The chemistry of vanadate chelate esters of monoionized aromatic diols and methoxyphenolate

Abstract

Two ONO donor tridentate Schiff base ligands, two aromatic 1,2-diols and a monomethyl ether derivative of aromatic 1,2-diol are used in this work. The ONO donor ligands are deprotonated forms of N-(1-hydroxyphenyl)salicylaldimine (H 2L 1) and N-(1-hydroxyphenyl)napthaldimine(H 2L 2) (general abbreviation H 2L). The concerned diols are catechol (H 2cat), its 3 , 5 - Bu 2 t derivative (H 2dbcat) and the monomethyl ether derivative of aromatic 1,2-diol is 2-methoxyphenol (HMecat), commonly known as guaiacol. The syntheses of hexa-/penta-coordinated vanadate esters of monoionized aromatic 1,2-diols and 2-methoxyphenolate, with diionized N-salicylidene/ N-napthalidine-α-aminophenol as coligands are described and the reactivities of the compounds are reported. The concerned vanadate esters are [VO(L)(Hcat)], [VO(L)(Hdbcat)] and [VO(L)(Mecat)], where Hcat, Hdbcat and Mecat are monoionised forms of H 2cat, H 2dbcat and HMecat, respectively. The complexes are electroactive in MeCN solution. Molecular oxygen reacts smoothly with the oxovanadium(V) complexes quantitatively, furnishing the corresponding o-quinone. In the presence of the aromatic diol or guaiacol the reaction becomes catalytic. The X-ray structure of [VO(L 2)(Mecat)] has also been reported.