CuO nanostructures of variable shapes as an efficient catalyst for [3 + 2] cycloaddition of azides with terminal alkyne

Abstract

CuO nanostructures of variable shapes: CuO nanospheres (5–10 nm), CuO nanorods (W × L = 24–27 nm × 124–140 nm) and CuO nanowires (W × L = 8–10 nm × 230–270 nm) have been synthesised to study the effect of shape of the catalyst on the Cu(I)-catalysed “click” azide–alkyne cycloaddition. Cu(I) species were generated in situ by the reduction of CuO nanostructures in the presence of sodium ascorbate. CuO nanowires exhibited highest catalytic efficiency for the cycloaddition reaction between azide and terminal alkyne, featuring short reaction time, soft reaction conditions and complete regioselectivity. We have further extended the study by using azides with varying functional groups (–OCH₃ and –NO₂) and studied the effect of shape of the nanostructures on the rate of the reaction and yield of the triazole products. The activity trend observed was: CuO-NW > CuO-NR > CuO-NS, irrespective of the presence of electron withdrawing or donating groups on the azide.