Abstract
Ni(P(OPh)3)4 and Ni(P(OEt)3)4 catalyze tile reaction of aryl and vinyl halides with olefins (l-leck reaction) and alkynes. © 1997 Elsevier Science Ltd. The formation of C-C bonds by the reaction of aryl halides with olefins (Heck reaction) in presence of palladium catalysts is a well studied reaction) We have been investigating the use of other metal catalysts for this reaction based on the known mechanism of the Pd catalyzed vinylation reaction. The key step in the reaction mechanism is the oxidative addition of a low valent coordinatively unsaturated metal complex to the aryl halide followed by olefin coordination, migratory insertion and reductive elimination. We have reported the use of Co(1), Rh (I) (Wilkinson's Catalyst) and Ir(1) (Vaska's complex) successfully based on this rationale, 2 We decided to investigate other new catalysts for the Heck reaction based on the reaction mechanism viz. a metal complex capable of oxidative addition reductive elimination and undergoing ligand dissociation and association. NiCI2(PPh3)2 is known to catalyze the reaction of aryl and aliphatic halides with olefins in the presence of Zn dust to give mixtures of addition and substitution products) But it is not a very useful catalyst for the Heck reaction because it gives different types of products with ethylacrylate (addition product) and styrene (substitution product). The highly active and air sensitive complex, Ni(PPh3)4, generated in situ by the action of Et3AI on Ni(acac)2, has been used for the intramolecular reaction of aryl halides with olefins to form indoles: Ni(P(OPh)3)4 and Ni(P(OEt)3)4 are stable metal complexes of Ni(0) and are well known to undergo ligand dissociation, oxidative addition and reductive elimination reactions and have been used to catalyze the reaction of allyl acetates with nucleophiles, s We report here, the first use of these stable Ni(0) metal complexes, for the activation of aryl halides for reaction with olefins (Heck reaction) and alkynes.
Published Version
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