1101–1264

Currently known as: Angewandte Chemie International Edition

    1. Cover Picture (Angew. Chem. Int. Ed. Engl. 9/1992)

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199211011

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      The cover picture shows a garlic bulb surrounded by some of the most important organosulfur compounds and intermediates that can be isolated from it. Besides the preparative and analytical aspects of these compounds and the analogous substances from onion, which interest pure chemist, E. Block also discusses the medicinal effects attributed to the Allium genus in his article on page 1135ff. and closes with comments on odor and indigestion caused by these plants.

    2. Graphical Abstract (Angew. Chem. Int. Ed. Engl. 9/1992)

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199211012

  1. Reviews

    1. Top of page
    2. Reviews
    3. Highlights
    4. Communications
    5. Book Reviews
    1. Synthetic Approaches toward Molecular and Polymeric Carbon Allotropes (pages 1101–1123)

      Professor Dr. François Diederich and Dr. Yves Rubin

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199211013

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      All-carbon rods, rings, spheres, and networks are certainly worthwhile goals for research when one considers the important roles of graphite and diamond in technology, and the fascinating properties of C60 and the higher fullerenes. These targets are significantly closer thanks to the syntheses of protected polyynes and cyclopolyynes, the precursors of molecules like 1. Compounds such as tetraethynylethene may serve as building blocks for novel carbon networks. The deliberate synthesis of fullerenes from smaller units remains a challenge.

    2. Flexible Molecules with Defined Shape—Conformational Design (pages 1124–1134)

      Prof. Dr. Reinhard W. Hoffmann

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199211241

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      For only a fraction of a second is the standard perception of molecular shape valid. As a rule molecules are constantly changing conformations—completely flexible molecules as well as those that exist only in specific conformations. Preferred conformations of the main chain can be stabilized by additional hydrogen bonds, as is observed in the structure of the antibiotic, rifamycin S (right, accentuated region of the molecule). The principles that define the shape of these molecules are important, for instance, in the design of biologically active compounds.

    3. The Organosulfur Chemistry of the Genus Allium – Implications for the Organic Chemistry of Sulfur (pages 1135–1178)

      Professor Eric Block

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199211351

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      Garlic and onion, the best known representatives of the Allium genus form the basis of this review on organosulfur compounds. It covers the biosynthesis of the S-alk(en)yl-L-cysteine-S-oxides, the precursors of the compounds responsible for flavor and odor, the enzymatic transformations that occur when the bulbs are crushed, and the elucidation of structures and reaction sequences, as well as the physiological effects caused by the plants' chemical components. Two of the many interesting compounds are singled out here: the lacrimatory factor in onion (1) and the antithrombotic agent, Ajoen (2), in garlic.

  2. Highlights

    1. Top of page
    2. Reviews
    3. Highlights
    4. Communications
    5. Book Reviews
    1. meso Epoxides in Asymmetric Synthesis: Enantioselective Opening by Nucleophiles in the Presence of Chiral Lewis Acids (pages 1179–1180)

      Dr. Ian Paterson and Dr. David J. Berrisford

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199211791

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      The metal center coordinates to the epoxide oxygen atom, and the chiral ligand environment enables a nucleophile to discriminate between the formally enantiotopic carbon–oxygen bonds. The method developed by W. A. Nugent functions along this principle: the reaction of a range of meso epoxides with tri-alkylsilyl azides can be catalyzed by a new chiral Lewis acid derived from zirconium and gives β-azido alcohols in very good enantiomeric excesses. Nu = N3, R1R2 = CH3, (CH2)4, etc.

    2. “Non-Coordinating” Anions: Underestimated Ligands (pages 1181–1182)

      Dr. Manfred Bochmann

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199211811

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      Interactions between tetraarylborates and co-ordinatively unsaturated cationic metal fragments have apparently received little attention till now. However, model complexes for Ziegler–Natta polymerization show that such cation–anion interactions influence the catalytic activity of these systems. Using as example the Nb complex 1, Pampaloni et al. (p. 1235 ff.) have shown that BPhmath image can in fact coordinate to metals as a chelating ligand through two η6 interactions—not only as a simple counterion or a η2-, η3-, or η6-coordinating ligand.

