Methylation of C(sp 3 )-H/C(sp 2 )-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(CH2 CH2 PPh2 )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 ·6H2 O/PP3 /K2 CO3 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.