Relative reactivities and absolute rate constants of the reactions of haloarenes with i-PrMgCl·LiCl were investigated in THF at 0 °C. The rate of the halogen–magnesium exchange decreases in the series ArI > ArBr > ArCl (relative reactivities: 10¹¹:10⁶:1). Preliminary experiments show that the p-tolylsulfinyl group is exchanged slightly faster than iodide, while a tosyl group is exchanged at least 10⁴ times more slowly than a bromide.