Visible light photoredox catalyzed deoxygenations and polymer-tagged photocatalysts

This thesis starts with a brief introduction to visible light mediated photoredox catalysis. Therefore underlying photo-physical processes are presented followed by showcasing of two very recent, trendsetting publications in the area. Within the chapter “Photochemical Deoxygenations” research results concerning photochemical C–O bond scission reactions are detailed. Preliminary studies with phosphonate esters as activation groups for C–O bonds led to the employment of 3,5-bis(trifluoromethyl)benzoates as activating unit. After optimization of the reaction conditions and discussion of the reaction mechanism the substrate scope and limitations of the process are shown. Subsequently experiments towards an in situ activation of alcohols followed by performance of the photochemical reaction step in continuous flow are described. The following section deals with the expansion of the developed photochemical C–O bond fragmentation reactions towards the formation of new C–C bonds. After efforts to use unactivated alcohol derivatives in intramolecular cyclizations and activated alcohol derivatives in intermolecular bond formations prove to be unfruitful, intramolecular cyclizations from activated benzoates leading to chiral tetrahydrofuran derivatives are realized. The synthesis of suitable substrates and their photochemical performance is evaluated. The chapter “Polymer-tagged Photocatalysts” deals with the immobilization of iridium-based photocatalysts with homogeneously soluble polymers and their recycling. Studies with biscyclometalated iridium complexes result in an easily recyclable derivative of [Ir(ppy)2(dtb-bpy]+. Its application in the decarboxylative synthesis of isoquinolinones with visible light is investigated. Optimization of the catalyst design and streamlining of the synthesis are shown. In the second part of the chapter a triscyclometalated iridium complex is synthesized and repeatedly used for photoredox reactions in a batch process. Experiments towards automatic catalyst recovery and reusage in a continuously operating microreactor setup for photoreactions complete the investigations with polymer-tagged photocatalysts