Reactions of Alkynes with Dicarbonyl(η-cyclopentadienyl)iridium

Six organometallic complexes have been isolated from the reaction between (η-C5H5)Ir(C0)2 and hexafluorobut-2-yne at 120-160�. Both the cis and trans isomers of the σ-bridging alkyne complex (η C5H5)2Ir2(CO)2(CF3C2CF3) were obtained; the cis isomer is slowly transformed to the trans isomer at 160�. These complexes do not react further with alkynes. Two other products were identified as an iridiocyclobutenone complex and a iridiocyclopentadiene complex, viz.(η-C5H5){IrC(CF3)=C(CF3)CO}(CO) and (η-C5H5){IrC(CF3)=C(CF3)C(CF3)}(CO)These complexes are also inert to further reaction with hexafluorobut-2-yne, and the iridiocyclopentadiene complex could not be converted into the cyclopentadienone complex (η-C5H5)Ir{C4(CF3)4-CO). The spectroscopic properties of a product of formula (η-C5H5)Ir(CF3C2CF3)2(C4HF5) indicate it incorporates a 1-(2',2'-difluoroethenyl)-1,2,3,4,5-pentakis(trifluoromethyl)cyclopenta-2,4-diene ligand. The final product was formulated as (η-C5H5)Ir2(CO)3(CF3C2CF3)2H and five alternativestructures are consistent with the spectroscopic data. The related reaction between (η-C5H5)Ir(CO)2 and but-2-yne at 180� gives a small amount of hexamethylbenzene plus the maleoyl complex(η-C5H5){IrC(O)(Me=C(Me)C(O)}(CO).