WO3 nanospheres with improved catalytic activity for visible light induced cross dehydrogenative coupling reactions

Abstract

Three tungsten oxides (WO3-W1 to WO3-W3) with different morphologies were prepared and characterized by XRD, SEM, TEM and HR-TEM measurements. The as-synthesized tungsten oxides were screened as photocatalysts for visible-light-driven cross dehydrogenative coupling (CDC) reactions along with commercially available WO3-W4. Preliminary studies showed that WO3-W1 with hollow sphere morphology efficiently photocatalyzed oxidative CH functionalization as compared to other tested samples, by using molecular oxygen as a benign oxidant. The superior photocatalytic performance of WO3-W1 can be attributed to its larger surface area and pore structure which was supported by nitrogen adsorption-desorption measurements. Further, this protocol was used to synthesize α-functionalized tertiary amines in good to excellent yields by irradiating a mixture of WO3-W1, tertiary amine, and nucleophiles (nitromethane or ketones) to visible light under aerobic conditions. Moreover, WO3-W1 can be recycled and reused with no obvious change in catalytic activity, indicating that this is an environmentally friendly and economical protocol and also underlines the robustness of the catalysts in light mediated cross dehydrogenative coupling reactions. It is hoped that our results could offer useful information for designing of new heterogeneous semiconductors for photoredox catalytic organic reactions.