Angewandte Chemie International Edition in English

Cover image for Vol. 32 Issue 3

March 1993

Volume 32, Issue 3

Pages 313–456

Currently known as: Angewandte Chemie International Edition

    1. Cover Picture (Angew. Chem. Int. Ed. Engl. 3/1993)

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199303131

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      The cover picture shows the space-filling model of a tetraethynyltetrahydro[12] annulene protected fourfold by Si(iPr3)3. Its core is a planar framework of 20 carbon atoms, as the superimposed structural formula clearly indicates. This representation is based on the X-ray crystallographic data of the compound, which is astonishingly stable despite the considerable strain of the central twelve-membered ring. Its electronic absorption spectrum indicates the presence of an antiaromatic [4n] π-electron perimeter, and its purple solutions look remarkably similar to the solutions of C60. More about this compound as well as the analogously constructed [18]annulene, a very promising starting material for new planar hydrocarbon networks, are reported by F. Diederich et al. on pages 406 ff. Also A. de Meijere et al. show with their synthesis of the perspirocyclopropanated [3]rotane (p. 401 ff) a route to new carbon modifications—since the C60 boom a topical field of research.

  1. Reviews

    1. Top of page
    2. Reviews
    3. Highlights
    4. Communications
    5. Book Reviews
    1. Defect Chemistry: Composition, Transport, and Reactions in the Solid State; Part I: Thermodynamics (pages 313–335)

      Prof. Dr. Joachim Maier

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199303133

      The deviations from ideal structure, the point defects, are the basis of defect chemistry. This field enables the description of the chemistry in the solid state in an analogous way to the well-known chemistry in the solvent water, and the interpretation of a whole range of important phenomena in such varied fields as catalysis, battery research, corrosion, sensors, and electronics in a unified manner; this is also of immense significance for an abundance of applications. In the first part of this review the emphasis is placed on the equilibrium thermodynamics of defects; the second part, which will appear in the next issue, is concerned primarily with the kinetic aspects.

    2. Carbohydrates as Chiral Auxiliaries in Stereoselective Synthesis. New Synthetic Methods (90) (pages 336–358)

      Prof. Dr. Horst Kunz and Dr. Karola Rück

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199303361

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      With too many functional groups and too many chiral centers, carbohydrates were considered too complex to serve as chiral auxiliaries in stereoselective synthesis. Recent work has shown, however, that the steric, stereoelectronic, and complexation properties of these cheap, regenerable natural products can be employed in a variety of reactions. One example is the Diels–Alder reaction of cyclopentadiene with acrylate bound to a carbohydrate matrix (1) to yield adduct 2.

    3. Dynamic Solvent Effects on Electron-Transfer Reactions (pages 359–377)

      Dr. Hans Heitele

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199303591

      What effects do the solvent dynamics have on the course of reactions? Attempts at answering this question for the test case of electron-transfer reactions are described here. The progress in theory as well as improvements in experimental methods made valuable contributions to our knowledge and prepared the way for the first insights into the molecular implications of reaction coordinates, potential energy surfaces, and the motion on them for reactions in the condensed phase. The problems encountered are, in particular, the correct interpretation of the many degrees of freedom that can influence the reactions.

  2. Highlights

    1. Top of page
    2. Reviews
    3. Highlights
    4. Communications
    5. Book Reviews
    1. Nitric Oxide, NO, an Intercellular Messenger (pages 378–380)

      Prof. Dr. Hans-Joachim Galla

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199303781

      Physiology, biochemistry, and analytical chemistry in the last few years have extensively studied NO, a colorless gas of relatively high stability, which, however, in physiological media has a lifetime of only a few seconds. According to new findings NO, which is formed, so to speak, from arginine in a short cut in the urea cycle, plays a very important role, for example, in the control of processes in the brain, of peristalsis in the intestine, and of erectile organs. Recently a specific sensor for the measurement of the NO content in blood vessels was described.

    2. Heterogeneous Catalysis—Still Magic or Already Science? (pages 381–383)

      Prof. Dr. Robert Schlögl

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199303811

      Heterogeneous catalysis is still regarded as black magic, since the development of practical catalysts is dependent on empirical facts. Research in this area has been restricted by the complexity of solid catalyst systems, the many interrelated factors that determine the reaction mechanism, and the fact that these catalytic processes cannot be analyzed in situ. This highlight describes scientific approaches that could lead catalyst research out of its infancy, but also warns against misinterpretion of new results.

