Direct functionalization of unactivated C–H bonds catalyzed by group 3–5 metal alkyl complexes
This perspective summarizes direct C–H bond functionalization reactions catalyzed by group 3–5 metal alkyl complexes. Metal–carbon bonds of group 3–5 metals have potentially high reactivity toward both C–H bond activation reactions through the intrinsic σ-bond metathesis pathway and insertion of unsaturated organic molecules. Upon the combination of these two elemental steps, direct C–H bond functionalization reactions of (hetero)aromatic compounds, methane, alkylamines, and terminal alkynes, proceed through C(sp)–H, C(sp2)–H, and C(sp3)–H bond activation reactions. Here we review as catalysts for these transformations not only simple metallocene complexes but also non-metallocene complexes supported by a variety of ligands, which are often superior in terms of catalyst design and catalytic activity.