Having established this catalytic system to efficiently perform alkylation of heteroarenes with nbe and styrenes, we next turned our attention to investigating the mechanism of the transformation. Based on previous nickel-catalyzed C(sp 2 )-H functionalization studies, we hypothesized that this reaction operates through a ligand-to-ligand hydrogen transfer (LLHT) mechanism where a concerted oxidative addition, migratory insertion bypasses the formation of a discrete nickel-hydride intermediate. C-H functionalization that proceed through LLHT often exhibit a characteristic fast, reversible C-H activation and rate-determining reductive elimination. To probe this characteristic, we conducted parallel KIE experiments with deuterium-labelled 5-phenylbenzofuran at 50 °C. The absence of kinetic isotope effect (KIE=1.0) suggests that C-H activation is not involved in the rate-determining step, as expected in the LLHT mechanism (Scheme 6a).