  3. Communications

    1. Top of page
    2. Reviews
    3. Highlights
    4. Communications
    5. Book Reviews
    1. BNC Isosteres of Cyclopropane and a Borylated Diazoester from Diazo Compounds and (Dimethylamino)bis(trifluoromethyl)borane (pages 384–385)

      Dipl.-Chem. Andreas Ansorge, Prof. Dr. David J. Brauer, Prof. Dr. Hans Bürger, Dipl.-Chem. Thomas Hagen and Dr. Gottfried Pawelke

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199303841

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      By “cyclopropanation” with diazo compounds, the first azoniaboratacyclopropane derivatives 2–4 are formed from (CF3)2B[DOUBLE BOND]NMe2 (1); in these B and N have the coordination number 4. As a result of the CF3 groups 1 reacts like an alkene and not like other aminoboranes. The three ring atoms of the benzyl(trimethylsilyl) derivative 4 form an almost equilateral triangle with the distances BN 1.560(5), BC 1.595(5), and CN 1.567(4)Å.

    2. Stereochemistry of Norbornyl [RIGHTWARDS ARROW] Norpinyl Rearrangements (pages 385–387)

      Prof. Dr. Wolfgang Kirmse and Dipl.-Chem. Dirk Minkner

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199303851

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      Bridged, chiral (A) and open, achiral intermediates (B) can occur during the cationic norbornyl [RIGHTWARDS ARROW] norpinyl rearrangement. As stereochemical results show, CN and CF3 substituents favor A, double bonds (allyl resonance) in contrast favor B. Combination of these structural elements allows the proof of both types of carbocations.

    3. Synthesis, Properties, and Structure of —A New Type of PtII Metallacyclopentane Complexes (pages 387–388)

      Prof. Dr. Hans-Otto Fröhlich, Dipl.-Chem. Ralf Wyrwa and Dr. Helmar Görls

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199303871

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      The highly symmetrical compound 1 decomposes only at 249 °C despite the β-hydrogen atoms of the two butane-1,4-diyl groups at the platinum(II) center. Compound 1 is formed from the reaction of [(1,5-cod)PtCl2] (cod = 1,5-cyclooctadiene) with 1,4-Li2C4H8 and N, N, N′, N′-tetramethylethylenediamine.

    4. An Al[BOND]Al One-Electron π Bond (pages 388–390)

      Dr. Christian Pluta, Priv.-Doz. Dr. Klaus-R. Pörschke, Prof. Dr. Carl Krüger and Dr. Knut Hildenbrand

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199303881

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      Not a reductive rupture, but a strengthening of the Al[BOND]Al bond is the result of the reduction of the dialane 1 with lithium. The salt isolated after addition of TMEDA contains the radical anion of 1, in which, as results of an X-ray structural analysis show, the Al[BOND]C bonds are distinctly longer (+0.06 Å) and the Al[BOND]Al bond considerably shorter (−0.13 Å) than in 1 itself. These findings are in accord with results of MO calculations, which indicate a stabilization of the Al[BOND]Al bond by the additional electron.

    5. Superexchange through Orthogonal Magnetic Orbitals in π-Type Organic Triradicals: Quartet Ground State in Ga(3,5-dtbsq)3 (pages 391–392)

      David M. Adams, Prof. Andrea Dei, Prof. Dr. David N. Hendrickson and Prof. Dr. Arnold L. Rheingold

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199303911

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      The central gallium(III) ion propagates the pairwise ferromagnetic exchange interactions between the S = 1/2 ligands in the title complex 1, which lead to an S = 3/2 ground state, as magnetic susceptibility measurements of 1 have shown. These types of complexes are important for the design of molecular ferromagnets. 3,5-dtbsq = 3.5-di-tert-butyl-1,2-semiquinone anion; the tBu substituents are omitted in the structure shown on the right.

