Stability of Catalytic Centres in Light‐Driven Hydrogen Evolution by Di‐ and Oligonuclear Photocatalysts

A review. In recent decades, mimicking natural photosynthesis by artificial photocatalysis represented a major research direction with the ultimate goal of reducing fossil fuel consumption through efficient solar energy harvesting. To transfer molecular photocatalysis from the lab scale to an industrially relevant process, it is important to overcome instability problems of the catalysts during light‐driven operation. As it is well‐known that many of the typically utilized noble metal‐based catalytic centres (e. g. Pt and Pd) undergo particle formation during (photo)catalysis and thus switch the whole process from a homogeneous into a heterogeneous one, an understanding of the factors governing particle formation is crucially needed. The review therefore focuses on di‐ and oligonuclear photocatalysts bearing a range of different bridging ligand architectures for drawing structure‐catalyst‐stability relationships in light‐driven intramolecular reductive catalysis. In addition, ligand effects at the catalytic centre and their implications for catalytic activity in intermolecular systems will be discussed, as will important insights into the future design of operationally stable catalysts. Photocatalytic water reduction: This review is focused on the catalytically active metal centre for photocatalytic water reduction and summarizes the main decomposition pathways turning a molecular photocatalyst into a heterogeneous, colloid‐based catalytic system. Moreover, strategies to obtain molecularly operating oligonuclear photocatalysts are presented.