Palladacycles: Effective Catalysts for a Multicomponent Reaction with Allylpalladium(II)-Intermediates

Palladium(II) complexes with an auxiliary bidentate ligand featuring one C-Pd bond and a Pd-N-donor bond (palladacycles) have been shown to afford improved yields of homoallylic amines from a three-component coupling of boronic acids, allenes and imines in comparison to the yields of homoallylic amines achieved with the originally reported catalyst (Pd(OAc)₂/P(t-Bu)₃), thus extending the scope of the reaction. ³¹P NMR monitoring studies indicate that distinct intermediates featuring Pd-P bonds originate in the reactions catalyzed by either Pd(OAc)₂/P(t-Bu)₃ or the pallada(II)cycle/P(t-Bu)₃ systems, suggesting that the role of the pallada(II)cycles is more complex than just precatalysts. The importance of an additional phosphine ligand in the reactions catalyzed the pallada(II)cycles was established, and its role in the catalytic cycle has been proposed. Insights into the nature of the reactive intermediates that limit the performance of the originally reported catalytic systems has been gained.