Thermolysis of [(η5-C5H5)Co(PPh3)(η2-DMAD)], revisited: a solid state analysis reveals the true structure of the triphenylphosphine–alkyne coupling product

Thermolysis of the η2-alkyne complex (η5-C5H5)Co(PPh3)[η2-(MeO2C)CC(CO2Me)] (1-DMAD) leads to formation of an ortho-metalated vinyl-phosphonium derivative (η5-C5H5)Co[η2-(MeO2C)HCC(CO2Me)PPh2(η1-o-C6H4)] (4) as well as a small amount of the tricobalt bis(carbyne) cluster [(η5-C5H5)Co]3[μ3,η3-C(CO2Me)]2 (3-CO2Me). Thermolysis of 1-DMAD in the presence of added triphenylphosphine gives 4 as the major product, with no evidence for formation of 3-CO2Me. Complexes 4 and 3-CO2Me were characterized by X-ray crystallographic analyses.