Hyperconjugation Controls One-Bond Carbon-Tin Coupling Constants in Anomeric Tin Compounds: A Theoretical Study

Area of Science:

• Organometallic Chemistry
• Computational Chemistry
• Organic Chemistry

Background:

• One-bond ¹¹⁹Sn-¹³C couplings in organostannanes are sensitive to stereoelectronic effects.
• Quantitative understanding of hyperconjugation's impact on ¹J(Sn-C), especially at anomeric centers, is limited.

Purpose of the Study:

• To establish quantitative rules linking hyperconjugation to ¹J(Sn-C) in cyclic organostannanes.
• To develop a mechanistic framework for predicting tin-carbon coupling constants and assigning anomeric configuration.

Main Methods:

• Density Functional Theory (DFT) calculations were performed on 77 cyclic scaffolds.
• Natural Bond Orbital (NBO) analysis was used to quantify antiperiplanar donor → σ*_(C-_Sn) delocalization.
• Calculated couplings were validated against experimental ¹J(C-H) data and known trends.

Main Results:

• ¹J(Sn-C) magnitude directly correlates with the extent of hyperconjugative donation.
• Equatorial isomers generally exhibit larger ¹J(Sn-C) than axial isomers (β > α hierarchy), except in sulfur-containing rings.
• An empirical scaling factor improves agreement between calculated and experimental coupling constants.

Conclusions:

• A practical, mechanistic framework for predicting ¹J(Sn-C) and assigning anomeric configuration in organotin compounds has been developed.
• The study provides insights into stereoelectronic effects governing tin-carbon couplings.
• The findings are applicable to various cyclic organostannanes, including those with sulfur heteroatoms.