1,4-Divinylphenylene-bridged diruthenium complexes terminated with deprotonated 2-mercaptopyridine or 2- or 8-mercaptoquinoline co-ligands

Abstract

Four 1,4-divinylphenylene-bridged diruthenium complexes [{Ru(CO)(κ²[N,S⁻]-L)(PⁱPr₃)₂}₂(μ-(CH=CH)₂–C₆H₄-1,4)] [IIa]–[IId] terminated with potentially non-innocent chelating κ²[N,S⁻] ligands of L derived of 2-mercaptopyridines or 2- or 8-mercaptoquinolines are presented. Those hexa-coordinated, 18-valence electrons (VEs) complexes were successfully prepared via subsequent treatment of the five-coordinated, 16-VEs [{Ru(CO)Cl(PⁱPr₃)₂}₂(μ-(CH=CH)₂–C₆H₄-1,4)] precursor [I] with the corresponding deprotonated bidentate κ²[N,S⁻] of 2-mercaptopyridines or 2- or 8-mercaptoquinolines. Our obtained results were compared to the closely related 1,4-divinylarylene-bridged diruthenium with κ²[N,O⁻] of 2-hydroxypyridines or 2- or 8-hydroxyquinolines. They were conventionally investigated in their neutral state via common NMR and UV/Vis/IR spectroscopic techniques, as well as in their two attainable redox states by UV/Vis/NIR, IR spectro(electro)chemistry as well as with cyclic voltammetry and with electron spin resonance. Those experimental results were complimented by the computational calculations. Our results refer that each 2-mercaptopyridines-derived complexes [IIa] and [IIb] existed as two geometrical isomers with a ratio of 1:18 that differed with respect to the orientation of the two κ²[N,S⁻] donor atoms relative to the C≡O and vinyl groups in the octahedral equatorial spheres, while in the case of the two-fused rings of 2- or 8-mercaptoquinolines-derived complexes [IIc] and [IId], however, only one isomer is formed, which is attributed to the steric hindrance reasons. Complexes [IIa]–[IId] undergo two consecutive, (electro)chemically reversible one-electron oxidation processes in low attainable potentials. All results refer to the strong contributions of the 1,4-divinylphenylene linker into the two individual redox processes and a full delocalization of the electron hole and the unpaired spin density over the entire π-conjugated 1,4-divinylphenylene diruthenium backbone with only minor involvement of the peripherally attached κ²[N,S⁻] donor ligands.

Graphical abstract