Comparison of Redox Activity between 2‑Aminothioether and 2‑Aminothiophenol: Redox-Induced Dimerization of 2‑Aminothioether via C–C Coupling

Three chemical reactions of two 2-aminothioethers and 2-aminothiophenol with CpRu^IICl­(PPh₃)₂ (Cp^– = cyclopentadienyl anion), under identical reaction conditions, are reported. While 2-(methylthio)­aniline, H₂L¹ and an analogous substrate, 2-(phenylthio)­aniline yielded dicationic dinuclear complexes [(PPh₃)­CpRu^II(L^3/L⁴)­Ru^IICp­(PPh₃)]­Cl₂ (where L³ = (4<i>E</i>)-4-(4-imino-3-(methylthio)­cyclohexa-2,5-dienylidene)-2-(methylthio)­cyclohexa-2,5-dienimine ([<b>1a</b>]­Cl₂) and L⁴ = (4<i>E</i>)-4-(4-imino-3-(phenylthio)­cyclohexa-2,5-dienylidene)-2-(phenylthio)­cyclohexa-2,5-dienimine ([<b>1b</b>]­Cl₂)), the reaction with 2-aminothiophenol (H₂L²) produced a mononuclear complex [(PPh₃)­CpRu^II(L²)]Cl (where L² = 6-iminocyclohexa-2,4-dienethione) ([<b>2</b>]­Cl). All these complexes are obtained in high yields (65%–75%). Formations of the products from the above reactions involve a similar level of oxidation of the respective substrate, although their courses are completely different. A comparison between the above two chemical transformations are scrutinized thoroughly. Characterizations of these complexes were made using a host of physical methods: X-ray crystallography, nuclear magnetic resonance (NMR), cyclic voltammetry, ultraviolet–visible (UV-vis), electron paramagnetic resonance (EPR) spectroscopy, and density functional theory (DFT). The complexes [<b>1a</b>]­Cl₂ and [<b>1b</b>]­Cl₂ showed intense metal-to-ligand charge transfer transition in the long wavelength region of the spectrum, at 860 and 895 nm, respectively, and displayed two reversible electron transfer (ET) processes at [<b>1a</b>]²⁺: −0.28 and −0.52 V; [<b>1b</b>]²⁺: −0.13 and −0.47 V, along with an irreversible ET process at 0.76 and 0.54 V, respectively. The ET processes at negative potentials are due to successive reductions of the bridging ligand, which are characterized by EPR and UV-vis spectroscopy. The one-electron reduced compound, [<b>1a</b>]⁺, showed a intraligand charge transfer transition (ILCT) at 1530 nm. The complex [<b>2</b>]⁺ showed a reversible ET process at −0.36 V and two irreversible ET processes at −1.04 and 1.18 V, respectively. DFT calculations were used to support the spectral and redox properties of the complexes and also to throw light on the difference of redox behavior between thioether and thiophenol substrates