Mannich products of kojic acid and N-heterocycles and their Ru(II)-arene complexes: Synthesis, characterization and stability

Ru(II)-η6-p-cymene compds. bearing pyrone-derived ligands, which were obtained by Mannich reactions between kojic acid and piperidine or morpholine analogs, have been synthesized. The compds. were characterized by NMR spectroscopy, mass spectrometry, thermogravimetric anal. and, in the case of 2,6-dimethylmorpholine-derived ligand I, by x-ray diffraction anal. The chlorido complexes are prone to aquation in aq. soln. which results in the formation of dimers. Dimer formation can be inhibited by in situ replacement of the chlorido ligand by imidazole yielding compds. which are significantly more stable in water, as demonstrated by 1H NMR spectroscopy.