Seven-Membered Cyclic Potassium Diamidoalumanyls

Area of Science:

• Organometallic Chemistry
• Main Group Chemistry
• Coordination Chemistry

Background:

• Seven-membered cyclic potassium alumanyl species are rare in inorganic chemistry.
• Understanding the structure and reactivity of alkali metal-supported aluminum compounds is crucial for developing new synthetic methodologies.

Purpose of the Study:

• To synthesize and characterize novel seven-membered cyclic potassium alumanyl species.
• To investigate the reactivity of these species with various substrates, including C-H bonds and Lewis acids.
• To explore the structural diversity, including monomeric and charge-separated forms, and the nature of Al-K interactions.

Main Methods:

• Synthesis of potassium alumanyl species via reduction of iodide precursors.
• Isolation of dimeric, monomeric, and charge-separated species.
• Reactions with toluene, boron trifluoride, and isocyanates.
• Structural characterization using X-ray crystallography.
• Density Functional Theory (DFT) calculations.

Main Results:

• Isolation of dimeric potassium alumanyl species [{SiN^Mes }AlK]₂ and [{SiN^Dipp }AlK]₂ supported by K-aryl interactions.
• Synthesis of an extremely encumbered dialumane [{SiN^Dipp }Al]₂ via partial oxidation.
• Reductive activation of toluene's C-H bond by [{SiN^Dipp }AlK]₂ yielding a benzyl hydridoaluminate.
• Nucleophilic reactions with BPh₃ and isocyanates to form Al-B and Al-C bonded products.
• Disruption of dimeric structure by crown ether or cryptand leading to monomeric [{SiN^Dipp }Al-K(18-cr-6)] and charge-separated [{SiN^Dipp }Al]^- species.
• DFT calculations revealing significant HOMO-LUMO energy gaps for the alumanyl anion.

Conclusions:

• Novel cyclic potassium alumanyl species can be synthesized and isolated in various forms.
• These compounds display versatile reactivity, including C-H activation and reactions with Lewis acids.
• The study provides rare insights into direct Al-K bonding and the formation of stable alumanyl anions.