Development of Sustainable Catalytic Methodologies

Abstract

This thesis develops sustainable catalytic methodologies by investigating complexation behaviour and the catalytic potential of Cu(II) complexes synthesised via mechanochemical methods in A3 and Chan–Lam coupling reactions, as well as the selective formation of alkenes through hydroalkoxylation. Chapter 1 introduces key chemical concepts and literature relevant to the thesis. Section 1.1 outlines fundamental principles of sustainable chemistry, specifically mechanochemistry, photocatalysis, and traditional catalytic methods. Section 1.2 covers essential topics in coordination chemistry important for ligand design and the study of copper complexes, while Section 1.3 presents the organic scaffolds explored in this work, including propargylamines, N-aryl-substituted imidazoles, and cis-alkenes. Section 1.4 summarises the key aims. Chapter 2 provides a solvent-free synthetic protocol for preparing Cu(II)–salen complexes via mechanochemical methods. The study investigates coordination behaviour, evaluates catalytic efficiency in A3 coupling for propargylamine synthesis, and outlines the synthetic scope and associated challenges. This approach grants access to a library of structurally defined, recoverable, and catalytically competent complexes for sustainable synthesis. Chapter 3 introduces a sustainable photocatalytic method for synthesising propargylamines using Cu(II)–salen complexes for A³ coupling under visible light. It examines LMCT-based activation, catalytic efficiency under UV and blue light, and factors such as solvent, radicals, and substrate ratios, enabling a fast, green, and scalable synthesis. Chapter 4 presents a Cu(II)-catalysed strategy for synthesising N-substituted imidazoles using Chan–Evans–Lam coupling with phenylboronic acids. The study optimises catalytic conditions and substrate ratios to enhance C–N bond formation. The method offers a mild, environmentally friendly option with good substrate tolerance and efficient reactivity below 60 °C, expanding the utility of hybrid pyridine-benzotriazole Cu(II) systems in sustainable cross-coupling. Chapter 5 introduces a novel Cu(II)-catalysed method for selective hydroalkoxylation of alkynes, enabling unprecedented Z-enol ether synthesis under mild conditions. The study explores structural and electronic requirements, optimises reaction parameters, and identifies ligand–copper systems delivering near-quantitative yields. Chapter 6 consolidates the thesis’s contributions by demonstrating eco-friendly catalytic methods using Cu(II) complexes across diverse transformations. It highlights industrial applicability and proposes future research directions. Experimental, synthetic, and crystallographic data are presented in Chapters 7 and 8.