Tricyanoborane‐Functionalized Anionic N‐Heterocyclic Carbenes: Adjustment of Charge and Stereo‐Electronic Properties
Ludwig Zapf, Sven Peters, Rüdiger Bertermann, Udo Radius, Maik Finze
Abstract
Abstract 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‐ylidene (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 8 , 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 effectively fine‐tuned via the number of tricyanoborane substituents.