The reactions of Ru 3(CO) 12 with terminal acetylenes of the type HCCCRR′X (R = CH 3 R′ = C 2H 5, C 6H 5, CH 3, X = OH, Cl, H) were studied. For R = CH 3, R′ = C 6H 5 and X = OH good yields of 1 1 trinuclear complexes of the type HRu 3(CO) 9(CCCRR′X) (II and III) are obtained, while only small yields of the analogous compounds are obtained with the other acetylenes. Both II and III can be dehydrated at room temperature in the presence of excess trifluoroacetic acid to yield the complexes HRu 3(CO) 9[CH 3(H)CC(CH 3)C 2] (VIII) and HRu 3(CO) 9[CH 2C(C 6H 5)C 2] (VII). The crystal structure of VII has been determined by X-ray diffraction methods. Crystals are triclinic, space group P 1 with Z = 2 in a unit cell of dimensions a 9.675(8), b 14.096(12), c 8.985(8) Å, α 93.78(8), β 117.17(11), υ 92.15(8)°, V 1085(2) Å 3. The structure has been solved from diffractometer data by Patterson and Fourier methods and refined by full-matrix least-squares to R = 0.057 for 3715 observed reflections. The molecule is formed by a triruthenium cluster, in a nearly equilateral arrangement, bound to nine terminal CO groups; one hydridic hydrogen atom is bridge-bonding two ruthenium atoms on one side of the cluster. The substituted acetylene is bound to the three metals via a σ bond to one ruthenium and two η bonds to the other two ruthenium atoms, in a way quite similar to that found in the analogous t=butyl acetylide complex (I). The olefinic CC bond distance is regular (1.337 Å) indicating that there is no conugative interaction of the olefin with the cluster.