Significant progress has been accomplished in directed C–H functionalization through the use of earth-abundant and inexpensive first-row transition metals. Among these base metals, Co is especially attractive in view of its versatile applications in C–H functionalization, in both low- and high-valent states. In this vein, catalytic Co(III) species can be generated from the dissociation of a Cp*Co(III) catalyst or through the oxidation of a low-valent cobalt catalyst in the presence of an oxidant. In this feature article, we will discuss the breakthroughs in Cp*Co(III)-promoted C–H functionalization. In this field, C(sp²)–H functionalization has been extensively studied and developed. In contrast, few C(sp³)–H functionalization reactions have been reported.

Alkenylation of unactivated arenes and 6-arylpurines with terminal alkynes in high yields using Cp*Co(CO)I₂ as catalyst under mild conditions is described. This method shows outstanding functional group compatibility and can be applied in the design of a mitochondria-targeted imaging dye.

Electrochemical intermolecular C–N formation/cyclization of ketones with 2-aminopyridines using catalytic hydriodic acid as the redox mediator was developed, providing imidazo[1,2-a]pyridines under more environmentally benign conditions. The reaction proceeds in a simple undivided cell, using low toxic ethanol as the solvent, without external oxidants, and exhibits high atom economy. A variety of ketones including acetophenones, unsatruated and alkyl ketones are amenable to this reaction, affording the corresponding products in moderate to excellent yields. A three-component tandem reaction realizing C–N, C–S/C–Se bond formation can also be achieved under standard conditions.

The phosphorylation of the ortho C–H bonds in benzamides containing an 8-aminoquinoline moiety as a bidentate directing group with H-phosphonates using copper as a catalyst under mild temperature conditions is described. This method shows high functional group compatibility and selectively gives mono-substituted products.

A metal-free direct alkylation of C–H bonds adjacent to an oxygen or nitrogen atom was developed. This reaction occurred between saturated heterocycles and ethynylbenziodoxolones under mild conditions. A series of 2-alkynyl cyclic alkanes that contain oxygen or nitrogen atoms were prepared in moderate to good yields.