Hydrocarbon solutions of W2(μ-CSiMe3)2X4(W-W) compounds, where X = CH2SiMe3 and O-i-Pr, have been found to react with diphenyldiazomethane, N2CPh2, at room temperature to give the 1:1 adducts W2(μ-CSiMe3)2X4(N2CPh2) (1, X = CH2SiMe3; 2, X = O-i-Pr). The dinuclear center of the alkylidyne compound acts as a source of electrons reducing the diazoalkane to a NNCPh2 hydrazonido(2-) ligand. Both compounds have been characterized by 1H, 13C, and IR spectroscopy. The molecular structure of W2(μ-CSiMe3)2(CH2SiMe3)4(N2CPh2) (1) shows that NNCPh2 is terminally bound to one W atom resulting in a pseudo-trigonal-bipyramidal geometry at that W atom wherein the coordinated NNCPh2 ligand and one of the alkylidyne bridges occupy the axial positions. The other W atom is in a pseudotetrahedral environment. The W-N distance of 1.767 (10) Å together with the WNN angle of 158.2 (8)° suggests partial donation of the nitrogen lone pair to give significant W≡N character. Thermolysis of 1 at 120 °C in toluene solution results in loss of Si(CH3)4 (1 equiv) and generates, via C-H bond activation, a compound which we formulate, on the basis of 1H and 13C NMR spectroscopic data, as (Me3SiCH2)2W(μ-CSiMe3)2W-(CH2SiMe3)(NN═C(Ph)-o-C6H4). At no time was alkylidene formation observed from either thermolysis or photolysis of solutions of 1. On the basis of low-temperature 1H NMR, 13C NMR, and IR spectroscopic data, we formulate that 2 is structurally related to 1. The molecule is fluxional on the 1H NMR time scale due to a pseudorotational process occurring about the trigonal-bipyramidal W atom, ΔG*rot= 13.4 kcal/mol. Neither thermolysis at 120 °C nor photolysis of hydrocarbon solutions of 2 generate alkylidene-containing products, but rather dissociation of N2CPh2 occurs with regeneration of W2(μ-CSiMe3)2(O-i-Pr)4. Crystal data for 1 at -159 °C: a = 21.163 (5) Å, b = 22.639 (4) Å, c = 10.403 (1) Å, β = 91.73 (1)°, Z = 4, dcalcd= 1.441 g cm-3, and space group P21/a.