Bis(imino)acenaphthene (BIAN)-Supported N‑Heterocyclic Carbene Palladium Complexes with Ancillary Ligands: Readily Activated Precatalysts for Direct C–H Arylation of Thiophenes

We report herein a highly efficient direct C–H arylation of thiophenes with (hetero)­aryl bromides by bulky bis­(imino)­acenaphthene (BIAN)-supported N-heterocyclic carbene palladium complexes. The relationship between the structure of palladium complexes with ancillary ligands and catalytic properties was discussed. Upon a low palladium loading of 0.01–0.05 mol %, the bulky palladium complex was successfully used to catalyze the cross-coupling of a variety of thiophens with (hetero)­aryl bromides under aerobic conditions. Furthermore, it provides a practical and straightforward access to poly­(3-hexylthiophenes) with high molecular weight and high HT value under aerobic reaction conditions. To access the mechanistic of the transformation, experiment investigation and DFT calculations on the direct arylation were performed, which supported the involvement of a Pd(0)/Pd(II) CMD process.