Despite the growing interest in iron catalysis and hydroamination reactions, iron-catalyzed hydroamination of unprotected primary aliphatic amines and unactivated alkenes has not been reported to date. Herein, a novel well-defined four-coordinate β-diketiminatoiron(II) alkyl complex is shown to be an excellent precatalyst for the highly selective cyclohydroamination of primary aliphatic alkenylamines at mild temperatures (70-90 °C). Both empirical kinetic analyses and the reactivity of an isolated iron(II) amidoalkene dimer, [LFe(NHCH2 CPh2 CH2 CHCH2 )]2 favor a stepwise σ-insertive mechanism that entails migratory insertion of the pendant alkene into an iron-amido bond associated with a rate-determining aminolysis step.
Allylic sulfoxides, via [2,3]-sigmatropic rearrangement and oxidative addition of the resulting allylic sulfenate esters to Pd(0), are found to be excellent precursors of sulfenate anions. This hitherto unknown reactivity is applied in a new Pd(0)-catalyzed domino sequence involving sulfenate anion generation followed by arylation to afford aryl sulfoxides.
This Perspective article outlines some of the recent advancements in the development of (chiral) metal-free and late transition metal catalysts for hydroamination of unactivated alkenes.
Copper-phosphido-borane complexes were synthesized and isolated for the first time. Their structures were experimentally and computationally investigated. They were shown to display catalytic activity in C(sp)-P bond formation.
Understanding and controlling molecular recognition mechanisms at a chiral solid interface has been addressed in metal–organic framework catalysts for the asymmetric transfer hydrogenation reaction.
A new and smooth approach towards alkynylphosphine derivatives is described. It relies on the unprecedented catalytic coupling of secondary phosphine boranes with alkynyl bromides using the CuI/1,10-phenanthroline couple.
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) (kH/kD) of 2.7 (90 °C). Eyring analysis afforded ΔH≠=22.2 kcal mol−1, ΔS≠=−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−Namido σ bond at the monomer {N^N}FeII amido compound; 2) turnover‐limiting Fe−C σ bond aminolysis at the thus generated transient {N^N}FeII alkyl intermediate and 3) regeneration of the catalytically competent {N^N}FeII 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.
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