The Chloroazaphosphatrane Motif for Halogen Bonding in Solution

Area of Science:

• Supramolecular Chemistry
• Organophosphorus Chemistry

Background:

• Halogen bonding (XB) is a key non-covalent interaction.
• Conventional XB receptors often utilize iodine-based motifs.
• Verkade superbases are known for their unique structural and electronic properties.

Purpose of the Study:

• To explore chloroazaphosphatranes as a novel class of halogen bond (XB) donors.
• To synthesize and characterize chloroazaphosphatranes with varying substituents.
• To evaluate their anion binding affinities and compare them to existing XB receptors.

Main Methods:

• Synthesis of functionalized chloroazaphosphatranes.
• Nuclear Magnetic Resonance (NMR) titration experiments to determine binding constants with various anions (Cl-, Br-, I-, AcO-, CN-).
• ³¹P NMR spectroscopy to assess halogen bonding interactions using triethylphosphine oxide (TEPO).

Main Results:

• Chloroazaphosphatranes function as effective halogen bond donors.
• Anion binding affinities are comparable to conventional iodine-based XB receptors.
• The strength of the XB interaction is influenced by the basicity of the parent Verkade superbase.
• Protonated azaphosphatrane analogues showed no significant anion affinity.
• ³¹P NMR shifts confirmed the halogen bonding capabilities.

Conclusions:

• Chloroazaphosphatranes represent a new and versatile class of halogen bond donors.
• This discovery expands the range of available XB motifs beyond traditional C_Ar-I bonds.
• The modulable synthesis allows for tuning XB donor properties for specific applications.