Synthesis, characterization, and photoinduced CO-release reactivity of a Pb(II) flavonolate complex: Comparisons to Group 12 analogs

The synthesis, characterization, and photoinduced CO-release reactivity of [(6-Ph2TPA)Pb(3-Hfl)]ClO4 (1; 6-Ph2TPA = N,N-bis((6-phenyl-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine; 3-Hfl = anion of 3-hydroxyflavone) is reported and compared with Group 12 analogues ([(6-Ph2TPA)M(3-Hfl)]ClO4 (M = Hg(II) (2), Cd(II) (3), Zn(II) (4)). The Pb(II) complex exhibits unique features within this group of complexes in terms of its structural and spectroscopic features involving the coordinated flavonolate ligand. Similar to the Group 12 compounds, irradiation of 1 at 300 nm in an O2-containing environment results in the quantitative release of CO and the formation of a Pb(II) O-benzoylsalicylate (O-bs, depside) complex via a photoinduced dioxygenase-type reaction. Comparison of the quantum yield for the reaction of the Pb(II) flavonolate complex (Φ = 0.21(6)) versus the reactions of the structurally-related Group 12 metal complexes (6-Ph2TPA)M(3-Hfl)]ClO4 (M = Hg(II) (2, Φ = 0.31(2)), Cd(II) (3, Φ = 0.28(2)), Zn(II) (4), Φ = 0. 09(1)) revealed that flavonolate complexes of a heavy metal ion (Cd(II), Hg(II), Pb(II)) exhibit a higher reaction quantum yield than the Zn(II) derivative. Both Pb(II) and Zn(II) flavonolate complexes were found to be catalysts for the oxidative photoinduced degradation of 3-hydroxyflavone. The combined results of these investigations suggest that metal contaminants typically present in soil, including toxic heavy metal ions, might facilitate the oxidative decomposition of plant-derived flavonols via photoinduced reactions.