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

A simple catalytic process for the C−H arylation of (poly)flluoroarenes with aryl pinacol boronates mediated by a Pd/Ag system without added ligand is reported. This reaction can be carried out in air, generating unsymmetric biaryl products in up to 98 % yield. DFT calculations indicate that the presence of an electron-rich aryl ligand at Pd(II) intermediate reduces the energy barrier for the CMD process with C₆F₅H to give [Pd(DMF)₂(Ar)(C₆F₅)], and thus the desired cross-coupling product is obtained.

Abstract

We report the synergistic combination of Pd(OAc)₂ and Ag₂O 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 [PdL₂(C₆F₅)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 C₆F₅H and the Pd(II) species formed after transmetalation between the Pd(II)X₂ 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.

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