期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 16, 期 5, 页码 1670-1678出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.200902071
关键词
Heck reaction; homogeneous catalysis; metallacycles; palladium; X-ray diffraction
资金
- Ministero dell'Istruzione, dell'Universita e della Ricerca
The isolation of sigma-alkylpalladium Heck intermediates, possible when beta-hydride elimination is inhibited, is a rather rare event. Performing intramolecular Heck reactions on N-allyl-2-halobenzylamines in the presence of [Pd(PPh3)(4)], we isolated and characterized a series of stable bridged palladacycles containing an iodine or bromine atom on the palladium atom. Indolyl substrates were also tested for isolation of the corresponding complexes. X-ray crystallographic analysis of one of the indolyl derivatives revealed the presence of a five-membered palladacycle with the metal center bearing a PPh3 ligand and an iodine atom in a cis position with respect to the nitrogen atom. The stability of the sigma-alkylpalladium complexes is probably a consequence of the strong constraint resulting from the bridged junction that hampers the cisoid conformation essential for beta-hydride elimination. Subsequently, the thus obtained bridged five-membered palladacycles were proven to be effective precatalysts in Heck reactions as well as in cross-coupling processes such as Suzuki and Stille reactions.
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