Labile Rhodium(I)–N-Heterocyclic Carbene Complexes

The neutral square-planar complexes Rh­(acac)­(IPr)­(η2-olefin) have been prepared from [Rh­(μ-Cl)­(IPr)­(η2-olefin)]2 (IPr = 1,3-bis-(2,6-diisopropylphenyl)­imidazol-2-carbene; olefin = cyclooctene, ethylene) and sodium acetylacetonate (acac). Protonation of the acetylacetonato complexes with triflic acid opens the way to the formation of the putative bare [Rh-IPr]+ fragment that has been stabilized at low temperature by labile ligands such as triflate, cyclooctene, and acetonitrile to generate Rh­(OTf)­(IPr)­(η2-coe), [Rh­(IPr)­(η2-coe)­(NCCH3)2]­OTf, and [Rh­(IPr)­(NCCH3)3]­OTf complexes. The derivative [Rh­(IPr)­(η2-coe)­(NCCH3)2]­OTf was further characterized by an X-ray diffraction analysis.