Kinetics and mechanism of the stoichiometric oxygenation of the ionic zinc(II) flavonolate complex [Zn(fla)(idpa)]ClO4 (fla = flavonolate;: idpa=3,3′-iminobis(N,N-dimethylpropylamine))

The preparation and characterization of [Zn-II(4 'R-fla)(idpa)]ClO4 (fla = flavonolate; idpa = 3,3 ' -iminobis (N,N-dimethyl-propylamine) complexes are described. Oxygenation of [Zn-II(fla)(idpa)]ClO4 in dimethylformamide solution at elevated conditions gives [Zn-II(idpa)(O-bs)]ClO4 (O-bs = O-benzoylsalicylate) and carbon monoxide. The oxygenolysis of [Zn-II(fla)(idpa)]ClO4 in DMF was followed by electronic spectroscopy and the rate constants were determined according to the rate law -d[{Zn-II(fla)(idpa))ClO4]/dt = k(obs) [{Zn-II(fla)(idpa)}ClO4][O-2]. The rate constant, activation enthalpy and entropy at 373 K are as follows: k(obs) (M(-1)s(-1)) = (3.11 +/- 0.12) x 10(-3), DeltaH(double dagger) (kJ mol(-1)) = 75 +/- 5, DeltaS(double dagger) (J mol(-1) K-1) = -96 +/- 13. The reaction fits a Hammett linear free energy relationship for 4 ' -substituted flavonols, and electron-releasing groups make the oxygenation reaction faster In the course of the reaction O-2(.-) was formed suggesting a SET mechanism. [Zn-II(fla)(idpa)]ClO4 does not catalyze the oxygenation of flavonols. (C) 2001 Elsevier Science B.V. All rights reserved.