Diphenyl-2-thienylphosphine, Ph 2 PC 4 H 3 S (1), reacts with [Ru 3 (CO) 12 ] in refluxing toluene to give the compound [Ru 3 (µ 2 -H)(µ 3 -Ph 2 PC 4 H 2 S)(CO) 9 ] (2) (59%), cyclometalated at the thiophene ring, with smaller amounts of the cluster [Ru 3 (µ 2 -H)(µ 3 -Ph 2 PC 4 H 2 S)(CO) 8 (Ph 2 -PC 4 H 3 S)] (3) (10%), which is a substituted derivative of 2 and may also be formed by substitution at 2 with ligand 1. The single-crystal X-ray structure of cluster 2 shows that it contains the µ 3 -ligand Ph 2 PC 4 H 2 S bound through phosphorus to one Ru atom, through a σ-Ru-C bond to another and by an η 2 interaction to the third. There is a dynamic interchange between the σ and η 2 interactions of the thienyl group leading to NMR coalescence and a time-averaged plane of symmetry. The corresponding process would be nondegenerate in the substituted compound 3 (X-ray structure reported) and is quenched. Thermal treatment of cluster 2 with [Ru 3 (CO) 12 ] gave two tetranuclear clusters, [Ru 4 (µ 4 -PPh)(µ 4 -C 4 H 2 S)(CO) 11 ] (5) by elimination of benzene and the known cluster [Ru 4 (µ 4 -PPh)-(µ 4 -C 6 H 4 )(CO) 11 ] (6) by elimination of thiophene. Although compounds 5 and 6 are stoichiometrically equivalent, their single-crystal X-ray structures show that they adopt different geometries. The structure of 6 was shown to be the same as that reported previously for the compound derived from PPh 3 . Each has an approximate square of metal atoms capped on one side by µ 4 -PPh and on the other by µ 4 -thiophyne (C 4 H 2 S) or µ 4 -benzyne (C 6 H 4 ), respectively. The C 6 H 4 ligand is coordinated as a 6-electron donor, tilted with respect to the Ru 4 plane, with the coordinated C-C bond parallel to an Ru-Ru edge, whereas C 4 H 2 S is coordinated as a 4-electron donor, perpendicularly and diagonally across the Ru 4 plane in a manner related to known alkyne clusters of the type [Ru 4 (µ 4 -PPh)(µ 4 -alkyne)(CO) 11 ].