1 research outputs found
Mechanistic Investigations of Photoinduced Oxygenation of Ru(II) Bis-bipyridyl Flavonolate Complexes
We previously reported that a Ru-bound
flavonolate model of flavonol dioxygenases, [Ru<sup>II</sup>(bpy)<sub>2</sub>(3-hydroxyfla)]Â[PF<sub>6</sub>], photochemically reacts with
dioxygen in two different manners. Broad-band excitation generates
mixtures of products characteristic of 1,3-addition of dioxygen across
the central pyrone ring, as is observed in enzymatic reactions. However,
low temperature excitation at wavelengths longer than 400 nm generates
a unique Ru-bound 2-benzoatophenylglyoxylate product resulting from
a 1,2-dioxetane intermediate. Herein, we investigate this reactivity
in a series of RuÂ(II)Âbis-bipyridyl flavonolate complexes [Ru<sup>II</sup>(bpy)<sub>2</sub>(3-hydroxyfla<sup>R</sup>)]Â[PF<sub>6</sub>] (bpy
= 2,2′-bipyridine; fla = flavonolate; R = <i>p</i>-OMe (<b>1</b>), <i>p</i>-Me (<b>2</b>), <i>p</i>-H (<b>3</b>), <i>p</i>-Cl (<b>4</b>)), and [Ru<sup>II</sup>(bpy)<sub>2</sub>(5-hydroxyfla)]Â[PF<sub>6</sub>] (<b>5</b>). The complexes’ structures, photophysical
and electrochemical properties, and photochemical reactivity with
oxygen were investigated in detail. Two different reaction product
mixtures, from 1,2- and 1,3-additions of dioxygen, are observed by
illumination into distinct excitation/emission manifolds. By analogy
to previous reports of excited state intramolecular proton transfer,
the two manifolds are attributed to tautomeric diradicals that predict
the observed reactivity patterns