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

Abstract

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.

N-heterocyclic carbene complexes of Group 6 metals

“…This reactivity is similar to that of Fischer carbene complexes in which CO substitution with donor ligands is disburdened too[72]. With similar imidazolinylidene (with smaller N-C-N angle) chromium complexes, the substitution of CO onlyThe strong σ donating carbene ligand leads to a shortening of the W-CO trans bond compared to the W-CO cis[67]. W-7a, R 1 = iPr, R 2 = nBu, n = 2 W-7b, R 1 = iBu, R 2 = nBu, n = 1…”

“…3 M(0) carbonyl complexes with mono-NHC ligands with saturated backbone prepared via free carbene route[67,72].…”

π‐Face Donor Properties of N‐Heterocyclic Carbenes in Grubbs II Complexes

“…Several useful synthetic approaches for the synthesis of such compounds have been reported in the literature. [51][52][53][54][55][56][57] Typically, in a stepwise manner an unsymmetrical oxalyl diamide is converted into the respective diamine under strongly reducing conditions using BH 3 or LiAlH 4 , followed by ring closure. This approach is not compatible with substituents sensitive towards reduction.…”

Latent ruthenium olefin metathesis catalysts featuring a phosphine or an N-heterocyclic carbene ligand

“…The resulting solid was purified via column chromatography (TSI silica) using a gradient of ethyl acetate and MeOH to give 6 in two different fractions (71 mg and 37 mg) as one yellow (6a) and one green (6b) solid in 72% yield. Major isomer ( [18].…”