Catalytic conversion of 2,4,5-trisubstituted imidazole and 5-substituted 1H-tetrazole derivatives using a new series of half-sandwich (η6-p-cymene) Ruthenium(II) complexes with thiophene-2-carboxylic acid hydrazone ligands

A new series of half-sandwich (eta(6) -p-cymene) ruthenium(II) complexes with thiophene-2-carboxylic acid hydrazide derivatives [Ru(eta(6) -p-cymene)(Cl)(L)] [L = N'-(naphthalen-1-ylmethylene)thiophene-2-carbohydrazide (L-1), N'-(anthracen-9-ylmethylene)thiophene-2-carbohydrazide (L-2 ) and N'-(pyren-1-ylmethylene)thiophene-2-carbohydrazide (L-3)] were synthesized. The ligand precursors and their Ru(II) complexes (1-3) were structurally characterized by spectral (IR, NMR and mass spectrometry) and elemental analysis. The molecular structures of the ruthenium(II) complexes 1-3 were determined by single-crystal X-ray diffraction. All complexes were used as catalysts for the one-pot three-component syntheses of 2,4,5-trisubstitued imidazole and 5-substituted 1H-tetrazole derivatives. The catalytic studies optimized parameters as solvent, temperature and catalyst. The catalysts revealed very active for a broad range of aromatic aldehydes presenting either electron attractor or electron donor substituents and, although less active, moderate to high activities were observed for alkyl aldehydes.

Automated summary

A new series of half-sandwich ruthenium(II) complexes with thiophene-2-carboxylic acid hydrazide derivatives were synthesized and used as catalysts for the synthesis of imidazole and tetrazole derivatives. The catalysts showed high activity towards aromatic aldehydes with various substituents, while exhibiting lower activity towards alkyl aldehydes.