Silyl Groups Are Strong Dispersion Energy Donors

Area of Science:

• Computational Chemistry
• Organic Chemistry
• Supramolecular Chemistry

Background:

• Silyl groups are frequently utilized as protecting groups in organic synthesis.
• Their role beyond mere protection, specifically their noncovalent interactions, is less understood.
• Cyclooctatetraene (COT)-based molecular systems offer a platform to study these interactions due to conformational flexibility.

Purpose of the Study:

• To experimentally and computationally investigate the noncovalent interactions between silyl groups.
• To quantify the contribution of these interactions to the stability of different molecular conformations.
• To assess the influence of silyl group size and substitution on noncovalent interactions.

Main Methods:

• Synthesis and characterization of cyclooctatetraene (COT)-based molecular balance with varying silyl group substitutions.
• Determination of thermodynamic equilibria using nuclear magnetic resonance (NMR) spectroscopy.
• Computational analysis using symmetry-adapted perturbation theory (SAPT) at the sSAPT0/aug-cc-pVDZ level.

Main Results:

• A preference for the folded 1,6-disubstituted COT isomer was observed for most silyl groups.
• London dispersion interactions were identified as the primary stabilizing force for the folded isomer.
• The tris(trimethylsilyl)silyl "supersilyl" group showed different behavior due to its extreme bulk.

Conclusions:

• Silyl groups are significant contributors to dispersion energy, impacting molecular conformation.
• These noncovalent interactions should be considered during the planning of synthetic strategies.
• The findings highlight the active role of silyl groups beyond their function as protecting groups.