Transient π-coordination enables nucleophilic borylation of simple arenes

Borylation of an arene typically proceeds <i>via</i> transition-metal-catalyzed C-H activation. We report here that transient π-coordination to chromium activates 1 equiv. of a simple arene towards nucleophilic borylation with B₂(pin)₂ in the presence of an additive such as K₂CO₃ or KF. The transient activation of the substrate is achieved <i>via in situ</i> ligand exchange with a naphthalene chromium complex, followed by borylation of the resulting arene chromium complex. Electron-rich and sterically hindered arenes, challenging substrates for transition-metal-catalyzed C-H borylation, react well under these conditions. Mechanistic studies support an anionic mechanism, where a borate species undergoes nucleophilic addition to the arene chromium complex, followed by hydride migration.