Phosphazenyl Phosphine Proton Sponges: Does the Proton-Chelating Effect Enhance Their Basicity?

Area of Science:

• Organic Chemistry
• Supramolecular Chemistry

Background:

• Proton sponges are organic compounds with high basicity.
• Phosphazenyl phosphines are a class of compounds with potential basic properties.

Purpose of the Study:

• To investigate the gas-phase basicity and solvent basicity of novel proton sponges derived from phosphazenyl phosphines.
• To explore how structural modifications influence the basicity of these compounds.

Main Methods:

• Synthesis of aromatic and aliphatic scaffolds bearing phosphazenyl phosphine substituents.
• Measurement of pKa values in acetonitrile solvent.
• Determination of gas-phase proton affinities (PA).

Main Results:

• Proton sponges exhibited high basicity, with pKa up to 42.0 and PA up to 307.0 kcal mol⁻¹.
• Basicity was modulated by varying the distance between phosphazenyl phosphine units.
• The proton-chelating effect (ΔPA) moderately influenced basicity.

Conclusions:

• The studied proton sponges are exceptionally strong organic bases.
• ΔPA is influenced by factors beyond electron-pair repulsion and hydrogen bonding, including mesomeric, inductive, and dispersion effects.
• These findings expand the understanding of superbase chemistry and the factors governing proton sponge basicity.