Organofunctionalized borotungstate polyoxometalates as tunable photocatalysts for oxidative dimerization of amines.

Organofunctionalized borotungstate Keggin polyoxometalates, ( n Bu 4 N) 3 H[HBW 11 O 39 (P(O)Ph) 2 ] (PBW 11 ), ( n Bu 4 N) 3 H[HBW 11 O 39 (As(O)Ph) 2 ] (AsBW 11 ), and ( n Bu 4 N) 4 [HBW 11 O 39 (PhSiOSiPh)] (SiBW 11 ), 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 ( n Bu 4 N) 5 [BW 12 O 40 ], with PBW 11 showing the largest shift at +100 mV. All clusters were evaluated as photocatalysts for the oxidative dimerization of amines where the organophosphonate hybrid PBW 11 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.