N-heterocyclic carbenes bearing two, one and no nitrogen atoms at the ylidene carbon: insight from theoretical calculations

Dalton Trans. 2009 Sep 21:(35):7015-28. doi: 10.1039/b906969k. Epub 2009 Jul 3.

Abstract

Electronic structure, thermodynamic stability and ligand properties in LRh(CO)2Cl complexes of a series of N-heterocyclic carbenes (NHCs) were studied at the DFT level. The systems under study are: imidazolin-2-ylidene (1), imidazolidin-2-ylidene (2), cyclic(alkyl)(amino)carbene (CAAC, 3), pyrazolin-3-ylidene (4), pyridin-2-ylidene (5), and pyridin-4-ylidene (6). The main structural feature influencing the properties of these species is the number of nitrogen atoms at the ylidene carbon. A decrease of the number of nitrogen atoms on the one hand leads to an increase in donor ability and ligand-to-metal bond strength, but lowers the stability of the NHC on the other hand. The number of nitrogen atoms can be taken as a key parameter for the classification of carbenes into 2N-NHC, 1N-NHC and r-NHC (r = remote).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Carbon / chemistry*
  • Computer Simulation*
  • Crystallography, X-Ray
  • Heterocyclic Compounds / chemistry*
  • Ligands
  • Methane / analogs & derivatives*
  • Methane / chemistry
  • Models, Molecular
  • Molecular Structure
  • Nitrogen / chemistry*
  • Organometallic Compounds / chemistry*
  • Rhodium / chemistry
  • Thermodynamics

Substances

  • Heterocyclic Compounds
  • Ligands
  • Organometallic Compounds
  • carbene
  • Carbon
  • Rhodium
  • Nitrogen
  • Methane