Publication Details (including relevant citation information):
Dmitry Tsvelikhovsky,[a] Inna Popov,[b] Vitaly Gutkin,[b] Alina Rozin,[a] Azariya Shvartsman,[a] and Jochanan Blum*[a]
Eur. J. Org. Chem. 2009, 98–102
We describe two different pathways by which palladium-cat- alyzed Heck and Suzuki coupling reactions take place. When sol–gel entrapped palladium acetate was used as a catalyst, the reactions proceed by the formation of metallic nanopar- ticles. Such particles were already formed during the immo- bilization of the palladium salt. Upon application of palla- dium derivatives of proline, tyrosine, or alanine, either in their homogeneous or in their sol–gel entrapped version, no Pd0 particles could be detected, even when the couplings were carried out in boiling mesitylene (161 °C) or during prolonged reaction periods (48 h). The reactions in the presence of the amino acid derivatives proceeded at a higher rate than those by the entrapped palladium acetate. The existence of palladium nanoparticles was investigated with the aid of high-resolution scanning transmission electron microscopy equipped with energy dispersive X-ray spectroscopy, as well as by X-ray photoelectron spectroscopy.