Reactions of Alkynes with Dicarbonyl(η-cyclopentadienyl)iridium

Abstract

Six organometallic complexes have been isolated from the reaction between (η-C₅H₅)Ir(C0)₂ and hexafluorobut-2-yne at 120-160º. 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 160º. 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 180º gives a small amount of hexamethylbenzene plus the maleoyl complex

(η-C₅H₅){IrC(O)(Me=C(Me)C(O)}(CO).