title: Unsymmetrically N,N'-substituted saturated carbenes: synthesis, reactivity and preparation of a rhodium(I) carbene complex.
abstract: A versatile synthesis of unsymmetrically N,N'-substituted saturated carbenes is described. The novel racemic imidazolidin-2-ylidenes rac-5 have been synthesized by reductive desulfurization of the corresponding imidazolidin-2-thiones rac-4. The thiones were prepared in two reaction steps from aldimines and secondary amines. Three different substituents at N1, N3 and C4 of the five-membered N-heterocyclic ring can be introduced by choice of suitable aldimines and secondary amines. The dimerization behaviour (diaminocarbene/enetetramine equilibrium) for the unsymmetrically N,N'-substituted imidazolidin-2-ylidenes has been investigated by NMR spectroscopy. Unsymmetrically N-iPr and N-iBu substituted N-heterocyclic carbenes undergo a slow dimerization, whereas N-tBu substituted derivatives are stable as monomeric carbenes indefinitely. The carbene ligand rac-5d has been coordinated to rhodium(I) to give the square-planar rhodium carbene complex [Cl(cod)Rh(rac-5d)]rac-6d which has been characterized by an X-ray diffraction analysis.
authors.affiliation: Institut für Anorganische und Analytische Chemie der Westfälischen Wilhelms-Universität Münster, Corrensstrasse 36, 48149, Münster, Germany. fehahn@uni-muenster.de
authors.forename: F Ekkehardt
authors.initials: FE
authors.lastname: Hahn
authors.forename: Duc
authors.initials: D
authors.lastname: Le Van
authors.forename: Martin
authors.initials: M
authors.lastname: Paas
authors.forename: Roland
authors.initials: R
authors.lastname: Fröhlich
mesh_terms: D000588:Amines / Q000737:chemistry; D019281:Dimerization; D006838:Hydrocarbons / Q000138:chemical synthesis / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008697:Methane / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry; D008956:Models, Chemical; D008958:Models, Molecular; D012238:Rhodium / Q000737:chemistry*; D013455:Sulfur / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D000588:Amines; D006838:Hydrocarbons; C030011:carbene; D013455:Sulfur; D012238:Rhodium; D008697:Methane