Development of Biaryl N-Heterocyclic Carbene Ligands Featuring Non-Covalent Interactions

Abstract

The field of organotransition-metal chemistry has extensively studied the development of novel and efficient catalysts for homogeneous catalysis. N-Heterocyclic carbenes (NHCs) are a powerful class of ligands in transition metal catalysis due to their strong electron-donating ability and excellent synthetic flexibility. They have been recognized as such since the stable free carbene was isolated by Arduengo in 1991. Various structural modifications have been employed to adjust the electronic and steric characteristics of NHC ligands, based on the prototypical imidazolylidene skeleton. Imidazo[1,5- a]pyridin-3-ylidene (ImPy) ligands have a rigid bicyclic structure comprising a C5-positioned aryl group. Aryl substituents of the bicyclic ImPy are positioned near a metal coordination sphere, thus allowing for bonding interactions of the metal with substituent. Additionally, ImPy ligands can be synthesized via a concise synthetic route, enabling the convenient incorporation of numerous functional substituents. In line with our interest to developing advanced NHC-based catalysts, we suggest a variety of ligands that feature non-covalent interactions. The present thesis describes the development of imidazopyridine-based NHC transition metal complexes and their application to chemical reactions: diastereoselective addition and desymmetric C-N bond formation. In catalyst design, the Cu-F interaction play a crucial role in stabilizing catalyst and reaction intermediate, thereby influencing the reactivity of catalytic processes. Additionally, fluorine atom, which is not impose spatial demands, can fundamentally alter the performance of the catalyst. The fluorinated aryl groups on the ligand structures also improve the π-back-donation from the metal. Chapter 2 describes the synthesis of fluorinated ImPy ligand (F-ImPy), characterized by a Cu-F interaction and a C5-aryl substituent and their application in the diastereoselective additions of 1,3- PhD/CH 20182101