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Experimental and Computational Mechanistic Studies of the β‐Diketiminatoiron(II)‐Catalysed Hydroamination of Primary Aminoalkenes
Author(s) -
Lepori Clément,
Bernoud Elise,
Guillot Régis,
Tobisch Sven,
Hannedouche Jérôme
Publication year - 2019
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201804681
Subject(s) - hydroamination , chemistry , aminolysis , catalysis , amination , intramolecular force , kinetics , stereochemistry , medicinal chemistry , computational chemistry , organic chemistry , physics , quantum mechanics
A comprehensive mechanistic study by means of complementary experimental and computational approaches of the exo ‐cyclohydroamination of primary aminoalkenes mediated by the recently reported β‐diketiminatoiron(II) complex B is presented. Kinetic analysis of the cyclisation of 2,2‐diphenylpent‐4‐en‐1‐amine ( 1 a ) catalysed by B revealed a first‐order dependence of the rate on both aminoalkene and catalyst concentrations and a primary kinetic isotope effect (KIE) ( k H / k D ) of 2.7 (90 °C). Eyring analysis afforded Δ H ≠ =22.2 kcal mol −1 , Δ S ≠ =−13.4 cal mol −1 K −1 . Plausible mechanistic pathways for competitive avenues of direct intramolecular hydroamination and oxidative amination have been scrutinised computationally. A kinetically challenging proton‐assisted concerted N−C/C−H bond‐forming non‐insertive pathway is seen not to be accessible in the presence of a distinctly faster σ‐insertive pathway. This operative pathway involves 1) rapid and reversible syn ‐migratory 1,2‐insertion of the alkene into the Fe−N amido σ bond at the monomer {N^N}Fe II amido compound; 2) turnover‐limiting Fe−C σ bond aminolysis at the thus generated transient {N^N}Fe II alkyl intermediate and 3) regeneration of the catalytically competent {N^N}Fe II amido complex, which favours its dimer, likely representing the catalyst resting state, through rapid cycloamine displacement by substrate. The collectively derived mechanistic picture is consonant with all empirical data obtained from stoichiometric, catalytic and kinetics experiments.