Eco-friendly and benign synthesis of 5-(aryl)alkyl substituted NH-tetrazoles via protonated MCM-41@Silyl-ⁿPr-DABCO-H nanocatalyst and DFT study

In this manuscript, we report the development of a multi applicable metal-free nanostructured catalyst, silica-MCM-41@Silyl-ⁿPr-DABCO-H as a Lewis acid character, which serves as an efficient and reusable catalyst for the synthesis of 5-substituted NH-tetrazoles via a one-pot [2 + 3] cycloaddition reaction between (aromatic)aliphatic nitriles and/or aryl cyanate and sodium azide. MCM-41 mesoporous silica functionalized with DABCO was synthesized by a multistep method. The structure of this multi applicable catalyst have been characterized by FT-IR, SEM, TEM, EDS, XRD, and TGA-DTA techniques and confirm the integrity of the structure and composition of the catalyst. It has shown catalytic activity in the production of NH-tetrazoles with good to excellent yields and could be recovered through seven reaction cycles. The reaction mechanisms were interpreted with the aid of quantum DFT studies, and the modified catalyst showed better catalytic efficiency than classical homogeneous catalysts such as NH₄⁺. The results obtained in this study proved silica-MCM-41@Silyl-ⁿPr-DABCO-H as an eco-friendly, metal-free alternative for organic syntheses in pharmaceutical applications where interest in NH-tetrazole derivatives is high due to their wide biological activities. The present study brings into light not only the practical applicability of this catalyst but also throws light on its mechanistic pathways with the aid of advanced computational techniques.