As a general mechanism proposal, a Pd(ii)-H migration insertion process is not able to well explicate the Pd-catalyzed hydroamination of amines and 1,3-dienes. Here we demonstrate that 1,3-dienes form electron-neutral and HOMO-raised η2-complexes with Pd(0) via π-Lewis base activation, which undergoes protonation with a variety of acidic sources, such as Brønsted acids, Lewis acid-activated indazoles, and Pd(ii) pre-catalyst triggered ammonium salts. The resultant π-allyl palladium complexes undergo the amination reaction to give the final observed products. FMO and NPA analyses have revealed the nature of Pd(0) mediated π-Lewis base activation of 1,3-dienes. The calculation results show that the π-Lewis base activation pathway is more favourable than the Pd(ii)-H species involved one in different reactions. Further control experiments corroborated our mechanistic proposal, and an efficient Pd(0) mediated hydroamination reaction was developed.
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