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

Three mononuclear Ge(iv) compounds, [(CH)Ge(CHNO)] (1), [(CH)Ge(CHNO)] (2), and [(CH)Ge(CHNO)] (3), have been synthesized by the reaction of pro-ligands H2L1 (CHNO), H2L2 (CHNO), and H2L3 (CHNO) with (CH)GeCl 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.