Dottorato in SCIENZE CHIMICHE

Titolo della tesi: Selectivity study in the functionalization of organic compounds promoted by radical and radical-like species

Oxidative C-H functionalization of organic substrates promoted by cheap, eco-friendly and selective systems has received a great attention in recent years, since it allows to convert relatively unreactive bonds, ubiquitous in organic molecules, into functional groups suitable for further transformations. Oxidation of sulfides to sulfoxides is another important process due to the presence of sulfinyl functional group in many natural products and biologically active compounds, like anti-inflammatory or antibiotic drugs. Moreover, sulfoxides are important reagents in organic synthesis: in fact, chiral sulfoxides have been used as auxiliaries in asymmetric synthesis. In this thesis, the use of biomimetic nonheme iron complexes and N-hydroxyphthalimide (NHPI) as efficient and selective catalysts for the oxidation of alkylaromatic compounds, alcohols, and sulfides by hydrogen atom transfer (HAT) or S-oxidative processes has been described. Concerning the former systems, elucidation of mechanism and reactivity patterns of [(N4Py)FeII]2+ complex have been investigated in detail with respect to the generation of the iron-oxo and iron-peroxo active species both in common organic solvents and in non-common fluorinated solvents. For the N-hydroxyphthalimide catalyst, reactivity and selectivity patterns of the corresponding N-oxyl radical (PINO) in S-oxidation from sulfur compounds have been analysed by kinetic and product studies. In addition, the two systems can be used together in a mediated system, in which NHPI acts as efficient mediator in the oxidations of organic compounds promoted by the nonheme iron(IV)-oxo complex, enhancing its reactivity and expanding its oxidizing ability. In the mediated system, the increase of reactivity is associated to the oxidation of the mediator to the corresponding phthalimide-N-oxyl radical, which efficiently abstracts hydrogen atoms from the substrates regenerating the mediator NHPI. The possibility of a change of selectivity in the C-H functionalization of alkylaromatic compounds and alcohols has been studied in the presence of the NHPI mediator as a result of the different polar effects operating in the HAT processes promoted by [(N4Py)Fe(IV)=O]2+ and PINO radical. Furthermore, a change of chemoselectivity in the competitive oxidation of sulfides, alkylaromatic compounds and alcohols by effect of variation of the oxidizing species in the absence or in the presence of the NHPI mediator has been investigated.