Mechanoactivated Celite as a Catalyst for C‒H Bond Perfluoroalkylation and Other Radical Reactions

Herein, we report that Celite (diatomaceous earth) commonly viewed as an innocent filter aid or support material, or Earth-abundant, non-toxic metal oxides are efficient mechanoactivated catalysts for arene and heteroarene C─H bond radical trifluoromethylation and pentafluoroethylation, with the activity comparable with previously reported mechanochemical methods utilizing piezoelectric materials. Celite was also applied for mechanochemical dibromination of a double bond with N-bromosuccinimide, eliminating the need to use of lithium titanate as a piezoelectric mechanoredox catalyst. Mechanoactivation via ball milling in the presence of minimal amount of solvent was crucial to observe the reactivity, while sonication or using a pre-ground suspension in a bulk solvent were not efficient. The EDX studies and comparison with individual metal oxides suggest a possible role of trace metal oxides in mechanoinduced reactivity. Celite could be recycled and reused several times without significant loss of activity. This approach offers environmentally benign, biocompatible and inexpensive nature-inspired materials as efficient mechanocatalyts and conceptually broadens the scope of mechanoactivated solids to the materials previously deemed inert.