From Sn(II) to Sn(IV): Enhancing Lewis Acidity Via Oxidation

Area of Science:

• Organometallic Chemistry
• Lewis Acidity Studies
• Tin Chemistry

Background:

• Lewis acidity is a fundamental chemical property influencing reactivity.
• Understanding Lewis acidity trends in tin compounds is crucial for catalysis.
• The electronic and steric effects of ligands significantly impact metal center acidity.

Purpose of the Study:

• To demonstrate the increased Lewis acidity from Sn(II) to Sn(IV) oxidation states.
• To investigate the effect of ligand substitution on tin's Lewis acidity.
• To provide experimental and computational evidence for enhanced Lewis acidity.

Main Methods:

• Synthesis and characterization of tin complexes: Tp^Me2SnOTf, Tp^Me2SnF(OTf)₂, and Tp^Me2Sn(OTf)₃.
• ¹¹⁹Sn NMR spectroscopy to probe electronic environments.
• Modified Gutmann-Beckett titration to quantify Lewis acidity.
• Computational analysis (e.g., DFT) to model electronic structure.
• Catalytic phosphine oxide deoxygenation as a reactivity probe.

Main Results:

• Oxidation from Sn(II) to Sn(IV) demonstrably increases Lewis acidity.
• Substitution of fluoride by triflate in Tp^Me2SnF(OTf)₂ to form Tp^Me2Sn(OTf)₃ further enhances Lewis acidity.
• Multiple methods, including spectroscopy, titration, computation, and catalysis, corroborate the observed acidity trends.

Conclusions:

• Tin(IV) species exhibit significantly higher Lewis acidity compared to their Sn(II) counterparts.
• Triflate ligands are effective in further increasing the Lewis acidity of Sn(IV) complexes.
• The synthesized tin complexes serve as valuable Lewis acids for catalytic applications.