Cu(II) coordinated N-bearing heteropolyacid-based poly(ionic liquid)s for allylic oxidation of cyclohexene to 2-cyclohexene-1-one with O2 under mild conditions

To bridge transition metal complexes and heterogeneous catalysts for allylic oxidation of cyclohexene to 2-cyclohexene-1-one with O2 under mild conditions, Cu(II) coordinated N-bearing heteropolyacid-based poly(ionic liquid)s (Cu-PDVD-PW) were herein synthesized as novel heterogeneous catalysts. The physicochemical properties of the catalysts were investigated by BET, TG, XPS, FT-IR and SEM/EDS analysis. The results indicated that the as-prepared Cu-PDVD-PW catalyst inherited appreciable mesopores and excellent thermal stability from the N-bearing poly(ionic liquid)s, which could increase the mass transfer rate and provide more accessible active sites. Significantly, the Cu2+ cations were homogeneously and stably coordinated on the N-bearing poly(ionic liquid)s, which greatly improved the catalytic performance for cyclohexene oxidation toward 2-cyclohexene-1-one with O2 under mild conditions. Specifically, the 3% Cu-PDVD-PW catalyst exhibited 75.9% conversion of cyclohexene with a selectivity towards 2-cyclohexene-1-one of 45.5% and no activity loss within five cycles under the optimum reaction conditions.