Structural and electrochemical comparison of trinuclear ruthenium oxo clusters [Ru₃(OAc)₆O(L)₃]⁺and [Ru₃(OAc)₆O(L)₂(CO)] (L = imidazole, benzimidazole, and 4-phenylpyridine)

Abstract

The triruthenium oxo clusters [Ru3(OAc)6O(L)3]+ and [Ru3(OAc)6O(L)2(CO)] possess unique electronic characteristics that vary based on the ligands L. Here we report an investigation of the structural, electrochemical, and optical properties of clusters with imidazole, benzimidazole, and 4‐phenylpyridine ligands. The complexes [Ru3(OAc)6O(L)3]+ [1+: L = imidazole (im); 2+: L = benzimidazole (benzim); 3+: L = 4‐phenylpyridine (4PP)] and [Ru3(OAc)6O(L)2(CO)] (1‐CO and 3‐CO) were synthesized by reaction of either [Ru3(OAc)6O(MeOH)3]+ or [Ru3(OAc)6O(MeOH)2(CO)], respectively, with the corresponding heterocycle. We further discovered that [3]OAc could be reduced to the mixed‐valence neutral state 3 by refluxing the complex under nitrogen in methanol. Single‐crystal X‐ray structure analysis of hexa‐μ2‐acetato‐μ3‐oxido‐tris(1H‐imidazole)triruthenium hexafluorophosphate acetonitrile hemisolvate, [Ru3(C2H3O2)6O(C3H4N2)3]PF6·0.5CH3CN, [1]PF6, hexa‐μ2‐acetato‐carbonylbis(1H‐imidazole)‐μ3‐oxido‐triruthenium methanol monosolvate, [Ru3(C2H3O2)6O(C3H4N2)(CO)]·CH3OH, 1‐CO, hexa‐μ2‐acetato‐μ3‐oxido‐tris(4‐phenylpyridine)triruthenium pentahydrate, [Ru3(C2H3O2)6O(C11H9N)3]·5H2O, 3, and hexa‐μ2‐acetato‐carbonyl‐μ3‐oxido‐bis(4‐phenylpyridine)triruthenium methanol monosolvate, [Ru3(C2H3O2)6O(C11H9N)2(CO)]·CH3OH, 3‐CO, show the expected triruthenium μ3‐oxo core and N‐coordination of the ligands. Cyclic voltammetry revealed quasi‐reversible and irreversible redox couples in [1]PF6, 1‐CO, and [2]PF6, while [3]PF6 and 3‐CO exhibit reversible redox couples. The optical properties of these richly colored species were investigated using UV–Vis spectroscopy.

A pyrazine‐bridged trimer of oxo‐centered triruthenium–carbonyl clusters and the supramolecular assembly built from multiple noncovalent contacts

“…We find that the CO-attached Ru atoms (Ru1, Ru4, and Ru7) show longer Ru-O eq distances than the pyrazine-attached Ru-O eq distances, suggesting that the CO stabilizes Ru in the lower valence than the pyrazine does. In the literature, [26,36,37,[41][42][43] crystallographic characterizations of the [Ru 3 O(RCOO) 6 (CO)L 2 ] complexes are reported for variable terminal ligands L with N-or Oheterocycles such as 1-azabicyclo[2,2,2]octane (abco), [26] THF, [36] and 1-methyl-4,4 0 -bipyridinium ion. [37] The triangular cores observed in all of these complexes show identical structural features to those in 1.…”