Quercetinase model studies. The oxygenation of flavonol catalyzed by a cationic 2,2′-bipyridine copper(II) flavonolate complex

The catalyst [Cu II(bpy)(fla)]ClO 4, 1, was prepared from Cu(CH 3CN) 4ClO 4, 2,2′-bipyridine (bpy), flavonol (flaH), and dioxygen in acetonitrile at ambient conditions. The flavonolato copper complex 1 reacts with molecular oxygen slowly at room temperature but reasonably fast at around 100°C in acetonitrile or DMF to the O-benzoylsalicylato copper complex [Cu II(bpy)( O-bs)]ClO 4 in good yield. Kinetics of the oxygenation of 1 shows that there are two kinetically not interpretable segments of the reaction, however 1 is a good catalyst for the oxygenation of flavonol to O-benzoylsalicylic acid ( O-bsH) at around 100°C. Kinetic studies of the catalytic reaction resulted in the rate expression −d[flaH]/d t= k obs[flaH][catalyst] 2[O 2] 2. The reaction constant at 100°C was found to be k obs=7.20±0.13×10 10 mol −4 dm 12 s −1, with activation parameters Δ H ‡=80.83±3.14 kJ mol −1, Δ S ‡=179.61±8.82 J mol −1 K −1.