Tetrabutylammonium bromide (TBAB) was found to improve the ligand-free copper-catalyzed cross-couplings of aryl halides with arylboronic acids. In the presence of 10 mol% of CuI and 20 mol% of TBAB, a variety of aryl halides underwent the coupling with arylboronic acids smoothly to afford the corresponding products in moderate to good yields.
tetrabutylammonium bromide - copper(I) iodide - aryl halide - arylboronic acid - Suzuki-Miyaura cross-coupling reaction