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

AbstractNonaromatic, “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.