Persilylated phosphoranyl radicals: the first persistent noncyclic phosphoranyl radicals

Area of Science:

• Organometallic Chemistry
• Radical Chemistry
• Spectroscopy

Background:

• Phosphoranyl radicals are key intermediates in various chemical reactions.
• Previous studies have focused on cyclic phosphoranyl radicals.
• The synthesis and characterization of persistent noncyclic phosphoranyl radicals remain underexplored.

Purpose of the Study:

• To synthesize and characterize persistent noncyclic phosphoranyl radicals.
• To investigate the decay mechanisms of these novel radicals.
• To determine the influence of steric bulk on radical stability and reactivity.

Main Methods:

• UV-photolysis of bis(trialkylsilyl) peroxides and tris(trialkylsilyl) phosphites.
• Electron Paramagnetic Resonance (EPR) spectroscopy for radical detection and characterization.
• Kinetic analysis of radical decay using pseudo-first-order conditions.

Main Results:

• Persistent noncyclic phosphoranyl radicals were successfully prepared and observed via EPR.
• EPR parameters confirmed a trigonal-bipyramidal structure with the unpaired electron in an equatorial site.
• Radical decay occurred through S(H)2 homolytic substitution and alpha-scission, both decelerated by increased steric bulk of alkyl groups.

Conclusions:

• The study reports the first successful synthesis and EPR observation of persistent noncyclic phosphoranyl radicals.
• The decay mechanisms are sensitive to steric effects, with bulkier alkyl groups leading to slower reaction rates.
• These findings provide valuable insights into the structure, stability, and reactivity of phosphoranyl radicals.