DEVELOPMENT OF BASE METAL-CATALYZED HYDROGEN TRANSFER AND CROSS-COUPLING REACTIONS

The replacement of noble metals with less toxic and less expensive base metals in catalysis is a research topic of growing importance. The work of this thesis is focused on (i) the use of iron catalysts for reactions involving hydrogen transfer and (ii) the development of nickel-catalysed C-heteroatom coupling reactions following the ‘metallaphotoredox’ approach exploiting readily available organic photocatalysts. Thanks to their attractive features, (cyclopentadienone)iron complexes (CICs) have been applied in several transformations. However, important limitations such as the moderate catalytic activity of this class of complexes and the absence of effective chiral catalysts for enantioselective methodologies are preventing a more widespread application. In my PhD work I studied different strategies to overcome these limitations. I synthesized and tested several CICs in reactions involving hydrogen transfer steps, with a particular focus on catalytic hydrogenations and transfer hydrogenation of C=O and C=N bonds. Moreover, employing a highly active pre-catalyst already available in our research group I developed an effective protocol for the regiodivergent reductive ring opening of epoxides by catalytic hydrogenation. In the second part of my project, I developed a nickel-catalytic metallaphotoredox methodology for C-O and C-N cross-coupling reactions exploiting readily available organic photocatalysts instead of the previously employed Ir- and Ru-photocatalysts. Finally, Donor-Acceptor cyanoarenes – a class of organic dyes possessing some peculiar features – was successfully employed in the cross-coupling of, respectively, alcohols and amines with aryl halides promoted by nickel. The substrate scope of these transformations was thoroughly investigated, and several fluorescence quenching experiments allowed us to propose a catalytic cycle.