Atom‐Economic Electron Donors for Photobiocatalytic Halogenations

In vitro cofactor supply and regeneration has been a major obstacle for biocatalytic processes, in particular on a large scale. Peroxidases often suffer from inactivation by their oxidative co‐factor. Combining photocatalysis and biocatalysis offers an innovative solution to this problem, but lacks atom economy due to the sacrificial electron donors needed. Herein, we show that redox‐active buffers or even water alone can serve as efficient, biocompatible electron sources, when combined with photocatalysis. Mechanistic investigations revealed first insights into the possibilities and limitations of this approach and allowed for adjusting the reaction conditions to the specific needs of biocatalytic transformations. Proof‐of‐concept for the applicability of this photobiocatalytic reaction setup was given by enzymatic halogenations.