Basicity Limits of Neutral Organic Superbases

Area of Science:

• Computational Chemistry
• Organic Chemistry
• Physical Chemistry

Background:

• Superbasicity in neutral organic compounds is a key area of research for catalysis and synthesis.
• Understanding the relationship between molecular structure and basicity is crucial for designing new superbasic molecules.
• Previous studies have explored various classes of neutral bases, but limits of superbasicity remain an active investigation.

Purpose of the Study:

• To explore the potential limits of superbasicity in different families of neutral bases.
• To develop a model for predicting superbasicity based on molecular framework expansion.
• To identify novel classes of organosuperbases with unprecedented basicity.

Main Methods:

• Density Functional Theory (DFT) computations were employed to investigate various core structures of non-ionic organosuperbases.
• A predictive model was developed to describe the dependence of basicity on the molecular framework.
• The model was validated and used to quantitatively predict ultimate basicities and substituent effect saturation rates.

Main Results:

• Guanidino phosphorus carbenes are predicted to achieve gas-phase basicity around 370 kcal/mol, representing the highest basicity for neutral bases.
• Classical substituted alkylphosphazenes are predicted to reach pKa values of approximately 50 in acetonitrile, exceeding previous expectations.
• A model was successfully proposed and validated for predicting the basicity limits based on molecular framework.

Conclusions:

• This study identifies new frontiers in neutral superbasicity, with guanidino phosphorus carbenes as exceptionally strong bases.
• The developed model provides a quantitative tool for predicting and designing highly basic neutral compounds.
• The findings significantly advance the understanding of superbasicity and open avenues for novel synthetic applications.