C–C Bond Elimination from High-Valent Mn Aryl Complexes

Manganese complexes have been considered as a cheap and readily available alternative to commonly used precious metal catalysts in C–C bond coupling reactions. Although high-valent Mn aryl intermediates have been proposed in such reactions, a mechanistic understanding of possible organometallic intermediates in Mn-mediated C–C coupling is still lacking due to their high reactivity. We report the synthesis of stable, isolable Mn­(III) aryl complexes obtained by oxidative addition of aryl bromide or aryl chloride. These complexes react with a range of organometallic alkylating or arylating reagents (alkyl and aryl Grignard reagents, MeLi, ZnMe₂) to undergo C­(sp²)–C­(sp³) or C­(sp²)–C­(sp²) bond coupling, and a preliminary catalytic system could be demonstrated. The reagent scope and yield of the C­(sp²)–C­(sp³) coupled product can further be increased by addition of TEMPO as an oxidant, generating alkyl radicals.