Effect of Enhanced RuO2 Layer on the Sustainability of Ru/MMT Catalyst towards [3+2] Cycloaddition Reaction

摘要

Ru NP’s supported on MMT acts as robust catalyst for the synthesis of 5-substituted 1H-tetrazoles via [3+2] cycloaddition reaction under mild conditions. Structural analysis of composite suggests it to be consisting of mixed phases of well dispersed Ru NP’s core coated with RuO2 layer having particle size of 3– 5 nm with strong acidic character. The versatility of the catalyst is evaluated for different nitriles and sodium azide in DMF solvent at 110℃ that afford excellent yields with significant TON, TOF values and the catalytic activity is retained during five successive cycles. XRD, TEM and XPS analyses of used catalysts reveals the enhanced RuO2 layer on the Ru site forming a p-n junction on the surface of the catalyst which facilitates the activation of nitrile; a key step in tetrazole synthesis. Plausible mechanism involves simultaneous activation of nitriles and adsorption of azide on the catalyst surface followed by cyclization through click process. Thus, it may be argued that Ru~0 core and RuO2 shell along with MMT support significantly contributes for sustained catalytic activity of Ru/MMT composite in a synergistic manner.