Tantalum vs Niobium MCF nanocatalysts in the green synthesis of chromene derivatives

Abstract

TaMCF silicas modified with alkaline metals can be considered a novel family of highly efficient bifunctional catalysts involved in the synthesis of chromene derivatives, from salicylaldehyde 2 and acetonitrile compounds, under mild conditions, showing enhanced catalytic performance than their NbMCF analogues. The observed reactivity was mainly attributed to the higher basicity of the Me/TaMCF but also the texture of the samples. The Me/TaMCF silicas showed higher Brønsted basicity than the Nb ones as indicated by the stronger interaction between alkali metals and Ta in the UV–vis and the test reaction experiments.On the other hand, the basicity of Me/TaMCF together the reactivity degree and steric hindrance of the starting acetonitriles are key factors influencing the reaction selectivity. In conclusion, the basicity of the samples plays an important role initiating the reaction by activation of nucleophile but also a compromise between alkaline cation size and basicity is required.