bluuebunny/crossref_metadata_2025 huggingface dataset:
[(η5‐C5Me5)(CO)2MPP(2,4,6‐tBu3C6H2)] (M = Fe, Ru), the First Diphosphenyl Complexes
Authors: Weber Lothar , Reizig Klaus
Published: December 2003

The transition‐metal‐substituted diphosphenes 2 (M = Fe, Ru) were obtained from the disilylphosphido complexes 1 and a dichlorophosphane. Complexes with MPP structural moieties were previously unknown.
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[μ‐N2H2{Ru(PPh3)dttd}2], the First Diazene Complex with Sulfur‐Coordinated Transition Metal Centers (dttd = 2,3,8,9‐Dibenzo‐1,4,7,10‐ tetrathiadecane(2 –))
Authors: Sellmann Dieter , Böhlen Elmar , Waeber Michael , Huttner Gottfried , Zsolnai Laslo
Published: December 2003

The complex 2, in which trans‐N2H2 bridges two ruthenium centers, could, as illustrated below, be obtained from the hydrazine complex 1. 2 forms blackish‐green crystals with 2 CH2Cl2. Complexed diazene, such as is present in 2, is probably the key compound in the reduction of N2 at the iron and/or molybdenum centers of nitrogenases.
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Selectivity of the Anodic Oxidation of CH‐ and CH2‐Groups; Selective Oxidation of Steroids at C‐6
Authors: Hembrock Annegret , Schäfer Hans J. , Zimmermann Gesine
Published: December 2003

Anodic oxidation results in comparatively good chemoselectivity; the ratio of attack at tertiary to attack at secondary C atoms is 12 : 1 for decalin. The regioselectivity of anodic oxidation may be controlled by inductive effects in the case of chlorides (e.g., chlorocyclohexane) and fatty acids. Remarkably, the steroids androstane and cholestane undergo oxidation mainly at C‐6.
Hexa‐tert‐butyldisilane–the Molecule with the Longest SiSi Bond
Authors: Wiberg Nils , Schuster Harald , Simon Arndt , Peters Karl
Published: December 2003

Steric repulsion of the tert‐butyl groups in the disilane 2 results in a Si‐Si distance about 35 pm greater than that usually found in disilanes. 2 is formed via a radical intermediate upon reaction of nitrosyl cations with 1, MNa, K.
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Periodic Potential Surfaces in Crystal Structures
Authors: Nesper Reinhard , von Schnering Hans‐Georg
Published: December 2003

The combined representation of experimentally determined crystal structures and calculated periodic potential surfaces is possible with a new program system. It is shown that the zero potential surfaces in particular are topologically very similar to the corresponding periodic minimal surfaces of the same symmetry. The periodic potential surfaces also enable stratements to be made about the properties of crystals.
Resonance Raman Spectroscopy, and Its Application to Inorganic Chemistry. New Analytical Methods (27)
Authors: Clark Robin J. H. , Dines Trevor J.
Published: December 2003

Resonance Raman spectra are obtained when the wave number of the exciting radiation is close to, or coincident with, that of an electronic transition of the scattering species. Such spectra are usually characterized by a very large enhancement of the intensities of particular Raman bands, sometimes with the appearance of intense overtone and combination tone progressions. The technique provides detailed information about excited electronic states because it is only the vibrational modes associated with the chromophore that are resonance‐Raman active. Additionally, the high sensitivity is such that compounds at concentrations as low as 10−6 mol/L may be detected, enabling resonance Raman spectroscopy to be used as an analytical tool and for the study of chromophores in molecules of biological interest.
The Three‐Dimensionally Non‐Molecular Polyadamantanoid Structure of Cd(SPh)2
Authors: Craig Don , Dance Ian G. , Garbutt Robert
Published: December 2003

Crystalline Cd(SPh)2 is {(μ‐SPh)6Cd4(μ‐SPh)4/2}, an inorganic polymer. It consists of Cd4(SPh)6 cages having adamantane‐like structure, each of which is linked with four surrounding cages by four SPh bridges. The three‐dimen‐113Cd‐NMR spectrum indicates that the polymer forms Cd10(SPh)20 molecules having tetraadamantanoid structure upon solution in dimethylformamide.
New Methods for the Synthesis of Glycosides and Oligosaccharides—Are There Alternatives to the Koenigs‐Knorr Method? [New Synthetic Methods (56)]
Authors: Schmidt Richard R.
Published: December 2003

Glycoproteins, glycolipids, and glycophospholipids (glycoconjugates) are components of membranes. The oligosaccharide residue is responsible for intercellular recognition and interaction; it acts as a receptor for proteins, hormones, and viruses and governs immune reactions. These significant activities have stimulated interest in oligosaccharides and glycoconjugates. With their help it should be possible to clarify the molecular basis of these phenomena and to derive new principles of physiological activity. Major advances in the synthesis of oligosaccharides have been made by the use of the Koenigs‐Knorr method, in which glycosyl halides in the presence of heavy‐metal salts are employed to transfer the glycosyl group to nucleophiles. The disadvantages of this procedure have led to an intensive search for new methods. Such methods will be discussed in this article. Emphasis is placed on glycoside and saccharide formation by 1‐O‐alkylation, on the trichloroacetimidate method, and on activation through the formation of glycosylsulfonium salts and glycosyl fluorides.
H3CPCH2: An Ylide with Two‐Coordinate Phosphorus?
Authors: Bock Hans , Bankmann Martin
Published: December 2003

