Dynamic torsional motion of a diruthenium complex with four homo-catecholates and first synthesis of a diruthenium complex with mixed-catecholates

Dynamic properties of a diruthenium complex with ligand-unsupported Ru–Ru triple bonds, Na2[Ru2(3,6-DTBCat)4] (1), were studied using variable-temperature 1H NMR. Structural freedom derived from the ligand-unsupported structure leads to torsional motion about the Ru–Ru bonds in THF and in DMF. The observed solvent dependency corresponds to the electrostatic interactions between the diruthenium complex and Na+ counter cations, which are sensitive to the polarity of solvents. In addition, a new diruthenium complex, [{Na(THF)2(H2O)}{Na(THF)0.5(H2O)}{Ru2(3,6-DTBCat)2(H4Cat)2}] (2·2.5THF·2H2O), with a ligand-unsupported Ru–Ru bond surrounded by two different kinds of catecholate derivatives, has been synthesized and crystallographically characterized. The complex, which was characterized by single-crystal structural analysis, will provide an opportunity to investigate not only static molecular structures but also dynamic physicochemical properties in comparison with analogues containing four identical catecholate derivatives.