Synthesis, Structure and Spectroscopic Characterization of Halfsandwich RuII Complexes containing 1,8-Naphthalimide Ligands

A series of half-sandwich RuII complexes containing two pairs of isomeric pyridine-functionalized 1,8-naphthalimides were synthesized and fully characterized. The solid state structures of three out of the eight complexes synthesized were also determined. The ligands were obtained reacting 1,8-naphtalenic anhydride with 4-aminopyridine (ligand L1), 3-aminopyridine (ligand L2), 4-aminomethylpyridine (ligand L3) and 3-aminomethylpyridine (ligand L4). Each ligand was used to synthesize a pair of complexes: a neutral one, of formula [(p-cymene)RuLCl2], and an ionic one, of formula [(p-cymene)RuL2Cl](TfO). L3 and L4 resulted stronger ligands than L1 and L2, as demonstrated by ligand competition experiments. Analysis of the solution behavior of the complexes indicated that they undergo a fast ligand solvolysis in pure dmso-d6 or in CDCl3/(CD3)2SO mixtures. The solution stability of the complexes containing ligands L1 and L2 was lower than the stability of the complexes containing ligands L3 and L4. These findings can be rationalized considering the reduced coordinating ability of pyridine when directly attached to the electron withdrawing naphthalimide platform.