Tricyanoborane‐Functionalized Anionic N‐Heterocyclic Carbenes: Adjustment of Charge and Stereo‐Electronic Properties

The 1-methyl-3-(tricyanoborane)imidazolin-2-ylidenate anion ( 2 ) was obtained in high yield by deprotonation of the B(CN) 3 -methylimidazole adduct 1 . Regarding charge and stereo-electronic properties, anion 2 closes the gap between well-known neutral NHCs and the ditopic dianionic NHC, the 1,3‑bis(tricyanoborane)imidazolin-2-ylidenate dianion ( IIb ). The influence of the number of N -bonded tricyanoborane moieties on the σ-donating and π-accepting properties of NHCs was assessed by quantum chemical calculations and verified by experimental data on 2 , IIb , and 1,3-dimethyl­imidazolin-2-yilidene (IMe, IIa ). Therefore NHC 2 , which acts as a ditopic ligand via the carbene center and the cyano groups, was reacted with alkyl iodides, selenium, and [Ni(CO) 4 ] yielding alkylated imidazoles 3 and 4 , the anionic selenium adduct 5 , and the anionic nickel tricarbonyl complex 6 , respectively. The results of this study prove that charge, number of coordination sites, buried volume (% V bur ) and σ-donor and π-acceptor abilities of NHCs can be tuned effectively via the number of tricyanoborane substituents.