Characterization of the Initial Intermediate Formed during Photoinduced Oxygenation of the Ruthenium(II) Bis(bipyridyl)flavonolate Complex.

A ruthenium(II) flavonolate complex, [Ru(II)(bpy)2fla][BF4], was synthesized to model the reactivity of the flavonol dioxygenases. The treatment of dry CH3CN solutions of [Ru(II)(bpy)2fla][BF4] with dioxygen under light leads to the oxidative O-heterocyclic ring opening of the coordinated substrate flavonolate, resulting in the formation of [Ru(II)(bpy)2(carboxylate)][BF4] (carboxylate = O-benzoylsalicylate or benzoate) species, as determined by electrospray ionization mass spectrometry. Moderation of the excitation and temperature allowed isolation and characterization of an intermediate, [Ru(II)(bpy)2bpg][BF4] (bpg = 2-benzoyloxyphenylglyoxylate), generated by the 1,2-addition of dioxygen to the central flavonolate ring.