An Isolable Triarylphosphine Radical Cation Electronically Stabilized by Through-Space Radical Delocalization

Area of Science:

• Organometallic Chemistry
• Radical Chemistry
• Materials Science

Background:

• Triarylphosphine radical cations are typically stabilized by sterically bulky substituents.
• Previous stabilization strategies limit the electronic properties and geometries of these radical cations.

Purpose of the Study:

• To synthesize and characterize a novel triarylphosphine radical cation stabilized by electronic effects.
• To explore a new stabilization mechanism for radical cations using "through-space" radical delocalization.
• To investigate the structural and electronic properties of the resulting radical cation.

Main Methods:

• Synthesis of the triarylphosphine radical cation [P(8-Br-C10H6)3][BArF24].
• Single-crystal X-ray diffraction for structural analysis.
• Electron Paramagnetic Resonance (EPR) spectroscopy for electronic characterization.
• Density Functional Theory (DFT) computations for mechanistic studies.

Main Results:

• Successful synthesis and characterization of a thermally stable triarylphosphine radical cation, [1][BArF24].
• Structural analysis revealed a tricapped tetrahedral geometry, distinct from previously known phosphine radical cations.
• EPR spectroscopy and DFT calculations confirmed spin delocalization over phosphorus and bromine atoms, forming a four-center, seven-electron bond.
• Demonstrated electronic stabilization via "through-space" radical delocalization, a novel approach.

Conclusions:

• A new strategy for stabilizing triarylphosphine radical cations through electronic "through-space" delocalization has been developed.
• The resulting radical cation exhibits unique structural and electronic properties, including a 4c-7e bond.
• This work opens new avenues for designing and synthesizing novel radical cations with tailored electronic properties.