PROTONATION OF METAL-METAL BONDS IN CP2RU2(CO)(3)(PR3) AND CP2MO(2)(CO)(4)(PR3)(2)

Despite the much higher basicity expected for the Ru bearing the PR3 l igand in Cp(PR3)Ru(mu-Co)(2)Ru(Co)Cp, NMR studies demonstrate that pro tonation of this complex with CF3SO3H occurs at the Ru-Ru bond, rather than at the more basic Ru. As determined by calorimetric titration at 25.0 degrees C in 1,2-dichloroethane solvent, the enthalpy of protona tion (Delta H-MHM) Of the Ru-Ru bond is higher in CP2RU2(CO)(3)(PMe3) (-30.0(4) kcal/mol) than in its carbonyl analogue Cp2Ru2(CO)(4) (-18.4 (1) kcal/mol). Enthalpies (Delta H-MHM) for protonation of the Mo-Mo b ond in the dinuclear Mo complexes CP2Mo2(CO)(4)(PR3)(2) show that the PMe3 complex (-27.4(2) kcal/mol) is dramatically more basic than its P Me2Ph analogue (-18.9(5) kcal/mol); Considering the Delta H-MHM values as measures of the basicities of the complexes, these results show th at the basicities of metal-metal bonds are highly sensitive to the nat ure of their associated ligands. In addition, evidence indicates that Ru-Ru bonds are more basic than Ru in comparable mononuclear complexes . The structures, as determined by X-ray crystallographic studies, of Cp2Ru2(CO)(3)(PMe3) and its protonated derivative Cp2Ru2(CO)(3)(PMe3)( mu-H)+CF3SO3- are also discussed.