Helicenic N-heterocyclic carbenes (helicenic NHCs) : synthesis and study of the physico-chemical and catalytic properties / Pallova, Lenka  

Public ISBD Titre : Helicenic N-heterocyclic carbenes (helicenic NHCs) : synthesis and study of the physico-chemical and catalytic properties Type de document : texte imprimé Auteurs : Pallova, Lenka, Auteur ; Vincent Cesar, Directeur de thèse ; Bastin, Stéphanie, Directeur de thèse ; Bastin, Stéphanie Année de publication : 2020 Langues : Anglais (eng) Tags : HELICENES  CARBENES N-HETEROCYCLIQUES  CATALYSE ASYMETRIQUES A L'OR(I) Résumé : "This PhD thesis is focused on the chemistry of helicenic N-heterocyclic carbenes (NHCs) thus merging two domains of intense research, namely the chemistries of helicenes and of N-heterocyclic carbenes. The main objective is to develop new classes of helicenic NHC ligands based on the imidazo[1,5-a]pyridin-3-ylidene (IPy) platform functionalised in position 5 of the heterobicycle with adequate helicenic moieties. The functionalisation of the rigid bicyclic IPy structure in position 5 provides L-shaped helicenic NHC ligands which are expected to be well-suited for asymmetric gold(I) catalysis. The synthesis, the study of physico-chemical and catalytic properties of new helicenic NHCs are displayed. First the novel synthesis of C2-symmetric fluorenyl-derived [5] and [7] helicene-like molecules (flu[n]helicenes) is described. The developed synthetic pathway to access flu[5]- and flu[7]helicenes comprises three synthetic steps and has been optimised on a multi-gram scale. Firstly, the symmetrical 1,5-diketones are prepared by base-assisted condensation of formaldehyde with two equivalents of ?-tetralone or 3,4-dihydrophenanthren-4-one. Then an intramolecular McMurry reaction between the two carbonyl moieties of 1,5-diketones affords the partially-hydrogenated (or saturated) fluoreno[5]- and fluoreno[7]helicenes with an internal tetra-substituted, overcrowded C=C bond. The chiral separation and structural characterisation of the different diastereomers are presented as well as their chiroptical properties. The desired fluorenyl-derived [5] and [7] helicene-like molecules are obtained in a final dehydrogenative aromatisation of the saturated fluoreno[5]- and fluoreno[7]helicenes with overall yields of 43% and 22% respectively. The prepared flu[5]- and flu[7]helicenes were then grafted on the 5-bromoimidazo[1,5-a]pyridinium bromide salts via a nucleophilic aromatic substitution (SNAr) to afford the L-shaped helicenic imidazopyridinium salts functionalised at the C5 position of the IPy platform. The latter precursors were monodeprotonated to generate zwitterionic fluorenide-imidazopyridinium compounds or deprotonated twice to yield the corresponding stable free anionic NHCs. The latter were cleanly coordinated to gold(I) centre generating in situ anionic gold(I) complexes, which could be further transformed into a zwitterionic helicenic gold(I) complex by addition of triphenylphosphine, or reprotonated on the helicenic moiety with an acid affording the helicenic NHC-gold(I) complexes. The detailed study of the kinetic and thermodynamic conformers of these gold(I) complexes is presented indicating a possible Au···H-C contact between the acidic helicene proton of the cyclopentadiene ring and the AuI centre. The preliminary results obtained in cycloisomerisation of 1,6-enynes showed low catalytic activity, which might be due to the presence of the acidic helicenic proton of the cyclopentadiene ring in the gold(I) complex. In order to avoid this deleterious acidic proton on the fluorenyl-derived helicenic moiety, the latter was derivatized by alkylation. Depending on the protocol, the alkyl moiety was either installed on the central apical position or on one carbon of the inner rim of the cyclopentadiene ring creating a new centre of chirality on the helicene moiety and inducing axial and helical chirality. The derivatized helicenic NHC-gold(I) complexes were prepared in hundreds of mg and were resolved by chiral HPLC. Their activity in the asymmetric gold(I)-catalysed transformations notably in cycloisomerisation of 1,6-enynes is presented." Document : Thèse de Doctorat Etablissement_delivrance : Université de Toulouse 3 Date_soutenance : 05/11/2020 Ecole_doctorale : Sciences de la Matière (SdM) (Toulouse) Domaine : Chimie