Ruthenium(II) bipyridine complexes bearing new keto–enol azoimine ligands: Synthesis, structure, electrochemistry and DFT calculations

Abstract

The novel azoimine ligand, PhNHNC(COCH3)NHPh(CCH) (H2L), was synthesized and its molecular structure was determined by X-ray crystallography. Catalytic hydration of the terminal acetylene of H2L in the presence of RuCl3·3H2O in ethanol at reflux temperature yielded a ketone (L1=PhNNC(COCH3)NPh(COCH3) and an enol (L2=PhNNC(COCH3)NPhC(OH)CH2) by Markovnikov addition of water. Two mixed-ligand ruthenium complexes having general formula, trans-[Ru(bpy)(Y)Cl2] (1–2) (where Y=L1 (1) and Y=L2 (2), bpy is 2.2′-bipyrdine) were achieved by the stepwise addition of equimolar amounts of (H2L) and bpy ligands to RuCl3·3H2O in absolute ethanol. Theses complexes were characterized by elemental analyses and spectroscopic (IR, UV–Vis, and NMR (1D 1H NMR, 13C NMR, (DEPT-135), (DEPT-90), 2D 1H–1H and 13C–1H correlation (HMQC) spectroscopy)). The two complexes exhibit a quasi-reversible one electron Ru(II)/Ru(III) oxidation couple at 604mV vs. ferrocene/ferrocenium (Cp2Fe0/+) couple along with one electron ligand reduction at −1010mV. The crystal structure of complex 1 showed that the bidentate ligand L1 coordinates to Ru(II) by the azo- and imine-nitrogen donor atoms. The complex adopts a distorted trans octahedral coordination geometry of chloride ligands. The electronic spectra of 1 and 1+ in dichloromethane have been modeled by time-dependent density functional theory (TD-DFT).