| Titre : |
Functionalized imidazo[1,5-a]pyridin-3-ylidene ligands : synthesis, coordination chemistry and implementation in Au(I) catalysis |
| Type de document : |
texte imprimé |
| Auteurs : |
Idir Benaissa, Auteur ; Vincent Cesar, Directeur de thèse ; Bastin, Stéphanie, Directeur de thèse |
| Langues : |
Français (fre) |
| Tags : |
CARBENES SYNTHESIS HOMOGENEOUS CATALYSIS HETEROCYCLES GOLD LIGANDS |
| Résumé : |
"This PhD work concerns the chemistry of N-heterocyclic carbenes (NHCs) and its main objective consists in the development of new NHC ligands based on the imidazo[1,5-a]pyridin-3-ylidene (IPy) platform whose position 5 is functionalized by an anionic or neutral, and potentially chiral barbituric heterocycle. The major advantage of this rigid bicyclic structure lies in the "L-shaped" geometry of the generated ligands, which is particularly well adapted to gold (I) catalysis. In a first time, the chemistry of an achiral version of this family is reported. After describing the synthetic pathway to the zwitterionic precursors, the anionic and neutral gold(I) complexes supported respectively by an anionic NHC and neutral NHC ligands obtained by C- and O-functionalization of the malonate part of the barbiturate heterocycle were synthesized and characterized. The comparative study of these complexes as pre-catalysts in alkyne hydroelementation and domino reaction reactions, involving cycloisomerization of 1,6-enyne followed by nucleophilic addition, showed that the O-methylated ligand complex is the best in the series, as well as superior to conventional NHCs in both activity and selectivity (TON and TOF). The remarkable efficacy of these Au(I) complexes has been rationalized by the electronic and steric stabilization of the active species of cationic gold(I) by the NHC ligand. In a second step, the oxidation process of Au(I) to Au(III) complexes using an external oxidant was studied in detail, and showed that the anionic ligand rearranged from monodentate in Au(I) complex to LX-type bidentate ligand in Au(III) complexes, resulting from a deformation of the barbituric heterocycle and rehybridization of the central malonic carbon atom. This behavior is general as soon as the coordination geometry of the metal center leaves a cis coordination site next to the carbenic center. The complexes of Pd(II), Rh(I), Ir(I) and Mn(I) are thus synthesized and characterized. Structural analysis of the complexes shows that the degree of malonic carbon hybridization is a function of the electrophilicity of the metal, with a more pronounced sp3 character when the electron-density on the metal is lower. A library of three chiral ligands has been synthesized from (S)-(-)-1-phenylethylamine as the source of chiral information through a convergent synthesis strategy similar to that of achiral derivatives. The corresponding Au(I) complexes have been synthesized and used as pre-catalysts in 1,6-enyne domino reactions and provide access to good yields and enantiomeric excesses of up to 70%. In parallel, the reactivity of the 5-bromoimidazo[1,5-a]pyridinium platform with malonate esters and 2-arylacetate esters has been developed. This study proves the intermediacy of free NHCs as reaction intermediates in the synthesis of fused heterotricyclic mesoionic compounds."
|
| Document : |
Thèse de Doctorat |
| Etablissement_delivrance : |
Université de Toulouse 3 |
| Date_soutenance : |
26/11/2019 |
| Ecole_doctorale : |
Sciences de la Matière (SdM) (Toulouse) |
| Domaine : |
Chimie organométallique de coordination |
| Localisation : |
lcc |
| En ligne : |
http://thesesups.ups-tlse.fr/4517/ |
Functionalized imidazo[1,5-a]pyridin-3-ylidene ligands : synthesis, coordination chemistry and implementation in Au(I) catalysis [texte imprimé] / Idir Benaissa, Auteur ; Vincent Cesar, Directeur de thèse ; Bastin, Stéphanie, Directeur de thèse . - [s.d.]. Langues : Français ( fre)
| Tags : |
CARBENES SYNTHESIS HOMOGENEOUS CATALYSIS HETEROCYCLES GOLD LIGANDS |
| Résumé : |
"This PhD work concerns the chemistry of N-heterocyclic carbenes (NHCs) and its main objective consists in the development of new NHC ligands based on the imidazo[1,5-a]pyridin-3-ylidene (IPy) platform whose position 5 is functionalized by an anionic or neutral, and potentially chiral barbituric heterocycle. The major advantage of this rigid bicyclic structure lies in the "L-shaped" geometry of the generated ligands, which is particularly well adapted to gold (I) catalysis. In a first time, the chemistry of an achiral version of this family is reported. After describing the synthetic pathway to the zwitterionic precursors, the anionic and neutral gold(I) complexes supported respectively by an anionic NHC and neutral NHC ligands obtained by C- and O-functionalization of the malonate part of the barbiturate heterocycle were synthesized and characterized. The comparative study of these complexes as pre-catalysts in alkyne hydroelementation and domino reaction reactions, involving cycloisomerization of 1,6-enyne followed by nucleophilic addition, showed that the O-methylated ligand complex is the best in the series, as well as superior to conventional NHCs in both activity and selectivity (TON and TOF). The remarkable efficacy of these Au(I) complexes has been rationalized by the electronic and steric stabilization of the active species of cationic gold(I) by the NHC ligand. In a second step, the oxidation process of Au(I) to Au(III) complexes using an external oxidant was studied in detail, and showed that the anionic ligand rearranged from monodentate in Au(I) complex to LX-type bidentate ligand in Au(III) complexes, resulting from a deformation of the barbituric heterocycle and rehybridization of the central malonic carbon atom. This behavior is general as soon as the coordination geometry of the metal center leaves a cis coordination site next to the carbenic center. The complexes of Pd(II), Rh(I), Ir(I) and Mn(I) are thus synthesized and characterized. Structural analysis of the complexes shows that the degree of malonic carbon hybridization is a function of the electrophilicity of the metal, with a more pronounced sp3 character when the electron-density on the metal is lower. A library of three chiral ligands has been synthesized from (S)-(-)-1-phenylethylamine as the source of chiral information through a convergent synthesis strategy similar to that of achiral derivatives. The corresponding Au(I) complexes have been synthesized and used as pre-catalysts in 1,6-enyne domino reactions and provide access to good yields and enantiomeric excesses of up to 70%. In parallel, the reactivity of the 5-bromoimidazo[1,5-a]pyridinium platform with malonate esters and 2-arylacetate esters has been developed. This study proves the intermediacy of free NHCs as reaction intermediates in the synthesis of fused heterotricyclic mesoionic compounds."
|
| Document : |
Thèse de Doctorat |
| Etablissement_delivrance : |
Université de Toulouse 3 |
| Date_soutenance : |
26/11/2019 |
| Ecole_doctorale : |
Sciences de la Matière (SdM) (Toulouse) |
| Domaine : |
Chimie organométallique de coordination |
| Localisation : |
lcc |
| En ligne : |
http://thesesups.ups-tlse.fr/4517/ |
|  |
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