4.2. Synthesis of 3-Aminopropyl Silica Gel-Bound Copper(II)-Catalyst 3-Cu

A mixture of 3-aminopropyl silica gel (3) (5.015 g, 4.5 mmol of amino group), Cu(OAc)₂·H₂O (903 mg, 4.5 mmol), and methanol (25 mL) was stirred at 20 °C for 48 h. The insoluble material was collected by filtration, washed carefully with methanol until the filtrate was colorless (around 10 × 5 mL), and air-dried to give the copper(II) catalyst 3-Cu. Blue powder (5.163 g).