Substitution reactions of [Ru₆C(CO)₁₇](1) have yielded [Ru₆C(CO)_17–nL_n](L = PPh₂Et, n= 1 and 2; L = P(OMe)₃, n= 1–4). The structure of [Ru₆C(CO)₁₆(PPh₂Et)](2) was determined by X-ray diffraction and used as a basis for interpreting the n.m.r. data of the other complexes. Complex (1) and the two PPh₂Et derivatives all exhibit one ¹³CO n.m.r. signal at room temperature. Infrared spectral studies indicated that [Ru₆C(CO)₁₆(PPh₂C₂H₄R)][R Si(OEt)_x(O–Si)_3–x] is formed when (1) is interacted with phosphinated silica gel under ambient conditions. At 50 °C, a second substitution by a surface phosphine occurs. By 100 °C (in vacuo), the cluster integrity is lost and cis-[Ru(CO)₂(O–Si)₂(PPh₂C₂H₄R)₂] is considered to be the carbonyl-containing species. Complex (2) is monoclinic, space group P2₁/n, with a= 18.754(3), b= 17.624(3), c= 22.841(3)Å, β= 91.94(2)°, and Z= 8. The structure was determined using 10 739 observed intensities and refined to R= 0.043. Complex (2) has a similar molecular geometry to that of (1), with one CO group substituted by a PPh₂Et ligand. The phosphine lies asymmetrically over the bridging carbonyl, and renders each molecule enantiomeric.