Spirocyclic Diaminocarbenes: Synthesis, Coordination Chemistry, and Investigation of Their Dimerization Behavior

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 lithiu...

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Bibliographic Details
Published in:Chemistry : a European journal 2005-08, Vol.11 (17), p.5080-5085
Main Authors: Hahn, F. Ekkehardt, Paas, Martin, Le Van, Duc, Fröhlich, Roland
Format: Article
Language:English
Subjects:
carbenes
dimerization
enetetramines
nitrogen heterocycles
tungsten
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Summary: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 [W(11)(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. To dimerize or not? That is the question! Nonaromatic unsymmetrically N,N′‐substituted diaminocarbenes 3 (n=1, 2) with a spirocyclic structure can be obtained in a two‐step reaction starting from secondary amines and ketimines 1 via the imidazolidin‐2‐thiones 2. The proton‐catalyzed dimerization of carbenes 3 is reversible under special circumstances.
ISSN:0947-6539
1521-3765
DOI:10.1002/chem.200500306