Tetragonal Cu2Se nanoflakes: synthesis using selenated propylamine as Se source and activation of Suzuki and Sonogashira cross coupling reactions

Abstract

The metastable tetragonal Cu₂Se phase as nanoflakes has been synthesized for the first time by treating CuCl₂ taken in a mixture (1 : 1) of 1-octadecene and oleylamine with H₂N–(CH₂)₃–SePh dissolved in 1-octadecene. Powder X-ray diffraction (PXRD), HRTEM, SEM-EDX and XPS have been used to authenticate the nanoflakes. The XPS of Cu₂Se nanoflakes indicates oxidation states of Cu and Se as +1 and −2 respectively. The size of the majority of Cu₂Se nanoflakes was found to be between 12 and 14 nm. The nanoflakes have been explored for Suzuki and Sonogashira cross coupling reactions in the presence of TBAB in DMF and DMSO respectively. For Suzuki coupling conversion was found upto ∼86% in 15 h at 110 °C when loading of Cu was 1 mol%. In case of Sonogashira coupling conversion was found upto 82% in 15 h at 160 °C (Cu loading: 1 mol%). The catalytic efficiency of Cu₂Se nanoflakes for Suzuki coupling reaction is greater than that for Sonogashira coupling. These nanoflakes have been found reusable for a second time. Most probably TBAB facilitates the release of CuBr from the nanoflakes which catalyze both reactions, as catalytic efficiency is very low in the absence of TBAB and CuBr has been found to activate readily both the coupling reactions. In comparison to many other copper based nano-crystals, the present nanoflakes are a better activator.