Pd-Catalyzed Oxidative C-H Arylation of (Poly)fluoroarenes with Aryl Pinacol Boronates and Experimental and Theoretical Studies of its Reaction Mechanism.

We report the synergistic combination of Pd(OAc) 2 and Ag 2 O for the oxidative C-H arylation of (poly)fluoroarenes with aryl pinacol boronates (Ar-Bpin) in DMF as the solvent. This procedure can be conducted easily in air, and without using additional ligands, to afford the fluorinated unsymmetrical biaryl products in up to 98 % yield. Experimental studies suggest that the formation of [PdL 2 (C 6 F 5 ) 2 ] in DMF as coordinating solvent does not take place under the reaction conditions as it is stable to reductive elimination and thus would deactivate the catalyst. Thus, the intermediate [Pd(DMF) 2 (Ar F )(Ar)] must be formed selectively to give desired arylation products. DFT calculations predict a low barrier (5.87 kcal/mol) for the concerted metalation deprotonation (CMD) process between C 6 F 5 H and the Pd(II) species formed after transmetalation between the Pd(II)X 2 complex and aryl-Bpin which forms a Pd-Ar rich species. Thus a Pd(Ar rich )(Ar poor ) complex is generated selectively which undergoes reductive elimination to generate the unsymmetrical biaryl product.