Superacidity of closo-dodecaborate-based Brønsted acids: a DFT study

Area of Science:

• Computational Chemistry
• Acid-Base Chemistry
• Materials Science

Background:

• Superstrong Brønsted acids are crucial for various chemical transformations.
• Dodecaborane cages offer a promising scaffold for designing novel superacids.
• Understanding structure-acidity relationships is key to developing stronger acids.

Purpose of the Study:

• To computationally explore the gas-phase acidities (GA) of novel dodecaborane-based Brønsted acids.
• To investigate the effect of substituents on the acidity of these dodecaborane derivatives.
• To predict the pKa values of these acids in solution and compare them with existing superacids.

Main Methods:

• Density Functional Theory (DFT) B3LYP method with a 6-311+G** basis set was employed for gas-phase acidity calculations.
• Different protonation geometries were analyzed based on substituent effects.
• SMD and cluster-continuum models were used to estimate pKa values in 1,2-dichloroethane (DCE).

Main Results:

• The dodecatrifluoromethyl derivative of H2A (B12(CF3)12H1H2) was identified as the strongest acid, comparable to known superacids.
• Many anionic dodecaborane derivatives exhibited gas-phase acidities above the superacidity threshold.
• Perfluorinated dodecaborane derivatives showed significantly lower pKa values in DCE, indicating exceptional solution acidity.

Conclusions:

• Dodecaborane derivatives represent a promising class of superstrong Brønsted acids.
• The synthetic accessibility of B12H12H2 derivatives enhances their potential for practical applications.
• These findings pave the way for the development of new, highly effective acid catalysts.