Reaction of amines with 1,3-dienes catalysed by nickel complexes

Abstract

Reactions of morpholine, piperidine, pyrrolidine, di-n-propylamine, n-butylamine, aniline, and p-anisidine with buta-1,3-diene in the presence of catalytic quantities of nickel acetylacetonate and di-isopropoxyphenylphosphine have been studied. Mixtures of 1 : 1 (butenyl) and 2 : 1 (octadienyl) amine products are produced and the reaction with morpholine has been studied in detail to examine the factors determining the product mixtures. Butenyl adduct formation is favoured by (a) a 3 : 1 ratio of phosphine–nickel salt concentration, (b) use of nickel halides with ethanol solvent, and (c) a low effective concentration of butadiene. A product mixture containing 86% octadienyl adduct was obtained by using a preformed Ni⁰ complex Ni[P(OPh)₃]₄. Reaction of morpholine and isoprene gave mainly a 1 : 1 adduct and small amounts of a 2 : 1 adduct; a similar reaction with trans-piperylene gave only a 1 : 1 adduct. The mechanism of the reactions is discussed in terms of formation of the butenyl and octadienyl adduct formation from π-allylnickel and bis-π-allylnickel complexes. The use of cocatalysts such as sodium borohydride in the reactions is discussed. Isomerisation of branched to linear butenyl adduct has been demonstrated to occur.