Mesoporous silica supported samarium as recyclable heterogeneous catalyst for synthesis of 5-substituted tetrazole and 2-substituted benzothiazole

Synthesis of nitrogen-containing heterocycles such as tetrazoles and benzothiazoles gains immense importance as they are omnipresent structural modules often utilized in pharmaceuticals. In the present study, well ordered MCM-41 type mesoporous silica with large pore (l-MSN) was synthesized and impregnated with samarium nitrate (Sm@l-MSN). Due to high abundance of samarium relative to many catalytically active transition metals (e.g. Ru, Ir, Pt), it may offer an opportunity to develop sustainable catalysts for organic conversions. The synthesized materials were characterized using nitrogen sorption, scanning electron microscopy, energy-dispersive X-ray, elemental mapping and transmission electron microscopy. The catalytic efficiency of the materials was explored for the synthesis of tetrazoles and benzothiazoles, two very important heterocyclic moieties in medicinal chemistry and biology. The catalyst was readily recovered and recycled up to five consecutive runs without noteworthy loss of activity or leaching.