"Assessing the Potential of Zwitterionic NHC · CS2 Adducts for Probing the Stereoelectronic Parameters of N-Heterocyclic Carbenes"

Lionel Delaude, Albert Demonceau, and Johan Wouters

journal cover 
          source: European Journal of Inorganic Chemistry
            year: 2009
      first page: 1882
       last page: 1891
             doi: 10.1002/ejic.200801110
graphical abstract

Abstract: Five imidazol(in)ium-2-dithiocarboxylates bearing cyclohexyl, mesityl, or 2,6-diisopropylphenyl substituents on their nitrogen atoms were prepared from the corresponding N-heterocyclic carbenes (NHCs) by reaction with carbon disulfide. They were characterized by IR, UV/Vis, and NMR spectroscopy, and by thermogravimetric analysis. Their molecular structures were determined by X-ray diffraction. For the sake of comparison, tricyclohexylphosphonium dithiocarboxylate was also examined. The data acquired were scrutinized to evaluate their usefulness for assessing the steric and electronic properties of NHC ligands. Because of their outstanding ability to crystallize, the five NHC · CS2 betaines were found to be highly suitable for probing the steric influence of nitrogen atom substituents on imidazolylidene-based ligand precursors via XRD analysis, while the corresponding NHC · CO2 adducts were deemed more appropriate for evaluating the σ-donating properties of carbene ligands.

Keywords: Betaines, Carbenes, Ligand Effects, Nitrogen Heterocycles, Zwitterions

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