For corrigendum see DOI:10.1002/anie.198603821
[Bi2IIIS34]4−, the Hitherto Sulfur‐Richest Complex
Authors: Müller Achim , Zimmermann Marion , Bögge Hartmut
Published: December 2003

Sulfur complexes are always full of surprises: Reaction of BiCl3 with a polysulfide solution in acetonitrile furnishes the complex anion [Bi2S24]4− in which the Bi atoms are coupled by an S ligand. In each case two bidentate S ligands complete the square‐pyramidal coordination of the two Bi atoms. Neither a complex with coupled S ligands nor one with bidentate S ligands was previously known.
The Concept of Strain in Organic Chemistry
Authors: Wiberg Kenneth B.
Published: December 2003

“Die Ringschließung ist offenbar diejenige Erscheinung, welche am meisten über die räumliche Anordnung der Atome Auskunft geben kann. Wenn eine Kette von 5 und 6 Gliedern sich leicht, eine von weniger oder mehr Gliedern sich schwierig oder auch gar nicht schließen läßt, so müssen dafür offenbar räumliche Gründe vorhanden sein.… Die vier Valenzen des Kohlenstoffatoms wirken in den Richtungen, welche den Mittelpunkt der Kugel mit den Tetraederecken verbinden, und welche miteinander einen Winkel von 109°28′ machen. Die Richtung der Anziehung kann eine Ablenkung erfahren, die jedoch eine mit der Größe der Letzteren wachsende Spannung zur Folge hat,”[

Ring formation is evidently the reaction that can provide the most important information on the spatial arrangement of atoms. Steric reasons should explain the observation that 5‐ or 6‐membered chain undergoes ready closure, whereas a shorter or longer chain undergoes difficult or no closure.… The four valences of the carbon atom act in the directions that connect the center of a sphere with the corners of a tetrahedron and form angles of 109°28′ with one another. The direction of the attraction can deviate, but this in increasing strain as the sizes of the latter increase.

] This is the quintessence of the “ring‐strain theory” formulated by Adolf von Baeyer over one hundred years ago. Although it is today only one facet of the many aspects of strain theory, it has repeatedly stimulated experimental and theoretical chemists. Among the most spectacular of the recent successes in synthetic chemistry are the syntheses of tetra‐tert‐butyltetrahedrane and [1.1.1]propellane. The reasons for the great stability of these two highly strained compounds are completely different. The experimental findings as well as the results of theoretical analysis by means of molecular mechanics and ab initio calculations have contributed decisively to our present state of knowledge of the structure, energy, and reactivity of organic compounds.
Synthesis of O‐Glycopeptides of the Tumor‐Associated TN‐ and T‐Antigen Type and Their Binding to Bovine Serum Albumin
Authors: Kunz Horst , Birnbach Stefan
Published: December 2003

The synthesis of immunologically relevant conjugates from bovine serum albumin (BSA) and glycotripeptides with TN‐ and T‐antigen structures has been achieved for the first time. In the glycoserylserylthreonines, two monosacharide (TN) and two disaccharide (T) units are α‐glycosidically linked with serine and threonine; they correspond to the N‐terminal structural elements of glycophorin A with M blood group characteristics. The synthesis is accomplished by means of a special protecting group technique (Sacch = mono‐ or disaccharide unit).
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Organic Synthesis at High Temperatures. Gas‐Phase Flow Thermolysis [New Synthetic Methods (57)]
Authors: Karpf Martin
Published: December 2003

The preference for carrying out synthetic organic reactions at the lowest possible temperature is due to the expectation that the selectivity often increases with decreasing temperature, as is confirmed by many examples and also theoretically justified. Selectivity, however, is not the only problem at high temperatures; further factors include the frequently limited thermal stability of the functional groups and structural elements not directly involved in the transformation. In spite of these limitations, the advantages of high temperatures and the greatly improved knowledge of the mechanisms of dynamic gas‐phase processes accumulated in recent years can be exploited in directed organic synthesis. In this review the synthetic potential of gas‐phase flow thermolysis will be described from the viewpoint of the synthetic chemist with the aid of typical examples of application.
The Pentagonal Column and the ReO3‐Type Structure
Authors: Marinder Bengt‐Olov
Published: December 2003

The pentagonal column (PC), consisting of MX7 bipyramids sharing their equatorial edges with five MX6 octahedra, is a structural feature frequently occurring in association with frameworks of the ReO3‐type, where it enables accomodation of an anion deficiency. The present article discusses the geometry of the PC and its compatibility with the ReO3‐type structure, which naturally emerges from the finding that a PC may result from twinning of an ReO3‐type structure on the unit cell level. A new symbolism is presented which facilitates visualization of a large variety of crystal and defect structures of MX3–x stoichiometry. This symbolism may also serve as a convenient aid in deriving models of possible new structures that may be of value in the interpretation of HREM images.
The Palladium‐Catalyzed Cross‐Coupling Reactions of Organotin Reagents with Organic Electrophiles [New Synthetic Methods (58)]
Authors: Stille John K.
Published: December 2003

