Treatment of Co2(CO)6(μ-dmad) (where dmad = dimethyl acetylenedicarboxylate) with the bidentate ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) in the presence of added Me3NO affords the new alkyne compound Co2(CO)4(bpcd)(μ-dmad) in good yield. Both IR and P NMR spectroscopies indicate that the bpcd ligand is coordinated to a single cobalt center in a chelating fashion in solution. The solid-state structure of Co2(CO)4(bpcd)(μ-dmad) is identical to the solution structure Co2(CO)4(bpcd)(μ-dmad), as determined by X-ray diffraction analysis. Co2(CO)4(bpcd)(μ-dmad) crystallizes in the triclinic space group P-1, a = 10.7460(8) Å, b = 11.628(2) Å, c = 15.077(1) Å, α = 95.831(9)°, β = 91.205(7)°, γ = 101.526(9)°, V = 1834.7(3) Å, Z = 2, and dcalc = 1.514 g/cm; R = 0.0489, Rw = 0.0528 for 2854 reflections with I > 3σ(I). The thermal reactivity of Co2(CO)4(bpcd)(μ-dmad) has been briefly explored by spectroscopic methods, and evidence is presented for the attack of one of the PPh2 groups on an alkyne carbon atom in Co2(CO)4(bpcd)(μ-dmad) to from the zwitterionic hydrocarbyl compound Co2(CO)4(μ-η:η:η:η-(MeO2C) = C(CO2Me)PPh2 upon thermolysis. The redox chemistry of both Co2(CO)4(bpcd)(μ-dmad) and Co2(CO)4[μ-η:η:η:η-(MeO2C)= C(CO2Me)PPh2 has been explored by cyclic voltammetery.(Figure is included in full-text article.)