    3. Enantioselective Rhodium(II) Catalysts (pages 1183–1185)

      Prof. Dr. Henri Brunner

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199211831

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      Dimeric rhodium(II) compounds of the type [Rh2(OAc)4] are valuable catalysts for carbene reactions, for example for the formation of cyclopropanes from olefins and diazo compounds. As yet no catalyst can compete with [Rh2((5S)-mepy)4] (1, mepy is the methyl ester of the ([BOND])-(S)-pyrrolidinone-5-carboxylic acid deprotonated at the N atom), a new enantioselective catalyst for reactions such as the cyclopropenation of acetylenes with diazo compounds and for the formation of five-membered rings in intramolecular CH insertions. (For two of the ligands in 1 only the ligating atoms are drawn.)

    4. New Impetus for Inorganic Host-Guest Chemistry (pages 1185–1188)

      Dr. Hans Reuter

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199211851

      Already in 1826 Berzelius described (NH4)3[(PO4)Mo12O36]. Its anion consists of a shell of twelve MoO6 octahedrons surrounding a P atom, but can also be described as a central phosphate ion whose O atoms form part of the shell. Related to this ancient chemistry are more recent findings in inorganic supramolecular chemistry, which include results as diverse as the characterization of Cd(CN)2 · neopentane, in which the host Cd(CN)2 forms a network structure trapping neopentane within its cavities in an ordered fashion, and the binding of a NH4Cl dimer in a giant anionic cage, described by A. Müller et al. in this issue (see p. 1192).

  3. Communications

    1. Top of page
    2. Reviews
    3. Highlights
    4. Communications
    5. Book Reviews
    1. Selective Oxidation of Methane to CO and H2 over Ni/MgO at Low Temperatures (pages 1189–1190)

      Dr. Vasant R. Choudhary, Ajit S. Mammon and Dr. Subhash D. Sansare

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199211891

      Very active, selective, and efficient—a Ni/MgO catalyst converts methane at relatively low temperatures (300–700 °C) to H2 and CO in the molar ratio 2:1. The high activity of the catalyst makes it possible to operate at high space velocities (low contact times) and therefore in the region of kinetic control for the selectivity.

    2. trans-2-tert-Butylcyclohexanol, a Simple Selectively Optimized Cyclohexanol Auxiliary (pages 1190–1192)

      Dipl.-Chem. Peter Esser, Dr. Helmut Buschmann, Markus Meyer-Stork and Prof. Dr. Hans-Dieter Scharf

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199211901

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      An economical auxiliary comparable to 8-phenylmenthol, trans-2-tert-butylcyclohexanol (1) was derived as a “structurally minimized” cyclohexanol with an optimized induction potential by application of the isoinversion principle and the structure–selectivity relationship of the cyclohexanol auxiliaries. A simple preparation of both enantiomers of 1 is possible on a large scale by the enzymatic saponification of a technical-grade product.

    3. A Novel Host/Guest System with a Nanometer Large Cavity for Anions and Cations: [2NHmath image, 2Cl ⊂ V14O22(OH)4(H2O)2-(C6H5PO3)8]6− (pages 1192–1195)

      Prof. Dr. Achim Müller, Dipl.-Chem. Kai Hovemeier and Dipl.-Chem. Ralf Rohlfing

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199211921

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      A polytopic host for several cations and anions or cation/anion aggregates was previously unknown. The anion of the title (structure depicted on the right) is a host/guest system in which the “host”—the shell—consists of electrophilic and nucleophilic components. The cation/anion aggregate (NH4)2Cl2, a section of the NH4Cl ion lattice, is incorporated as “guest”.