    6. Synthesis and Structure of a Trimeric Cyclometalated Coordination Compound with a Hydrophobic Cavity (pages 392–394)

      Dr. Stéphane Rüttmann, Dr. Alan F. Williams and Dr. Gérald Bernardinelli

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199303921

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      A molecular tricorn is the best description of complex 2, which arises from ligand 1 and palladium(II) acetate by cyclopalladation and trimerization. Since 2 has a hydrophobic cavity, it may serve as a host for neutral guest molecules, such as acetonitrile. • = Pd.

    7. Stereodivergent Enantioselective Synthesis by Exploiting Unusually Large Kinetic H/D Isotope Effects on Deprotonation (pages 394–396)

      Prof. Dieter Hoppe, Mario Paetow and Folker Hintze

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199303941

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      On deprotonation of chiral deuterated carbamates like the reaction of (S)-1 with sec-butyllithium to form (R)-2, unusually high kinetic isotope effects kH/kD of 70 or greater are observed. These point to the participation of a quantum mechanical tunnel effect and can be exploited for enantioselective transformations based on the discrimination by the base of H and D in otherwise identical environments. The procedure is particularly suitable for highly selective syntheses of stereospecific deuterium- and tritium-labeled alcohols.

    8. Fixation and Reduction of Dinitrogen by Vanadium(II) and Vanadium(III): Synthesis and Structure of Dinitrogenmesitylvanadium Complexes (pages 396–397)

      Dr. Richard Ferguson, Dr. Euro Solari, Prof. Dr. Carlo Floriani, Prof. Dr. Angiola Chiesi-Villa and Dr. Corrado Rizzoli

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199303961

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      Two short V[BOND]N bonds and a long N[BOND]N bond, as well as a sodium atom that is situated in the cavity created by the VNNV unit and two mesityl (mes) ligands are the intriguing characteristics of the anion of complex 1. It is formed by the reduction of [V(mes)3(thf)] with Na under N2 and on protonation yields NH3 and N2H4. Two mes ligands at both V and V′ are omitted from the picture shown on the right.

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    9. Stereoselective Protonation of Boron Enolates (pages 398–399)

      Dr. Thomas Haubenreich, Prof. Dr. Siegfried Hünig and Dr. Hans-Joachim Schulz

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199303981

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      Due to the different coordinations of acetic acid and trifluoroacetic acid to the boron atom of the enolate 1, two reaction mechanisms result for the protonation of 1. The protonation with acetic acid leads to an enrichment of the (R) isomer (R)-2. while with trifluoroacetic acid (S)-2 is favored. R* = isopinocampheyl.

    10. DBU and DBN are Strong Nucleophiles: X-Ray Crystal Structures of Onio- and Dionio-Substituted Phosphanes (pages 399–401)

      Dr. Robert Reed, Dr. Régis Réau, Dr. Françoise Dahan and Dr. Guy Bertrand

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199303991

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      New light is thrown on the reactivity of the reagents DBU and DBN, which are often used in base-induced dehydrohalogenations, by their reaction with chloro- and dichlorophosphanes. They form chloride salts with onio- and dionio-substituted phosphanes as cations; that is, DBN and DBU behave as nucleophiles! After anion exchange with KPF6 these salts can be obtained in crystalline form. The dication 1, for example, was characterized by X-ray diffraction. R = (cyclo-C6H11)2N.

    11. Perspirocyclopropanated [3]Rotane—A Section of a Carbon Network Containing Spirocyclopropane Units? (pages 401–403)

      Dr. Sergei I. Kozhushkov, Prof. Dr. Armin de Meijere, Dipl.-Chem. Thomas Haumann and Priv. Doz. Dr. Roland Boese

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199304011

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      The increase in strain in branched triangulanes has hardly any influence on the bond lengths. This is shown by the comparison of the structures of twofold (1), fourfold (2), and sixfold cyclopropanated (3) [3]rotanes. In 3, which is prepared in six steps from perspirocyclopropanated bicyclopropylidene (4), the bonds of the central three-membered ring are significantly longer than in [3]rotane. In spite of its high total strain, 3 is stable up to 250 °C.

