Ruthenium(II) as a Novel “Labile” Partner in Thermodynamic Self-Assembly of Heterobimetallic d–f Triple-Stranded Helicates
✍ Scribed by Stéphane Torelli; Sandra Delahaye; Andreas Hauser; Gérald Bernardinelli; Claude Piguet
- Book ID
- 101833831
- Publisher
- John Wiley and Sons
- Year
- 2004
- Tongue
- English
- Weight
- 323 KB
- Volume
- 10
- Category
- Article
- ISSN
- 0947-6539
No coin nor oath required. For personal study only.
✦ Synopsis
Abstract
Unsymmetrical substituted bidentate benzimidazol‐2‐ylpyridine ligands L2 and L3 react with [Ru(dmso)~4~Cl~2~] in ethanol to give statistical 1:3 mixtures of fac‐[Ru(L__i__)~3~]^2+^ and mer‐[Ru(L__i__)~3~]^2+^ (i=2, 3; Δ__G__⊖~isomerisation~=−2.7 kJ mol^−1^). In more polar solvents (acetonitrile, methanol), the free energy of the facial⇌meridional isomerisation process favours mer‐[Ru(L__i__)~3~]^2+^, which is the only isomer observed in solution at the equilibrium (Δ__G__⊖~isomerisation~≤−11.4 kJ mol^−1^). Since the latter process takes several days for [Ru(L2)~3~]^2+^, fac‐[Ru(L2)~3~]^2+^ and mer‐[Ru(L2)~3~]^2+^ have been separated by chromatography, but the 28‐fold increase in velocity observed for [Ru(L3)~3~]^2+^ provides only mer‐Ru(L3)~3~~2~ after chromatography (RuC~60~H~51~N~9~O~8~Cl~2~, monoclinic, P__2~1~/n, Z=4). The facial isomer can be stabilised when an appended tridentate binding unit, connected at the 5‐position of the benzimidazol‐2‐ylpyridine unit in ligand L1, interacts with nine‐coordinate lanthanides(III). The free energy of the facial⇌meridional isomerisation is reversed (Δ__G⊖~isomerisation~≥11.4 kJ mol^−1^), and the RuN bonds are labile enough to allow the quantitative thermodynamic self‐assembly of HHH‐[RuLu(L1)~3~]^5+^ within hours (RuLu(L1)~3~~4.5~Cl~0.5~(CH~3~OH)~2.5~: RuLuC~106~H~109~Cl~0.5~N~21~O~19~S~4.5~F~13.5~, triclinic, P$\bar 1$, Z=2). Electrochemical and photophysical studies show that the benzimidazol‐2‐ylpyridine units in L1–L3 display similar π‐acceptor properties to, but stronger π‐donor properties than, those found in 2,2′‐bipyridine. This shifts the intraligand π→π^*^ and the MLCT transitions toward lower energies in the pseudo‐octahedral [Ru(L__i__)~3~]^2+^ (i=2, 3) chromophores. The concomitant short lifetime of the ^3^MLCT excited state points to efficient, thermally activated quenching via low‐energy Ru‐centred d–d states, a limitation which is partially overcome by mechanical coupling in HHH‐[RuLu(L1)~3~]^5+^.