The compound formed by the reaction of trans-Mo(N-2)(2)(Et(2)PC(2)H(4)PEt(2))(2) with ethyl acetate in refluxing toluene under argon has been reformulated as the bridging dinitrogen complex {Mo(CO)(Et(2)PC(2)H(4)PEt(2))(2)}(2)(mu-N-2) (1), in contrast with the previously proposed formulation of Mo(CO)(Et(2)PC(2)H(4)PEt(2))(2) (2). In refluxing p-xylene and under argon, compound 1 eliminates the bridging dinitrogen ligand to form the nitrogen-free compound 2. The reaction of trans-Mo(N-2)(2)(Bu(2)(i)PC(2)H(4)PBu(2)(i))(2) with ethyl acetate in refluxing toluene under argon gives directly the nitrogen-free compound Mo(CO)(Bu(2)(i)PC(2)H(4)PBu(2)(i))(2) (3). The molecular structures of compounds 1 and 3 have been determined by single-crystal X-ray diffraction studies. Compound 1 contains an end-on bridging dinitrogen ligand. Compound 3 attains a formal 18-electron configuration by virtue of an agostic Mo ... H-C interaction between the molybdenum atom and an aliphatic gamma-C-H bond of the alkyldiphosphine ligand. On the basis of the agostic Mo ... C and Mo ... H distances, the agostic interaction in 3 appears to be stronger than that in the related compound Mo(CO)(Ph(2)PC(2)H(4)PPh(2))(2) which involves an ortho aromatic C-H bond of the diphosphine ligand. Crystallographic data for 1 : monoclinic, space group C2/c, a = 24.270(2) Angstrom, b = 44.233(4) Angstrom, c = 20.378(2) Angstrom, beta = 90.725(9)degrees, V = 21875(3) Angstrom(3), Z = 16, and R = 0.048. Crystallographic data for 3 : orthorhombic, space group Pna2(1), a = 18.332(4) Angstrom, b = 22.066(4) Angstrom, c = 10.589(2) Angstrom, V = 4283(2) Angstrom(3), Z = 4, and R = 0.034.