Low-Valence Triruthenium Compounds via Substitution of a Bridging Acetate in the Parent Ru₃O(OAc)₆ Cluster Core by 2,2‘-Azobispyridine (abpy) or 2,2‘-Azobis(5-chloropyrimidine) (abcp)

Reaction of oxo-centered Ru3III,III,III precursor [Ru3O(OAc)6(py)2(CH3OH)](PF6) (1) with 1 equiv of 2,2‘-azobispyridine (abpy) or 2,2‘-azobis(5-chloropyrimidine) (abcp) induced the formation of stable Ru3III,III,II derivatives [Ru3O(OAc)5{μ-η1(N),η2(N,N)-L}(py)2](PF6) (L = abpy (2), abcp (3)). As established in the structure of 3 by X-ray crystallography, 2 or 3 is derived from 1 by substitution of the axial methanol and one of the bridging acetates in the parent Ru3O(OAc)6 cluster core with abpy or abcp in an μ-η1(N),η2(N,N) bonding mode. Reduction of 3 by hydrazine induces isolation of one-electron reduced neutral Ru3III,II,II product Ru3O(OAc)5{μ-η1(N),η2(N,N)-abcp}(py)2 (3a). As revealed by electrochemical and spectroscopic studies, substituting one of the bridging acetates in the parent Ru3O(OAc)6 cluster core by abcp or abpy modifies dramatically the electronic and redox characteristics in the triruthenium derivatives. Relative to that for the parent compound [Ru3O(OAc)6(py)3](PF6) (E1/2 = −0.46 V), triruthenium-based redox potential in the redox process Ru3OIII,III,III/Ru3OIII,III,II is significantly anodic-shifted to E1/2 = +0.36 V for 2 and E1/2 = +0.53 V for 3. Furthermore, the anodic shifts of redox potentials are progressively enhanced with a decrease of the formal oxidation states in the triruthenium cluster cores. As a consequence of remarkable positive shifts for redox potentials, the low-valence Ru3III,III,II and Ru3III,II,II species are stabilized and accessible.