Kinetic studies on the copper(II)-mediated oxygenolysis of the flavonolate ligand.: Crystal structures of [Cu(fla)2] (fla = flavonolate) and [Cu(O-bs)2(py)3] (O-bs = O-benzoylsalicylate)

The complex [Cu(fla)(2)] has been prepared by treating copper(II) chloride with sodium flavonolate in tetrahydrofuran solution. Crystallographic characterisation of the complex [Cu(fla)(2)]. 2CHCl(3) has shown that the co-ordination geometry around the copper(II) ion is square planar. Oxygenation of [Cu(fla)(2)] in dimethylformamide solution at ambient conditions gives [Cu(O-bs)(2)] (O-bs=O-benzoylsalicylate) and carbon monoxide. Crystallographic characterisation of [Cu(O-bs)(2)] on crystals obtained from pyridine as [Cu(O-bs)(2)(py)(3)]. 0.91py revealed that the co-ordination geometry of the copper(II) ion is square pyramidal with trans O atoms of O-bs and N atoms of py ligands in basal and an N atom of py in apical position. The oxygenolysis of [Cu(fla)(2)] in DMF was followed by electron spectroscopy and the rate constants were determined according to the rate law -d[Cu(fla)(2)]/dt=k[Cu(fla)(2)][O-2]. The rate constant, activation enthalpy, entropy and free energy at 373 K are as follows: k/mol dm(-3) s(-1)=(1.57 +/- 0.08)x10(-2), Delta H double dagger/kJ mol(-1)=53 +/- 6, Delta S double dagger/J K-1 mol(-1)=-138 +/- 11, Delta G double dagger/kJ mol(-1)=105 +/- 2. The reaction fits a Hammett linear free energy relationship and a higher electron density on copper results in a faster oxygenation reaction.