Title : Synthesis, investigation, and DFT studies on Bis(alkenylruthenium) complexes with free? Rotating and rotationally restricted biaryl bridges
A new series of biaryl-bridged dinuclear alkenylruthenium complexes with varied torsion angle ? between the planes of the phenyl rings have been prepared via regio- and stereospecific insertion of the -C≡CH bond of the corresponding terminal 4,4’-diethynylbiphenyl derivatives into the Ru-H bond of the hydride complex HRu(CO)Cl(PiPr3)2 (Figure 1). These square pyramidal five-coordinated, 16-valence electrons (VEs) complexes have been characterized in their neutral state by usual IR, UV/Vis and NMR spectroscopy, and in their two different accessible oxidized states, by IR, UV/Vis/NIR spectroelectrochemistry and by EPR spectroscopy as well as by electrochemical methods and by (TD)-DFT calculations. Our results indicate that the torsion angle strongly modulates and tunes the electronic coupling between the two ruthenium-vinyl moieties significantly. They confirm that σ-bonded divinylbiphenylenes constitute a particularly interesting class of non-innocent ligands in organometallic systems. Electrochemical studies showed that these complexes undergo two reversible, consecutive one-electron oxidation processes. The splitting of the redox waves, ΔE½, and the comproportionation constants (Kc) vary as the torsion angle changes, suggesting a strong electronic interaction between the two styryl ruthenium moieties (Kc = 2.9×103) when the two phenyl rings are planar, and a weak interaction (Kc = 18) when they are orthogonal to each other. In IR spectroelectrochemistry, the magnitude of the CO band shifts and the band splitting in the mixed-valent radical cations likewise depend significantly on the torsion angle between the planes of the two phenyl rings. Charge distributions in the radical cations vary from 67:33% when biphenyl bridge is close to planar to 97:3% when the phenyl rings are orthogonal to each other. Complexes with low torsion angle display strong electrochromic behaviour in three distinct states with a strong NIR band in their mixed-valent states. No such band was, however, observed in the case where the two phenyl rings are orthogonal to each other.
Audience Take Away:
- Non-innocent ligands in organometallic systems.
- Bis(alkenylruthenium) organometallic chemistry.
- (TD)-DFT calculations.
- Torsion angle