2005 Fiscal Year Final Research Report Summary
Solvent-free Catalytic Reaction : Ideal Green Reaction Using Silicon Catalysts with Weakly Coordinating Anion
| Project/Area Number |
15350062
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Synthetic chemistry
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| Research Institution | Osaka City University (2004-2005)
Osaka Prefecture University (2003) |
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Principal Investigator |
HATANAKA Yasuo Osaka City University, Graduate School of Engineering, Department of Applied Chemistry, Professor, 大学院工学研究科, 教授 (80344117)
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| Project Period (FY) |
2003 – 2005
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| Keywords | Solvent-free Reaction / Acid Catalysts / Silicon Lewis Acids / Aldol Reaction / Michael Reaction |
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| Research Abstract |
Chloride abstraction from pentacoordinate chlorosilanes by sodium or cesium salts of weakly coordinating anions such as B[3,5-(CF_3)_2CoH_3]_4- (TFPB) and carabadodecaborate gave tetracoordinate silyl cations having intramolecularly coordinating amide groups. X-ray structure analysis of these salts indicates the near-planar geometries at the silicon atoms reflecting sp^2 planarity and markedly long Si-O bond distances. The positive charge located in the silicon atoms would be stabilized by weak intramolecular O□Si coordination. The ^<29>Si NMR spectra also support silylium ion character of the silicon atoms. These salts exhibit effective catalytic activity as Lewis acid to promote the cross-aldol reaction between silyl enol ethers and less reactive carbonyl compounds such as ketones and aliphatic aldehydes, affording high yields of the corresponding aldol adducts. Furthermore, cationic silicon species, which were generated in situ by protodesilylation of silicon enolates with [H(OEt_2)_2]+[B(C_6F_5)_4]-, exhibited high catalytic activity as a Lewis acid in the aldol reaction of ketones with silicon enolates under the solvent-free conditions. Thus, sterically hindered less reactive ketones smoothly reacted with silicon enolates in the presence of cationic silicon catalyst, giving aldol products in high yields. Silyl cations, which were prepared from 5-coordinate chlorosilanes, showed high catalytic activity in promoting the Michael addition of silicon enolates to α,β-unsaturated carbonyl compounds or nitriles.
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