METAL PORPHYRIN COMPLEXES: SMART CATALYSTS TO PROMOTE ECO-FRIENDLY C-C AND C-N BOND FORMATIONS

Cyclopropanes and nitrogen-containing compounds, such as aziridines, indoles and amines, are interesting molecules from a synthetic point of view because they are often used as building blocks in organic synthesis. They also constitute the active part of many natural and synthetic products owing to their biological and pharmaceutical properties. Over the years, the scientific community focused its attention in the development of new eco-friendly catalytic process to obtain these compounds in good yields and selectivity respecting the basic principles of ‘green chemistry’. Based on these concepts, carbene and nitrene transfer reactions are useful synthetic strategies to produce compounds stated above and they can be efficiently promoted by metal porphyrin complexes due to their high catalytic activity and chemical versatility. The first part of this thesis describes the synthesis of cyclopropanes using chiral iron porphyrin complexes which show a ‘Totem’ tridimensional structure. In the second half part of the thesis we describe the ruthenium porphyrin-catalysed nitrene-transfer reactions to synthesis nitrogen-containg compounds. In Chapter II we describe the synthesis of new ‘Totem porphyrin ligands’ and their iron(III) porphyrin complexes to promote cyclopropanation reactions. Since, high diastereo- and enantioselectivities are attributed to a synergic action of the active metal center with the ligand periphery, several structural modifications of the ligand skeleton were performed to give catalysts whose efficiency could be maximised by a metal/periphery synergy to promote stereoselective cyclopropanation reactions. In Chapter III we describe the Ru(TPP)CO-catalysed aziridination of styrenes by aryl azides in mesoreactors under continuos flow conditions. We also report the reactivity of aziridines towards carbon dioxide. The coupling reaction between aziridines and carbon dioxide, the most abundant greenhouse gas, is one of the most important routes to obtain oxazolidinones. The mechanism of this reaction was also computationally investigated by using DFT methods. In Chapter IV we report the synthesis of indoles by an intermolecular reaction between aryl azides and aryl alkynes using a ruthenium bis-imido complex as the catalyst. The generality of the reaction was proved by synthesising several indoles from differently substituted aryl azides and alkynes. We also performed kinetic and DFT studies to clarify the reaction mechanism. In Chapter V we describe the influence of the axial ligand electronic features on the catalytic activity of ruthenium porphyrin complexes in promoting amination reactions. The influence was studied both from an experimental and theoretical (DFT study) points of view, by comparing the catalytic performance of Ru(TPP)CO to that of Ru(TPP)(py)2 (py=pyridine) complex.