Silver-modified polyniobotungstate for the visible light-induced simultaneous cleavage of C–C and C–N bonds
Shujun Li, Na Li, Gang Li, Yubin Ma, Mengyao Huang, Qingchun Xia, Qianyi Zhao, Xuenian Chen
Abstract
Silver-modified polyniobotungstate based on Nb/W mixed-addendum polyoxometalate with formula Ag<sub>9</sub>[P<sub>2</sub>W<sub>15</sub>Nb<sub>3</sub>O<sub>62</sub>]·21H<sub>2</sub>O (<strong>Ag-Nb/W</strong>) was synthesized and then characterized by various analytical and spectral techniques. <strong>Ag-Nb/W</strong> was proven to be an efficient photocatalyst for the oxidative ring opening of 2-phenylimidazo[1,2-<i>a</i>]pyridine via the simultaneous cleavage of C–C and C–N bonds. Under visible light (430–440 nm) and with oxygen as an oxidant at room temperature, <strong>Ag-Nb/W</strong> can catalyze the rapid transformation of various 2-phenylimidazo[1,2-<i>a</i>]pyridine derivatives to produce the corresponding oxidative ring-opening product N-(pyridin-2-yl) amides in good isolated yields ranging from 65% to 78%. As a heterogeneous photocatalyst, <strong>Ag-Nb/W</strong> showed excellent sustainability and recyclability in the recycling experiments. Infrared (IR) spectroscopy and X-ray diffraction (XRD) analysis indicated that <strong>Ag-Nb/W</strong> could retain its integrity after catalysis. A possible mechanism involving the singlet oxygen for the catalytic reaction was proposed.