Volume 23, Issue 8
Currently known as: Angewandte Chemie International Edition
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198405391
Charge transfer reactions on porphyrin-quinone systems have been the subject of numerous studies in recent years. A compound in which the structural prerequisites are ideal for such a study is described by H. A. Staab et al. in a communication on p. 623 f.
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198405392
Prof. Dr. K. Peter C. Vollhardt
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198405393
Dicarbonyl(η5-cyclopentadienyl) cobalt functions as a matrix for the formation of bonds between unsaturated organic species. A straightforward example is outlined below. The method has been used for the synthesis of natural products and molecules of theoretical interest.
Prof. Dr. Manfred T. Reetz
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198405561
The stereoselectivity of the diastereogenic title reactions can be controlled by using either Lewis-acidic or non-chelating reagents. Decisive are the electronic and/or steric factors in the intermediate and educt, respectively.
Prof. Charles J. Sih and Ching-Shih Chen
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198405701
The enormous advantages presented by enzymes and intact cells as reducing agents are illustrated using the example of ketones. From the underlying principles described, strategies for controlling the stereochemical course of microbial reductions can be developed.
Prof. Larry E. Overman
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198405791
The title reactions, leading to formation of CO, CN, CS, or CC σ bonds, have found wide application. At a catalyst concentration of 1M, the reaction rate is often increased by a factor of 1010 to 1014.
Dr. Karl Heinz Dötz
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198405871
On the borderline between organic and inorganic chemistry, transition metals are finding use in organic synthesis. The rapid advances made in this area of chemistry are delineated using the example of carbene complexes, which in less than twenty years have developed from laboratory curiosities into useful synthetic reagents. These compounds not only function as carbene-transfer agents but also undergo cycloadditions.
Herbert Fisch, Dr. Hans Pritzkow and Prof. Dr. Walter Siebert
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406081
Stabilization of the B4C2 skeleton as a classical boron-carbon compound with cyclohexane structure has been achieved for the first time by introduction of electronically active dimethylamino groups. In the crystal, 2 adopts a chair conformation. Because they are electron deficient, compounds of the type (RB)4(CR′)2, R,R′ = H, alkyl, have carbaborane structures.
Priv.- Doz. Dr. Wolfgang Kaim
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406131
Simultaneous generation of persistent radical anions and radical cations following single-electron transfer — an unusual phenomenon for organic compounds of main group metals — is facilitated by using electron-rich and sterically hindered donors 1. Compound 2, for example, functions as an acceptor.
Renate Gross and Priv.-Doz. Dr. Wolfgang Kaim
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406141
The extraordinary π-back bonding capacity of the MnCp(CO)2 moiety as well as the stability of the reduced form are revealed by studies of the complex 1. The oxidized state corresponding to the Creutz-Taube ion 2 is not stable because of electrocatalytic substitution by the solvent (CpC5H5, C5H4Me, C5Me5).
Priv.-Doz. Dr. Wolfgang Kaim and Andreas Schulz
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406151
The same redox behavior–except for a reversal in sign — is displayed by the long-known p-phenylenediamine 1 (R = alkyl, aryl) and the novel B,B,B′,B′-tetramesityl-p-phenylenediborane 2. Electrochemical and ESR/ENDOR studies reveal that the acceptor strength of the dimesitylboryl substituent is only surpassed by the nitro group.
Prof. Dr. Alan H. Cowley, Prof. Dr. Peter Jutzi, Franz X. Kohl, Jonathan G. Lasch, Dr. Nicholas C. Norman and Ewald Schlüter
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406161
Silylated cyclopentadienyl groups are about to gain a place for themselves as ligands in coordination chemistry. Until now, silylcyclopentadienyl groups were first lithiated and then converted by metal chlorides into complexes. Now, silyl groups have been introduced for the first time into a pre-formed metallocene 1. Lithiation and silylation yield the unusually distorted hexasilylstannocene derivative 2.
Prof. Dr. Kiyoshi Matsumoto
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406171
High yields of nitro alcohols in the reaction of nitroalkanes with ketones (Henry reaction) could, until now, only be obtained in a limited number of special cases. However, use of high pressure and n-Bu4NF as catalyst considerably extends the range of application of the Henry reaction.