    4. The Thermal Conversion of Poly[(silylene)-diacetylene] Metal Oxide Composites: A New Approach to β-SiC[BOND]MC Ceramics (pages 1195–1197)

      Prof. Robert Corriu, Philippe Gerbier, Prof. Christian Guérin and Dr. Bernard Henner

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199211951

      Cross-linking of 1, formation of a SiC network, and reduction of the encapsulated TiO2 particles are the three steps in the reaction of poly[(dimethylsilylene)diacetylene] (1) and TiO2 which produces SiC[BOND]TiC ceramics [Eq. (a)]. The reduction of the metal oxide in this case is possible at much lower temperatures than with carbon alone. This method can be applied to a number of metal oxides, and also B2O3. The ceramic's composition can be modulated by variation of the polymer.

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    5. (Organoarsonato)polyoxovanadium Clusters: Properties and Structures of the VV Cluster [V10O24(O3AsC6H4-4-NH2)3]4− and the VIV/VVCluster [H2{V6O10(O3AsC6H5)6}]2− (pages 1197–1200)

      Dr. M. Ishaque Khan, Yuanda Chang, Dr. Qin Chen, Prof. Hakon Hope, Sean Parking, Dr. D. P. Goshorn and Prof. Jon Zubieta

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199211971

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      Three {V3O13} units linked to form a ring that encloses the central V atom are found in the VV title compound. The VIV/VV cluster consists of a layered structure composed of three {V2As2O4} rings. These are further examples of the exotic structures which are par for polyoxometalates. They show the profound influence that even a subtle change in the organic ligand can exert on the structure. The structure of the VV compound is shown on the right. • = V.

    6. Novel Polyether Copolymers Consisting of Linear and Dendritic Blocks (pages 1200–1202)

      Dr. Ivan Gitsov, Karen L. Wooley and Prof. Jean M. J. Fréchet

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212001

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      The quantitative end-capping of polyethylene glycols with bromine-substituted, dendritic, aromatic polyethers 1 produces amphiphilic block copolymers. In solvents in which both blocks are only slightly soluble or in which only one block is soluble, micelles form. Depending on the solvent, they can alter their size and shape.

    7. Indigoid para-Quinodimethanes (pages 1202–1205)

      Prof. Rudolf Gompper, Dipl.-Chem. Robert Kellner and Dr. Kurt Polborn

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212021

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      Indigoid compounds which absorb light with as long a wavelength as possible are an attractive synthetic goal, since they are potential materials for optical data storage. In this report the synthesis of homologues of indigoid compounds with para-quinodimethane units are described; compounds like 1 absorb at wavelengths considerably longer than those of the related vinylogues.

    8. [Lithium Piperidide–Piperidine]4: Crystal Structure of an Oligomeric 1:1 Lithium Amide–Amine Mixed Complex, an Intermediate in the N-Lithiation of Amines (pages 1205–1207)

      Prof. Dr. Gernot Boche, Ira Langlotz, Michael Marsch, Dr. Klaus Harms and Prof. Dr. Norma E. S. Nudelman

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212051

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      A model for the mechanism of formation of ladder structures for lithium amides is provided by the title compound 1, the first oligomeric mixed complex of a lithium amide with an amine (structure depicted to the right, where one piperidine ligand has been omitted from each of Li1 and Li2). The structure in the solid state is in accord with results of calculations on similar 1:1 complexes as well as with 13C NMR studies in solution. Reactions of lithium piperidide with CO in the presence of piperidine also suggest that such complexes are reactive intermediates.

    9. Interactions Between Acyclic and Cyclic Peralkylammonium Compounds and DNA (pages 1207–1208)

      Prof. Dr. Hans-Jörg Schneider and Dipl.-Chem. Thomas Blatter

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212071

      Increments of 5 ± 1 kJmol−1 per salt bridge satisfactorily yield the energy of ionic interactions between polyamines and calf thymus DNA. This value lies in the same range as those of numerous inorganic and organic ion pairs. Peralkylated polyamines have almost the same affinity for DNA as protonated polyamines; hydrogen bonds thus have little effect on the binding. Relatively rigid azoniacyclophanes sometimes have a higher affinity although the arene units are not intercalated.

