SUSTAINABLE CATALYSIS VIA IRON AND ZINC COMPLEXES: FROM TUNABLE METALLATE SYSTEMS TO PHOTOCHEMICAL REACTIVITY

This thesis investigates the use of iron and zinc complexes as sustainable catalysts for transformations of small, strained heterocycles in the field of carbon dioxide valorization, as well as the synthesis of iron complexes as catalysts for photochemical oxidation. In the first part of the work, tetrahalometallate complexes of iron and zinc were employed as bifunctional catalysts for the cycloaddition of carbon dioxide to aziridines and epoxides, yielding oxazolidinones and cyclic carbonates, respectively. These catalysts operate through a dynamic equilibrium between a neutral metal halide acting as a Lewis acid and free halide anions acting as nucleophiles. Immobilization of these metallates on anion exchange resins generated heterogeneous catalysts that combined high activity with ease of recovery and, in some cases, improved selectivity due to cooperative effects between the support and the active species. The second part of the thesis focuses on macrocyclic pyclen based iron complexes. These ligands stabilize iron centers in well defined oxidation and spin states, allowing detailed spectroscopic characterization and controlled photochemical reactivity. Mössbauer spectroscopy proved essential for resolving ambiguities arising from structural data and for identifying iron speciation in catalytic systems. Under visible light irradiation, iron pyclen complexes promoted aerobic oxidation of benzylic substrates, demonstrating that properly designed iron complexes can perform selective photoredox transformations. The final part of the work explores pincer type ligand frameworks as platforms for metal ligand cooperativity. A new NCN pincer ligand was designed to extend carbene based reactivity to iron, motivated by recent advances in PC(sp3)P systems. Although the targeted iron carbene complexes could not be obtained, the synthetic studies aims at providing a foundation for future developments.