Ruthenium(II) mediated C–H activation of substituted acetophenone thiosemicarbazones: Synthesis, structural characterization, luminescence and electrochemical properties

Treatment of [RuHCl(CO)(AsPh3)3] with 4′-substituted acetophenone thiosemicarbazone derivatives in methanol under reflux afford a series of air stable new ruthenium(II) cyclometalated complexes containing thiosemicarbazone of general formula [Ru(L)(CO)(AsPh3)2]. The 4′-substituted acetophenone thiosemicarbazone ligands behave as a dianionic terdentate C, N and S donors (L) and coordinates to ruthenium via aromatic carbon, the imine nitrogen and thiol sulfur. The compositions of the complexes have been established by elemental analysis, and spectral methods (FT-IR, UV–Vis, 1H NMR, ESI-MS) and X-ray crystallography. In chloroform solution all the complexes exhibit metal-to-ligand charge transfer transitions (MLCT) in the visible region and are emissive at room temperature with quantum yield of 0.001–0.005. The crystal structure of one of the complexes [Ru(4CAP-PTSC)(CO)(AsPh3)2] (4) has been solved by single crystal X-ray crystallography and it indicates the presence of a distorted octahedral geometry in these complexes. All the complexes exhibit a quasi reversible one electron reduction (RuII/RuI) in the range −0.83 to −0.86 V. The formal potential of all the couples correlate linearly with the Hammett constant of the para substituent in phenyl fragment of the acetophenone thiosemicarbazone ligands.