Bioinspired Trispyrazolylborato Nickel(II) Flavonolate Complexes and Their Reactivity Toward Dioxygen

Aiming at structural and functional mimics of the active site of the Ni II containing quercetin‐2,4‐dioxygenase Ni II flavonolate complexes Tp*Ni X [Tp* = hydrotris(3,5‐dimethyl)pyrazolylborate, X = 3‐hydroxy flavonolate (Fla), 3‐hydroxy thioflavonolate (SFla), 3‐hydroxy selenoflavonolate (SeFla)] were synthesized and characterized by spectroscopic methods and X‐ray crystallography. The complex Tp*NiFla reacts with O 2 via dioxygenation of bound flavonolate to benzoic acid and salicylic acid as one should expect for a functional model of the enzyme. Modification of the carbonyl function of the flavonolate to the corresponding C=S and C=Se compounds retained dioxygenase like reactivity, but did not lead to an increase of reaction rate as had been anticipated due to a weaker interaction of S/Se with the central nickel atom.