    10. A Novel Six-Center Deprotonation–Lithiation Reaction Mechanism Supported by the X-Ray Structure Analysis of a Lithium Carbazolide (pages 1209–1210)

      Dipl.-Chem. Christoph Lambert, Dipl.-Chem. Frank Hampel and Prof. Dr. Paul von Raguė Schleyer

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212091

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      The metalation of an amine by a lithium alkoxide in protic medium possibly proceeds by the two-step six-center deprotonation–lithiation mechanism sketched below. Evidence for this reaction pathway comes from the X-ray structure analysis of [Li(tBuOH)2(thf)2][cb] (Hcb = carbazole), which exhibits a disordered proton between a carbazole N atom and an O atom of a tBuOH molecule. This compound thus provides a model for the precurser complex 1 and the product complex 2 of the deprotonation. The subsequent rearrangement of 2 to 3 could occur stepwise rather than by a converted mechanism.

    11. Dynamic Proton Exchange in the Hydrogen Dihydroxide Ion H3Omath image of the Hydroxosodalite Hydrate [Na4(H3O2)]2[SiAlO4]6: 1H MAS NMR Spectroscopic Evidence (pages 1210–1212)

      Dr. Günter Engelhardt, Dipl.-Chem. Peter Sieger and Prof. Dr. Jürgen Felsche

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212101

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      The activation energy is only about 40 kJ mol−1 for the dynamic exchange between the central and the terminal H atoms in the H3Omath image ion. This was shown by solid-state NMR spectroscopy on the title compound, in which the H3Omath image ions occur isolated in sodalite cages. Since the splitting of H3Omath image into H2O and OH requires an energy of approximately 100 kJ mol−1, such a pathway for the exchange is less likely than the mechanism depicted in (a).

    12. Chelate Complexes of Tripodal, Aliphatic Triisocyanide Ligands (pages 1212–1214)

      Prof. Dr. F. Ekkehardt Hahn and Dipl.-Chem. Matthias Tamm

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212121

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      The distinct low-field shift of the NMR resonance for the central methine proton of the ligand, which penetrates the deshielded region of the anisotropic sphere of the three N[TRIPLE BOND]C bonds of the complexes 1 (M = Cr, W), suggested the assignment of the in configuration for this complex. The X-ray structure analysis confirmed the assignment. The synthesis of 1 shows that aliphatic isocyanides with few framework atoms can also form chelate complexes with transition metals.

    13. The Electrochemical Oxidation of [CoII(salen)] in Solvent Mixtures—An Example of a Ladder Scheme with Coupled Electron-Transfer and Solvent-Exchange Reactions (pages 1215–1217)

      Dipl.-Chem. Emerich Eichhorn, Prof. Dr. Anton Rieker and Priv.-Doz Dr. Bernd Speiser

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212151

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      Every electron-transfer reaction of a complex process on the electrode, in which individual electron-transfer and chemical reaction steps are coupled in such a way that a cyclic sequence results, was observed separately for the first time in the electrochemical investigation of the CoII complex 1. This is crucial for the detailed description of the catalytic activity of 1, because, as shown here, the redox reactions are strongly dependent on solvent.

    14. The Reaction of Tetramesityldisilene with As4: Synthesis and Structure of a Novel Arsenic–Silicon Tricyclic Ring System (pages 1217–1218)

      Dr. Robin P. Tan, Nadia M. Comerlato, Dr. Douglas R. Powell and Prof. Robert West

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212171

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      An As2Si2, an AsSi2, and an As3 ring are all found in the tricyclic compound 1, which is accessible from Mes2Si[DOUBLE BOND]SiMes2 (Mes = 2,4,6-trimethylphenyl) and As4. A second product, a diarsadisilabicyclo[1.1.0]butane derivative with a butterfly structure, can also be obtained by heating 1.

