Special-selective C-H oxidation of toluene to benzaldehyde by a hybrid polyoxometalate photocatalyst including a rare [P6W48Fe6O180]30- anion

It is a challenge to develop new photocatalysts for high selective oxidation of primary carbon-hydrogen (C-H) bonds with O-2 under mild condition. Herein, a novel hybrid K-6(H2O)(8)H-24(C26H16N4O4)(8) [P6W48Fe6O180]center dot 6H(2)O (FeW-DPNDI) was firstly synthesized by incorporating a rare Fe-substituted trimeric Dawson derivative and photosensitizer N,N'-bis(4-pyridylmethyl)naphthalene diimide (DPNDI) via solvothermal method. In FeW-DPNDI, [P6W48Fe6O180](30)- and DPNDI are orderly arranged in the three-dimensional framework by the anion center dot center dot center dot p interaction and C-H center dot center dot center dot O hydrogen bonds, that is beneficial to promote the electron transfer among components. FeW-DPNDI is a typical n-type semiconductor with the calculated energy level at 2.22 V vs. NHE of the highest occupied molecular orbital (HOMO) and -0.57 vs. NHE of the lowest unoccupied molecular orbital (LUMO), which is theoretically feasible for the reduction O-2 to O-2(center dot-) because of the more negative potential of CB than the standard redox potential (E(O-2(center dot-)/O-2) = - 0.33 V vs. NHE). The proton conductivity of FeW-DPNDI is 2.0 x 10(-4) S cm(-1) at 98% relative humidity and 358 K. FeW-DPNDI exhibits special selectivity for generating benzaldehyde in the photocatalytic oxidation of stubborn C-H bond of toluene under mild condition. Moreover, FeW-DPNDI can be easily isolated from the products and reused. FeW-DPNDI is the first example of the trimmer of Fe-substituted Dawson derivative, but also the first hybrid POM explored in the activating C-H bond of toluene under white light irradiation. (C) 2020 Elsevier Inc. All rights reserved.