Study of the reactivity of [Fe2(CO)6(.mu.-CO)(.mu.-CPhCPhH)]- toward the MeOC(O)C.tplbond.CC(O)OMe and CF3C.tplbond.CCF3 alkynes. Crystal structure of the products resulting from two different modes of combination of the alkynes with the bridging ligands [Fe2(CO)6(.mu.-C(C(O)OMe)C(C(O)OMe)C(O)CPhCPhH)]- and [Fe2(CO)6(.mu.-CPhCPhC(CF3)C(CF3)H)]-