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(ArF)(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-Arrich species. Thus a Pd(Arrich)(Arpoor) complex is generated selectively which undergoes reductive elimination to generate the unsymmetrical biaryl product.
