Os(H)(3)ClL2 (L = (PPr3)-Pr-i or (PBu2Me)-Bu-t) are shown to be useful "precursors" to "OsHClL2", which react with vinyl ethers to form first an eta (2)-olefin adduct and then isomerize to the carbenes, OsHCl[CMe(OR)]L-2. Subsequent Rand L-dependent reactions involve C(sp(2))-OR bond cleavage, to make either carbyne or vinylidene complexes. The mechanisms of these reactions are explored, and the thermodynamic disparity of Ru versus Os and the influence of the OR group and the spectator phosphine ligands are discussed based on DFT (B3PW91) calculations.