The cross‐coupling of organotin reagents with a variety of organic electrophiles, catalyzed by palladium, provides a novel method for generating a carbon‐carbon bond. Because this mild, versatile reaction is tolerant of a wide variety of functional groups on either coupling partner, is stereospecific and regioselective, and gives high yields of product, it is ideal for use in the synthesis of elaborate organic molecules. When the coupling reaction is carried out in the presence of carbon monoxide, instead of a direct coupling, carbon monoxide insertion takes place, stitching the two coupling partners together and generating a ketone.
Heterogeneous Catalysis of Ammonia Synthesis at Room Temperature and Atmospheric Pressure
Authors: Aika Ken‐ichi
Published: December 2003

The dream of many chemists, the nonenzymatic catalytic synthesis of ammonia from N2 and H2 at room temperature and normal pressure, has been achieved with a potassium‐containing ruthenium/active carbon system. Even though the activity of the catalyst is small (0.011 mmol NH3 per day and gram of catalyst), this discovery represents a beginning. In comparison, nitrogenase from Klebsiella pneumoniae produces 0.25 mmol NH3 per minute and gram of protein.
[Cu36I56]20⊖—a Novel Polyanion in the Compound (pyH)2[Cu3I5]
Authors: Hartl Hans , Fuchs Joachim
Published: December 2003

The largest discrete iodocuprate(I) ion observed so far has been identified in the compound (pyH)2[Cu3I5]. 36 CuI tetrahedra are linked through common edges to form a highly symmetrical polyanion [Cu36I56]20⊖ with the extremely rare symmetry 432 (O).
Understanding Reaction Dynamics in Coordination Chemistry—Application of High Pressure Techniques
Authors: van Eldik Rudi
Published: December 2003

In order to understand the dynamics of chemical reactions in general, detailed information on electronic, structural and kinetic properties is required. The key questions on how chemical reactions actually occur can in many cases only be answered in terms of information obtained from kinetic studies. In conventional kinetic studies of chemical reactions in solution, the variables usually selected include concentration, acidity, solvent, and temperature. In recent years, pressure has become an additional selected variable in such studies. It enables the measurement of the volume of activation and the construction of reaction volume profiles and thus assists in the elucidation of the underlying mechanism; it also completes the comprehension of reaction kinetics by adding another kinetic parameter that the suggested reaction mechanism must account for. Furthermore, the volume of activation is the only transition state property that can be correlated with the corresponding ground state property in an experimentally simple manner. In this paper, the insights so gained in our understanding of the dynamics of reactions involving coordination complexes will be presented. Such reactions are of fundamental interest to chemists since they often form the basis of catalytic, biological, environmental and energy related processes. Any additional information that will add to the understanding of the reaction dynamics is therefore of exceptional importance.
[m.m]Metallocenophanes: Synthesis, Structure, and Properties
Authors: Mueller‐Westerhoff Ulrich T.
Published: December 2003

Metallocenophanes are metallocenes in which the cyclopentadienyl ligands are linked intramolecularly through CmHn or CmHnX (X = heteroatom) chains. Two main classes of metallocenophanes are known: in [m]metallocenophanes the ligands of one metallocene are connected by a bridge (or by several bridges); in [m.n]metallocenophanes two (or more) metallocenes are brought together into one molecule by bridging groups. This article briefly describes the first class (mononuclear complexes) and then concentrates on the second (binuclear complexes). The [1.1]metallocenophanes, which are produced by linking two metallocene moieties through two C1, bridges, are of particular interest and are characterized by a variety of unusual and useful properties: they are very flexible conformationally; hydride abstraction from the CH2 bridges produces carbenium ions that are greatly stabilized by the adjacent metallocene moieties; deprotonation of one of the CH2 bridges is surprisingly easy and leads to the unusual situation that an intramolecular CHċC hydrogen bond stabilizes a carbanion; protonation of both metallocene moieties causes the liberation of one mole of hydrogen per mole of [1.1]metallocenophane, thereby allowing the use of these compounds as catalysts for the formation of hydrogen in acidic aqueous solutions.
Synthesis and Crystal Structure of μ‐Thiobis[tris(diethyldithiocarbamato)molybdenum(IV)‐Toluene 1:1, a Compound Containing a Rare MoSMo Core
Authors: Jasim Khalid S. , Chieh Chung , Mak Thomas C. W.
Published: December 2003

Molybdenum‐sulfur complexes, which are of interest, for example, as model compounds for the active sites of some enzymes, are known in abundance. Mo‐S‐Mo structural units, on the other hand, have only been found in the anion of K6[Mo2(μ‐S)(CN)12] and in the neutral title compound 1, which is formed upon passing a stream of air through a solution of [Mo2(S2CNEt2)6]] in toluene.
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Nature of Ni and Cu Species in Reduced Bimetallic NiCu/Al2O3 Catalysts
Authors: Sankar Gopinathan , Rao C. N. Ramachandra
Published: December 2003

What effect does the simultaneous presence of the elements nickel and copper in a hydrogenation catalyst have on the kind of species formed upon catalytic reduction? X‐ray photoelectron and Auger electron spectroscopy have been employed in an attempt to answer this question. Ni0, Ni2⊕, Cu0, and Cu⊕ species were detected, Ni0 increasing with the copper content and Cu0 increasing with the nickel content.
Geometric and Topological Thinking in Organic Chemistry
Authors: Turro Nicholas J.
Published: December 2003

