|Ph.D Student||Molev Victoria|
|Subject||Reduction Processes of R2E=CR'2 Systems; E=Si,Ge,Sn|
|Department||Department of Chemistry||Supervisors||? 18? Yitzhak Apeloig|
|Dr. Dmitry Bravo-Zhivotovs|
This thesis studies silenes, compounds with a Si=C double bond, and their reduction. In addition, efforts were made to synthesize compounds with E=C double bonds (E = Ge, Sn) via a Peterson-type olefination. In a separate project, novel bis-silylketones (R3Si)2C=O were synthesized and their reduction was studied.
A new general method for the synthesis of (R3Si)3ELi, E = Si, Ge, Sn, reagents in 80-95% yield was developed. The method involves the reaction of Cl4E with R3SiLi in hexane followed by THF addition. Two new and four known R3SiLi reagents were prepared using this method and were all characterized by X-ray crystallography. These reagents were reacted with 2-adamantanone. A variety of reaction routes were observed depending on the size of the silyl substituents and on E. A stable silene, (t-BuMe2Si)2Si=2-Ad, was obtained only in the reaction of (t-BuMe2Si)3SiLi?2THF with 2-adamantanone, while reaction of (t-BuMe2Si)3GeLi with 2-adamantanone yields a novel b-H-substituted digermyllithium. Reaction of the larger ((t-Bu)2MeSi)3ELi?nTHF (E = Si, Ge, Sn) with 2-adamantanone yielded only the corresponding stable radicals (R3Si)3E?.
Two new methodologies for the synthesis of R2R’SiLi (R≠R’) using Me2N and MeO protecting groups were developed. Using a Me2N protecting group two new reagents (t-BuMe2Si)2((t-Bu)2MeSi)SiLi?2THF and (t-BuMe2Si)((t-Bu)2MeSi)2SiLi?2THF were prepared in 75-80% yield and were reacted with 2-adamantanone, both yielding the same new stable silene, (t-BuMe2Si)((t-Bu)2MeSi)Si=2-Ad, (1).
Reaction of (Me3Si)2Si=Ad, 2 (generated in-situ from its dimer) with a Na/K alloy at 60oC yields a mixture of oligomers. The repeating unit of the oligomers, [Si-Si-C], is identical to the repeating unit of the polycarbosilane, obtained in the thermolysis of 2 at 120-150oC. Isolation and characterization of these oligomers strongly supports the structure proposed for the polycarbosilane. Reaction of 1 with (t-Bu)2MeSiNa in hexane/THF led to the first observation of a silene anion-radical by EPR spectroscopy. Analysis of the EPR spectrum shows that 1-? is a silyl-substituted carbon-centered radical with the Na bonded to the silicon in the b-position to the radical center.
Reaction of the two new bis-silyl ketones prepared in this study with R3SiLi yields two new anion-radical dimers, which were isolated and characterized by EPR spectroscopy and X-ray crystallography. These are the first isolated anion-radicals of acylsilanes which are not stabilized by aromatic substituents. The calculated spin density in these anion-radicals is located 70% on the carbonyl carbon and 20% on the oxygen atom.