The clusters Ru-3(CO)(10)L-2, where L = PMe2Ph or PPh3, are shown by NMR spectroscopy to exist in solution in at least three isomeric forms, one with both phosphines in the equatorial plane on the same ruthenium center and the others with phosphines in the equatorial plane on different ruthenium centers. Isomer interconversion for Ru-3(CO)(10)(PMe2Ph)(2) is highly solvent dependent, with DeltaH(double dagger) decreasing and DeltaS(double dagger) becoming more negative as the polarity of the solvent increases. The stabilities of the isomers and their rates of interconversion depend on the phosphine ligand. A mechanism that accounts for isomer interchange involving Ru-Ru bond heterolysis is suggested. The products of the reaction of Ru-3(CO)(10)L-2 with hydrogen have been monitored by NMR spectroscopy via normal and para hydrogen-enhanced methods. Two hydrogen addition products are observed with each containing one bridging and one terminal hydride ligand. EXSY spectroscopy reveals that both intra- and interisomer hydride exchange occurs on the NMR time scale. On the basis or the evidence available, mechanisms for hydride interchange involving Ru-Ru bond heterolysis and CO loss are proposed.