The beginning student of organic chemistry is often bewildered by what appears to be an enormous maze of random structural variations and reactions that can be mastered only by tedious memorization. To the organic chemist, however, the same subject is often a beautifully ordered discipline of elegant simplicity. An important value of learning organic chemistry is the mastering of “organic thinking,” an approach to intellectual processing whereby the “sameness” of many families of structures and reactions is revealed. This article offers the author's personal views of organic thinking and explores the intellectual and scientific foundations of organic chemistry and of the powerful methods that provide the field with a platform for making rapid conceptual and experimental advances. It is proposed that these methods involve a geometric and topological approach to scientific reasoning within the framework of scientific paradigms that guide experimental design and execution. The basis of this approach is considered in relation to day‐to‐day thinking, problem solving, and the psychological drive for intellectual closure. The power of the approach is illustrated by the analysis of several photochemical and chemiluminescent reactions.
Bis(pentamethylcyclopentadienyl)diphosphene—a Molecule with Fluxional Structure and Reactive PC Bond
Authors: Jutzi Peter , Meyer Udo , Krebs Bernt , Dartmann Mechthild
Published: December 2003

What potential does the pentamethylcyclopentadienyl ligand Cp* have in diphosphene chemistry? An indication is provided by the synthesis of the crystalline diphosphene Cp*PPCp* from Cp*PCl2. The two Cp* ligands kinetically stabilize the PP bond, resulting in a fluxional structure (degenerate [1,5]‐sigmatropic rearrangements). They may be successively replaced by bulky amino or alkyl ligands.
Novel Modifications of Gold, Rhodium, and Ruthenium—M13 Clusters as Building Blocks of “Superclusters”
Authors: Schmid Günter , Klein Norbert
Published: December 2003

Not alchemistry but rather chemistry is the basis for preparing a gold modification: [Au55(PPh3)12Cl6] can be degraded to naked Au13 clusters in CH2Cl2 solution by application of a 20‐V d.c. potential, the outer layer of the cluster being lost. These smaller clusters reorganize, in turn, the form superclusters (Au13)13 and microcrystallites [(Au13)13]n, whose structure were determined by means of their X‐ray powder data.
Heterometallic Dinuclear Complexes by Ethene Displacement with Grignard Compounds or Diorganomagnesium Compounds
Authors: Jonas Klaus , Koepe Gerd , Krüger Carl
Published: December 2003

The incorporation of a complete Grignard compound into the coordination sphere of a transition‐metal atom has been achieved for the first time by the reaction of 1, a well‐known source of CpCo, with phenylmagnesium bromide in tetrahydrofuran (THF) in the presence of N,N,N′,N′‐tetramethylethy‐lenediamino (TMEDA). In the product 2, bonds exist between Co and Mg, Mg and Cphenyl, and Co and Cphenyl.
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Fast Ionic Conduction in LiI·4 Methanol: [Li(CH3OH)4]+I−
Authors: Weppner Werner , Welzel Wilfried , Kniep Rüdiger , Rabenau Albrecht
Published: December 2003

The lithium ion conductor with the highest known conductivity at room temperature is the title compound. A further unique feature is its surprising stability toward lithium. These properties can be understood in terms of the crystal structure. The compound shows promise as a solid electrolyte for lithium batteries having high energy density.
Totally Synthetic Routes to the Higher Monosaccharides
Authors: Danishefsky Samuel J. , DeNinno Michael P.
Published: December 2003

The evolution of a strategy to synthesize the title compounds is described. Three principal developments allowed realization of this goal: (1) the attainment of high margins of diastereofacial selectivity and regioselectivity in the construction of pyranoid systems via the Lewis acid‐catalyzed cyclocondensation reaction of activated dienes and aldehydes; (2) the exploitation of stereoselective reactions for functionalization of the pyranoid matrix; and (3) the discovery of stereoselective reactions for extending the chiral biases of pyranoid systems to newly emerging stereogenic centers on side chains. The coordination of these components in the synthesis of target systems of high biological interest is described.
High‐Pressure LiGe with Layers Containing Two‐ and Four‐Coordinate Germanium Atoms
Authors: Evers Jürgen , Oehlinger Gilbert , Sextl Gerhard , Becker Hans‐Otto
Published: December 2003

The preparation, from a Zintl‐phase with a semimetal, of a high‐pressure phase in which the coordination in the semimetal partial structure is no longer reconcilable with the Zintl‐Klemm concept has been accomplished for the first time with LiGe. At normal pressure LiGe can still be classed under the Zintl phases, whereas LiSn can no longer be so classified. The LiGe high‐pressure phase crystallizes in a novel structure type, which is made up of layers containing two‐ and four‐coordinate germanium and which shows close relationships to the structures in LiSn and LiPb.
Crystal Structure of [α‐Nitrobenzyllithium · Ethanol]n; A Lithium Nitronate‐Ethanol Interaction
Authors: Klebe Gerhard , Böhn Karl Heinz , Marsch Michael , Boche Gernot
Published: December 2003

The title compound 2 is a lithium nitronate which crystallizes out with ethanol. Ethanol crystallizes during the preparation of 2 from 1 and lithium ethoxide outlined below, but is also present as solvent. Remarkable features of crystalline 2 are, in particular, the bonding of Li⊕ to nitronate and ethanol O‐atoms and the OH ⃛O bridges from ethanol to a nitronate O‐atom.
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CC‐Linkages of Ethene with CO2 on an Iron(0) Complex—Synthesis and Crystal Structure Analysis of [(PEt3)2Fe(C2H4)2]
Authors: Hoberg Heinz , Jenni Klaus , Angermund Klaus , Krüger Carl
Published: December 2003