    15. Matrix Isolation of Diisocyanogen CNNC (pages 1218–1220)

      Prof. Günther Maier, Dr. Hans Peter Reisenauer, Dipl.-Chem. Jürgen Eckwert, Dr. Claudia Sierakowski and Dipl.-Chem. Thomas Stumpf

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212181

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      Four years ago diisocyanogen 1 was believed to have been isolated. The substance later proved to be the isomer isocyanogen. A successful generation of 1 by microwave discharge in an atmosphere of acetylene and nitrogen is reported here. Both molecules are cleaved into single C and N atoms and these recombine to form 1 among other products.

    16. The Tandem Sakurai–Carbonyl–Ene Reaction: A New and Highly Stereoselective Sequential Transformation and Its Use for the Synthesis of Steroid Derivatives (pages 1221–1222)

      Prof. Dr. Lutz F. Tietze and Dr. Matthias Rischer

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212211

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      In only a few steps, the synthesis of the BCD part of methyl-substituted steroids such as 1 is possible from the aldehyde 4. The crucial step of the synthesis is the tandem reaction of 2 to 3 named in the title, which is mediated by Me3SiOTf or EtAlCl2—with different stereoselectivities.

    17. Indirect 113Cd,14N Spin-Spin Coupling Constants as a Structural Probe of Solid Cadmium Thiocyanate Complexes (pages 1222–1224)

      Dr. Klaus Eichele and Prof. Dr. Roderick E. Wasylishen

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212221

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      The number of the N-bound thiocyanato ligands is only a part of the wealth of information that can be extracted from the 113CdNMR spectrum of solid 1. For instance, the splitting in the well-resolved multiplet signals (see right), which results from direct and indirect 113Cd[BOND]14N coupling appears to be a measure of the Cd[BOND]N distances. In contrast, NMR studies of metal thiocyanates in solution are rather uninforma-tive.

    18. The Structure and Stability Trends of Fluoro(methyl)plumbanes (pages 1224–1226)

      Martin Kaupp and Prof. Dr. Paul von R. Schleyer

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212241

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      Dramatic deviations from ideal tetrahedral geometry and destabilization despite contracted bond lengths—these features of the series of fluoro(methyl)plumbanes are revealed by ab initio pseudopotential calculations. In Me2PbF2 (1) (calculated structure depicted), the C-Pb-C angle is almost 135°! The introduction of fluorine substituents thus has markedly different effects on plumbanes than on alkanes and silanes.

    19. [(η5-Cp)2Sn(μ-η5-Cp)Na · PMDETA], a Compound with a Trigonal-Planar “Paddle Wheel” Triorganostannate Ion (pages 1226–1227)

      Matthew G. Davidson, Dr. Dietmar Stalke and Dr. Dominic S. Wright

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212261

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      An organotin(II) anion with three η5-Cp ligands and a Sn atom in a trigonal-planar environment are found in the title compound 1 (see diagram), obtained from the reaction of CpNa, [Cp2Sn], and PMDETA (mol ratio 1:1:1). This [Cp3Sn] ion is linked to the Na+ ion by a μ-η5-Cp bridge. Compound 1 is a polymeric array in the solid state due to intermolecular C(H) … Na interactions. PMDETA = (Me2NCH2CH2)2NMe.

    20. Opening of an Aza-closo-dodecaborane to an Aza-nido-dodecaborate (pages 1227–1229)

      Franc Meyer, Dr. Jens Müller, Prof. Peter Paetzold and Priv.-Doz. Roland Boese

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212271

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      A nido derivative of the hypothetical tridecaborate closo-B13Hmath image is a fitting description of the anion [MeNB11H11(OMe)] (1) which is prepared from the reaction of the icosahedral closo-NB11H12 with methyl triflate and methanol. Upon addition of MeOH to the intermediate MeNB11H11 a boron atom is not cleaved, and the nido derivative is not formed, as is the case for C2B10H12, which is isoelectronic with NB11H12.

