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 CCl4 to afford the zwitterionic 2‐halogenoimidazolium borates (WCA‐NHC)X (X=I, Br, Cl; WCA=B(C6F5)3, B{3,5‐C6H3(CF3)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(C6F5)3) formed several complexes of the type (WCA‐IDipp)I⋅L (L=C6H5Cl, C6H5Me, CH3CN, THF, ONMe3), 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 [PPh4][(WCA‐IDipp)I(WCA‐NHC)] (NHC=IDipp, IMes). The corresponding bromine complex [PPh4][(WCA‐IDipp)2Br] 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.

The lithium complexes [(WCA-NHC)Li(toluene)] of anionic N-heterocyclic carbenes with a weakly coordinating borate moiety (WCA-NHC, WCA = B(C 6 F 5 ) 3 , NHC = IDipp = 1,3bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) were used for the preparation of silver(I) or copper(I) WCA-NHC complexes. While the reactions in THF with AgCl or CuCl afforded anionic mono-and dicarbene complexes with solvated lithium counterions [Li(THF) n ] + (n = 3, 4), the reactions in toluene proceeded with elimination of LiCl and formation of the neutral phosphine and arene complexes [(WCA-NHC)M(PPh 3 )] and [(WCA-NHC)M(η 2 -toluene)] (M = Ag, Cu). The latter were used for the preparation of chlorido-and iodido-bridged heterobimetallic Ag/Ru and Cu/Ru complexes [(WCA-NHC) M(μ-X) 2 Ru(PPh 3 )(η 6 -p-cymene)] (M = Ag, Cu, X = Cl; M = Ag, X = I). Surprisingly, these complexes resisted the elimination of CuCl, AgCl, or AgI, precluding WCA-NHC transmetalation.

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The reaction of 1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene (IDipp) with n‐BuLi in the presence of sodium and potassium bis(trimethylsilyl)amide was studied, and the resulting polymeric dicarbene species were reacted with the fluoroboranes tris(pentafluorophenyl)borane, B(C6F5)3, and tris[3,5‐bis(trifluoromethyl)phenyl]borane, B(m‐XyF6)3 to produce sodium and potassium salts of an anionic N‐heterocyclic carbene with a weakly coordinating borate moiety (WCA‐NHC).

Iodine complexes of anionic N‐heterocyclic carbenes (NHC) act as electrophiles towards a variety of nucleophiles, with the interactions ranging from noncovalent charge‐transfer or halogen bonding to covalent 3‐center, 4‐electron bonding. Hypervalent (10‐X‐2) bis(carbene)iodine(I) and ‐bromine(I) complexes could be isolated and structurally characterized, and computational studies reveal that London dispersion involving the bulky NHC ligands (R=Dipp, Mes) contributes significantly to the stability of these systems. More information can be found in the Full Paper by M. Tamm et al. on page 4349.