Selective Formation of Epoxylimonene Catalyzed by Phosphonyl/Arsonyl Derivatives of Trivacant Polyoxotungstates at Low Temperature
Résumé
The catalytic performances of three organophosphonyle/arsonyle derivatives of POMs were evaluated for the epoxidation of limonene in acetonitrile, using aqueous H2O2 as the oxidant. All three W-based POMs catalysts operated without any additional transition-metal ions and displayed excellent conversion for the limonene to temperatures varying from 4 to 50°C. Furthermore, the use of B,α−[NaHAsW9O33{P(O)R}2] 3-(R = t Bu,-CH2CH2CO2H) complexes led to the complete conversion of limonene to epoxylimonene at 4°C. The selectivity of the reaction was modulated by varying the reaction solvent, and it was found that allylic reactions were favoured in ethanol. The effect of the catalyst protonation was also investigated by DFT calculations, highlighting the role of protons in the epoxidation process.
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