Powerful low-valent photocatalysts and luminophores based on earth-abundant metals

Facing a growing world population and the concomitant increase in resource and energy consumption, researchers are challenged to make use of sustainable energy sources such as sunlight. Consequent efforts to utilize light as an energy source in chemical reactions established photocatalysis as a major research area. Most of the catalysts used are based on d6 metal complexes which usually consist of precious metals such as ruthenium(II), rhenium(I) or iridium(III). Although these complexes are generally robust and easily tunable to one’s needs, they are limited in their reduction power. This limitation hampers their efficient use in demanding organic reactions or the efficient design of solar fuel production systems.
In Chapters I and II, a short general introduction followed by a short overview over the relevant theoretical background are given.
Chapter III begins with a discussion of an introductory project which was concerned with the design of a strongly reducing, acid-stable ruthenium tris(2,20-bipyridne) derivative. The presented complex is robust enough to be employed as a photosensitizer in proton coupled electron transfer (PCET) reactions in presence of strong organic acids.
Subsequently, this thesis presents a new approach to the challenge of designing photocatalysts
with low excited state oxidation potentials. The use of chelating aryl isocyanide ligands with a fully aromatic ligand scaffold gives access to robust, earth-abundant molybdenum(0) photocatalysts. These catalyst are some of the strongest ever reported, and catalyse very demanding reduction reactions that have not been accessible with other photocatalysts before. Additional studies exploring the scope of these ligands yielded the first homoleptic chromium(0) complex to be luminescent in solution at room temperature. Also, two homoleptic nickel(0) complexes described in this thesis showed 3MLCT emission at low temperature and related copper(I) complexes (Appendix A) were found to be blue emitters in solution as well as the solid state. Chapter IV summarizes the results of this thesis and gives a perspective for future developments. The detailed description of the synthesis and experiments are found in
Chapter V.