A DFT investigation into the origin of regioselectivity in palladium-catalyzed allylic amination

The addition of amines or aziridines to prenylacetate is catalyzed by palladium phosphine complexes. The first-formed products have recently been shown to be the branched olefins R2NCMe2CH=CH2, R = alkyl, or R2 = 1,2-C6H10, for example. DFT calculations using the MPW1K functional were performed on reactions of the suspected intermediate η3-prenyl complex [Pd(η3-Me2CCHCH2)(PH3)2]+ with dimethylamine and ethylene imine. The activation barrier for the nucleophilic attack by the amine or the aziridine is calculated to be similar for either the sterically hindered site of the π-allyl ligand to produce the branched olefin complex or the unhindered site to give the linear olefin complex. Therefore, these calculations do not reveal the experimentally observed preference for attack. This observation, along with the experimental observation of lack of isomerization of the branched olefin product of the aziridine reactions, appears to rule out the intermediacy of a π-allyl complex [Pd(η3-Me2CCHCH2)L2]+, L = phosphine or L2 = diphosphine in the C–N bond-forming reaction.Key words: allyl palladium, amine, aziridine, DFT, mechanism, catalysis.