Bifunctional N-Heterocyclic-Carbene (NHC) Ligands in Metal-Catalyzed C-H Bond Functionalization

La fonctionnalisation directe des liaisons Carbone-hydrogène (C-H) a pris, au cours des deux dernières décennies, une place de plus en plus importante en synthèse organique. En particulier, la fonctionnalisation CH catalysée par un métal de transition (TM) a connu une amélioration croissante de ses performances, permettant ainsi d'élargir la palette d'outils disponibles pour la synthèse de matériaux organiques, de produits naturels et de principes actifs. Néanmoins, le développement de nouvelles transformations de liaisons C-H fonctionnant efficacement en conditions douces avec une large tolérance aux groupements fonctionnels et une sélectivité élevée reste un enjeu majeur. Parallèlement, les carbènes N-hétérocycliques (NHCs) sont devenus des ligands de choix en chimie de coordination et en catalyse. Leurs propriétés uniques sont a l’origine de catalyseurs robustes de métaux de transition permettant des stratégies de synthèse plus efficaces. Cependant, l'utilisation des ligands NHCs dans des procédés métallo-catalysés de fonctionnalisation C-H reste a ce jour limitée. Par ailleurs, les composes organoborés sont des intermédiaires polyvalents en chimie de synthèse. Les stratégies mettant en jeu la fonctionnalisation C-H représentent sans nul doute l’approche la plus simple pour accéder a ces blocs de synthèse. Cette Thèse décrit une stratégie efficace et simple pour la préparation de complexes de métaux de transition portant des ligands chélates de type NHC-carboxylate sans précédent dans la littérature. Ces complexes, présentent une efficacité et une sélectivité élevée en tant que catalyseurs dans des réactions de borylation regiosélective de liaisons C-H dites ≪ inertes ≫ en conditions douces, et notamment photochimiques.The direct functionalization of inert CH bonds has emerged over the past two decades as an increasingly important synthetic tool. In particular, transition metal (TM)-catalyzed C-H functionalization has witnessed continuing improvements in performance, allowing expansion of the toolbox available for organic material synthesis, natural products synthesis, and drug-discovery programs. In spite of this success, there is still a need for the development of methodologies to efficiently enable C-H bond transformation under mild conditions. During the past two decades, N-heterocyclic carbenes (NHCs) have become ubiquitous ligands in coordination chemistry and catalysis. Their unique properties, including strong σ- donation, are responsible for forming robust TM catalysts that allow for the development of more efficient synthetic procedures. Nevertheless, the use of NHC ligands in transition metal-catalyzed C-H functionalization has remained limited. Because organoboron compounds are versatile intermediates in synthetic chemistry, the development of new catalytic systems for selective borylation of unactivated C-H bonds would afford new perspectives in organometallic and catalysis. Herein, this Thesis discloses an efficient and straightforward strategy to access various types of transition metal complexes bearing bidentate NHC-carboxylate ligands which were fully characterized including solid-state structures. These unprecedented complexes possessing chelating-NHC ligands exhibited high efficiency and selectivity in site selective borylation of inert C-H bonds under mild conditions including a photosensitizer-free photocatalytic conditions

Chiral N-Heterocyclic Carbene Ligands Enable Asymmetric C-H Bond Functionalization

International audienceThe asymmetric functionalization of C‐H bond is a particularly valuable approach for the production of enantioenriched chiral organic compounds. Chiral N‐Heterocyclic Carbene (NHC) ligands have become ubiquitous in enantioselective transition‐metal catalysis. Conversely, the use of chiral NHC ligands in metal‐catalyzed asymmetric C‐H bond functionalization is still at an early stage. This minireview highlights all the developments and the new advances in this rapidly evolving research area

Visible Light Induced Rhodium(I)-Catalyzed C-H Borylation

International audienceAn efficient visible light induced rhodium(I)-catalyzed regioselective borylation of aromatic C-H bonds is reported. The photocatalytic system is based on a single NHC-Rh complex capable of both harvesting visible light and enabling the bond breaking/forming at room temperature. The chelating nature of the NHC-carboxylate ligand was critical to ensure the stability of the Rh complex and to provide excellent photocatalytic activities. Experimental mechanistic studies evidenced a photooxidative ortho C-H bond addition upon irradiation with blue LEDs, leading to a cyclometalated Rh -hydride intermediate

Ruthenium–NHC complex-catalyzed P( iii )-directed C–H borylation of arylphosphines

International audience(NHC)(arene)Ru(II) complexes with bidentate LX-type NHC-carboxylate ligands were efficiently synthesized and fully characterized including solid-state structures. The strong coordination of the NHC carboxylate ligand and the labile character of the arene ligand are highlighted. These unprecedented Ru(II) complexes demonstrated efficient catalytic activities in the selective P(III)-directed C–H borylation at the ortho position of arylphosphines, representing the first report of the use of a ruthenium–NHC based catalyst in C–H borylation

Iridium(I) complexes with bidentate NHC ligands as catalysts for dehydrogenative directed C-H silylation

International audienceA series of (NHC)(cod)Ir(I) complexes bearing NHC-carboxylate ligands were efficiently synthesized and fully characterized. Their solid-state structures confirmed the bidentate coordination mode of these LX-type NHC ligands. These unprecedented iridium(I) complexes demonstrated efficient catalytic activities in dehydrogenative directed C-H silylation of arenes, and allowed for excellent ortho-selectivity control with aromatic silylating agents