The first water soluble metal-enediyne complexes have been prepared by displacement of the dihydrogen ligand of [Os(II)(en) 2( η 2-H 2)(H 2O)](OTf) 2 (en = ethylenediamine, OTf = CF 3SO 3 −), 1, with an enediyne molecule, cis-1,6-bistrimethylsilyl-3-ene-1,5-diyne, 2. Different σ donor ligands can be introduced to the trans position of the enediyne ligand to prepare different metal-enediyne complexes. The single crystal X-ray analysis of trans-[Os(en) 2( η 2-L)Br] +Br − (L = cis-1,6-bistrimethylsilyl-3-ene-1,5-diyne), 4, shows that the osmium(II)(en) 2 moiety binds specifically to the double bond of the enediyne molecule. This structure represents a new mode of metal-enediyne coordination. 4 crystallizes in the monoclinic space group P2 1/a, with Z = 4, a = 13.150(2) A ̊ , b = 11.38(4) A ̊ , c = 18.413(9) A ̊ , and β = 100.74(2)° . The structure was solved by direct methods and refined to conventional agreement indices R = 0.054 and R w = 0.048 with 2880 unique reflections for which 1 > 3 σ(1).