Noninnocent Azo-Aromatic Cobalt(II)-Catalyzed sp C-H Alkylation of Fluorenes with Alcohols.

Herein, employing well-defined redox noninnocent cobalt(II) complexes an efficient sp C-H alkylation of fluorenes using alcohols as alkylating agents to result in alkylated fluorenes is reported. The catalytic protocol was versatile with various fluorenes and benzyl alcohols. It also showed very good functional group tolerance with both alcohols and fluorenes. Moreover, an efficient single-step and simultaneous di C-C as well as both C-C and the C-N alkylation reaction of fluorenes was observed with this catalytic protocol. Such selective single-step dialkylation of fluorenes is indeed beneficial. Several control experiments, deuterium labeling, and H NMR kinetic studies have revealed a ligand radical-based borrowing hydrogen mechanism involving the azo-aromatic complexes of cobalt as catalysts for the alkylation of fluorenes.