The dihydrogen complex OsCl2(eta(2)-H-2)(CO)(PiPr(3))(2) (1) has been prepared by reaction of the monohydride OsHCl(CO)(PiPr(3))(2) (2) with HCl. Complex 1 reacts with carbon monoxide and tert-butyl isocyanide to give OsHCl(CO)(L)(PiPr(3))(2) (L = CO (3), tBuNC (4)) and HCl. The reaction of 1 with phenylacetylene affords the carbene derivative OsCl2(=CHCH(2)Ph)(CO)(PiPr(3))(2) (5), which can be also obtained by reaction of OsC{(E)-CK=CHPh}Cl(CO)(PiPr(3))(2) (6) with HCl. The molecular structure of 5 has been determined by X-ray crystallography. Crystals of 5 are orthorhombic, space group Pbca, with unit cell dimensions a=13.641(2) Angstrom, b = 15.698(2) Angstrom, and c = 29.059(4) Angstrom. The structure was solved and refined using 3185 unique, observed reflections, R = 0.0412 and R(w) = 0.0380. The coordination around the osmium atom can be described as a distorted octahedron with the two triisopropylphosphine ligands occupying trans positions. The PhCH(2)CH moiety, clearly bonded to the metal through an Os-C double bond, is situated in a relative trans position to a chloride ligand. Complex 1 reacts with 2-methyl-1-buten-3-yne to give OsCl2{=CHCH=C(CH3)(2)}(CO)(PiPr(3))(2) (7). The reaction of 2 with 2-methyl-1-buten-3-yne leads to OsC{(E)-CH=C(H)(CH3)=CH2}Cl(CO)(PiPr(3))(2) (8), which gives 7 by reaction with HCl. Complex 1 also reacts with 1,7-octadiyne. The reaction produces a mixture of products from which the binuclear mu-bis-carbene compound [(PiPr(3))(2)(CO)Cl2Os]{=CH(CH2)(6)CH=}[OsCl2(CO)(PiPr(3))(2)] (11) was identified by NMR spectroscopy. Complex 11 can be prepared as an analytically pure solid by reaction of [(PiPr(3))(2)(CO)ClOs]{CH=CH(CH2)(4)CH=CH}[OsCl(CO)(PiPr(3))(2)] (12) with HCl. Complex 12 was obtained from the reaction of 2 with 1,7-octadiyne.