Priv.-Doz. Dr. Hans Heinz Karsch, Dipl.-Chem. Hans-Ulrich Reisacher and Dr. Gerhard Müller
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406181
The first structure determination of a phosphacumulene by X-ray diffraction indicates that the 1,3-diphosphaallene 1, synthesized independently, is a genuine allene analogue. Isolated molecules are present in the crystal and the bulky substituents are arranged othogonally. The PC bonds of the almost linear PCP moiety are markedly shorter (1.63 Å) than “normal” PC double bonds (1.68–1.72 Å); the CS bonds in CS2 are also shorter than the CS bonds in thioketones
Prof. Dr. Rolf Appel, Peter Fölling, Bernhard Josten, Dr. Mustafa Siray, Volker Winkhaus and Falk Knoch
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406191
Novel, independent syntheses of phosphacumulenes are reported for the 1-phosphaallene 1 and the 1,3-diphosphaallene 2. 1 is prepared via a Wittig reaction from R PCO and Ph3PCPh2. 2 is obtained from the same educt with RP(X)SiMe3; as desired, the reactions can be performed using either a two-step (XH) or one-step (XLi) procedure.
Dr. Alexander J. Kos, Dr. Timothy Clark and Prof. Dr. Paul von Ragué Schleyer
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406201
The structure of the simplest dilithium salt of an α,α′-diketo dianion, the title compound 1,3-dilithioacetone, is still unknown. However, according to ab initio calculations, the chiral structure 1 with Y-conjugation is preferred to the four other structures investigated.
Prof. Dr. Hans Dietrich, Dr. Waruno Mahdi, Dipl.-Chem. Dieter Wilhelm, Dr. Timothy Clark and Prof. Dr. Paul von Ragué Schleyer
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406211
The first X-ray structure analysis of a monomeric dilithium salt with an α,α′-keto dianion was successfully carried out on the TMEDA complex 1. With approximate C2 symmetry, 1 is chiral. Comparison of the experimentally determined structure with that calculated semiempirically (MNDO) reveals good overall agreement. According to ab initio calculations, 2 has an analogous structure.
Priv.-Doz. Dr. Theodor Troll, Dr. Georg W. Ollmann and Helga Leffler
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406221
Tetraketone 4 can be prepared electrochemically by reduction of 1 in the presence of ClMe3Si. Apart from 2, the polycycle 3 is also formed (R SiMe3), and is converted into 4 by desilylation and hydrolysis.—Phthalic anhydride reacts differently.
Dipl.-Chem. Jürgen Weiser and Prof. Dr. Heinz A. Staab
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406231
p-Benzoquinone-porphyrin-p-benzoquinone is the layer sequence in the sandwich compound shown on the cover. This compound is formed in 0.1% yield from 1, RCHO and pyrrole in refluxing propionic acid. The four bridges in the sandwich compound are short and contain no heteroatoms. It may serve as a model for the study of biochemically important electron-transfer reactions.
Priv.-Doz. Dr. Gerhard Erker, Klaus Berg, Dr. Reinhard Benn and Gerhard Schroth
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406251
For the designed synthesis of transition-metal catalysts for organic reactions a detailed knowledge of the strong intramolecular interactions between the ligands in simple metal complexes is indispensable. In appropriately substituted allyl(diene)ZrCp complexes, such interactions lead to the formation of one isomer of the complex system with very high diastereoselectivity. Thus, the 55 :45 mixture of anti-2 and syn-2 rearranges thermally into >95% anti-1.
Prof. Dr. Helmut Werner, Wilfried Paul and Ralf Zolk
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406261
Generation of the first methylenearsane in the coordination sphere of rhodium has been achieved by reaction of C5Me5Rh(CO)(I)(CH2I) with LiAsHPh. In solution, the complex 1, E As, obtained surprisingly affords the cyclic product 2, in which the RhAs3-ring is puckered.
Priv.-Doz. Dr. Dieter Cremer and Dr. Elfi Kraka
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406271
Formation of a covalent bond is not necessarily associated with an increase in electron density in the bonding region. This can be established by analysis of the single electron density distributions ρ(r) with the aid of the assigned Laplace field ▽2ρ(r). For “bonds without bonding electron density ρ(r)”, it is decisive that the density ρ(r) actually present in the region between the atoms results in a decrease in the local energy density and, hence, produces a stabilizing effect.
Dr. Karin Weiss and Petra Kindl
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406291
The ability of heteroallenes to undergo metathesis reactions could be demonstrated using the carbodiimides 2. The stoichiometric reaction 1 + 2 3 + 4 is the first example of a metathesis of heteroallenes with carbene complexes such as 1. The isocyanidetungsten complexes 3 thus obtained function as catalysts for the (equally novel) metathesis of symmetrical to “mixed” carbodiimides RNCNR′.
Prof. Dr. E. A. V. Ebsworth, Dr. John H. Holloway, Nicholas J. Pilkington and Dr. David W. H. Rankin
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406301
Oxidative fluorination of a PF2- to a PF4 -ligand with XeF2 permits preparation of the title compound 1, in which a metal atom is bonded to a pentacoordinated P atom
Prof. Dr. Helmut Quast and Dr. Josef Christ
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406311
Formation of the bishomoaromatic species 2, a system with delocalized electrons, from the isomeric semibullvalene 1 can be deduced from the temperature-dependent reversible changes in the UV spectrum. 2 is defined molecule and not the transition state in the Cope rearrangement of 1.
