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Ligands ambiphiles pyridine/borane et phosphine /borane : Synthèse, Structure, Coordination et Réactivité

Abstract : The present contribution deals with the use of ambiphilic molecules featuring both a Lewis base and a Lewis acid site, as ligands in organometallic chemistry.

In the first chapter, a bibliographic study describes the behaviour of Lewis acids of group 13 in organometallic chemistry. Their role as co-catalysts is examined in order to better understand how the Lewis acid could behave in a complex featuring an ambiphilic ligand. The different coordination modes of those ligands are reviewed. The rare contributions dealing with the reactivity of those complexes are also examined.

The second chapter describes the synthesis by carbon-boron coupling of a new family of ambiphilic ligands, namely 2-picolylboranes. Depending on the borane substituents, they are obtained as dimer or closed monomer via inter or intramolecular donor-acceptor dative interaction. The behaviour of 2-picolylBCy2 in solution is examined in details by NMR. An equilibrium between a dimer and a closed monomer form is evidenced. Theoretical calculations ascertain our conclusions. Coordination of this ligand to several transition metal precursors is studied. A rare example of donnor→Ru-Cl→acceptor bridged interaction is characterised in the complex [(p-cym)RuCl2(2-picolylBCy2)].

In the third chapter, the synthesis by hydroboration of an other family of ambiphilic ligands 1,2-phosphinoethylborane is described. Two neutral and their corresponding cationic ruthenium arene complexes bearing those ligands are characterised. Preliminary catalytic experiments such as hydrosilylation of benzaldehyde with one of the cationic complex reveal the rapid degradation of the catalyst into an original ruthenacycle complex. Its reactivity over chloroborane and chloroalane is studied.
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Submitted on : Tuesday, April 15, 2008 - 10:10:54 AM
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J. Vergnaud. Ligands ambiphiles pyridine/borane et phosphine /borane : Synthèse, Structure, Coordination et Réactivité. Chimie. Université Paul Sabatier - Toulouse III, 2007. Français. ⟨tel-00273327⟩

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