Mononuclear organogermanium(IV) catalysts for a [3 + 2] cycloaddition reaction

Three mononuclear Ge(IV) compounds, [(C₆H₅)₂Ge(C₁₃H₈N₂O₄)] (1), [(C₆H₅)₂Ge(C₁₄H₁₀N₂O₅)] (2), and [(C₆H₅)₂Ge(C₁₄H₁₁NO₃)] (3), have been synthesized by the reaction of pro-ligands H2L1 (C₁₃H₁₀N₂O₄), H2L2 (C₁₄H₁₂N₂O₅), and H2L3 (C₁₄H₁₃NO₃) with (C₆H₅)₂GeCl₂ in the presence of triethylamine. All compounds were characterized by FT-IR spectroscopy and NMR spectroscopy. Single crystal X-ray diffraction analysis shows that the germanium(IV) atom exhibits a five-coordinated geometry in compounds 1 and 2. All compounds were screened as Lewis acid catalysts in the [3 + 2] cycloaddition reaction between sodium azide and various nitriles. The reactions resulted in the formation of 5-substituted 1H-tetrazoles with yields of up to 96%. Based on the experimental findings and DFT calculations, a plausible mechanism is proposed for the [3 + 2] cycloaddition reaction.