Gram‐Scale Photocatalysis with a Stable and Recyclable Chromium(III) Photocatalyst in Acetonitrile and in Water

Abstract The use of stable photosensitizers made on a multigram‐scale from cheap and available starting materials offers an extraordinary opportunity to translate small‐scale proof‐of‐concept photoreactions to widespread applications in non‐specialized laboratories, thereby promoting the implementation of light‐driven syntheses. Herein, we report an easy, multigram‐scale preparation of the exceptionally photo‐ and redoxstable chromium(III) complex [Cr(tpe) 2 ] 3+ (tpe=1,1,1‐tris(pyrid‐2‐yl)ethane) at room temperature. This photocatalyst was successfully employed in acetonitrile and in the “green” solvent water as demonstrated in visible‐light induced Schenck‐Ene reactions, Newman‐Kwart rearrangements, radical cation Diels‐Alder cycloadditions, oxidative decarboxylation and trifluoromethylation reactions with excellent substrate conversions and high turnover numbers. Gram‐scale photocatalytic reactions were conducted using a simple round‐bottom flask as reaction vessel and irradiation with energy‐efficient blue LEDs or even with sunlight. The stable photocatalyst was successfully recycled in up to 90–92% yields after the photoreactions.