This Review describes the application of nitroxides to synthesis and polymer chemistry. The synthesis and physical properties of nitroxides are discussed first. The largest section focuses on their application as stoichiometric and catalytic oxidants in organic synthesis. The oxidation of alcohols and carbanions, as well as oxidative C-C bond-forming reactions are presented along with other typical oxidative transformations. A section is also dedicated to the extensive use of nitroxides as trapping reagents for C-centered radicals in radical chemistry. Alkoxyamines derived from nitroxides are shown to be highly useful precursors of C-centered radicals in synthesis and also in polymer chemistry. The last section discusses the basics of nitroxide-mediated radical polymerization (NMP) and also highlights new developments in the synthesis of complex polymer architectures.

An intramolecular Mannich reaction (HNMe2, TiCl4) was used to convert 1,1'‐diacetylferrocene to the unsaturated amino[3]ferrocenophane 2. Subsequent hydrogenation gave 3. To obtain enantiomerically pure chelate P,P‐[3]ferrocenophane ligands the readily available pure dimethylamino[3]ferrocenophane enantiomers (R,R)‐3 and (S,S)‐3 each were treated with butyllithium followed by chlorodiphenylphosphane to yield the chelate P,N‐[3]ferrocenophanes (R,R,Rpl)‐10 and (S,S,Spl)‐10, respectively. Their treatment with HPPh2 in glacial acetic acid resulted in substitution of the –NMe2 group by –PPh2 with overall retention of configuration to yield (R,R,Rpl)‐11 and (S,S,Spl)‐11, respectively (both characterized by X‐ray diffraction). Similarly, the reaction of (R,R,Rpl)‐10 or (S,S,Spl)‐10 with dicyclohexylphosphane/HOAc yielded the pure (R,R,Rpl)‐12 and (S,S,Spl)‐12 enantiomers, respectively. Both these compounds were also characterized by X‐ray crystal structure analyses. (R,R,Rpl)‐12 was employed in catalytic asymmetric hydrogenation and also in asymmetric alternating carbon monoxide/propene copolymerization. A catalyst that was generated in situ from the chelate P,P‐[3]ferrocenophane ligand and palladium acetate gave the CO/propene alternating copolymer with a good activity and high asymmetric induction. The catalyst derived from the reaction of (R,R,Rpl)‐11 with [Rh(cod)2]BF4 was employed in the enantioselective hydrogenation of dimethyl itaconate (DMI) (13, ca. 95 % ee, R‐configured product) and methyl α‐acetamidocinnamate (MAC) 14 (ca. 24 % ee, R‐configured product). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Cooperative effects can be observed in various research areas in chemistry; cooperative catalysis is well-established, the assembly of compounds on surfaces can be steered by cooperative effects, and supramolecular polymerization can proceed in a cooperative manner. In biological systems, cooperativity is observed in protein-protein, protein-lipid and protein-molecule interactions. Synergistic effects are relevant in frustrated Lewis pairs, organic multispin systems, multimetallic clusters and also in nanoparticles. However, a general approach to determine cooperativity in the different chemical systems is currently not known. In the present concept paper it is suggested that, at least for simpler systems that can be described at the molecular level, cooperativity can be defined based on energy considerations. For systems in which no chemical transformation occurs, determination of interaction energies of the whole system with respect to the interaction energies between all individual component pairs (subsystems) will allow determination of cooperativity. For systems comprising of chemical transformations, cooperativity can be evaluated by determining the activation energy of the synergistic system and by comparing this with activation energies of the corresponding subsystems that lack an activating moiety. For more complex systems, cooperativity is generally determined at a qualitative level.

Nitroxide werden in der Synthese und in der Polymerchemie verwendet. In diesem Aufsatz werden zunächst Methoden zur Herstellung von Nitroxiden und deren physikalische Eigenschaften besprochen. Der folgende Abschnitt beschreibt die Verwendung von Nitroxiden als stöchiometrische und katalytische Oxidationsmittel in der organischen Synthese. Die Oxidation von Alkoholen und Carbanionen spielt dabei ebenso eine wichtige Rolle wie oxidative C‐C‐Bindungsknüpfungen. Anschließend widmet sich ein Abschnitt der Rolle von Nitroxiden als Abfangreagentien für C‐zentrierte Radikale in der Radikalchemie. Nitroxide, die sich von Alkoxyaminen ableiten, fungieren als nützliche Ausgangsmaterialien für C‐zentrierte Radikale, deren Einsatz in der Synthese und in der Polymerchemie beschrieben wird. Der letzte Abschnitt stellt die Grundlagen der Nitroxid‐vermittelten Polymerisation (NMP) vor und zeigt neuere Entwicklungen beim Design komplexer Polymerarchitekturen auf.

Carbene catalysed redox activation of α,β-unsaturated aldehydes is applied for generation of α,β-unsaturated acyl azoliums which undergo cyclopropanation upon reaction with a sulfur ylide and an alcohol to give the corresponding cyclopropanecarboxylic acid esters. With chiral carbenes good to excellent diastereo and enantioselectivities are obtained.