525.5mg of the (S)-tBuBox ligand (1.75mmol) and anhydrous CuCl2 233.5mg (1.785 mmol) was stirred in freshly-distilled anh. dichloromethane (15mL) for 15 min. The obtained greenish-yellow solution was filtered through a PTFE disc filter (using a syringe, the filter washed with anh. dichloromethane 5mL). To this filtrate containing the CuCl2 complex, a solution of AgSbF6 1202.5mg (3.50 mmol) in anh. dichloromethane 5mL was added dropwise via canula. The mixture was stirred for 3 hours in dark, then filtered through celite. The celite pad was washed with wet dichloromethane, 4x15mL (obtained by shaking freshly distilled dichloromethane with few drops of water and filtering through a plug of cotton).
The obtained light-blue filtrates were evaporated very slowly (over 2 h, to avoid bumping and to obtain a more crystalline material) and the residue was then dried on higvac.
Y = 1.509g of a light blue solid (100% th). The product is slightly hygroscopic but stable – it can be stored at room temperature over extended period of time.