N-Heterocyclic Carbenes with a Nido-C2B9 Carborane Backbone

摘要

Main observation and conclusion The steric and electronic properties of N-heterocyclic carbenes (NHCs) can be modified by the exocyclic substituents at the nitrogen atoms,by 1-3 atoms' replacements of the five-membered imidazolium skeleton and by the changes of the backbones.Herein,we report the usage of nido-C2B9 carborane anions as the backbones of NHCs.Stirring the mixture of secondary amino o-carboranes(1b-1e),triethyl orthoformate and HBF4·Et2O results in the unexpected cage-opening of o-carboranes to afford the nido-C2B9 car-borane anions supported N-heterocyclic carbene precursors (4b-4e).Deprotonation of 4b with sodium hexamethyldisilazide at-78℃ affords the N-heterocyclic carbene ligand,which was used to form an Au(Ⅰ) NHC complex (5).DFT calculations revealed a high-lying lone pair orbitals of the carbene ligands,predicting their strong o-donating abilities.