The first metal‐induced syntheses of dicarboxylic acids from ethylene and the C1 building block CO2 have been achieved by use of the title compound 2, an unsaturated 16‐electron Fe0 system. By addition of ligands, the reactions can be controlled to give either the methylmalonic acids 1 or the isomeric succinic acids 3 preferentially.
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MNDOC Calculations of the Potential Surfaces for Photochemical α‐Cleavage
Authors: Reinsch Manfred , Höweler Udo , Klessinger Martin
Published: December 2003

A combination of a semiempirical MO calculation and a limited configuration interaction calculation has been used successfully for the prediction of photoproducts as a function of the excited state of the reactant. As example, the α‐cleavage of formaldehyde was investigated. The potential hypersurfaces of the S0 Sa and Ta states for planar formaldehyde were calculated as functions of the CH1 distance and of the H2CO angle.
Control of the Electronic Structure of Organic Conductors as Exemplified by [NMP][TCNQ] Charge‐Transfer Complexes
Authors: Miller Joel S. , Epstein Arthur J.
Published: December 2003

Through replacement of cations with neutral molecules of similar shape and polarizability in a highly conducting “metal‐like” change‐transfer organic conductor, the deliberate control of the electronic structure from a quarter to a half‐filled band is possible. This goal has been achieved with the N‐methylphenazinium (NMP) salt of the tetracyanoquinodimethane (TCNQ) anion by partial replacement of the cation with phenazine. A detailed study of the optical, electrical, and magnetic properties of these conducting molecular solids has lead to the evolution of a broad understanding of the physics of one‐dimensional organic conductors and a reinterpretation of the mechanism of electron transport in such solids. Phenomena such as switching from a low coulomb repulsion two‐chain conductor to a high coulomb repulsion one‐chain conductor as well as soliton‐assisted electron transport are observed.
Synthesis of Glycopeptides, Partial Structures of Biological Recognition Components [New Synthetic Methods (67)]
Authors: Kunz Horst
Published: December 2003

Glycopeptides are partial structures of the connecting regions of glycoproteins and, like these, always contain glycosidic bonds between the carbohydrate and peptide parts. Glycoproteins are not only widely distributed but are also decisive factors in post‐translational biological selectivity, especially in biological recognition. Targeted syntheses of glycopeptides require stereoselective formation of the glycosidic bonds between the carbohydrate and the peptide parts and protective group methods that enable selective deblocking of only one functional group in these polyfunctional molecules. These heavy demands have been met by the well‐established use of benzylic protective groups, which can be removed by hydrogenolysis, combined with the use of base‐labile 2‐phosphonioethoxycarbonyl (Peoc) or 9‐fluorenylmethoxycarbonyl (Fmoc) protective groups or of bromoethyl esters, which can be removed under neutral conditions. The acidolysis of tert‐butyloxycarbonyl (Boc) groups and of tert‐butyl esters has also been successfully used, although, under acidic conditions, anomerization or rupture of the glycosidic bonds may occur, especially when nucleophiles are present. The stable, two‐stage 2‐(pyridyl)ethoxycarbonyl (Pyoc) protective groups allow a more reliable synthesis of complex glycopeptides since they can be removed, after modifications, under mild conditions. Particularly suitable for the synthesis of sensitive glycopeptides are the stable allyl protective groups. They can be removed from the complex glycopeptides in a highly selective and effective manner by means of noble‐metal catalysts under practically neutral conditions. These methods have been employed to synthesize glycopeptides corresponding to partial structures of interesting glycoproteins. Deprotected glyopeptides representing tumor‐associated antigen structures can be coupled to bovine serum albumin, which serves as a biological carrier molecule, without the necessity of using an artificial coupling component (spacer).
Emission of Microparticles from Automotive Sources—X‐ray Photoelectron Spectroscopy in Environmental Analysis
Authors: Schlögl R. , Indlekofer G. , Oelhafen P.
Published: December 2003

In the last fifteen years the necessity for efficient environmental protection has become generally accepted. However, before practical measures can be taken, a comprehensive assessment of the present environmental situation should be made, taking into consideration the risks involved in as well as the positive effects of any planned environmental changes—whether natural or man made. This clearly calls for close cooperation between the various scientific disciplines. For example, the treatment of exhaust fumes from motor vehicles has been of primary importance in measures taken to restrict the recent damage caused to woodland areas. The introduction of 3‐Way‐Catalyst technology has been regarded as a viable countermeasure. The following report is intended to describe a method for examining some side effects of catalyst usage. Accordingly, the chemical composition of microparticles emitted from combustion motors through the use of catalysts will be examined and some possible changes in the environment caused by such particles will be briefly considered. As in the area of research into catalysts for industrial synthesis a knowledge of the surface structure of such particles, i.e. the boundary layer between emission product and environment, is necessary in the investigation into their effects. Consequently, a surface sensitive technique from solid state physics, X‐ray photoelectron spectroscopy (XPS or ESCA) has found novel use in the area of environmental analysis. In the following report emphasis will be placed on the description of measurement techniques and the interpretation of the results obtained. After a critical consideration of the experimental methods, examples from two different series of measurements on diesel and Otto motors equipped with soot filters or 3‐way‐catalysts respectively, will be given. Hopefully, this report will also stimulate establishment of the use of EPS in environmental research techniques.
The Influence of Substituents on Double‐Bond Localization, e.g. in s‐Indacene
Authors: Heilbronner Edgar , Yang Zhong‐Zhi
Published: December 2003

