A novel non-insertive mechanism for neutral organozirconium-catalyzed aminoalkene hydroamination: Density functional theory survey

In this article, the reaction mechanism of neutral organozirconium-catalyzed intramolecular aminoalkene hydroamination is investigated by using density functional theory (DFT) method. Three distinct pathways, migratory olefin σ-insertion, [2π + 2π] cycloaddition, and C–N ring closure triggered by concurrent proton-transfer at the Cdouble bond; length as m-dashC linkage, are mainly considered to explore the reaction mechanism. After the initiation of reaction, we designed three routes starting from two different possible intermediates (Zr-alkyl heterocycle 5 and metallocyclic amido intermediate 4). Our results indicate that the favored channel 1–2 in route 1 (C-terminal protonolysis → migratory insertion → protonolysis) is likely to undergo, which thanks to the benefit of the significant irreversibility of intermediate 6. Intermediate 6 is formed via the C-terminal protonolysis of one metallocyclic amido complex 4·S-1. The overall reaction mechanism could be described as [2π + 2π] cycloaddition because metallocyclic amido intermediate 4, which determines the overall reaction, could be formed via the reaction initiation and the catalyzed cycle of channel 1–2. It is found that the catalyzed cycle of channel 1–2 by metallocyclic amido intermediate would be the main manner in the reaction after all initial catalyst are converted into metallocyclic amido intermediate in one round. Our results rule out the suggested proton-triggered C–N ring closure concerted process in the experiment.