    12. Activation of the C2 Position of Purine by the Trifluoromethanesulfonate Group: Synthesis of N2-Alkylated Deoxyguanosines (pages 404–406)

      Dr. Thomas Steinbrecher, Dipl.-Chem. Christa Wameling, Prof. Dr. Franz Oesch and Dr. Albrecht Seidel

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199304041

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      The nucleophilic substitution of the OTf group in 1a, b by amines and aminoalcohols opens a new route to N2-alkylated deoxyguanosines. Starting from 1 a,b, biologically relevant N2-deoxyguanosine adducts of carcinogenic alkylating agents are obtained, for example the ultimate carcinogenic (±)-anti-dihydrodiolepoxide of benzo[a]pyrene. TBDMS = tert-butyldimethylsilyl. a: R1 = p-nitrophenylethyl, b: R1 = allyl; Tf = CF3SO2.

    13. Stable [12]- and [18]Annulenes Derived from Tetraethynylethene (pages 406–409)

      John Anthony, Prof. Francois Diederich and Dr. Carolyn B. Knobler

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199304061

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      Perethynylated dehydroannulenes are accessible by oxidative Hay coupling of a tetraethynylethene with a free cis-enediyne unit. Besides a yellow derivative with a planar, aromatic 18π-electron perimeter, compound 1 was isolated. This interesting molecule has a strained, planar antiaromatic 12-membered ring; dilute solutions of 1 are violet and resemble solutions of C60.

    14. [Mo2(CCH)4(PMe3)4], the Parent Dimetallapolyyne (pages 409–411)

      Timothy C. Stoner, Dr. Steven J. Geib and Prof. Michael D. Hopkins

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199304091

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      A π(CC)-δ(MM)-π(CC) electron framework exists in the title compound 1, the simplest complex of the type [M2(CCR)4(PMe3)4], and the first to be characterized by X-ray crystallography. This dimetallapolyyne differs from the more highly substituted derivatives in its electronic properties; however, in several instances, the properties of 1 closely parallel its nearest organic analogue, the tetraethynylethene C10H14. L = PMe3.

    15. Tetracyanohydroquinone and its Dimorpholinium Salt: Hydrogen Bonds O[BOND]H … N or O H[BOND]N to Nitrogen Bases of Different Strengths (pages 411–414)

      Prof. Dr. Hans Bock, Dipl.-Chem. Wolfgang Seitz, Dr. Zdenek Havlas and Dr. Jan W. Bats

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199304111

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      How a network of hydrogen bonds is influenced by the basicity of a proton acceptor center is demonstrated particularly clearly by the title compounds: tetracyanohydroquinone, a relatively acidic phenol, forms linear molecular strings by self-association through hydrogen bonds between OH and CN groups—provided that addition of a stronger base such as morpholine does not cause hydrogen bonds to be formed preferentially between different molecules, with concomitant hydrogen transfer (see below).

    16. “Supersilyl” Compounds (R3Si)3SiSi(SiR3)3 and (R3Si)3SiC6H4Si(SiR3)3: Structures and Properties (pages 414–416)

      Prof. Dr. Hans Bock, Dipl.-Chem. Jochen Meuret and Dr. Klaus Ruppert

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199304141

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      Remarkable properties characterize organosilicon compounds like 1 and 2: some of their structures are distorted by steric overcrowding and their first ionization energies drop as a result of additional radical cation stabilization to unexpectedly low values. In the π-radical anion of 2 considerable spin delocalization in the SiSi3 frameworks is detected by ESR/ENDOR spectroscopy.

    17. The Triplet Biradical Tris(3,5-di-tert-butyl-4-oxophenylene)methane: Crystal Structure, and Spin and Charge Distribution (pages 416–418)

      Prof. Dr. Hans Bock, Dipl.-Chem. Andreas John, Dr. Zdenek Havlas and Dr. Jan W. Bats

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199304161

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      The first structurally characterized triplet diradical, the title compound, has approximate D3 symmetry with “propeller blades” of quinoidally distorted six-membered rings twisted in the same direction (picture on the right). According to calculations the spin and charge distributions differ considerably from one another. Organic triplet diradicals are of interest for the development of molecular ferromagnets.

