Chiral NHC–metal-based asymmetric catalysis

Steuerliganden für Katalysatoren

“…Das intrinsische Problem von NHCs ist jedoch, dass diese im Allgemeinen eine propellerartige Form aufweisen und sich die N-Substituenten sowie das koordinierte Metallatom frei um die jeweiligen Einfachbindungen drehen können. Derartige Rotationen führen zu einem teilweisen oder vollständigen Verlust der chiraler Information, was in der Folge niedrige Enantioselektivitäten in der asymmetrischen Katalyse nach sich ziehen kann [19]. Um dieser Problematik entgegenzuwirken, wurden in den letzten Jahren verschiedene Ansätze beschrieben, um chirale NHC-Komplexe zu synthetisieren, in denen die freie Drehbarkeit um die entsprechenden Bindungen gehemmt ist (Abbildung 7).…”

Synthesis of New Chiral Benzimidazolylidene–Rh Complexes and Their Application in Asymmetric Addition Reactions of Organoboronic Acids to Aldehydes

“…As excellent ligands for transition metals, NHCs have found multiple applications in some of the most important catalytic transformations in the chemical industry. As a logical extension of this development, chiral NHC ligands and their application in asymmetric catalysis are receiving increasing attention [11][12][13][14][15][16]. Despite considerable efforts devoted to this field, the design and synthesis of novel chiral NHCs to enhance their enantioselectivity is still a challenge.…”

Synthesis of New C2-Symmetric Six-Membered NHCs and Their Application for the Asymmetric Diethylzinc Addition of Arylaldehydes

“…These ligands, initially considered as mimics of phosphine [13], are now ubiquitous in organic chemistry because of their outstanding properties such as stronger σ-donor and weaker π-acceptor compared to the corresponding phosphane ligand, and the metal complexes of these ligands usually show better stability to moisture, air, and heat as well [14,15]. Naturally, the development of chiral NHCs and the application of these ligands in stereoselective catalysis are receiving considerable attention as a next step [16][17][18][19][20][21]. To date, most of the research has employed five-membered NHCs based on imidazole or imidazoline.…”