Isolable aryl-substituted silyl radicals: synthesis, characterization, and reactivity

Area of Science:

• Organosilicon Chemistry
• Radical Chemistry
• Inorganic Synthesis

Background:

• Silyl radicals are key intermediates in silicon chemistry.
• Aryl-substituted silyl radicals offer unique electronic and steric properties.
• Understanding their stability and reactivity is crucial for synthetic applications.

Purpose of the Study:

• To synthesize and characterize novel isolable aryl-substituted silyl radicals.
• To investigate the electronic structure and delocalization of the unpaired electron.
• To explore the solution behavior and reactivity of these silyl radicals.

Main Methods:

• Synthesis via reaction of iodosilanes with potassium graphite (KC8) in tetrahydrofuran (THF).
• Structural determination using X-ray crystallography.
• Electronic structure analysis via Electron Paramagnetic Resonance (EPR) spectroscopy.
• Reactivity and spectroscopic studies in solution.

Main Results:

• Four isolable aryl-substituted silyl radicals, (tBu2MeSi)2(Ar)Si(·), were successfully synthesized.
• X-ray crystallography confirmed a planar geometry around the silicon radical center for one derivative.
• EPR studies indicated no delocalization of the unpaired electron into the aryl substituent.
• Solution studies revealed an equilibrium between a phenyl-substituted silyl radical and its silene-type dimer.

Conclusions:

• Stable aryl-substituted silyl radicals can be synthesized and isolated.
• The unpaired electron is localized on the silicon atom, not delocalized into the aromatic ring.
• These silyl radicals can exist in equilibrium with silene dimers in solution, impacting their reactivity.