Silver(I) complexes of the freely stable carbenes 1,3-bis(2,4,6-trimethylphenyl)imidazolidin-2-ylidene (3) and 1,3-bis(2,6-diisopropylphenyl)imidazolidin-2-ylidene (4) were prepared from the imidazolinium chlorides 1 and 2, respectively, and silver oxide. These two air-stable and light-sensitive carbene complexes [AgCl(3)] (5) and [AgCl(4)] (6) were characterized by NMR spectroscopy, and the molecular structure of 6 was confirmed by X-ray diffraction. The imidazolidin-2-thiones 7 and 8 were obtained by reaction of the silver carbene complexes 5 and 6, respectively, with elemental sulfur at ambient
Nonaromatic, "saturated", spirocyclic N-heterocyclic diaminocarbenes 11 can be obtained from spirocyclic imidazolidin-2-thiones 10 by reductive desulfurization with potassium. The unsymmetrically N,N'-substituted spirocyclic imidazolidin-2-thiones were obtained by reaction of ketimines 9 with lithium N-butyl-N-lithiomethyldithiocarbamate (6). 13C NMR spectroscopy revealed that the unsymmetrically N,N'-substituted spirocyclic imidazolidin-2-ylidene 11 a undergoes a slow, acid-catalyzed dimerization to give the enetetramine 11 a=11 a, which exists in two isomeric forms (syn and anti). This reaction is reversible under special circumstances. Carbenes of type 11 react with [W(CO)6] to yield air-stable carbene complexes of type [W11(CO)5] (14). The molecular structures of two derivatives 14 a and 14 b were established by X-ray crystallography and show clear distortion of the five-membered N-heterocyclic ring, caused by the spirocyclic molecular structure of the carbene ligands of type 11.
Secondary amines and imines were used to prepare unsymmetrically substituted, non‐aromatic N‐heterocyclic carbenes via imidazolidine‐2‐thiones (rac‐1) as intermediates. The presence of only one sterically demanding substituent on one of the N atoms in rac‐2 is sufficient to prevent dimerization to the enetetramine.
Aus sekundären Aminen und Iminen sind unsymmetrisch substituierte nichtaromatische N‐heterocyclische Carbene wie rac‐2 über Imidazolidin‐2‐thione (rac‐1) als Zwischenprodukte zugänglich. Bereits ein einziger sterisch anspruchsvoller N‐Substituent in rac‐2 verhindert die Dimerisierung zum Entetramin.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.