Visible-light-initiated Sonogashira coupling reactions over CuO/TiO2 nanocomposites

Abstract

CuO/TiO₂ nanocomposites with different weight ratios of CuO were obtained by immersing TiO₂ in aqueous solution of Cu(NO₃)₂, followed by heat treatment at 400 °C. The resultant CuO/TiO₂ nanocomposites were fully characterized and their catalytic performance for light induced Sonogashira coupling reactions was investigated. CuO/TiO₂ nanocomposites show catalytic activity for the Sonogashira coupling between aryl alkynes and aryl iodides under visible light, with optimum performance realized over the 20 wt% CuO/TiO₂ nanocomposite. UV-vis DRS reveals that metal–metal charge transfer (MMCT) of Ti(III)/Cu(II) exists in the CuO/TiO₂ nanocomposite. When irradiated, accompanied by an electron transfer from Ti(III) to Cu(II), the Ti(III)/Cu(II) moiety is excited to generate Ti(IV)/Cu(I). The as-formed Cu(I) coordinates with the deprotonated phenylacetylene to form copper phenylacetylide, which acts as an active intermediate for Sonogashira coupling reactions. This study not only provides an efficient method to realize Sonogashira coupling reactions under visible light, but also highlights the great potential of photocatalysis in light induced organic syntheses.