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Organic Syntheses via Organometallics

In 1890 Mond, Lange and Quinke1) discovered the synthesis of Ni(CO)4 from metallic nickel and carbon monoxide. A few years later Sabatier and Senderens2) were led to attempt the preparation of a volatile compound similar to Ni[CO]4 using ethene instead of carbon monoxide, but without success. Nevertheless, in the course of these experiments they discovered catalytic hydrogenation. More than 60 years later we were able to realize the original idea of Sabatier in part when we managed to prepare first Ni[COD]2 3); and later Ni[C2H4]3 4). Numerous complexes of nickel(0) have since been synthesized.
G. Wilke

Diazadiene-Controlled C-C Coupling Reactions on Palladium and Iron

Transition metal centers can act as electrophiles or nucleophiles and also transfer electrons to or accept electrons from substrates. In addition the metals can act as simple templates and thus impose geometrical factors on two or more substrates. All of these features can be monitored by additional ligands. While for stoichiometric metal centered reactions drastic conditions and changes in the energy content of the metal compound are possible the energetic hypersurface for a good catalytic reaction must be rather smooth relative to the temperature. Since many substrates such as olefines, carbon monoxide or hydrogen are kinetically inert it seems unprobable that stable metal compounds are catalysts per se. Many of the activation steps in homogeneous catalysis therefore correspond to raising the total system to the ground level of the catalytic energy hypersurface. For a catalytic reaction in the mechanistic sense such a surface must not necessarily have a descend (almost degenerate catalyes such as olefin metathesis, H/D-scrambling, some olefin isomerizations), for a productive catalysis there should of course be a declining slope with the reaction coordinate. In the following paragraphs reactions involving the metal center activation, substrate binding and transformation, and product release will be discussed with many new examples from the catalytic chemistry of palladium and iron systems, in which diazadienes (DAD) constitute the control ligands [1].
H. tom Dieck, Chr. Munz, J. Ehlers

Highly Reactive π-Arene Iron Complexes and their use in Stoichiometric and Catalytic Cyclic Addition Reactions

Cyclic addition reactions of unsaturated organic molecules in the coordination sphere of transition metals have already been observed for several different systems. Our own approach to this field of chemistry involves the use of highly reactive transition metal complexes, which can be obtained from metal atom ligand cocondensation techniques [1]. This allows one to do the cyclic additions at low temperatures, which should have a considerable impact on the direction and selectivity of the reactions.
Dongqi Hu, Hans Pritzkow, Hartmut Schäufele, Catherine Tolxdorff, Ulrich Zenneck

Stereochemistry of Arenetricarbonylchromium Complexes Useful Intermediates for Stereoselective Syntheses

Since the discovery of ferrocene in 1951 metallocenes have attracted an everincreasing interest mainly for two reasons:
  • Their aromaticity gives rise to a wide variety of special reactions and interesting physicochemical properties (especially spectral data)
  • The particular (sandwichtype) molecular geometry and in connection with this their special symmetry is the basis of unique stereochemical features (1).
Karl Schlögl

Ironcarbonyl Complexes of Exocyclic Polyenes. The Tricarbonyl(1,3-Diene)Iron Moiety as Remote Substituent

The mono and dimetallic ironcarbonyl complexes of 5,6,7,8-tetramethylidenebicyclo[2.2.2]oct-2-ene, 5,6,7,8-tetramethylidenebicyclo[2.2.2]oct-2-yl and of 3,4,6,7-tetramethylidenebicyclo[2.2.1]oct-2-yl derivatives can be prepared stereoselectively. Their chemistry has been investigated and has unveiled several cases of useful lateral control by remote (diene)Fe(CO)3 moieties in SN1 solvolyses of esters, Friedel-Crafts acylation of (diene)Fe(CO)3 systems, nucleophilic reductions of ketones, hydrogen/deuterium exchanges of methylene groups α to carbonyl functions, and in Diels-Alder additions of exocyclic s-cis-butadiene moieties grafted onto bicyclic skeletons. The remote (diene)Fe(CO)3 group influences on the reactions through steric effects due to its bulk or/and through electronic effects. Depending on the electron demand of the reaction, the remote (diene)Fe(CO)3 group can act either as an electron-withdrawing substituent (inductive effect due to its permanent dipole) or as an electron-releasing substituent due to its polarisability.
Pierre Vogel, Raymond Roulet

