Wyniki wyszukiwania - BazTech

Ograniczanie wyników

1 Wiadomości Chemiczne

1 2009

Znaleziono wyników: 1

Liczba wyników na stronie

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych: palladium colloid

Sortuj według:

Ogranicz wyniki do:

Nanocząsteczkowe katalizatory palladowe w reakcjach tworzenia wiązań C-C

Trzeciak A. M., Ziółkowski J. J.

Wiadomości Chemiczne

2009

[Z] 63, 1-2

1-15

The important role of palladium nanoparticles has been recently demonstrated in many catalytic systems designed for C-C bond forming reactions [1-4]. There are examples of catalytic systems described earlier as homogeneous in which Pd(0) nanoparticles were now identified. In the article three different palladium catalytic systems are discussed. In the first one, Pd(0) nanoparticles, obtained by chemical reduction of PdCl2 and stabilized by polyvinylpyrrolidone, were used for Heck coupling in [Bu4N]Br medium. Decrease of nanoparticles size in reaction conditions was explained as a result of dissolution of Pd(0) colloid and simultaneous formation of catalytically active monomolecular anionic palladium complexes [33]. The second example presents application of Pd(II) and Pd(0) supported on alumina-based oxides in Suzuki-Miyaura reaction [36]. Reduction of Pd(II) to Pd(0) nanoparticles under reaction conditions was confirmed. In contrast to the first described case, in Suzuki-Miyaura reaction the size of Pd(0) nanoparticles was the same before and after the catalytic cycle. The catalytic activity of both palladium forms was quite high, however Pd(0) formed in situ was slightly more efficient as catalyst. In the third part of the article studies of palladium reduction in anionic complexes of [IL]2[PdX4] type are shown, where IL = imidazolium cation [37]. These complexes catalyzed well Suzuki-Miyaura cross-coupling, but they were not stable under reaction conditions and decomposed to Pd(0) nanoparticles and Pd black. Using ESI-MS method it was possible to identify polynuclear (Pd3, Pd5) intermediate forms, stabilized with imidazolium cations or N-heterocyclic carbenes. In all systems discussed in the article co-existence of Pd(0) nanoparticles and monomolecular complexes was observed. That is important for understanding of the nature of catalytically active forms in C-C bond forming reactions.