Ru 3 (CO) 4 (µ-H) 3 (µ-PCy 2 ) 3 (µ-dppm)] (2) (dppm ϭ Ph 2 PCH 2 PPh 2 ) reacts with CS 2 at room temperature and yields the open 50 valence electron cluster [Ru 3 (CO) 4 (µ-PCy 2 ) 2 (µ-dppm)-(µ 3 -S){µ 3 -η 2 -CSC(S)S}] (3) containing the unusual µ 3 -η 2 -C 2 S 3 mercaptocarbyne ligand. Compound 3 was characterized by single crystal X-ray structure analysis.