Ca²⁺ Stabilized by Carborate Anions: Synthesis, Structure, and Reactivity

Area of Science:

• Organometallic Chemistry
• Carborane Chemistry
• Catalysis

Background:

• Calcium carborate salts are explored for their unique structural and chemical properties.
• Understanding the coordination environment and Lewis acidity of calcium is crucial for catalytic applications.

Purpose of the Study:

• To synthesize and characterize novel calcium carborate compounds.
• To investigate the ion pairing behavior and Lewis acidity of these calcium salts.
• To evaluate their potential as catalysts in organic transformations.

Main Methods:

• Synthesis of calcium carborate salts: Ca[HexCB11Cl11]2, Ca[HCB11Cl11]2, and Ca[MeCB11Cl11]2·2(o-DFB).
• Structural determination of Ca[HCB11Cl11]2·4(o-DFB) using X-ray crystallography.
• Spectroscopic studies (11B NMR, DOSY NMR) to analyze ion pairing in solution.
• Density Functional Theory (DFT) calculations to determine Fluoride Ion Affinities (FIA).

Main Results:

• Successful synthesis and structural characterization of new calcium carborate complexes.
• Evidence of close ion pair formation in solution for the synthesized salts.
• DFT calculations revealed Fluoride Ion Affinities (FIA) for the calcium salts, indicating Lewis acidity.
• Calcium carborate salt 1 demonstrated catalytic activity in hydrosilylation, transfer hydrogenation, and carbonyl-olefin metathesis (COM).

Conclusions:

• The synthesized calcium carborate salts exhibit interesting structural and solution properties.
• The Lewis acidity of the calcium center is sufficient to coordinate small molecules and catalyze reactions.
• This work represents the first report of calcium compounds catalyzing carbonyl-olefin metathesis (COM).