Reductive silylation of polyoxovanadate surfaces using Mashima's reagent

Abstract

Here, we present the first example of reductive silylation for oxygen defect formation at the surface of a polyoxometalate. Upon addition of 1,4-bis(trimethylsilyl)dihydropyrazine (Pyz(SiMe₃)₂) to [V₆O₇(OMe)₁₂]¹⁻, quantitative formation of the oxygen-deficient vanadium oxide assembly, [V₆O₆(OMe)₁₂]¹⁻ was observed. Substoichiometric reactions of Pyz(SiMe₃)₂ with the parent cluster revealed the mechanism of defect formation; addition of 0.5 equiv. of Pyz(SiMe₃)₂ to [V₆O₇(OMe)₁₂]¹⁻ results in isolation of [V₆O₆(OSiMe₃)(OMe)₁₂]¹⁻. This reactivity was extended to reduced and oxidized forms of the cluster, [V₆O₇(OMe)₁₂]ⁿ (n = 2-, 0), revealing the consequences of modifying the oxidation states of remote transition metal ions on the stability of the siloxide functional group, and thus the extent of reactivity of the cluster surface with Pyz(SiMe₃)₂. The work offers a new understanding of the mechanisms of surface activation of reducible metal oxides via reductive silylation, and reveals new chemical routes for the formation of oxygen atom vacancies in polyoxometalate ions.