    21. Chain Elongation of Thiodipeptides with Proteases (pages 1229–1230)

      Dr. Carlo Unverzagt, Dipl.-Chem. Armin Geyer and Prof. Dr. Horst Kessler

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212291

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      The C-terminal elongation of thiopeptides 1 is not possible by chemical activation—thiazolones 2 are the major products. Now with proteases as catalysts, 1 has been converted without racemization into oligopeptides 3 with thioamide groups in defined positions. All = allyl.

    22. 2,4-Didehydrophenol—First Proof of a meta-Aryne by IR Spectroscopy (pages 1230–1233)

      Dipl.-Chem. Götz Bucher, Prof. Wolfram Sander, Prof. Elfi Kraka and Prof. Dieter Cremer

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212301

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      Photochemical decarboxylation of carbene 1 in an argon matrix at 10 K provides 2,4-didehydrophenol (2). This m-aryne was characterized by IR and UV/VIS spectroscopy; the experimental and the calculated (GVB/6-31G(d,p)) IR spectra are in good agreement. These findings suggest that 2 has a diradical, mono-cyclic structure; the isomeric bicyclic structure 3 can be ruled out.

    23. Hydride Transfer by Hydrido Transition-Metal Complexes. Ionic Hydrogenation of Aldehydes and Ketones, and Structural Characterization of an Alcohol Complex (pages 1233–1235)

      Dr. Jeong-Sup Song, Dr. David J. Szalda, Dr. R. Morris Bullock, Dr. Christophe J. C. Lawrie, Dr. Mikhail A. Rodkin and Prof. Jack R. Norton

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212331

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      The rate-determining step in the hydrogenation of aldehydes or ketones by hydrido complexes and acids appears to be the hydride transfer from the complex to the protonated carbonyl compound. The resulting alcohol is initially bound as ligand, as confirmed by an X-ray crystal structure analysis of the alcohol complex 1.

    24. [Nb{B(η6-C6H5)2(C6H5)2}(η2-H3CC2CH3)]: the First Compound with Bent Tetraphenylborate as 12-Electron Donor Ligand (pages 1235–1236)

      Prof. Fausto Calderazzo, Dr. Ulli Englert, Dr. Guido Pampaloni and Dr. Lucia Rocchi

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212351

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      The “counterion” BPhmath image functions a sandwich ligand in the niobium(I) complex 1. This is confirmed by the X-ray structure analysis of 1a. The BPhmath image complexes 1 are the first in which two of the four phenyl rings of the tetraphenylborate bind to one metal center. Such complexes could be important as model compounds for catalytic processes.

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    25. Alkyne(carbene) Complexes: Stabilization of an Intermediate of Carbene Annelation (pages 1236–1238)

      Prof. Dr. Karl Heinz Dötz, Dr. Thomas Schäfer, Friedrich Kroll and Klaus Harms

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212361

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      The coupling of alkyne and carbene ligands can be suppressed if the two ligands are bound by a rigid C2 bridge, as in 1, M = Mo, W. The chromium compound 1, M = Cr, is more reactive than its higher homologues: it undergoes—possibly via a dinuclear intermediate—a double alkyne insertion into the metal-carbene bond, which is followed by a “carbene dimerization” to give the chrysene framework.

    26. Homodiboriranides: The Simplest Negatively Charged Homoaromatic Compounds (pages 1238–1240)

      Peter Wiliershausen, Claudia Kybart, Nicolaos Stamatis, Prof. Dr. Werner Massa, Dr. Michael Bühl, Prof. Dr. Paul von Ragué Schleyer and Prof. Dr. Armin Berndt

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212381

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      Deshielding of the tricoordinated C atom, a ring inversion barrier of approximately 8 kcal mol−1 (Olah et al. determined a value of 8.4 kcal mol−1 for the parent compound of 1), a shorter B[BOND]B distance, and folding as in 1 and 2 (substituents here not defined) prove that 3 is homoaromatic. Very similar data were obtained for the parent compound C2B2Hmath image by ab initio calculations. Dur = 2,3,5,6-Me4C6H.