moléculaire Localisation : LCC En ligne : http://www.theses.fr/2020TOU30265 Helicenic N-heterocyclic carbenes (helicenic NHCs) : synthesis and study of the physico-chemical and catalytic properties [texte imprimé] / Pallova, Lenka, Auteur ; Vincent Cesar, Directeur de thèse ; Bastin, Stéphanie, Directeur de thèse ; Bastin, Stéphanie . - 2020. Langues : Anglais (eng) Tags : HELICENES  CARBENES N-HETEROCYCLIQUES  CATALYSE ASYMETRIQUES A L'OR(I) Résumé : "This PhD thesis is focused on the chemistry of helicenic N-heterocyclic carbenes (NHCs) thus merging two domains of intense research, namely the chemistries of helicenes and of N-heterocyclic carbenes. The main objective is to develop new classes of helicenic NHC ligands based on the imidazo[1,5-a]pyridin-3-ylidene (IPy) platform functionalised in position 5 of the heterobicycle with adequate helicenic moieties. The functionalisation of the rigid bicyclic IPy structure in position 5 provides L-shaped helicenic NHC ligands which are expected to be well-suited for asymmetric gold(I) catalysis. The synthesis, the study of physico-chemical and catalytic properties of new helicenic NHCs are displayed. First the novel synthesis of C2-symmetric fluorenyl-derived [5] and [7] helicene-like molecules (flu[n]helicenes) is described. The developed synthetic pathway to access flu[5]- and flu[7]helicenes comprises three synthetic steps and has been optimised on a multi-gram scale. Firstly, the symmetrical 1,5-diketones are prepared by base-assisted condensation of formaldehyde with two equivalents of ?-tetralone or 3,4-dihydrophenanthren-4-one. Then an intramolecular McMurry reaction between the two carbonyl moieties of 1,5-diketones affords the partially-hydrogenated (or saturated) fluoreno[5]- and fluoreno[7]helicenes with an internal tetra-substituted, overcrowded C=C bond. The chiral separation and structural characterisation of the different diastereomers are presented as well as their chiroptical properties. The desired fluorenyl-derived [5] and [7] helicene-like molecules are obtained in a final dehydrogenative aromatisation of the saturated fluoreno[5]- and fluoreno[7]helicenes with overall yields of 43% and 22% respectively. The prepared flu[5]- and flu[7]helicenes were then grafted on the 5-bromoimidazo[1,5-a]pyridinium bromide salts via a nucleophilic aromatic substitution (SNAr) to afford the L-shaped helicenic imidazopyridinium salts functionalised at the C5 position of the IPy platform. The latter precursors were monodeprotonated to generate zwitterionic fluorenide-imidazopyridinium compounds or deprotonated twice to yield the corresponding stable free anionic NHCs. The latter were cleanly coordinated to gold(I) centre generating in situ anionic gold(I) complexes, which could be further transformed into a zwitterionic helicenic gold(I) complex by addition of triphenylphosphine, or reprotonated on the helicenic moiety with an acid affording the helicenic NHC-gold(I) complexes. The detailed study of the kinetic and thermodynamic conformers of these gold(I) complexes is presented indicating a possible Au···H-C contact between the acidic helicene proton of the cyclopentadiene ring and the AuI centre. The preliminary results obtained in cycloisomerisation of 1,6-enynes showed low catalytic activity, which might be due to the presence of the acidic helicenic proton of the cyclopentadiene ring in the gold(I) complex. In order to avoid this deleterious acidic proton on the fluorenyl-derived helicenic moiety, the latter was derivatized by alkylation. Depending on the protocol, the alkyl moiety was either installed on the central apical position or on one carbon of the inner rim of the cyclopentadiene ring creating a new centre of chirality on the helicene moiety and inducing axial and helical chirality. The derivatized helicenic NHC-gold(I) complexes were prepared in hundreds of mg and were resolved by chiral HPLC. Their activity in the asymmetric gold(I)-catalysed transformations notably in cycloisomerisation of 1,6-enynes is presented." Document : Thèse de Doctorat Etablissement_delivrance : Université de Toulouse 3 Date_soutenance : 05/11/2020 Ecole_doctorale : Sciences de la Matière (SdM) (Toulouse) Domaine : Chimie moléculaire Localisation : LCC En ligne : http://www.theses.fr/2020TOU30265

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