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.

Bis(catecholato)germane: an effective catalyst for Friedel-Crafts alkylation reaction.

Bis(catecholato)germane, [Ge(C6H4O2)2(H2O)2] (1), was synthesized by the reaction of catechol and germanium oxide in water according to a reported method. Complex 1 was characterized by FT-IR spectroscopy, NMR spectroscopy and elemental analysis. Complex 1 was employed as a Lewis acid catalyst in the Friedel-Crafts alkylation reaction of indole with various aldehydes and ß-nitrostyrene derivatives separately. The yield of the product for the formation of bis(indolyl)alkanes and nitroalkylated indoles was up to 95% and 96%, respectively. These observations confirmed the catalytic efficacy of complex 1 as a Lewis acid in both reactions. Based on the experimental findings, a plausible mechanism is proposed for both reactions.