Abhineet Verma

By Arunava Manna, Abhineet Verma, Sumit K. Panja and Satyen Saha

Carbenes are highly reactive intermediates in organic synthesis. These divalent carbon species are generally transient in nature and cannot be isolated. However, they can form stabile metal complexes. Later on, the development of N-heterocyclic carbene (NHC) and other stable carbene led to the application of these carbon (II) donor ligands in the synthesis of complex natural products, transition metal catalysis, organo-catalysis and several other synthetic methodologies. Here in this short review, we will discuss the brief history of the development of carbenes, synthesis of stable carbenes (NHC in particular), and their applications in natural products synthesis transition metal chemistry/organometallics. In addition to synthesis and application, the chapter will consist of a detailed structural analysis of carbenes and exciting photophysics of this class of compounds. Special emphasis will be given to electronic structure. The role of carbene in the development of luminescent NHC transition metal complexes, the tuning of emission properties as well as their active role as photocatalysts in the reduction of CO2 will also be discussed.

Part of the book: Carbene

By Krishanu Bandyopadhyay, Abhineet Verma, Tamal Ghosh, Ravi Kumar Kanaparthi, Sudeena Nadendla and Satyen Saha

This chapter discusses the significant impact of N-heterocyclic carbene (NHC) ligands on the optical properties of metal complexes. It highlights the key role of NHC ligands in shifting the d−d transitions of these complexes to shorter wavelength regions, rendering them luminescent. The study focuses on NHC-based metal complexes involving copper, silver, platinum, iridium, and coinage metals, showcasing their luminescent properties and potential applications in organic light-emitting diodes (OLEDs). However, it also underscores a challenge: the quantum yields of these metal complexes may not be sufficient for practical applications. To address this issue, this chapter proposes modifying the NHC ligand with electron-rich substituents, aiming to reduce the HOMO-LUMO gap and shift d-d transitions into the UV region. Additionally, it introduces cyclic (alkyl)(amino)carbene (CAACs) as promising ligands for tuning the photophysical properties of metal complexes. CAACs are noted for their ability to decrease the HOMO-LUMO gap compared to NHCs and their electrophilic nature. Luminescent CAAC metal complexes are found to exhibit sub-microsecond lifetimes, making them suitable candidates for OLED applications. Ultimately, the research challenges researchers to better understand the structure, bonding, and properties of these complexes to create stable and highly luminescent materials using abundant and cost-effective metals like iron, copper, zinc, and silver.

Part of the book: Revolutionizing Energy Conversion - Photoelectrochemical Technologies and Their Role in Sustainability [Working title]