Electrochemistry of Ru2Cp′2(CO)4 and Ru2Cp2(CO)3(PMe3) and the estimation of Ru2(μ-H) bond dissociation enthalpies

The oxidation potentials for a series of diruthenium compounds have been measured. The heat of protonation (−ΔHMHM) and oxidation potentials (E1/2) for a series of Ru2Cp′2(CO)4 (Cp′=Cp2, Cp*2, C5H4CH2C5H4, (C5H4CH2)2, (C9H7)2, C10H8, (HBpz3)2) compounds and Ru2Cp2(CO)3(PMe3) were used to estimate the homolytic RuHRu bond dissociation enthalpy (BDEs) using a thermochemical cycle. Poor correlation between −ΔHMHM and E1/2 was observed, as anticipated, due to the effects of the bridging carbonyls on the heats of protonation. There is a correlation between the oxidation potentials and the average νCO bands for the protonated dimers as both are a measurement of the donor ability of the ligands. The calculated BDE values were also compared with values obtained for mononuclear ruthenium compounds.