Síntesis de nuevos complejos de paladio tipo pincer. Evaluación de su actividad catalítica en reacciones de acoplamiento cruzado en agua

Zusammenfassung

The syntheses and the most relevant catalytic properties of three new pincer palladium complexes are reported. A novel non-symmetrical PCN type and two new CNC type pincers containing N-heterocyclic carbene moieties are prepared by short synthetic routes with moderate overall yields. The catalytic activity of the latter palladium complexes in Suzuki- Miyaura, Heck, Sonogashira and Hiyama is evaluated, focusing on the use of water as the reaction solvent. These palladacycles feature excellent catalytic activity upon aforementioned cross-coupling reactions with competitive yields, catalyst loadings, and convenient reaction media. Good to excellent results (including high TON values and extended recycling procedures) are obtained in many couplings for a range of electronically dissimilar reaction partners, even when the reaction is performed in neat water. On the basis of a series of kinetics studies, Hg drop tests, several quantitative poisoning experiments and Transmission Electron Microscopy (TEM) images, the real role of the synthesized palladacycles, which probably is closely linked to the formation and active participation of palladium nanoparticles, is discussed. The syntheses of two new asymmetrical ligands, based on fenchyl moieties are also reported. The latter ligands were designed to generate new pincer-type frameworks and to induce asymmetric coupling reactions. This part of the Thesis was performed at the University of Cologne, Germany, under the supervision of Prof. Bernd Goldfuss.