Pentacoordinated Carboxylate [pi]-Allyl Nickel Complexes as Key Intermediates for the Ni-Catalyzed Direct Amination of Allylic Alcohols

Direct amination of allylic alcohols with primary and secondary amines catalyzed by a system made of [Ni(1,5-cyclooctadiene)2] and 1,1'-bis(diphenylphosphino)ferrocene was effectively enhanced by adding nBu4NOAc and molecular sieves, affording the corresponding allyl amines in high yield with high monoallylation selectivity for primary amines and high regioselectivity for monosubstituted allylic alcohols. Such remarkable additive effects of nBu4NOAc were elucidated by isolating and characterizing some nickel complexes, manifesting the key role of a charge neutral pentacoordinated η3-allyl acetate complex in the present system, in contrast to usual cationic tetracoordinated complexes earlier reported in allylic substitution reactions.