In a molecule with conjugated π bonds, which substituents favor localized double bonds? Heuristic rules to answer this question qualitatively have been derived in the framework of the Hückel model. Only the maximum eigenvalue of the unperturbed system is required along with the atomic orbital coefficients of the HOMO and LUMO and their energies.
Bond Stretch Isomerism in Bicyclo[1.1.0]tetrasilanes. Contrasts Between Strained Silicon and Carbon Ring Systems
Authors: Schleyer Paul von Ragué , Sax Alexander F. , Kalcher Josef , Janoschek Rudolf
Published: December 2003

Is bicyclotetrasilane expected to exhibit a markedly short or a markedly long central SiSi bond? Ab initio calculations at different levels of accuracy all gave two potential minima. The corresponding structures differ in the length of the central bond (by about 0.5 Å), the interflap angle (120 and 140°), and the HSiSi angle at the bridgehead atoms (140 and 90°). In all calculations, the structure with the long SiSi bond proved to be lower in energy. This order can be reversed, however, in derivatives with bulky substituents at the bridgehead atoms.
The Importance of Chemistry in the Development of High‐Performance Ceramics
Authors: Aldinger Fritz , Kalz Hans‐Jürgen
Published: December 2003

Due to their mechanical, thermal and chemical stability, high‐performance ceramics have a range of properties which makes it possible in many fields to go beyond the limits of use of the various classes of materials nowadays available. In spite of this favorable starting situation, the worldwide endeavors to introduce this new group of materials have suffered some setbacks in both conventional applications and in new technologies. The ultimate reason is that these materials are very brittle. After the introduction of fracture mechanics, designers in many fields have learned how to handle brittle materials and how to exploit the potential of their properties in components subject to extreme loadings. Materials scientists have also been very successful in developing ceramics with high strength and fracture toughness characteristics. Nevertheless, the field of use has hitherto been restricted, since, in many cases, the reliability of the components is inadequate. Small and very small defects, such as micropores and cracks, as well as any other chemical and physical inhomogeneity in the structure can cause catastrophic failure of the components due to the high brittleness. Since, on the one hand, these defects are as a rule caused by inadequate control of the process sequences and, on the other, the production processes comprise a large number of chemical process steps, it is to be hoped that consistent application of the way of thinking and procedures of a chemist will make an important contribution in overcoming these difficulties.
Computer‐Assisted Molecular Design (CAMD)—An Overview
Authors: Frühbeis Horst , Klein Robert , Wallmeier Holger
Published: December 2003

A new instrument, long established as CAD in engineering, is beginning to make its presence felt in chemical research laboratories: Computer‐Assisted Molecular Design (CAMD). The combined use of computer graphics and theoretical chemistry is opening up new perspectives in molecular research. Structures and properties of molecules such as spacefilling, charge distribution, or dynamic behavior can be determined and used for comparison. For research on complex systems like biomolecules (protein engineering), this new approach turns out to be indispensable.
Stereoselective Syntheses of Building Blocks with Three Consecutive Stereogenic Centers: Important Precursors of Polyketide Natural Products [New Synthetic Methods (68)]
Authors: Hoffmann Reinhard W.
Published: December 2003

Sequences of directly adjacent stereogenic centers were first discovered for the monosaccharides, which therefore constituted the first focus of interest in Stereoselective synthesis. The structures of many polyketide‐derived natural products that have been elucidated in recent years often exhibit longer sequences of stereogenic centers in which hydroxy‐substituted secondary carbon atoms alternate with tertiary carbon atoms. This finding inspired the development of methods allowing the specific construction of first two and then—more importantly–three neighboring stereogenic centers. The diverse methodologies that have thereby emerged reveal common principles and stress the variety of approaches possible in stereoselective synthesis.
The Development of Bioglass Ceramics for Medical Applications
Authors: Vogel Werner , Höland Wolfram
Published: December 2003

The enormous progress made in the field of medicine over the past few decades has been partly due to the introduction of new instruments but also a result of the use of new materials. It is impossible to imagine modern medicine without metals, alloys, sintered corundum, organic high polymers (also as composite materials), glassy carbon, etc. Bioglass ceramics open up new possibilities for medical treatment and constitute a new area of research in the natural sciences and medicine. Owing to their widely variable combinations of properties, bioglass ceramics can be more easily adapted to suit medical requirements than can customary implants. Two properties of bioglass ceramics are of primary importance: their biocompatibility, i.e., acceptance of the material by the tissues of the human body without irritation, rejection reactions, or toxic effects; and their bioactivity, i.e., the ability to establish firm intergrowths with tissues of the human body. This property is not shared by any of the classical biomaterials. A wide range of applications is envisaged for the bioglass ceramics that have so far been developed; some are still undergoing animal tests while others are being clinically tested in humans. Possible applications are the replacement of vertebrae and use in the middle ear, throat, nose, and eye, in the entire head region, in the shoulder and leg, and in dental prosthetics, in particular the replacement of dental roots (a hard tissue substitute in the broadest sense of the word). The question as to the behavior of a bone/bioglass ceramic contact or bond on a long‐term scale and on being exposed to varying mechanical stress has still not been satisfactorily answered, because interdisciplinary research in this field is still immature. All observations made so far indicate, however, that the materials do not cause any adverse effects.
Organometallic Rhodium(III) Complexes as Catalysts for the Photoreduction of Protons to Hydrogen on Colloidal TiO2
Authors: Kölle Ulrich , Grützel Michael
Published: December 2003

