The Weakly Coordinating Tris(trichlorosilyl)silyl Anion

Area of Science:

• Organosilicon Chemistry
• Main Group Chemistry
• Coordination Chemistry

Background:

• N,N-di(2,6-diisopropylphenyl)imidazo-2-ylidene (NHC^Dipp) is a bulky N-heterocyclic carbene used to stabilize reactive species.
• Silyl anions are typically highly basic and nucleophilic, limiting their synthetic utility.
• HSi(SiCl3)3 is a conjugate Brønsted acid whose deprotonation can yield novel silyl anions.

Purpose of the Study:

• To synthesize and characterize the silyl anion Si(SiCl3)3-.
• To investigate the properties of the conjugate Brønsted acid HSi(SiCl3)3.
• To evaluate the electronic structure and reactivity of the Si(SiCl3)3- anion.

Main Methods:

• Synthesis of the salt [NHC^Dipp-H...Cl...H-NHC^Dipp]Si(SiCl3)3 and the byproduct [NHC^Dipp-H+][Cl-] using a modified literature procedure.
• X-ray crystallography for structural characterization of the isolated crystalline products.
• Deprotonation of HSi(SiCl3)3 with NHC^Dipp or 1,2,2,6,6-pentamethylpiperidine (PMP) to obtain the silyl anion.
• Density Functional Theory (DFT) calculations to estimate acidity and analyze electronic structure (electrostatic potential, electron localizability).

Main Results:

• Isolation and X-ray crystallographic characterization of the salt containing the Si(SiCl3)3- anion.
• Successful synthesis of Si(SiCl3)3- in high yields via deprotonation of HSi(SiCl3)3.
• DFT calculations indicate HSi(SiCl3)3 is significantly more acidic than other H-silanes.
• DFT studies confirm Si(SiCl3)3- possesses low basicity and nucleophilicity compared to other silyl anions.

Conclusions:

• The novel silyl anion Si(SiCl3)3- has been successfully synthesized and characterized.
• The conjugate Brønsted acid HSi(SiCl3)3 exhibits enhanced acidity.
• The electronic properties of Si(SiCl3)3- suggest its potential as a weakly coordinating anion for stabilizing reactive silicon compounds.