AbstractThe five‐coordinate chloro(hydrido)‐ and hydrido(iodo)ruthenium(II) and ‐osmium(II) compounds [MHX(CO)(PiPr3)2] (1, 2, 6, 7) react with CS2to give the octahedral dithioformato complexes [MCl(CO)(PiPr3)2(η2‐S2CH)] (3, 4, 8, 9) in excellent yields. In the initial step, an addition of the heteroallene to the metal center occurs which is followed by insertion of CS2into the M—H bond. On treatment of the dichlororuthenium(II) derivative [RuCl2(CO)(PiPr3)2] (10), which is prepared from RuCl3· aq and PiPr3in methanol, with carbon disulfide insertion into one of the Ru—PiPr3bonds takes place to give the six‐coordinate ruthenium(II) complex12with zwitterion−S2CPiPr3+as a chelating ligand. While the reaction of [OsH(SPh)(CO)(PiPr3)2] (13) with MeSCN leads to addition of the thionitrile to the metal center, the starting material reacts with MeNCS by insertion of the heteroallene into the Os—SPh bond to give two stereoisomers15a, b, in which the nitrogen atom of the chelate ring is eithercisortransto the hydrido ligand. The octahedral methoxydithiocarbonato‐ and formatoosmium(II) compounds16and17are prepared from2and CS2or CO2in the presence of NaOMe. The crystal and molecular structures of4(M = Os),12and15