Organolanthanide-Mediated Intramolecular Hydroamination/Cyclization of Conjugated Aminodienes: A Computational Exploration of Diverse Mechanistic Pathways for the Regioselective Generation of Functionalized Azacycles Supported by a Lanthanocene-Based Catalyst Complex

Abstract

The complete catalytic reaction course for the organolanthanide-mediated intramolecular hydroamination/cyclization (IHC) of (4E,6)-heptadien-1-amine by a prototypical achiral Cp*(2)LaCH(TMS)(2) precatalyst is critically scrutinized by employing a gradient-corrected DFT method. The condensed free-energy profile for the overall reaction, comprised of thermodynamic and kinetic aspects of individual elementary steps, is presented. A computationally verified, revised mechanistic scenario has been proposed, which is consistent with the empirical rate law, accounts for crucial experimental observations, and provides a first understanding of the origin of the measured negative DeltaS(++). It involves rapid substrate association/dissociation equilibria and facile intramolecular diene insertion, linked to turnover-limiting protonolysis of the eta(3)-butenyl-Ln functionality, with the amine-amidodiene-Ln adduct complex representing the catalyst's resting state. The thermodynamic and kinetic factors that determine the high regio- and stereoselectivity of the mechanistically diverse IHC of aminodienes have been elucidated. These achievements allow a deeper understanding and a consistent rationalization of the experimental results for aminodiene IHC and furthermore enhance the insights into general mechanistic aspects of the organolanthanide-mediated cycloamination.