Sodium Alkyl(trimethylsilyl)amides: Substituent- and Solvent-dependent Solution Structures and Reactivities.
Qiulin You1, Yun Ma1, Ryan A Woltornist1
1Department of Chemistry and Chemical Biology Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, United States.
Journal of the American Chemical Society
|October 24, 2024
Summary
This study details the synthesis and structural analysis of sodium amide compounds, revealing solvent-dependent aggregation and reactivity. Crown ethers influence sodium amide behavior, with 15-crown-5 proving less effective than expected.
Area of Science:
- Organometallic Chemistry
- Solution-State Chemistry
- Spectroscopy and Computational Chemistry
Background:
- Sodium amide compounds are crucial in organic synthesis.
- Understanding their aggregation and solvation is key to controlling reactivity.
- Previous studies often assumed specific solvation behaviors.
Purpose of the Study:
- To synthesize and characterize novel sodium amide compounds, including isotopologues.
- To investigate the aggregation and solvation behavior of these amides in various solvents and with crown ethers.
- To elucidate the structure-reactivity relationships in aminolysis reactions mediated by these amides.
Main Methods:
- Synthesis of sodium isopropyl(trimethylsilyl)amide (NaPTA), sodium (1-phenylethyl)(trimethylsilyl)amide (NaPETA), and sodium tert-butyl(trimethylsilyl)amide (NaBTA).
- Solution structural studies using 29Si NMR spectroscopy, Method of Continuous Variations, and DFT computations.
- Quantitative kinetic studies of aminolysis reactions and crown ether complexation.
Main Results:
- NaPTA, NaPETA, and NaBTA were prepared, along with their 15N isotopologues.
- Dimer-monomer equilibria and solvation numbers were determined for various solvents and crown ethers, showing substituent and solvent dependence.
- Rate studies revealed a 47,000-fold variation in aminolysis rates, with dimer-based mechanisms in toluene and THF, and distinct behaviors for PMDTA- and diglyme-solvated species.
Conclusions:
- Solvation and aggregation significantly impact sodium amide reactivity.
- Crown ether efficacy varies, with 15-crown-5 being less effective than anticipated for accelerating sodium-mediated reactions.
- Detailed mechanistic insights into aminolysis reactions were gained, highlighting the importance of primary and secondary solvation shells.
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