    27. Novel Cross-Conjugated Compounds Derived from Tetraethynylethene (pages 1240–1242)

      Armen M. Boldi, John Anthony, Carolyn B. Knobler and Prof. Dr. François Diederich

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212401

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      The oxidative coupling of a tetraethynylethene derivative with a single free ethynyl function afforded a silyl-protected derivative la, which was characterized by an X-ray structure analysis. It was protodesilylated to the first C20H6 isomer 1b. Evidence of the expanded π-electron delocalization in the new cross-conjugated system comes from UV/VIS spectroscopy.

    28. Photoswitchable Association of an Azobenzne–Bipyridinium Diad to Eosin: Photostimulated “On-Off” Guest Binding (pages 1243–1244)

      Prof. Dr. Itamar Willner, Sharon Marx and Yoav Eichen

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212431

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      The reversible photoinduced cis–trans isomerization of the azobenzene unit in 1, together with the distinctly different association constants of the cis and trans isomers for the binding of 1 to eosin Y (2, K = 38 000 and 3000 M−1 1, respectively) can be utilized to construct a molecular switch for the formation and dissociation of the complex between 1 and 2 that is light-controlled. Such photo-switchable units are important in information storage systems and signal processing on the molecular level.

    29. Solid-State Columns Made from Twisted, Self-Complementary Terpyridine Units (pages 1244–1246)

      Chia-Yu Huang, Vince Lynch and Prof. Dr. Eric V. Anslyn

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212441

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      Hydrogen bonds can create order, even a type of order that may be used in the development of new materials. This was possible with the terpyridine 1, which is conformationally hindered by its two trimethylene bridges. In the solid state it has an α-helical structure in which the CO2Et groups project outwards at regular intervals.

    30. Pheromones of Marine Brown Algae; A New Branch of the Eicosanoid Metabolism (pages 1246–1248)

      Dr. Klemens Stratmann, Prof. Wilhelm Boland and Prof. Dieter G. Müller

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212461

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      The pool of polyunsaturated eicosanoids is used by female gametes of marine brown algae in the biosynthesis of their pheromones ectocarpene (A) and dictyotene (B). Higher plants synthesize these compounds from multiply unsatu-rated C12 fatty acids.

    31. Separation of Overlapping Multiplets in Two-Dimensional NMR Spectra by Selective “Injection” of Magnetization (pages 1248–1251)

      Catherine Zwahlen, Sébastien J. F. Vincent and Prof. Dr. Geoffrey Bodenhausen

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212481

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      A “poor man's” method is how the authors refer to their procedure to separate overlapping cross-peak multiplets in two-dimensional NMR spectra. A homonuclear Hartmann–Hahn coherence transfer precedes a soft-COSY pulse sequence, which enables, for example, the selection of the multiplet of the trans isomer of 1, R = CO2Et, R′ = Ph, from the superimposed multiplet of cis and trans isomers (see diagram on the right).

    32. Se2NCl3 and [Se2NCl2]+ [GaCl4], Chloride Nitrides of Trivalent Selenium (pages 1251–1253)

      Dr. René Wollert, Dipl.-Chem. Antje Höllwarth, Prof. Dr. Gernot Frenking, Prof. Dr. Dieter Fenske, Dr. Helmut Goesmann and Prof. Dr. Kurt Dehnicke

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212511

      Thumbnail image of graphical abstract

      The planar structure with C2v symmetry resembles a compass in the case of Se2NCl3 (1), a chlorine nitride, which is readily soluble and stable, but at the same time very reactive. The chlorine atom in 1 bridging the selenium atoms can be readily removed with GaCl3 to form [Se2NCl2][GaCl4] in which the cation is U-shaped. Both compounds have a diamagnetic singlet ground state.

