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

Three mononuclear Ge(IV) compounds, [(C 6 H 5 ) 2 Ge(C 13 H 8 N 2 O 4 )] (1), [(C 6 H 5 ) 2 Ge(C 14 H 10 N 2 O 5 )] (2), and [(C 6 H 5 ) 2 Ge(C 14 H 11 NO 3 )] (3), have been synthesized by the reaction of pro-ligands H2L1 (C 13 H 10 N 2 O 4 ), H2L2 (C 14 H 12 N 2 O 5 ), and H2L3 (C 14 H 13 NO 3 ) with (C 6 H 5 ) 2 GeCl 2 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 1 H -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.