The photoreduction of H+ to H2 by sunlight and colloidal TiO2 in the presence of the rhodium(III) complexes 1 (ppy = oligopyridine ligand, e.g., bipyridyl; L=H2O, Cl⊖, Br⊖, I⊖; n = 1, 2) is possible without the participation of colloidal platinum and is not restricted to alkaline solution. The complexes are thereby reduced, via the RhII stage, to RhI complexes, which then undergo transformation to the RhIII complexes with evolution of hydrogen. The course of the reaction was investigated by cyclic voltammetry and pulse radiolysis as well as by transient absorption spectroscopy.
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Diene, Alkyne, Alkene, and Alkyl Complexes of Early Transition Metals: Structures and Synthetic Applications in Organic and Polymer Chemistry
Authors: Yasuda Hajime , Nakamura Akira
Published: December 2003

An unprecedented series of highly reactive alkene‐and diene‐complexes of the early transition metals (Groups 3A–5A of the periodic system) have been isolated recently. Diene complexes of this sort (M  Ti, Zr, Hf, Nb, Ta) prefer, besides the (η4‐s‐cis‐diene)metal structure, either a novel bent η4‐metallacyclo‐3‐pentene structure or the unique (η4‐s‐trans‐diene)metal structure. In bis(diene)metal complexes of Nb and Ta the η4‐s‐cis‐dienes assume an unusual exo‐endo (supine‐prone) geometry. The MC bonds in these diene‐metal complexes generally exhibit highly polarized σ‐bonding along with π‐bonding character. The complexes therefore undergo a variety of regio‐ and stereoselective carbometalations with substrates containing CC, CO, or CN multiple bonds. Examples of the products that can be obtained include ketones, vinyl ketones, unsaturated primary, secondary, and tertiary alcohols, as well as diols and unsaturated acids. Mechanistic studies on the stoichiometric and catalytic conversions of unsaturated hydrocarbons provides, inter alia, some insights into the course of polymerization reactions.
RP‐Bridged Metal Carbonyl Clusters: Synthesis, Properties, and Reactions
Authors: Huttner Gottfried , Knoll Konrad
Published: December 2003

Metal carbonyl clusters possess a complicated chemistry that is only beginning to be understood. One of the main current goals in this area is thus an understanding of their reactivity. This article describes the syntheses and reactions of clusters that contain metal carbonyl fragments bridged by a main‐group element. But what is the sense of making such clusters still more complicated by the incorporation of main‐group elements? The example of μ3‐bridged carbonyl clusters will serve to show that the main‐group element plays an important role in the study of reaction paths; it holds the metal carbonyl fragments together even when the bonds between them are broken in the course of a reaction. Trinuclear μ3‐bridged clusters prove to be small enough to allow the analysis of typical cluster reactions (such as the reversible breaking of metal‐metal bonds) in terms of single reaction steps. They are also large enough to provide surprises by their multifaceted reactivity. It will be shown that a detailed study of trinuclear RX‐bridged metal carbonyl clusters (X  N, P, As, Sb, Bi)—a very small part of carbonyl cluster chemistry—can lead to a better understanding of the general reaction principles involved.
The Role of Debye Screening Length in Ordered Arrays of Cylindrical Nickel Dimethylglyoxime Particles
Authors: Okubo Tsuneo
Published: December 2003

The electrostatic repulsion between colloid particles and the important role of Debye screening length are exemplified by particles of nickel dimethylglyoxime. In sedimentation equilibrium in salt‐free solution, the cylindrical particles form hexagonal arrays like those formed by tobacco mosaic virus. These arrays can be observed under a microscope. The Young's modulus of the lattice structures is 0.47 Pa.
A 1‐Oxa‐2‐nickela‐5‐cyclopentanone from Ethene and Carbon Dioxide: Preparation, Structure, and Reactivity
Authors: Hoberg Heinz , Peres Yolande , Krüger Carl , Tsay Yi‐Hung
Published: December 2003

Complex 1 is a key intermediate in the Ni0‐promoted CC bond formation between alkenes and CO2; it contains 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) as ligand. The NiC bond of 1 can participate in further, regioselective insertion reactions with alkenes. The nickelacycle is thus a model complex for the study of Ni‐catalyzed reactions.
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Concerning the Structure of Benzene
Authors: Ermer Otto
Published: December 2003

The D6h structure of benzene has not yet been proven—that is the quintessence of an informative discussion in which all available experimental (and theoretical) findings were examined in order to determine whether or not they definitively rule out the “Kekule structure” (D3h.)‐Neither spectroscopic nor diffraction methods of analysis provide data that are in disagreement with the D3h, structure. The discussion of the structure of benzene in textbooks should therefore be formulated more carefully. Furthermore, one should exercise caution in analyzing the alternation of CC bond lengths in annulenes by X‐ray diffraction.
Preparation of F4SCHCOF by Isomerization of F5SCHCO
Authors: Krügerke Thomas , Buschmann Jürgen , Kleemann Gert , Luger Peter , Seppelt Konrad
Published: December 2003

The alkylidene sulfur tetrafluoride 3 containing a functional group may be prepared simply and in good yield in two steps starting from 1. The ketene 2 is also new. The driving force for the isomerization 2 → 3 is the transformation of cumulative double bonds to conjugated double bonds. An X‐ray structure analysis of 3 at −168°C revealed that the double bond system is cisoid‐planar.
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Liquid Crystalline Polymers
Authors: Finkelmann Heino
Published: December 2003