    18. Enantioselective Synthesis of α-Amino Acetals and α-Amino Acids by Nucleophilic 1,2-Addition to Diethoxyacetaldehyde SAMP Hydrazone (pages 418–421)

      Prof. Dr. Dieter Enders, Dr. Rudolf Funk, Dipl.-Chem. Martin Klatt, Dr. Gerhard Raabe and Dr. Eric R. Hovestreydt

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199304181

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      The nucleophilic 1,2-addition of organocerium compounds to α-SAMP/RAMP hydrazone acetals 1 is the basis of a new, highly enantioselective route to synthetically versatile α-amino acetals 2 and α-amino acids 3. R = Me, Et, nPr, iPr, nBu, tBu, Ph.

    19. Enantioselective Aldol Reactions with a Phosphoenolpyruvate Equivalent: Asymmetric Synthesis of 4-Hydroxy-2-oxocarboxylic Acid Esters (pages 421–423)

      Prof. Dr. Dieter Enders, Dr. Hubert Dyker and Dr. Gerhard Raabe

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199304211

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      A copy of a transformation in nature, the enantioselective transfer of pyruvate unit 1 to aldehydes is reported here. This new process which employs the hydrazone method allows the efficient synthesis of enantiomerically pure, benzyloxymethyl(BOM)-protected 4-hydroxy-2-oxocarboxylic acid esters (R)- and (S)-2.

    20. Diastereo- and Enantioselective Synthesis of C2-Symmetrical HIV-1 Protease Inhibitors (pages 423–425)

      Prof. Dr. Dieter Enders, Dr. Udo Jegelka and Dipl.-Chem. Barbara Dücker

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199304231

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      For AIDS treatment, highly interesting C2-symmetric HIV-1 protease inhibitors of the type 3 are available from 1 in diastereo- and enantiomerically pure form by the SAMP/RAMP-hydrazone method. Key steps are the efficient synthesis of the C2-symmetric ketones 2 and the stereospecific transformation of 1,3-diols into 1,3-diamines. The potential of the new method is demonstrated by the synthesis of the potent HIV-1 protease inhibitor A-74704.

    21. Silylamines with Pyramidal Coordination at Nitrogen (pages 425–427)

      Dr. Karin Ruhlandt-Senge, Ruth A. Bartlett, Dr. Marilyn M. Olmstead and Prof. Philip P. Power

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199304251

      The π component of the Si[BOND]N bond in silylamines has little if any influence on their structure—this was established from the X-ray structures of the silylamines 1–3. The structural analyses show that the coordination at the nitrogen centers is pyramidal rather than planar and that the Si[BOND]N distances are essentially invariant. Mes = 2,4,6-Me3C6H2, Triph = 2,4,6-Ph3C6H2.

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    22. Nucleophilic Substitution of Bis(cyclopentadienyl)-tin(II); Synthesis, Structure, and Solution Dynamics of trans-[(η3-Cp)Sn{μ2-N[DOUBLE BOND]C(NMe2)2}]2 (pages 428–429)

      Michael A. Paver, Dr. Dominic S. Wright and Dr. Dietmar Stalke

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199304281

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      Only one Cp ligand is replaced when [Cp2Sn] reacts with LiN[DOUBLE BOND](NMe2)2 to give rise to 1, the first oligomeric cyclopentadienyltin(II) complex and the first iminotin(II) complex. In THF 1 exists as a 1:1 mixture of the cis and trans isomers, in toluene only the cis isomer is observed, and in the solid state only the trans isomer is found.

    23. Facile Formation of Hexahydroporphyrin Complexes by Reduction of Octaethylisobacteriochlorinnickel(II) (pages 429–432)

      Dr. Goutam K. Lahiri and Prof. Alan M. Stolzenberg

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199304291

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      Under extremely mild conditions (room temperature) the hexahydroporphyrin 2 isomerizes to its tautomer 3. Complex 2 is the first metal complex with a 2,3,7,8,15,23-hexahydroporphyrin as ligand and is synthesized from 1 by reduction with sodium amalgam.

    24. Regiospecific Conversion of 3,4-Bis(trimethylsilyl)furan to 3,4-Disubstituted Furans: A Novel Suzuki-Type Cross-Coupling of Boroxines (pages 432–434)

      Zhi Zhong Song, Prof. Zhong Yuan Zhou, Prof. Dr. Thomas C. W. Mak and Dr. Henry N. C. Wong

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199304321

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      A versatile building block is found in the easily accessible 3,4-bis(trimethylsilyl)furan, which can be converted into boroxine 1 with BCl3 followed by aqueous workup. Subsequent Pd-catalyzed treatment with organic halides furnishes monoorganosilylfuran. Repetition of this reaction sequence affords 3,4-disubstituted furans, which are difficult to obtain by other methods.

