The derivatives of the H₂RuOs₃(CO)₁₃ and H₄Ru₄(CO)₁₂ carbonylhydride clusters containing functionalized (including chiral) phosphines were synthesized. The solid-state structure of H₂RuOs₃(CO)₁₂(Ph ₂P(C₄H₃S)) was determined by X-ray diffraction analysis. The structures of other compounds in solution were determined using IR and ¹H and ³¹P NMR spectroscopy. A study of the temperature dependences of the ¹H NMR spectra of the phosphine-substituted tetrahedral clusters along with the analysis of literature data for their analogs showed that compounds of this type exist in solution as an equilibrium mixture of isomers, which differ in arrangement of the hydride ligands at the cluster skeleton. Interconversion of the isomeric forms is due to migration of the hydride ligands over the cluster skeleton. A general model for this dynamic process was proposed. The model is consistent with both our data and earlier results of other authors.