posted on 2021-04-15, 15:10authored byYu-Tao He, Ayumu Karimata, Olga Gladkovskaya, Eugene Khaskin, Robert R. Fayzullin, Abir Sarbajna, Julia R. Khusnutdinova
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.