Lithium Anionic Dicarbenes or Acetylides: What is in the Name?

Area of Science:

• Organometallic Chemistry
• Main Group Chemistry
• Carbene Chemistry

Background:

• 1,3-Imidazolium salts are precursors to N-heterocyclic carbenes.
• Anionic dicarbenes (ADC) are versatile ligands and synthetic intermediates.
• Solid-state structures of Li(ADC) compounds were previously unknown.

Purpose of the Study:

• To synthesize and characterize novel C2-arylated anionic dicarbenes (Li(ADC)).
• To elucidate the solid-state structures of these Li(ADC) compounds.
• To explore the reactivity of Li(ADC) with electrophiles like triethylborane, CO2, and N2O.

Main Methods:

• Two-fold deprotonation of C2-arylated 1,3-imidazolium salts using n-butyllithium.
• Single-crystal X-ray diffraction studies to determine solid-state structures.
• Reactions of Li(ADC) with triethylborane, carbon dioxide, and nitrous oxide.

Main Results:

• Synthesis of Li(ADC) compounds (2-Ar) from corresponding imidazolium salts (1-Ar).
• Discovery of dimeric (n=2) and trimeric (n=3) acetylide-type structures ([ArC{N(Dipp)}(Dipp)NC≡CLi)]n, 3-Ar) in the solid-state.
• Formation of a monoanionic carbene complex with a weakly coordinating anion (Li[(ADC)(BEt3)], 4-Ph) and ring-closing products with CO2 (Li[(ADC)(CO2)2], 5-Ar) and N2O (Li[(ADC)N2O], 6-Ar).

Conclusions:

• The solid-state structures of anionic dicarbenes are characterized by acetylide-type oligomers.
• Li(ADC) compounds serve as valuable platforms for synthesizing novel organometallic complexes.
• The reactivity studies demonstrate the potential of Li(ADC) in forming new main group heterocycles.