Photochemical cobalt hydride catalysis for newly selective transformations

The first chapter of the thesis serves as an introduction to highlight the importance of transition metal hydride complexes in organic chemistry. In particular, the main synthetic approaches and reactivity of cobalt hydrides are described. Chapter 2 describes the development of different photoswitchable transformations using a catalytic system based on pinacolborane (a common hydroborating reagent) and the bench stable cobalt complex I, which has previously been reported to undergo photodissociation to II. The modification of the coordination sphere results in different mechanistic pathways that ultimately lead to a drastic change of the reactivity or selectivity of the system. Terminal alkenes can be either isomerised or hydroborated; enones undergo 1,2 or 1,4 hydroboration with a remarkable change of ambidoselectivity and the chemoselectivity in the hydroboration of ketoacids can be switched between the two different carbonyls with visible light as the only trigger. The first part of Chapter 3 describes a dual-catalytic platform for the cross-dehydrogenative-coupling between (benzo-)thiazoles and amines which combines low loadings of an iridium photoredox catalyst and a cobaloxime catalyst under blue light irradiation. This transformation occurs without stoichiometric oxidants, giving products in moderate to excellent yields. The second part of Chapter 3 describes a novel alkene hydroarylation methodology that relies on the combination of Metal-hydride Hydrogen-atom transfer (MHAT) catalysis and photochemistry. Feedstock starting materials such as styrenes are coupled with cyanopyridines with complete Markovnikov selectivity. The irradiation is necessary to form a cobalt hydride intermediate through a reductive pathway and to generate an arene radical from the cyanopyridine.