A cyclic compound, [Co-2(CO)(4)(mu (2)-HC=CSiMe3)(PPh2C=CPPh2)](2) 2, was identified from the reaction of bis(diphenylphosphino)acetylene with an alkyne-bridged dicobalt complex, (mu (2)-HC=CSiMe3)Co-2(CO)(6) 1. Crystal structure of 2 shows that it is a twelve-membered ring complex comprised of two DPPA coordinated pseudo-tetrahedral CO2C2 units. Further reaction of 2 with two equivalents of Co-2(CO)(8) resulted in the conversion of 2 into [Co-2(CO)(6){mu -P,P-(mu -PPh2C=CPPh2)}] [Co-2(CO)(4)(mu -HC=CSiMe3)] 3.