Fig. 1: Transition metal-catalyzed C–H activation via cyclometallation.
From: Ni-catalyzed benzylic β-C(sp3)–H bond activation of formamides
a The activation of C–H bonds at different position to the coordinating atom of directing groups is faced with varying levels of difficulty. γ-C–H bonds are the most easily activated via 5-membered metallacycles, while the activation of proximate β-C–H bonds via highly-strained 4-membered metallacycles is extremely challenging. b Only scarce examples on β-C–H bond activation via 4-membered metallacycles have been reported, and all of them rely on precious metals such as Pd, Rh, and Ru. c Proposed secondary β-C(sp3)–H bond activation: PO-ligated Ni–Al bimetal-catalyzed C–H bond activation via 4-membered nickelacycle. d 3d-Transition metal-catalyzed secondary C(sp3)–H bond activation via 4-membered nickelacycle (this work). DG Directing group. M Metal catalyst. FG Functional group. PG Protecting group.
