The reactions of diphenylpyridylphosphine ligand with H₂Os ₃(CO)₁₀ and H₄Ru₄(CO)₁₂ were studied. It was found that the thermodynamic products of these reactions, (μ-H)Os₃(CO)₉(μ₃,κ²- PhP(2-C₅H₄N)) (2) and H₃Ru₄(CO) ₁₀(μ₃,κ²-PhP(2-C₅H ₄N)) (4), are formed through the oxidative addition of a P-Ph bond in the coordinated ligand and subsequent reductive elimination of benzene. In the case of triosmium cluster an unusually stable intermediate compound, (μ-H)₂Os₃(CO)₈(μ₃, κ²-PhP(2-C₅H₄N))(Ph) (1), containing cis hydride and σ-bonded phenyl was isolated and fully characterized. This cluster eliminates benzene to give (2) only under heating above 50 °C. Reaction of H₄Ru₄(CO)₁₂ with diphenylpyridylphosphine gives first the H₄Ru₄(CO) ₁₀(μ,κ²-Ph₂P(2-C₅H ₄N)) cluster (3) with a bridging (P,N) coordination of the starting ligand, which easily converts into the phosphide cluster (4) at room temperature. The structures of the clusters (1)-(4) were established using ¹H and ³¹P NMR spectroscopy and X-ray crystallography. Variable temperature ¹H NMR study of (3) and (4) showed that the hydride environment in (3) is stereochemically nonrigid and complete exchange of all hydrides was observed at room temperature. The cluster (4) exists in solution as an equilibrium mixture of two isomers with different disposition of hydrides relative to the bridging pyridylphosphide moiety.