**Chapter 8 137** N-Heterocyclic Carbene Mediated Organocatalysis Reactions *by Yatheesh Narayana, Sandhya N.C., H.E. Dinesh, Sridhar B. Thimmaiah, Kanchugarakoppal S. Rangappa and Kempegowda Mantelingu*

Preface

Carbenes are important molecules in chemistry because of their photochemistry and high reactivity. They are usually short-lived, but some carbenes are highly stable, primarily stabilized by organometallic complexes. Generally, two types of carbenes are known: singlet carbene and triplet carbene. Both show unique photophysics, as well. Heterocyclic carbenes are currently emerging versatile ligands for organometallic complexes that can be used in medicinal and materials chemistry. For example, silver complexes with heterocyclic carbene complexes are found to exhibit antimicrobial and anticancer properties, while carbene-palladium complexes are known for their antitumor and antimicrobial activities. There are exciting reports on carbene complexes with rhodium, iridium, and platinum having intriguing biological activities. At present, Fischer carbene, Schrock carbene, and N-heterocyclic carbene (NHC) are the most popular carbenes. These carbenes are seen in applications such as cross-coupling, C-H, X-H insertion reactions, carbene

Over nine chapters, this book addresses important topics related to carbenes. The book begins with a chapter by Saha et al. that discusses the synthesis of important carbenes such as NHCs as well as their structural and photophysical studies.

Chapter 2 by Hideto reports on recent advances in cooperative NHC catalysis. The author highlights the application of several chiral NHC catalysts along with transition metal catalysts and photocatalysts to synthesize complex molecules. Chapter 3 by Bharti et al. focuses on the general structure and properties of carbene and NHC in particular. It discusses the unique properties of NHC and strategies for its synthesis. Chapter 4 by Tuna discusses the electronic and structural properties of carbene and carbene reactivity in organic synthesis. Chapter 5 by Varala et al. is on late transition metal (LTM)-NHC catalyzed transformations of renewable chemicals. The chapter also discusses the synthesis of biomass resources, fine chemicals, fuels, and intermediates with mechanistic aspects. Chapter 6 by Naceur et al. present an impressive review of novel NHC–silver (I) complexes. The authors discuss the synthesis and structural characterization of several derivatives along with studies of antimicrobial, antioxidant, and cytotoxicity potential. Chapter 7 by Babu is on imidazolium-based NHCs and metalmediated catalysis. Chapter 8 by Mantelingu et al. examines NHC-mediated organocatalysis reactions and the non-umpolung activity of bis-electrophile α and β unsaturated acylazoliums reaction with suitable bis-nucleophiles in organic synthesis. Finally, Chapter 9 by Iman reports on the versatility of NHCs in polymerization as true organocatalysts for producing many industrial polymers. In addition, the chapter describes their use in step-growth polymerization to achieve high molecular weight polymers and as transesterification agents in ring-opening

catalyzed polymerization reactions, and more.

polymerization.
