Non-classical Carbenes and their Derivatives for Small Molecule Activation and Metal-free Catalysis

Gautam, Nimisha (2025) Non-classical Carbenes and their Derivatives for Small Molecule Activation and Metal-free Catalysis. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Nimisha Gautam (17IP002)) 17IP002.pdf Restricted to Repository staff only Download (19MB)

Abstract

The research works presented in this PhD thesis entitled “Non-classical Carbenes and their Derivatives for Small Molecule Activation and Metal-free Catalysis” discusses the utilization of non-classical carbenes, particularly BICAAC and aNHC as promising ligands for the synthesis of main-group based compounds. Their catalytic potential as metal-free catalyst is examined across various transformations by small molecule activation including carbon dioxide activation, along with their functionalization. Additionally, the reactivity of main-group compounds is explored in detail. This thesis is structured into three chapters, beginning with the “Introduction”, which provides a comprehensive overview of classical and non-classical carbenes. This section describes the history and development of NHCs, aNHCs and BICAACs over time and provides an overview of how aNHC/BICAAC chemistry flourished in literature. The second chapter, “Results and Discussion”, is subdivided into three sections that provide a detailed description of the dissertation work carried out during the PhD tenure. Section 2.1 describes the utilization of BICAAC towards activation of B-H bond of pinacolborane and highlights the first application of BICAAC as a metal-free catalyst for reduction of various aromatic and aliphatic nitriles to amines under neat condition. Section 2.2 discusses the activation of two inert molecules, carbon dioxide and primary amides by BICAAC under metal-free condition. Such activation was developed into the first catalytic protocol for N-methylation of primary amides using CO2 as a C1 source. Section 2.3 presents the derivatization of aNHC for synthesis of mesoionic N-heterocyclic phosphinidene (mNHP) containing a highly polarized exocyclic phosphorus moiety. This mNHP’s reactivity for activation of small molecules such as BH3, CO2 and CS2 (nucleophilic reactivity) and Ar-F bond activation (redox reactivity) was studied. Further, this low-valent phosphorus compound served as an effective metal-free catalyst for S-formylation of thiols and hydrodefluorination reaction. The third chapter consists of the “Experimental Section”, which describes a detailed account of all the experimental procedures covered in Chapter 2. It includes synthetic and characterization data for all the compounds discussed in this thesis. This section also presents characterization details such as HRMS, NMR spectroscopic data, and single-crystal X-ray measurements for all newly synthesized compounds.

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