    33. Pyridine-2-thiolato Complexes of VII, VIII, and VIV with Unusual Structural Features (pages 1253–1255)

      Dr. John G. Reynolds, Dr. Shawn C. Sendlinger, Ann M. Murray, Dr. John C. Huffman and Prof. George Christou

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212531

      Thumbnail image of graphical abstract

      One of the extremely rare thiolatovanadium(II) complexes, [V(tmeda)(pyt)2] (1) is formed in the reaction of sodium pyridine-2-thiolate [Na(pyt)] with [VCl2(tmeda)2]. The octahedral structure of 1 is distorted because of the small bite angle of the pyt ligand. In both dinuclear complexes [Na(thf)2V(pyt)4] and [V2O2(pyt)4] (2) the pyt ligand has an unusual μ-η12 bonding mode, but in 2 the pyt bridge is unsymmetric.

    34. Aromatic Boron Heterocycles: The Generation of 1 H-Borepin and the Structure of Tricarbonyl(1-phenylborepin)molybdenum (pages 1255–1258)

      Prof. Dr. Arthur J. Ashe III, Dr. Jeff W. Kampf, Prof. Dr. Yasuhiro Nakadaira and Jennifer M. Pace

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212551

      Thumbnail image of graphical abstract

      A seven-membered aromatic ring system is attributed to 1H-borepin (1) based on NMR data. This long-sought parent compound of the borepins can be generated from the related chloroborepin and tributyltin hydride by Cl[BOND]H exchange. The borepin ring can function as an η7 ligand, as the structural data of 2 substantiate.

    35. Stepwise Stacking of Three Paramagnetic Metallocene Units: [CpNiCp(SiMe2)2CpCrCp(SiMe2)2CpNiCp] (pages 1258–1260)

      Pierre Bergerat, Dr. Janet Blümel, Dr. Monika Fritz, Dr. Johann Hiermeier, Dipl.-Chem. Peter Hudeczek, Olivier Kahn and Prof. Dr. Frank H. Köhler

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212581

      Thumbnail image of graphical abstract

      For molecular magnetic materials, 1 is the prototype of a stepped stack in which the different paramagnetic building blocks are cova-lently linked. Such a structure leads to antiferromagnetism. 1 can be considered to be a fragment of a polymer, but the experimental advantages of uniform composition and solubility that it offers allow examination by cyclovoltammetry and NMR spectroscopy.

    36. Chelate Stabilization of a Monomeric Lithium Tellurolate (pages 1260–1261)

      Dipl.-Chem. Heinz Gornitzka, Dipl.-Chem. Susanne Besser, Dr. Regine Herbst-Irmer, Dipl.-Chem. Ulrike Kilimann and Priv.-Doz Dr. Frank T. Edelmann

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212601

      Thumbnail image of graphical abstract

      Isolable, well-defined alkali metal tellurolates—of interest for organic synthesis as well as for the production of transition metal tellurides—are only known with bulky organic groups. By lithiation and chalcogenation, the tellurolate 3 has now been obtained from 1 in quantitative yield via the intermediate 2. Subsequent reactions demonstrate the usefulness of such tellurolates.

    37. 1,3-Dimetallabenzene Derivatives of Niobium or Tantalum (pages 1261–1263)

      Robert D. Profilet, Dr. Phillip E. Fanwick and Prof. Ian P. Rothwell

      Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.199212611

      Thumbnail image of graphical abstract

      Insertion of an alkyne into a metal–μ-alkylidyne bond leads to the six-membered dimetal-lacycles 1 and 2 (M = Nb, Ta). Spectroscopic and structural data support their formulation as dimetallabenzene derivatives. cbH = Carbazole.

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