Arene–Metal π‑Complexation as a Traceless Reactivity Enhancer for C–H Arylation

Current approaches to facilitate C–H arylation of arenes involve the use of either strongly electron-withdrawing substituents or directing groups. Both approaches require structural modification of the arene, limiting their generality. We present a new approach where C–H arylation is made possible without altering the connectivity of the arene via π-complexation of a Cr­(CO)₃ unit, greatly enhancing the reactivity of the aromatic C–H bonds. We apply this approach to monofluorobenzenes, highly unreactive arenes, which upon complexation become nearly as reactive as pentafluorobenzene itself in their couplings with iodoarenes. DFT calculations indicate that C–H activation via a concerted metalation–deprotonation transition state is facilitated by the predisposition of C–H bonds in (Ar–H)­Cr­(CO)₃ to bend out of the aromatic plane