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  Co(salen)-type oxygenation catalysts

Co(salen) and analogue compounds are used as biomimetic oxygen transfer catalysts for the preparative oxygenation of organic substrates. It is likely that electron-transfers and complexation reactions of the substrate to the Co central atom are part of the overall mechanism. Electrochemical redox processes of the catalyst are studied as model reactions for preparative oxygenations and enzyme processes. On one hand we characterize the structures of the catalysts in solvents which are also used in oxygenations (DMF, CH2Cl2, etc.), on the other hand we investigate the interaction of the Co-complexes with substrates (e.g., anilines, indoles) in the presence and absence of oxygen. Exchange reactions are described by a three-rung ladder scheme with coupled electron-transfer and ligand exchange step. The mechanism is a complex combination of electron transfer and chemical reaction steps. This also makes it interesting to a study by simulation techniques. The complexation of anilines to Co(salen) in acetonitrile was thus studied by a combination of simulation and experiments.

It is planed to synthesize and study a Co(salen) analogue with two centers of chirality, which incorporate formylhydroxy[2.2]paracyclophane in the ligand.

Coworkers in this project

Ulrich Bee, Emerich Eichhorn, Bernhard Gollas, Petra Marschner, Vili Mikic, Elena Popa, Dirk Ruff and Hartmut Stahl

We acknowledge funding of various aspects of this project by the Deutsche Forschungsgemeinschaft, Bonn - Bad Godesberg, the Volkswagen-Stiftung, Hannover, and the land Baden-Württemberg within a Landesforschungsschwerpunkt.

Publications from this project

E. Eichhorn, A. Rieker, B. Speiser und H. Stahl, Inorg. Chem., 36, 3307 - 3317 (1997); Electrochemistry of Oxygenation Catalysts. Part 3. Thermodynamic Characterization of Electron Transfer and Solvent Exchange Reactions of Co(salen)/[Co(salen)]+ in DMF, Pyridine and Their Mixtures.

E. Eichhorn, A. Rieker und B. Speiser, Z. anorg. allg. Chem., 623, 810 - 817 (1997); Elektrochemie von Oxygenierungskatalysatoren. Teil 7. Synthese und Elektrochemie von Komplexen des Co(salen)-Typs mit zwei potentiellen über Spacer angebundenen axialen basischen Liganden.

B. Gollas, B. Speiser, H. Stahl, J. Sieglen und J. Strähle, Z. Naturforsch., 51b, 388 - 398 (1996); Electrochemistry of Oxygenation Catalysts. Part 6. Electrosynthesis, Structure, Analytical, and Electrochemical Properties of [CoIII(salen)(DMF)2]+ X- Salts (X = PF6, ClO4).

B. Speiser und H. Stahl, Angew. Chem., 107, 1222 - 1224 (1995); Angew. Chem. Int. Ed., 34, 1086 - 1089 (1995); Elektrochemie von Oxygenierungskatalysatoren. 5. Mitteilung. Komplexierung von [N,N-Bis(salicyliden)ethylendiiminato]cobalt(III) durch Aniline in Dimethylformamid.

E. Eichhorn, A. Rieker, B. Speiser und H. Stahl, in S. Torii (Hrsg.), Novel Trends in Electroorganic Synthesis, Proc. 2nd Intl. Symp. on Electroorg. Synth., Kodansha, Tokyo, 1994 (Publ. 1995), S. 173 - 174 (ISBN: 4-06-207503-2); Electrochemical Investigation of Oxygenation Catalysts.

Eichhorn und B. Speiser, J. Electroanal. Chem., 365, 207 - 212 (1994); Electrochemistry of Oxygenation Catalysts. Part 4. Solvent Composition Dependent Isopotential Points in Cyclic Voltammograms of Co(salen)+.

E. Eichhorn, A. Rieker, B. Speiser, J. Sieglen und J. Strähle, Z. Naturforsch., 48b, 418 - 424 (1993); Electrochemistry of Oxygenation Catalysts. Part 2. Improved Synthesis, Crystal Structure, and Electrochemical Properties of N,N-Bis(salicyliden)-ethylenediaminato Cobalt(III) Chloride.

E. Eichhorn, A. Rieker und B. Speiser, Angew. Chem., 104, 1246 - 1248 (1992); Angew. Chem. Int. Ed., 31, 1215 - 1217 (1992); Elektrochemie von Oxygenierungskatalysatoren. Teil 1. Die elektrochemische Oxidation von N,N-Bis(salicyliden)ethylendiiminato-kobalt(II) in Lösungsmittelgemischen -- Ein Beispiel für ein Leiterschema mit gekoppelten Elektronentransfer- und Lösungsmittelaustauschreaktionen.

A. Nishinaga, S. Förster, A. Rieker, E. Eichhorn und B. Speiser, Tetrahedron Lett. 33, 4425 - 4428 (1992); Co(salen) Catalyzed Oxidation of 2,4,6-Trisubstituted Anilines with t-butyl Hydroperoxide.

 

© AG Speiser 2011