Organofunctionalized borotungstate polyoxometalates as tunable photocatalysts for oxidative dimerization of amines

Abstract

Organofunctionalized borotungstate Keggin polyoxometalates, (ⁿBu₄N)₃H[HBW₁₁O₃₉(P(O)Ph)₂] (PBW₁₁), (ⁿBu₄N)₃H[HBW₁₁O₃₉(As(O)Ph)₂] (AsBW₁₁), and (ⁿBu₄N)₄[HBW₁₁O₃₉(PhSiOSiPh)] (SiBW₁₁), were synthesized and structurally characterized. Cyclic voltammetry showed that the electronic properties of the clusters are dependent on the nature of the appended main group atoms (P, As, or Si). The first reduction potentials were found to shift positively with respect to that of the unmodified parent species (ⁿBu₄N)₅[BW₁₂O₄₀], with PBW₁₁ showing the largest shift at +100 mV. All clusters were evaluated as photocatalysts for the oxidative dimerization of amines where the organophosphonate hybrid PBW₁₁ was found to be the most active. This study demonstrates how organofunctionalization of polyoxometalates may be used to tune and improve their performance as photocatalysts for organic reactions.