Borylation of Simple Arenes Enabled by π-Coordination

Borylation of an arene typically proceeds via transition-metal-catalyzed C-H activation. We report here that pi-coordination to chromium activates an arene towards nucleophilic borylation with B2(pin)2 in the presence of an additive such as K2CO3 or KF. Moreover, we achieved transient activation of an arene via in situ 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.