    25. A Short Synthetic Route towards a Biologically Active Heparin-like Pentasaccharide with a Pseudo-Alternating Sequence (pages 434–436)

      Hans Lucas, Jan E. M. Basten, Dr. Peter Konradsson and Dr. Constant A. A. van Boeckel

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199304341

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      Simplification of the structure but maintenance of the biological activity—this (successful) strategy was the basis for the synthesis of 1, the “non-glycosamino” glycan analogue of the pentasaccharide domain of heparin responsible for binding antithrombin III. The disaccharide corresponding to the EF building block could be prepared from a protected derivative of fragment GH by basecatalyzed epimerization at C5. The number of synthetic steps was thus significantly reduced.

    26. A Simple One-Step Synthesis of Symmetrical Thiocrown Ethers and the Molecular Structure of an Unusual Sandwich-like Tetrametallic Silver Thiocrown Ether Complex (pages 436–439)

      Dr. Jilles J. H. Edema, H. Thijs Stock, Jan Buter, Prof. Dr. Richard M. Kellogg, Wilberth J. J. Smeets, Dr. Anthony L. Spek and Fre van Bolhuis

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199304361

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      Also in the presence of functional groups, the 2 + 2 cyclization of 1 and 2 to give thiocrown ethers 3 is achieved in good yields, if B(OiPr)3/Al(OiPr)3) is present. Furthermore a sandwich-like cationic complex [Ag4-(3b)2]4+ was prepared with 3b. This complex is also stable in solution.

    27. Structure of Diamagnetic [W(O-4-Me-C6H4)2Cl2(PMePh2)2] and Comparison with Related Paramagnetic 2,6-Diphenylphenoxido Complexes: A Steric Effect on π-Bonding and Electronic Structure (pages 439–441)

      Dr. Lauren M. Atagi and Prof. James M. Mayer

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199304391

      Steric differences alone explain why 1 has a diamagnetic and 2 a paramagnetic electronic ground state. In 1 the W[BOND]O bonds are 0.12 Å shorter, which results in a stronger W[BOND]O π bond and therefore a greater splitting of the t2g orbitals, which are degenerate for ideal octahedral symmetry. The bulky ligand in 2 precludes such short W[BOND]O bonds. Comparisons with other control compounds show that electronic effects are not a factor.

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    28. A New Photoreaction of γ,δ-Unsaturated Ketones: The Oxadi-π-ethane(ODPE) Rearrangement (pages 441–442)

      Dr. Johannes Leitich and Prof. Dr. Kurt Schaffner

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199304411

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      Only the intramolecular [2 + 2] cycloaddition to give the oxetanes 2 was hitherto known as a photoreaction for ketones of the type 1. However, under certain conditions a photoisomerization to give the compounds 3 is also possible. This reaction proceeds through a novel non-allylic 1,3 shift of an acyl group with the formation of a strained ring framework. Substituents include, for example, A = H; B, C = (CH2)4; R = Me.

    29. Organometallic Titanium Complexes with Unpaired Electrons: Syntheses and Structures of [{(η5-Cp)2 TiF2}3 Ti] and [{(η5-Cp′)2 TiF2}3Al] (pages 442–444)

      Dr. Feng-quan Liu, Dipl.-Chem. Heinz Gornitzka, Dr. Dietmar Stalke and Prof. Herbert W. Roesky

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199304421

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      Distorted octahedral and propeller-like are descriptions of how the central metal atoms are surrounded in the crystals of 1 and 2, respectively. These compounds are the first organometallic fluorotitanium(III) complexes and also the first paramagnetic titanium complexes with more than two Ti atoms. R = Cp.

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  4. Book Reviews

    1. Top of page
    2. Reviews
    3. Highlights
    4. Communications
    5. Book Reviews
    1. Book Review: The Meaning of Quantum Theory. By J. Baggott (page 454)

      Michael C. Böhm

      Version of Record online: 22 DEC 2003 | DOI: 10.1002/anie.199304541