Organolanthanide-Mediated Intermolecular Hydroamination of 1,3-Dienes:Mechanistic Insights from a Computational Exploration of Diverse Mechanistic Pathways for the Stereoselective Hydroamination of 1,3-Butadiene with a Primary Amine Supported by an a

摘要

The complete catalytic reaction course for the organolanthanide-mediated intermolecular hydroamina-tion of 1,3-butadiene and n-propyl-amine by an archetypical [Me_2Si(eta~5-Me_4C_5)_2NdCH(SiMe_3)_2] precatalyst was critically scrutinized by employing a reliable gradient-corrected DFT method.A free-energy profile of the overall reaction is presented that is based on the thorough characterization of all crucial elementary steps for a tentative catalytic cycle.A computationally verified,revised mechanistic scenario is proposed which is consistent with the experimentally derived empirical rate law and accounts for crucial experimental observations.It involves kinetically mobile reactant association/dissociation equilibria and facile,reversible intermolecular diene insertion into the Nd-amido bond,linked to turnover-limiting proto-nolysis of the eta~3-butenyl-Nd functionality.The computationally predicted effective kinetics(DElTAH_(tot)=11.3 kcalmol~(-1),DElTAS_(tot)=-35.7 e.u.)are in reasonably good agreement with experimental data for the thoroughly studied hydroamination of alkynes.The thermodynamic and kinetic factors that determine the almost complete regio-and stereoselectivity of the mechanistically diverse intermolecular 1,3-diene hydroamination have been unraveled.The present computational study complements experiments because it allows,first,a more detailed understanding and a consistent rationalization of the experimental results for the hydroamination of 1,3-dienes and primary amines and,second,enhances the insights into general mechanistic aspects of organolanthanide-mediated intermolecular hydroamination.