Prof. Dr. Achim Müller, Friedrich-Wilhelm Baumann, Dr. Hartmut Bögge, Michael Römer, Erich Krickemeyer and Klaus Schmitz
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406321
Novel CuS Anions with ring structures demonstrate, once again, the unusually versatile coordination behavior of polysulfide ions. [Cu3(S4)3]3⊖1, with a central (CuS)3 six-membered ring, and [(S6)Cu(S8Cu(S6)]4⊖2, with an S8 chain, were obtained by reaction of Cu(OAc)2 with S8 and H2S, respectively.
Dr. Wolfgang Tremel, Prof. Dr. Bernt Krebs and Dr. Gerald Henkel
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406341
The novel complex anions 1 and 2 with the ligand “S2-o-xyl” (o-xylene-α,α′-dithiolate) were prepared from CoCl2 and NiCl2, respectively, and S2-o-xyl2⊖. The Co2-complex 1 is an example of the rare syn-exo arrangement of the thiolate S atoms in the central Co2S2 ring. In the Ni3-complex 2, each of the Ni atoms is planar-coordinated by four sulfur atoms; the Ni3-skeleton is bent.
Prof. Dr. Dieter Fenske and Dipl.-Chem. Kurt Merzweiler
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406351
A facile approach to complexes with PhEEPh (E = P, As) as ligand is opened up by the reaction of 1 with PhE(SiMe3)2. Complexes 2 and 3 are formed by exchange of chlorine and Me3Si-migration, respectively. In the reaction of 2 with CH3COCl, the diphosphene ligand is displaced by Cl⊖; moreover, the Me3Si groups are substituted by CH3CO groups. Recrystallization of this compound leads exclusively to the meso-derivative 4.
Prof. Dr. Rolf W. Saalfrank, Dipl.-Chem. Walter Rost, Dipl.-Chem. Franz Schütz and Dipl.-Chem. Ulrike Röss
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406371
A general synthetic route to 1,1-allenedicarboxamides 3 is transallenation. For this purpose 1,3-bis (dialkylamino) allenes (synthetic equivalents of malonamide dianions 1) are allowed to react with disubstituted malonyl chlorides (synthetic equivalents of 1,1-vinylidene dications 2); R1NR2.
Priv.-Doz. Dr. Martin G. Peter, Lothar Grün and Dr. Hans Förster
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406381
A nondestructive method for investigating the exoskeleton of insects has facilitated structural information to be gained about the insoluble, fully sclerotized cuticle and about the highly polymeric chitin. It was known that the exoskeleton consists of chitin, proteins, and polyarenes. In contrast to previous suppositions, however, the transformation products of sclerotizating agents with 3,4-dihydroxyphenyl groups are predominantly present in the reduced state.
Priv.-Doz. Dr. Fritz R. Kreissl, Dipl.-Chem. Werner J. Sieber, Dr. Mathias Wolfgruber and Jürgen Riede
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406401
The novel title reaction is of general importance for catalytic processes such as CO reduction and the Fischer-Tropsch synthesis. Carbyne complexes like 1 even react with HCl in ether to yield acyl complexes such as 2.
Dr. Hans Peter Reisenauer, Prof. Dr. Günther Maier, Dr. Achim Riemann and Prof. Dr. Reinhard W. Hoffmann
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406411
The Simplest cyclic conjugated carbene is the title compound 2a 2b, generated by pyrolysis of the polycycle 1. Compound 2 is stable in an argon matrix at 10 K and has a singlet ground state. The “atomatic ylide structure” 2b makes a major contribution to the mesomerism.
Prof. Dr. Waldemar Adam and Dipl.-Chem. Thomas Oppenländer
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406412
The cleavage of cyclobutanes by short-wavelength UV radiation was studied using the example of the title compound 1, which contains no chromophoric substituents. 185 nm Irradiation of 1 in n-pentane leads preferentially to decompostion into 1,7-octadiene. Presumably, Rydberg excited states having radical cation character, such as 2, are involved.
Dov Tamarkin, Daphna Benny and Prof. Dr. Mordecai Rabinovitz
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406421
A dehydrogenative cyclization with C8K facilitates preparation of 1 and 2 from benzil and p,p′-dimethylbenzil, respectively. The constant rate of H2-formation during the reaction suggests a surface-controlled process.
Karl Heinz Dötz
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406431
Hans Günter Gassen
Article first published online: 22 DEC 2003 | DOI: 10.1002/anie.198406432