Pentacoordinate silicon complexes with dynamic motion resembling a pendulum on the S(N)2 reaction pathway

Area of Science:

• Organosilicon Chemistry
• Organic Synthesis
• Reaction Mechanisms

Background:

• Glutarimide derivatives offer unique coordination sites for silicon.
• Intramolecular pentacoordination at silicon is a key structural feature.
• Understanding substituent effects is crucial for reaction pathway elucidation.

Purpose of the Study:

• To synthesize and characterize glutarimide derivatives with specific silicon coordination.
• To investigate the influence of leaving group substituents on Si-O bond exchange.
• To model nucleophilic substitution at silicon using these derivatives.

Main Methods:

• Synthesis and characterization of glutarimide derivatives.
• Variable-temperature (29)Si NMR spectroscopy to study Si-O bond exchange.
• X-ray crystallography to determine molecular structures.
• Computational methods to determine activation parameters.

Main Results:

• Substituent effects (F, Cl, OTf, Br, I) on Si-O bond exchange were quantified.
• Activation parameters correlate with Si-O bond strength and leaving group ability.
• NMR and crystallographic data reveal a tetrahedral-to-pentacoordinate-to-tetrahedral transformation.
• A continuum of structures along the S(N)2 reaction profile was observed.

Conclusions:

• The glutarimide system provides a valuable model for nucleophilic substitution at silicon.
• Leaving group properties significantly impact the dynamics of Si-O bond exchange.
• The observed reaction pathway offers insights into silicon reaction mechanisms.