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. 2024 Aug 12;15(36):14685-14691.
doi: 10.1039/d4sc03534h. Online ahead of print.

Organofunctionalized borotungstate polyoxometalates as tunable photocatalysts for oxidative dimerization of amines

Nicole Tsang  1   2 , Alexander J Kibler  1   2 , Stephen P Argent  2 , Hon Wai Lam  1   2 , Kieran D Jones  1   2 , Graham N Newton  1   2
Affiliations

Organofunctionalized borotungstate polyoxometalates as tunable photocatalysts for oxidative dimerization of amines

Nicole Tsang et al. Chem Sci. .

Abstract

Organofunctionalized borotungstate Keggin polyoxometalates, ( n Bu4N)3H[HBW11O39(P(O)Ph)2] (PBW11), ( n Bu4N)3H[HBW11O39(As(O)Ph)2] (AsBW11), and ( n Bu4N)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 ( n Bu4N)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.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Fig. 1
Fig. 1. Summarized photocatalytic cycle of organic–inorganic hybrid borotungstate POM-mediated single electron transfer (SET) with amines. Blue dots = WVI, red dots = oxygen.
Fig. 2
Fig. 2. Synthesis of organic–inorganic hybrid borotungstates PBW11, AsBW11, and SiBW11 from the lacunary borotungstate.
Fig. 3
Fig. 3. X-ray crystal structure of K3H[HBW11O39(As(O)Ph)2] with disordered elements, solvent, and potassium cations omitted for clarity. Color code: blue = W, red = O, black = carbon, green = As, orange = B, pink = H.
Fig. 4
Fig. 4. (Left) CV of 1 mM of compounds BW12, PBW11, AsBW11, and SiBW11 in anhydrous DMF with 0.1 M nBu4NPF6 supporting electrolyte. (Right) CV of 1 mM of compounds PBW11 and PSiW11 in anhydrous DMF with 0.1 M nBu4NPF6 supporting electrolyte. All CVs were recorded at 100 mV s−1 using a glassy carbon working electrode (d = 3 mm and A = 0.071 cm2), Pt wire counter electrode and a AgNO3|Ag non-aqueous reference electrode. The standard potentials are highlighted for the redox processes.
Fig. 5
Fig. 5. POM-mediated photooxidative dimerization of benzyl amine under anaerobic or aerobic conditions. NMR yield determined by 1H NMR spectroscopic analysis using 1,3-benzodioxole as an internal standard.
Fig. 6
Fig. 6. Optimization of PBW11 photocatalyzed oxidative dimerization of benzyl amine illustrated as a color-coded radar diagram. Yields determined by 1H NMR analysis using 1,3-benzodioxole as an internal standard and presented as a percentage deviation from the model reaction.
Fig. 7
Fig. 7. Photocatalytic oxidative dimerization of various amines. Yields determined by 1H NMR analysis using 1,3-benzodioxole as an internal standard.
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