Cobalt-Catalyzed Borylation of Arenes Enabled by in Situ π-Coordination

π-Coordination of an arene to chromium enables cobalt-catalyzed C-H borylation with a simple catalytic system consisting of commercially available compounds, [Co(acac)₂] and a terpyridine derivative. Arenes can be directly borylated via in situ ligand exchange with a chromium η⁶-naphthalene precursor in a one-pot, two-step reaction. Electron-rich arenes, which have been a challenging substrate for cobalt-catalyzed C-H borylation, react well under these conditions, presumably because η⁶-coordination to chromium decreases the electron density on the arene to enhance the C-H activation step.