Low-valence oxo-centred triruthenium complexes by bridging acetate substitution with pyrazolyldiazine or pyridinyltetrazine ligands.

A series of oxo-centred triruthenium-acetate complexes with valence III,III,II were prepared by reactions of [Ru3(III,III,III)]+ precursor [Ru3O(OAc)6(py)2(CH3OH)]+ (1) with 3-chloro-6-(pyrazol-1-yl)pyridazine (cppd), 3-chloro-6-(3,5-dimethylpyrazol-1-yl)pyridazine (cmppd), 3,6-bis(pyrazol-1-yl)pyridazine (ppd), 3,6-bis(3,5-dimethylpyrazol-1-yl)pyridazine (mppd) or 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine (bptz). When neutral Ru3(III,III,II) precursor Ru3O(OAc)6(CO)(CH3OH)2 (2) was utilized, a stable low-valence Ru3(III,II,II) derivative complex was successfully isolated. As established through crystal structural analyses, they were derived from 1 or 2 by substitution of the axial methanol and one of six bridging acetates in the parent Ru3(mu3-O)(mu-OAc)6 cluster core as well as one axial pyridine in some cases. As revealed by electrochemical and spectroscopic studies, substituting one of the six bridging acetates in the parent Ru3(mu3-O)(mu-OAc)6 cluster core significantly modifies the electronic and redox characteristics. Compared with those for the parent compound [Ru3O(OAc)6(py)3]+, triruthenium-based redox potentials of these derivatives show remarkable positive shifts.