Methylation of C(sp3)–H/C(sp2)–H Bonds with Methanol Catalyzed by Cobalt System

A highly efficient Co-based catalytic system, composed of a commercially available Co salt, a tetradentate phosphine ligand P(CH₂CH₂PPh₂)₃(PP₃), and a base (denoted as [Co]/PP₃/base), is developed for the methylation of C(sp³)-H and C(sp²)-H bonds using methanol as a methylating reagent. The Co(BF₄)₂·6H₂O/PP₃/K₂CO₃ catalytic system showed high catalytic activity for the methylation of C-H bonds in aryl alkyl ketones, aryl acetonitriles, and indoles, with wide substrate scope and good functional group tolerance, and methyl-substituted products were obtained in good to excellent yields at 100 °C. This cheap, readily available, and highly efficient Co-based catalytic system may have promising applications in methylation reaction using methanol.