Ruthenium half-sandwich complexes with tautomerized pyrazolyl-pyridazine ligands: Synthesis, spectroscopic and molecular structural studies

Condensation of 1,4-dichloropyridazine with pyrazole, 3,5-dimethylpyrazole and 3-methylpyrazole yielded two types of pyrazolyl-pyridazine ligands, viz., (i) products of substitution on one side of the pyridazine as 3-chloro-6-(pyrazolyl)pyridazine (Cl–L1), 3-chloro-6-(3,5-dimethylpyrazolyl)pyridazine (Cl–L2) and 3-chloro-6-(3-methylpyrazolyl)pyridazine (Cl–L3), and (ii) products of substitution on both sides such as 3,6-bis(pyrazolyl)pyridazine (L1), 3,6-bis(3,5-dimethylpyrazolyl)pyridazine (L2) and tautomers of 3,6-bis(3-methylpyrazolyl)pyridazine (L3). The reactions of η6-areneruthenium complexes in methanol with the above mentioned pyrazolyl-pyridazine ligands form mononuclear complexes of the type [(η6-arene)Ru(Cl–L)(Cl)]+ and [(η6-arene)Ru(L)(Cl)]+; (arene = benzene and p-cymene; Cl–L = Cl–L1, Cl–L2, Cl–L3; L = L1, L2, L3). All these complexes are characterized by IR, NMR, mass spectrometry and UV–vis spectroscopy. The structures of some representative complexes are established by single crystal X-ray diffraction studies.