Diruthenium(II)diacetylide organometallic complexes with thienylethynyl bridging units: Synthesis, characterization and electrochemical properties

A series of soluble diruthenium(II)diacetylide complexes (M1-M3) by varying thienlylethynyl bridging ligands have been achieved by treating the appropriate thienylethynyl spacers (B1, B2 and B3 with one, two and three units of thienylethynyl respectively) with [Ru(dppe)Cp*Cl] and KF in THF/MeOH medium. The synthesized diruthenium(II) organometallic complexes have been thoroughly characterized by multinuclear NMR spectroscopy, FTIR and mass spectrometry. The photophysical and electrochemical studies of these soluble wire-like Ru(II) organometallic complexes (M1-M3) with aromatic π-extended bridges have been carried out to comprehend the electronic and electrochemical properties. The electronic delocalization in Ru(II)–C≡C–Ar–C≡C–Ru(II) (Ar = aromatic bridging ligand) conjugate through the bridging backbone is dependent on the bridging spacers. Potential difference (ΔE_1/2) and comproportionation constant (K_c) decrease with increasing the length of the thienylethynyl unit. The mixed-valence species, generated by single-electron oxidation, exhibits absorption in the near-infrared (NIR) region. Moreover, FTIR studies also reveal a change in \(\bar{\upsilon }\)(Ru-C≡C) stretching frequency of the mixed valence species, suggesting considerable participation of the bridging ligand in redox processes.

Graphical abstract

Electrochemical and electronic properties of the diruthenium(II)diacetylide organometallic conjugates have been modulated by varying the number of thienylethynyl bridging units.