N-Heterocyclic Carbene Derived Main-Group Compounds: Synthesis, Reactivity and Metal-Free Catalysis

Maji, Subir (2024) N-Heterocyclic Carbene Derived Main-Group Compounds: Synthesis, Reactivity and Metal-Free Catalysis. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Subir Maji (18RS061)) 18RS061.pdf - Submitted Version Restricted to Repository staff only Download (18MB)

Abstract

The research works presented in this PhD thesis entitled “N-Heterocyclic Carbene Derived Main-Group Compounds: Synthesis, Reactivity and Metal-Free Catalysis” discusses the utilization of N-heterocyclic carbene (NHCs), including classical (NHC) as well as non-classical carbenes (abnormal N-heterocyclic carbene, aNHC) as potential ligands for the synthesis of main-group based compounds and their catalytic applications as metal-free catalyst towards various transformations by using gas molecule activation and functionalization. In addition, the reactivity of such main-group compounds has also been explored. This thesis is divided into three chapters. The first is “Introduction,” which discusses an overview of NHC and aNHC. This section describes the history and development of NHCs and aNHCs over time and provides an overview of how NHC/aNHC chemistry flourished in literature. The second chapter, “Results and Discussion”, is subdivided into five sections describing the dissertation work carried out during the PhD tenure. Section 2.1 highlights the synthesis and utilization of NHC and aNHC stabilized main group compounds “borenium ions” for hydrogenating N-heterocycles in the presence of 1 atm hydrogen gas (H₂). Section 2.2 details the use of higher nucleophilic mesoionic N-heterocyclic olefin (mNHO) derived from aNHC as a metal-free catalyst for the reductive functionalization of carbon dioxide (CO₂) for the N-methylation of amines under mild conditions. This work represents the first catalytic application of mNHO. Section 2.3 discusses the first catalytic process for the N-methylation of sulfoximines using CO₂ as a C1 source. In this process, mNHO was utilized as a metal-free catalysis. This newly developed protocol is highly efficient for the N-methylation of various NH-sulfoximines. In the 2.4 section, a biologically important process known as S-formylation was developed using 1 atm CO2 under ambient conditions. This work represents the first chemical process for the S-formylation of thiol from CO2. In section 2.5, a series of novel air-stable mesoionic N-heterocyclic thiones (mNHTs) containing a highly polarized exocyclic thione moiety were synthesised from aNHCs and studied their independent HOMO/LUMO reactivity for the synthesis of various main group compounds and radical anions. The third chapter consists of the “Experimental Section,” which describes in detail all the experimental procedures for Chapter 2. This section includes all the synthetic and characterization data for all the compounds discussed in this thesis.

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