Metal-Induced Dimerisations of Cyclic Diacetylenes

At the beginning of our activities in the field of organometallic chemistry were spectroscopic and theoretical investigations concerned with π/σ interactions1. The comparison of the calculated energy levels of the highest occupied MO’s of hexadiyne-1,5 (1) and heptadiyne-1,6 (2) shows a remarkable influence on the chain length. The separation between the bonding (π+ i) and antibonding (π- i) linear combination of the “in plane” π-MO’s of two acetylene moieties is diminished if we connect them with an ethano bridge as in 1 (see Figure 1 left).
Rolf Gleiter, Michael Karcher, Detlef Kratz, Stefan Rittinger, Volker Schehlmann

Novel Catalytic Applications of Ruthenium Clusters

Novel catalytic C-N, C-C, and C-O coupling reactions of simple organic substrates have been discovered using anionic or neutral ruthenium clusters as homogeneous catalysts. All these reactions lead to new organic molecules thus demonstrating the unique catalytic potential of ruthenium clusters. In some cases the catalytic process can be explained in terms of a cycle involving exclusively intact cluster intermediates.
Georg Süss-Fink

Selective Organic Synthesis by Diene Complexes of Early Transition Metals

Since the development of new synthetic methods for novel 1,3-diene complexes of early transition metals,1 extensive investigations of their reactivities have been done by Prof. G. Erker and by us with mostly organic unsaturated compounds. The general scheme thus revealed is shown below.2
A. Nakamura, H. Yasuda

Metallacyclobutanes: Synthons and Catalysts

New synthetic approaches were developed to di-Grignard reagents which give a rather general access to a great variety of mono- and dimetallacyclobutanes. Their role in organic synthesis and in catalysis is discussed briefly.
F. Bickelhaupt

New Properties of Reagents by Complexation of Carbanions on Transition-Metals: Which Metal is in Each Case the Most Favorable One?

The transmetallation of carbanionid derivatives of Li, Mg or Zn by treating with transition-metal halides is the most important method for the preparation of transition-metal alkyls. This method seems to have no limitations with regard to the kind of the transition-metal and allows also the synthesis of very thermolabile alkyl derivatives, because the transmetallation occurs normally even below -60°C at a high rate. In those reactions the carbanionic residue is coordinated to a transition-metal according to Scheme 1, causing serious changes in the properties of the alkyl derivatives. The changes, stated in scheme 1, have proved to be useful in organic synthesis.
Thomas Kauffmann

Organometallic Transformations via C-H Bond Activation

The recent use of transition metal complexes to activate carbon-hydrogen bonds has allowed the conversion of hydrocarbons into functionalized organic molecules. New examples are described in which the adducts resulting from C-H bond oxidative addition are reacted with acetylenes and isocyanides. The complexes described include (C5Me5)Rh(PMe3)(R)H (R = H, CH3, Ph), (C5Me5)Rh(CNR)2, RhCl(PR3)2(CNR’), Fe(PMe3)2(CNR)3, and Ru(dmpe)2(naphthyl)H. Both aldimines and indoles are formed catalytically with these complexes.
William D. Jones, Valerie L. Chandler, Robert P. Duttweiler, Frank J. Feher, Edward T. Hessell, Grace C. Hsu, Walter P. Kosar

Remote Functionalization of Carbon-Hydrogen and Carbon-Carbon Bonds by Bare Transition Metal Ions in the Gas Phase

The selective functionaIization of C-H bonds remains one of the major focuses of catalytic and organic chemistry. High selectivity is often achieved by the presence of activating groups which induce the reactivity of the neighbouring C-H bonds by, for example, polarizing the bond, thus making the hydrogen more acidic, or by generally weakening the C-H bond. The selective functionalization of hydrocarbon segments of a molecule remote from any functional group represents a great challenge. While such reactions are common to enzymes which coordinate a functional group and geometrically select a specific section of the molecule (see, for example, the enzymatic conversion of stearic to oleic acid. Scheme 1), only a few cases in solution chemistry are reported [1] where a similar principle seems to be operative.
Gregor Czekay, Thomas Drewello, Karsten Eller, Carlito B. Lebrilla, Tilmann Prüsse, Christian Schulze, Norbert Steinrück, Detlev Sülzle, Thomas Weiske, Helmut Schwarz

