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σ‐Alkylpalladium Intermediates in Intramolecular Heck Reactions:Isolation and Catalytic Activity
Author(s) -
Beccalli Egle M.,
Borsini Elena,
Brenna Stefano,
Galli Simona,
Rigamonti Micol,
Broggini Gianluigi
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200902071
Subject(s) - chemistry , intramolecular force , heck reaction , stille reaction , medicinal chemistry , palladium , hydride , ligand (biochemistry) , catalysis , stereochemistry , photochemistry , metal , organic chemistry , biochemistry , receptor
The isolation of σ‐alkylpalladium Heck intermediates, possible when β‐hydride elimination is inhibited, is a rather rare event. Performing intramolecular Heck reactions on N ‐allyl‐2‐halobenzylamines in the presence of [Pd(PPh 3 ) 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 PPh 3 ligand and an iodine atom in a cis position with respect to the nitrogen atom. The stability of the σ‐alkylpalladium complexes is probably a consequence of the strong constraint resulting from the bridged junction that hampers the cisoid conformation essential for β‐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.