Dottorato in SCIENZE CHIMICHE

Titolo della tesi: Supramolecular systems involving transition metals: catalysis and translocation

Herein I report the results of the research work I carried out during my PhD. I mainly focused on two aspects of supramolecular systems involving transition metals: catalysis and translocation. Concerning catalysis, I worked on a supramolecular approach to C–H bond oxidation using non-heme metal complexes as catalysts. The outcomes of such research are presented in the first three chapters of this thesis. In Chapters 1 and 2 a family of bis-imino, self-assembled supramolecular non heme iron catalysts active in C–H bond oxidation is illustrated. The possibility to achieve selective oxidation of aromatic and aliphatic substrates has been explored by decorating the ligand scaffold of the self-assembled iron complexes with supramolecular receptors (Chapter 1) or with sterically hindered groups (Chapter 2). In the first case, the catalyst endowed with benzo 18 crown 6 receptor units showed site selectivity toward aromatic oxidation, but such property seemed to be not entirely ascribable to supramolecular recognition. In the second case, the insertion of large and sterically demanding groups on the catalyst backbone did not lead to the insurgence of steric effects on the catalyzed reaction. However, such findings reinforced a mechanistic hypothesis previously reported for analogous catalysts. Chapter 3 reports the preliminary results of a project carried out during my stay to the University of Girona under the supervision of Professor Miquel Costas. This project aims to exploit supramolecular self-assembly to provide with a recognition unit an already-known catalytically active iron (or manganese) complex. To do this, two receptor-bearing carboxylic acids have been synthesized. The carboxylic acid moiety will hopefully be able to bind to the metal center of the catalyst, providing it with the supramolecular receptor. The last two chapters concerns translocation processes of transition metal ions. Chapter 4 reports the reduction promoted by an activated carboxylic acid of the octahedral Cu2+ - terpyridine complex, to the tetrahedral Cu+ - neocuproine complex. In Chapter 5 the dissipative back-and-forth translocation of the Zn2+ ion between hexaaza 18 crown 6 and two terpyridine moieties, is described. For the investigation of both translocation processes, a combination of X-ray absorption and proton nuclear magnetic resonance spectroscopies with multivariate curve resolution analysis has been exploited in order to understand the concentration-time evolution of all relevant inorganic and organic species involved in the reactions.