The liquid crystalline behavior of low molecular weight compounds has been known for more than a century; synthetic polymers have been manufactured on a large scale for several decades, but just recently it was found possible to produce polymers using the structural principles of liquid crystalline compounds. The resulting materials have, as expected, unusual properties. Numerous applications, not only in opto‐electronics, are already anticipated for such materials.
How Chemistry and Physics Meet in the Solid State
Authors: Hoffmann Roald
Published: December 2003

To make sense of the marvelous electronic properties of the solid state, chemists must learn the language of solid‐state physics, of band structures. An attempt is made here to demystify that language, drawing explicit parallels to well‐known concepts in theoretical chemistry To the joint search of physicists and chemists for understanding of the bonding in extended systems, the chemist brings a great deal of intuition and some simple but powerful notions. Most important among these is the idea of a bond, and the use of frontier‐orbital arguments. How to find localized bonds among all those maximally delocalized bands? Interpretative constructs, such as the density of states, the decomposition of these densities, and crystal orbital overlap populations, allow a recovery of bonds, a finding of the frontier orbitals that control structure and reactivity in extended systems as well as discrete molecules.
Cluster of Clusters: Structure of the 37‐Atom Cluster [(p‐Tol3P)12Au18Ag19Br11]2⊕ and a Novel Series of Supraclusters Based on Vertex‐Sharing Icosahedra
Authors: Teo Boon K. , Hong M. C. , Zhang Hong , Huang D. B.
Published: December 2003

The title compound 1 can be regarded as a derivative of a “small supracluster”. This supracluster belongs to a series of vertex‐sharing icosahedra with a metal atom at the center of each icosahedron; the basic structural unit thus comprises 13 atoms. The simplest supracluster of 25 atoms (i.e. two units with a common corner; 2 × 13 − 1 = 25) is known. The 37‐atom cluster 1 and a 38‐atom analogue could be ascribed to a skeleton with 3 × 13 − 3 = 36 atoms, which additionally contains one or two apical Ag atoms, respectively. (Tol = tolyl)
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Molecular Beam Studies of Elementary Chemical Processes (Nobel Lecture)
Authors: Lee Yuan Tseh
Published: December 2003

Which internal degrees of freedom of a reactant influence the reaction probability and what consequences does this have on the course of elementary chemical processes? These questions, whose answers are very important for the understanding of reaction dynamics and for checking the predictions of quantum‐mechanical calculations, were addressed by the recipients of the 1986 Nobel Prize for Chemistry—Y. T. Lee, J. C. Polanyi, and D. Herschbach (his Nobel Lecture will appear in the December issue). They studied reactions by using the crossed molecular beam method or by measurement of IR chemiluminescence and were thereby able to determine the relative orientations of the reactants most favorable for a reactive collision, to prove some proposed reaction mechanisms to be invalid, to detect and interpret unexpectedly small activation energies, and to clarify the nature of the energy transfer between reactants and products.
Some Concepts in Reaction Dynamics (Nobel Lecture)
Authors: Polanyi John C.
Published: December 2003

The objective in this work has been one which I have shared with the two other 1986 Nobel lecturers, D. R. Herschbach and Y. T. Lee, as well as with a wide group of colleagues and co‐workers who have been responsible for bringing this field to its current state. That state is summarized in the title; we now have some concepts relevant to the motions of atoms and molecules in simple reactions, and some examples of the application of these concepts. We are, however, richer in vocabulary than in literature. The great epics of reaction dynamics remain to be written. I shall confine myself to some simple stories.

For corrigendum see DOI:10.1002/anie.198712982
Carbosilanes
Authors: Fritz Gerhard
Published: December 2003

Carbosilanes are compounds in which the elements carbon and silicon occupy alternate positions in the molecular framework. Formal replacement of every second carbon atom in the diamond lattice by a silicon atom gives silicon carbide, which exists, however, in several modifications characterized by different stacking orders. The SiC lattice is the basis of most carbosilanes.[1] These are divided on the basis of structural differences into carborundanes, silascaphanes, and molecules that no longer contain elements of the silicon carbide structure. In the carborundanes the Si–C six‐membered rings are arranged in the chair form, in the silascaphanes in the boat form. The molecular framework of the third group is derived from barrelane and asterane. The reactivity of the carbosilanes is determined mainly by the substituents on the skeletal atoms. The presence of SiH or Si–halogen groups leads to a high reactivity, while derivatives with organic groups on the silicon atoms and CH2 or CH groups in the skeleton are much less reactive. However, even such CH2 and CH groups permit certain characteristic reactions. Because of their structural features and the range of substituents that can be introduced, the carbosilanes are presently of considerable interest with respect to technological developments as precursors for ceramics.
Chemistry of the Silicon‐Silicon Double Bond
Authors: West Robert
Published: December 2003

Disilenes, compounds containing silicon‐silicon double bonds, can be isolated as thermally stable, yellow‐ or orange‐colored crystalline compounds; the substituent groups at silicon must be large (mesityl, tert ‐butyl, etc.) to prevent polymerization. Structural and spectro‐scopic studies indicate many similarities between the 3p–3p π bonding in disilenes and the 2p‐2p π bonding in olefins, but disilenes are much more reactive than alkenes. The reactions of disilenes lead to many new classes of silicon compounds, including three‐ and four‐membered rings which present novel problems in chemical bonding.