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Alkali Metal and Stoichiometric Effects in Intermolecular Hydroamination Catalysed by Lithium, Sodium and Potassium Magnesiates

Abstract

Main group bimetallic complexes, while being increasingly used in stoichiometric deprotonation and metal-halogen exchange reactions, have largely been overlooked in catalytic applications. This paper explores the ability of alkali metal magnesiates to catalyse the intermolecular hydroamination of alkynes and alkenes using diphenylacetylene and styrene as model substrates. By systematically studying the role of the alkali-metal and the formulation of the heterobimetallic precatalyst, these study establishes higher order potassium magnesiate ([(PMDETA)2K2Mg(CH2SiMe3)4 (7) as a highly effective system capable of catalysed the hydroamination of styrene and diphenylacetylene with several amines while operating at room temperature. This high reactivity contrast with the complete lack of catalytic ability of neutral Mg(CH2SiMe3)2, even when harser reaction conditions are employed (24h, 80oC). Through stoichiometric reactions, and structural and spectroscopic (DOSY NMR) investigations we shed some light on the potential reaction pathway as well as the constitution of key intermediates. These studies suggest that the enhance catalytic activity of 7 can be rationalised in terms of the superior nucleophilic power of the formally dianionic magnesiate {Mg(NR2)4}2- generated in situ during the hydroamination process, along with the ability of potassium to engage in -interactions with the unsaturated organic substrate, enhancing its susceptibility towards a nucleophilic attack by the amide anion.

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Publication details

The article was received on 01 Mar 2019, accepted on 16 Apr 2019 and first published on 16 Apr 2019


Article type: Paper
DOI: 10.1039/C9DT00923J
Citation: Dalton Trans., 2019, Accepted Manuscript

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    Alkali Metal and Stoichiometric Effects in Intermolecular Hydroamination Catalysed by Lithium, Sodium and Potassium Magnesiates

    L. Davin, A. Hernan-Gomez, C. McLauughlin, A. Kennedy, R. McLellan and E. Hevia, Dalton Trans., 2019, Accepted Manuscript , DOI: 10.1039/C9DT00923J

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