Three novel triosmium complexes with unusual coordination characteristics are reported. Treatment of the hydridotriosmium cluster (mu-H)(2)Os-3(CO)(10) With CNNPPh3 in CH2Cl2 gave complexes (mu-H)Os-3(CO)(10)(mu(2)-eta(2)-C(H)-NNPPh3) (1) and (mu-H)Os-3(CO)(10)(mu(2)-eta(1)-CHPPh3) (2). Complex 1 represents the first example of the existence of a coordinated phosphinazine ligand. An in-situ H-1 NMR study showed that the reaction of (mu-H)(2)Os-3(CO)(10) with CNNPPh3 produced complex 1 as the initial product in 100% conversion. The latter is not stable in solution and slowly eliminates nitrogen to form an unusual ylide complex 2 in quantitative yield. The thermolysis of 2 in refluxing toluene afforded (mu-H)(3)Os-3(CO)(9)(mu(3)-eta(1)-CCO2CH2Ph) (3) as a colorless compound. Complexes 1-3 were characterized by spectroscopic methods and single-crystal X-ray diffraction analysis. The interesting feature of structure 3 is the presence of a mu(3)-alkylidyne ligand where the symmetrically triply bridged CCo2CH2Ph fragment lies perpendicular to and above the triosmium triangle.