Asymmetric Synthesis Catalyzed by Chiral Ferrocenylphosphine-Transition Metal Complexes. 2. Nickel- and Palladium-Catalyzed Asymmetric Grignard Cross-Coupling

Article abstract of DOI:10.1021/ja00365a033

Various kinds of chiral ferrocenylphosphines, which have both planar and central elements of chirality and also a functional group on the side chain, have been used as ligands for nickel or palladium complex catalyzed asymmetric cross-coupling of secondary alkyl (1-phenylethyl, 2-octyl, and 2-butyl) Grignard reagents with organic halides such as vinyl bromide, (E)-β-bromostyrene, 2-bromopropene, and bromobenzene. (S)-N,N-Dimethyl-1-<(R)-2-(diphenylphosphino)ferrocenyl>ethylamine <(S)-(R)-PPFA> was one of the most effective ligands giving the coupling product, 3-phenyl-1-butene, of up to 68percent ee in the reaction of 1-phenylethylmagnesium chloride with vinyl bromide, and it was found that the ferrocene planar chirality is more important than the carbon central chirality and the dimethylamino group is the first requisite for the high selectivity.The stereoselectivity was not affected by introduction of substituents onto the diphenylphosphino group of ligand, but was strongly affected by changing the steric bulkiness of the secondary amino group on the ferrocenylphosphine side chain.A mechanism, where the coordination of the amino group on the ligand with the magnesium atom in the Grignard reagent plays a key role in a diastereomeric transition state, is proposed to account for the ferrocenylphosphine ligands causing a high asymmetric induction.