Halogen Complexes of Anionic N-Heterocyclic Carbenes

Area of Science:

• Organometallic Chemistry
• Supramolecular Chemistry
• Halogen Bonding

Background:

• Lithium complexes featuring weakly coordinating anionic borate moieties and N-heterocyclic carbenes (NHCs) are versatile synthetic intermediates.
• Anionic NHCs are valuable ligands in organometallic chemistry, offering unique electronic and steric properties.

Purpose of the Study:

• To synthesize and characterize novel zwitterionic 2-halogenoimidazolium borates.
• To investigate the halogen bonding capabilities of these new compounds.
• To explore the formation of hypervalent halogen complexes.

Main Methods:

• Reaction of lithium complexes with iodine, bromine, and carbon tetrachloride.
• Characterization of products using X-ray crystallography.
• Computational studies including Density Functional Theory (DFT) and Quantum Theory of Atoms in Molecules (QTAIM) analysis.

Main Results:

• Synthesis of zwitterionic (WCA-NHC)X compounds (X=I, Br, Cl).
• Demonstration of halogen bond donation by the iodine derivative, leading to complexes with Lewis bases.
• Formation of hypervalent bis(carbene)iodine(I) and a rare hypervalent bromine(I) complex.
• DFT and QTAIM analyses confirmed the significant role of London dispersion in stabilizing hypervalent complexes.

Conclusions:

• The synthesized zwitterionic halogenoimidazolium borates are effective halogen bond donors.
• These compounds serve as precursors to novel hypervalent halogen complexes.
• Computational methods provide insights into the bonding and stability of these unique organohalogen species.