Reaction of the dicobalt alkyne compound Co2(CO)6( -dmad) with the diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd). Spectroscopic properties, X-ray diffraction data, and thermal reactivity of the chelating isomer of Co2(CO)4(bpcd)( -dmad)

Abstract

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 31P 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) A, b = 11.628(2) A, c = 15.077(1) A, α = 95.831(9)°, β = 91.205(7)°, γ = 101.526(9)°, V = 1834.7(3) A3, Z = 2, and d calc = 1.514 g/cm3; R = 0.0489, R w = 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-η2:η2:η1:η1-(MeO2C)=C(CO2Me)PPh2C=C(PPh2)C(O)CH2C(O)] upon thermolysis. The redox chemistry of both Co2(CO)4(bpcd)(μ-dmad) and Co2(CO)4[μ-η2:η2:η1:η1-(MeO2C) C=C(CO2Me)PPh2C=C(PPh2)C(O)CH2C(O)] has been explored by cyclic voltammetery.