A metal π-Lewis base activation model for Pd-catalyzed hydroamination of amines and 1,3-dienes

Abstract

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.