N-functionalised expanded-ring N-heterocyclic carbenes: Synthesis, structure and catalysis

Abstract

The work presented in this thesis is concerned with the synthesis, metal coordination and applications of expanded (6- and 7-membered) N-functionalised heterocyclic carbenes. It is divided into four chapters, which cover the following areas of research. Chapter One includes the historical and literature review of preparations, reactions, and catalysis applications for different-types of NHC, while in Chapter Two, the syntheses characterisation and solid state properties of new 6- and 7-membered NHC salts (with Mes, DIPP, o-MeOPh and o-MeSPh A/-substituents) are discussed. A new method for synthesising saturated NHC salts, using potassium carbonate as a mild base for the deprotonation of the corresponding formamidines reacted with di-electrophiles under aerobic conditions is presented. Chapter Three describes the syntheses characterisation and solid state structure of rhodium and iridium complexes. Expansion of the ring provides carbenes with NCnhcN angle close to the sp2 angle (120 ), which forces the A/-substituents to bend closer to the metal center. Furthermore, the expanded carbenes are found to be more basic than their 5-membered analogues. The wide NCnhcN angles and greater donor abilities of the expanded NHC carbenes mean that their catalytic applications are interesting to study. Chapter Four presents the results of catalytic performance for the 6- and 7-membered NHC rhodium and iridium complexes in olefin hydrogenation reactions with molecular hydrogen. These complexes are also tested as catalysts in the transfer hydrogenation of ketones