Initial decarbonylation of CpWos3(Co)11(μ3-CTol) (1: Cp =η5-C5H5, Tol =p-C6H4Mc) with the Me3NO/MeCN followed by reaction with dihydrogen and water produces a dihydrido comlex CpWOs3(CO)10(μ3-CTol)(μ-H)2(2), a ‘butterfly’ cluster with a 60 valence electron (VE), and an oxo comlex CpWOs3(CO)10(μ-O)(μ3-CTol) (4) respectively. Complex 2 reacts either with carbon monoxide to produce the starting alkylidyne complex 1 by reductive elimination of dihydrogen or with PPh3to afford a 62 VE ‘butterfly’ complex. CpWOs3(CO)10(PPh3)(μ3-CTol)(μ-H)2(6). Thermolysis of 2 in the presence of water gives a hydrido oxo alkylidene complex,syn-CpWOs3(CO)9(μ-O)(μ-CHTol)(μ-H) (3a), in which the totyl substituent on the alkylidene carbon is orientedsynto the μ-oxo ligand. Thermolysis of 4 at 110°C induces decarbonylation to give a tetrahedral alkylidyne complex CpWOs3(CO)9(μ-O)(μ3-CTol) (5), which is reversibly converted back to 4 upon exposure to carbon monoxide. Complex 5 reacts with dihydrogen to afford a mixture of two isomeric hydrido oxo alkylidene complexes, antiCpWOs3(CO)9(μ-O)(μ-CHToL)(μ-H) (3b,c). Thesyn-isomer 3a is also produced from a mixture of 3b and 3c by thermolysis in boiling toluene. Compounds 2, 3a,b,c, 4, 5, and 6 haven been isolated as crystalline solids and characterized by spectroscopic (IR, MS,1H and13CMMR) and analytical data. The structures of 2 and 6 have been determined by single crystal X-ray diffraction studies. Compound 2 crystallizes in the orthorhombic space groupP212121with unit cell parametersa= 14.18(1),b= 28.46(1),,andZ= 8. Compound 6 crystallizes in the monoclinic space groupP21/nwith unit cell parametersa= 19.298(2),andZ= 4. Diffraction data were collected on a CAD4 diffractometer, and structures were refined toR= 0.0957 and 0.0510 for 2 and 6 respectively. Both 2 and 6 are based upon a ‘butterfly’ WOs3metal core with a respective dihedral angle of 114.3(2)° and 113.6(4)° between the W-Os(2)-Os(1) and W-Os(2)-Os(3) planes. Each molecule consists of three Os(CO)3units and a CpW(CO) fragment, except that the Os(1) center in 6 is additionally coordinated with PPh3. Theμ3-alkylidyne caps unsymmetrically the respective W-Os(2)-Os(3) face of both complexes.