Aktivierung von Mehrfachbindungssystemen auf Clustern

Die Gewinnung reaktiver Organometall-Cluster und die Verfügbarkeit von gezielten Synthesen haben es möglich gemacht, Substrate mit C-C-, C-N-, C-O- und N-N-Mehrfachbindungen facial auf diesen Clustern anzubinden. Dadurch werden ihr Bindungszustand und ihre Reaktivität stark verändert. In diesem Aufsatz werden einige Anknüpfungsreaktionen (Überdachungen) beschrieben sowie die dadurch möglich werdenden Isomerisierungen im Metallatom- wie im Ligandengerüst. Auf dem Cluster lassen sich Zwischenstufen einer hydrierenden Umwandlung vom Alkin zum Alkan und vom Nitril zum Amin isolieren und reversibel ineinander umwandeln. Eine kritische Zwischenstufe der enantioselektiven Olefin-Hydrierung wurde erstmalig faßbar. Typisch sind die Multimetall-induzierten Mehrfachbindungs-Spaltungen (C≡C, N=N, P=P) in der Ligandensphäre. Neue organische Reaktionen unter C-C- oder C- N-Verknüpfung werden möglich durch die Polarität von μ 3-Vinyliden-Liganden sowie über eine Erhöhung der Cluster-Reaktivität durch Einelektronen-Reduktion. Der thermische Zerfall eines Clusters mit Carben- und Nitrenliganden liefert die organischen Produkte der Kombination dieser Liganden.
Heinrich Vahrenkamp

Directed — and Undirected — Syntheses of Novel Organic Compounds via Iron, Cobalt and Chromium Complexes

Organometaliic compounds may be extremely useful intermediates in organic synthesis in a number of ways. In fact, with the help of metals and metal complexes one can bring about transformations, which cannot otherwise be achieved.[1] In this respect, we have started to engage in organometallic chemistry from three different viewpoints:
I. Metal Protected Syntheses of Highly Reactive Molecules
Spiro[2.5]octa-5,7-dien-4-one and 8-Methylenespiro[2.5]octa-4,6-diene
Dihydroacepentalene and the Acepentalene Problem
II. Metal Assisted Syntheses of Unconventional Molecules
Bridge Substituted and Bridge Anellated [2.2]Paracyclophandienes via Metal Complexes
A Simple Catalytic Route to Polycyclic Aromatic Compounds
III. Metal Promoted Syntheses of Organic Targets
The Pauson-Khand Reaction Revisited
Improving the Yield of Intermolecular Pauson-Khand Reactions
Iterative Construction of Linear and Angular Oligoquinanes
New Examples of Cyclopropyl Substituted Fischer Carbene Complexes
Armin de Meijere, Angelika Kaufmann, Rolf Lackmann, Hans-Christian Militzer, Oliver Reiser, Sten Schömenauer, Andreas Weier

Enantioselective Synthesis of Organic Compounds with Optically Active Transition Metal Catalysts and Transition Metal Compounds

Metabolism in man, animal and plant uses optically active compounds, e.g. L-amino acids, D-sugars etc. This metabolic stereospecificity manifests itself in macroscopic chiral structures such as snail shells, in which high stereoselectivities are observed. Other examples for plants are shown in Fig. 1.
Henri Brunner

Diolefin Iron Complexes — Useful and Versatile Tools in Organic Synthesis

This review aims to present our current work, which focuses on the preparation and use of Wittig reagents via allyl-Fe(CO)4 and dienyl-Fe(CO)3 complexes. We have applied these reagents, among others, to the highly stereoselective synthesis of naturally occurring triolefins. In a related topic, the reactivity of functionalized tricarbonyl(diene)iron complexes will be discussed with regard to their use in selective C-C coupling reactions.
A. Salzer

Donor-Acceptor-Substituted Cyclopropanes via Fischer Carbene Complexes

Fischer carbene complexes transfer their carbene ligand to a variety of different electron-deficient olefins to provide donor-acceptor-substituted cyclopropanes in good yields. Scope and limitations of this [2+1]-cycloaddition are described. Certain α,β-unsaturated nitriles suffer an insertion of the carbene into the C=N-bond to give new vinyl-substituted carbene complexes. The mechanism of this insertion reaction as well as that of the [2+1]-cycloaddition are discussed.
H.-U. Reißig


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