Regio- and stereo-chemistry in allylation of aryl Grignard reagents catalyzed by phosphine-nickel and -palladium complexes

Abstract

Nickel and palladium complexes with the 1,1′-bis(diphenylphosphino)ferrocene ligand effectively catalyze regioselective cross-coupling of allylic ethers such as 1- or 3-methyl-2-propenyl silyl ethers with aryl-Grignard reagents, where the nickel catalyst leads to carbon—carbon bond formation at the more substituted position while carbon–carbon bond formation occurs at the less substituted position in the case of the palladium catalyst. Allylation of cis- and trans-5-methyl-2-cyclohexenyl silyl ethers was found to proceed with inversion of configuration with both the nickel and palladium catalysts. The stoichiometric reaction of a (1-methyl-π-allyl)palladium complex with the phenyl-Grignard reagent in the presence of phosphine ligands was also studied. A mechanism involving formation of the π-allyl(aryl)ML 2 intermediate is proposed.