Olefin–acetylene metal complexes: olefin–hexafluorobut-2-yne complexes of rhodium(I)

Abstract

The compounds [Rh(acac)(C₂H₄)₂] and [Rh(dpm)(C₂H₄)₂] react with hexafluorobut-2-yne at ca.–78 °C to give [Rh(acac)(C₂H₄)(C₄F₆)] and [Rh(dpm)(C₂H₄)(C₄F₆)] respectively (acac = pentane-2,4-dionate; dpm = 2,2,6,6-tetramethylheptane-3,5-dionate). Similarly, [Rh(acac)(C₈H₁₄)₂] reacts with hexafluorobut-2-yne at ca.–78 °C to give [Rh(acac)(C₈H₁₄)(C₄F₆)](C₈H₁₄= cyclo-octene). The ethylene ligand in [Rh(dpm)(C₂H₄)(C₄F₆)] exhibits dynamic behaviour in solution with rotation of this ligand, which may be displaced from the rhodium by the olefins L = cyclo-octene, cycloheptene, propene, and cis-but-2-ene to give the complexes [Rh(dpm)(L)(C₄F₆)]. Reaction of [Rh(dpm)(C₂H₄)(C₄F₆)] with tetrafluoroethylene gives [Rh(dpm)(C₂H₄)(C₂F₄)] which reacts with hexafluorobut-2-yne at ca.–78 °C to reform [Rh(dpm)(C₂H₄)(C₂H₆)]. However, treatment of [Rh(dpm)(C₂H₄)(C₄F₆)] with either carbon monoxide or cyclo-octa-1,5-diene results in the displacement of both C₂H₄ and C₄F₆ from the rhodium. Reactions of [Rh(dpm)(L)(C₄F₆)](L = C₂H₄, cycloheptene, or cyclo-octene) with hexafluorobut-2-yne at room temperature afford the 1,3-diene complexes [Rh(dpm·C₄F₆)(1,3-diene)]{1,3-diene = 1,2,3,4,-tetrakis (trifluoromethyl)cyclohexa-1,3-diene; 2,3,4,5-tetrakis(trifluoromethyl)-bicyclo[5.4.0]undeca-2,4-diene; or 2,3,4,5-tetrakis(trifluoromethyl)bicyclo[6.4.0]dodeca-2,4-diene}. The complexes also contain a molecule of hexafluorobut-2-yne which has added 1,4 to the rhodium(I)β-ketoenolate ring. Similar complexes result from the reactions of [Rh(acac)(L)(C₄F₆)](L = C₂H₄ or cyclo-octene) and hexafluorobut-2-yne. Reactions of hexafluorobut-2-yne with the 4-aminopent-3-en-2-iminato(apemino-) complexes [Rh{HN C(Me)CHC(Me)NH}L₂](L = C₂H₄; L₂= cyclo-octa- 1,5-dieno), however, afford the hexakis(trifluoromethyl)benzene complex [Rh(apemino·C₄F₆){η⁴-C₆(CF₃)₆}] which also contains a molecule of C₄F₆ added 1,4 to the rhodium(I) apemino-ring.