N-Alkoxyimidazolylidines (NOHCs): nucleophilic carbenes based on an oxidized imidazolium core

We report the first preparation of N-alkoxyimidazolylidene (NOHC), a nucleophilic carbene based on an oxidized imidazolium core. The Arduengo-type analogous carbene center shows the most upfield ¹³C NMR shift compared to common NHCs. The obtained gold(I) complex of the carbene follows the ¹³C NMR upfield trend and shows the marked influence the alkoxy substituents. Similarly, the ⁷⁷Se and ¹⁵N NMR shifts of a range of NOHC-selenium adducts show increased σ-donation and decreased π-back donation in the bonding with the nucleophile. This extension of the NHC family provides altered electronic properties for the use of such carbenes as ligands or catalysts.