Halogen Complexes of Anionic N‐Heterocyclic Carbenes
Jenni Frosch, Marvin Koneczny, Thomas Bannenberg, Matthias Tamm
Abstract
Abstract The lithium complexes [(WCA‐NHC)Li(toluene)] of anionic N‐heterocyclic carbenes with a weakly coordinating anionic borate moiety (WCA‐NHC) reacted with iodine, bromine, or CCl 4 to afford the zwitterionic 2‐halogenoimidazolium borates (WCA‐NHC)X (X=I, Br, Cl; WCA=B(C 6 F 5 ) 3 , B{3,5‐C 6 H 3 (CF 3 ) 2 } 3 ; NHC=IDipp=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene, or NHC=IMes=1,3‐bis(2,4,6‐trimethylphenyl)imidazolin‐2‐ylidene). The iodine derivative (WCA‐IDipp)I (WCA=B(C 6 F 5 ) 3 ) formed several complexes of the type (WCA‐IDipp)I ⋅ L (L=C 6 H 5 Cl, C 6 H 5 Me, CH 3 CN, THF, ONMe 3 ), revealing its ability to act as an efficient halogen bond donor, which was also exploited for the preparation of hypervalent bis(carbene)iodine(I) complexes of the type [(WCA‐IDipp)I(NHC)] and [PPh 4 ][(WCA‐IDipp)I(WCA‐NHC)] (NHC=IDipp, IMes). The corresponding bromine complex [PPh 4 ][(WCA‐IDipp) 2 Br] was isolated as a rare example of a hypervalent (10‐Br‐2) system. DFT calculations reveal that London dispersion contributes significantly to the stability of the bis(carbene)halogen(I) complexes, and the bonding was further analyzed by quantum theory of atoms in molecules (QTAIM) analysis.