From the reaction of Os3(CO)9[mu-3-C(Et)NMe(CH)](mu-H)2 (1) with Me3NO in MeCN/CH2Cl2 solution the lightly stabilized complex Os3(CO)8(NCMe)[mu-3-C(Et)NMe(CH)](mu-H)2 (2) was obtained in 36% yield. Compound 2 reacts with PhC2Ph or TolC2Tol at 68-degrees-C to yield two isomers: Os3(CO)8[mu-3-eta-2-C(H)N(Me)C(Et)][eta-2-CArC(H)Ar](mu-H) 3a,b, 25%; 4a,b, 13%; Ar = Ph, Tol). Compounds 3a,b were isomerized to 4a,b at 97-degrees-C, but the reverse did not occur. At 97-degrees-C compounds 4a,b were isomerized further to Os3(CO)8[mu-3-ArC(H)CArCCN(Me)CEt](mu-H)2 (5a,b) in 20% yield. When 5a,b were treated with PMe2Ph at 68-degrees-C, the adducts Os3(CO)8(PPhMe2)[mu-3-ArH2CArCCN(Me)Cet](mu-H) (6a,b; Ar = Ph, Tol) were obtained in 30-40% yield. Compounds 3a, 4a, 5b, and 6a were characterized crystallographically. Compounds 3a and 4a contain sigma-pi diphenylvinyl ligands formed by insertion of the PhC2Ph molecule into the metal-hydrogen bonds of the hydride ligands. They are positioned on different edges of the cluster in 3a and 4a. In compound 5b the alkenyl ligand is coupled to the carbon atom that was formerly the bridging carbene ligand in 3a and 4a, and the hydrogen atom on that carbene carbon was shifted to the metal atoms. The addition of the PMe2Ph ligand to 5a resulted in a reductive elimination of a C-H bond to form a benzyl group in 6a. Crystal data: For 3a, space group = P1BAR, a = 12.056 (4) angstrom, b = 14.229 (4) angstrom, c = 9.932 (3) angstrom, alpha = 103.49 (3)-degrees, beta = 112.07 (2)-degrees, gamma = 65.68 (2)-degrees, Z = 2, 2777 reflections, R c = P1BAR, a = 10.381 (2) angstrom, b = 16.410 (3) angstrom, c = 9.250 (2) angstrom, a = 104.41 (1)-degrees, beta = 100.60 (1)-degrees gamma = 73.91 (1)-degrees, Z = 2, 2898 reflections, R = 0.039; for 5b, space group = P1BAR, a = 10.401 (2) angstrom, b = 17.534 (2) angstrom, c = 9.979 (2) angstrom, alpha = 92.31 (1)-degrees, beta = 116.15 (1)-degrees, gamma = 73.50 (1)-degrees, Z = 2, 3335 reflections, R = 0.032; for 6a, space group = P2/c, a = 12.740 (4) angstrom, b = 14.767 (4) angstrom, b = 14.767 (4) angstrom, c = 19.355 (3) angstrom, beta = 98.12 (2)-degrees, Z = 4, 4261 reflections, R = 0.022.
