|M.Sc Student||Molev Gregory|
|Subject||Reactions of Silyl Lithium Compounds with Silyl|
|Department||Department of Chemistry||Supervisor||? 18? Yitzhak Apeloig|
Several reactions of silyllithium compounds with silyl halides were studied. Our main purpose was the synthesis of new compounds, but the study lead also to important mechanistic insights. We present strong evidence that the discussed reactions proceed via a Single Electron Transfer (SET) mechanism.
The following major results were obtained:
(a) Several (R3Si)3SiLi - type compounds were synthesized in good yield by the halogen - metal exchange reaction. This is the first successful halogen - metal exchange reaction reported for (R3Si)3SiX-type compounds. With dibromosilanes the halogen - metal exchange reaction was used for the synthesis of disilenes and with a fluorobromoslane for the synthesis of the first stable fluoro-lithium silylenoid (R3Si)2SiFLi•3THF (R3Si = t-Bu2MeSi) 1 with unique structure as determined by X-ray spectroscopy. Reactions of 1 with several nucleophiles and electrophiles, yielding the corresponding substitution products, were studied.
(b) Non-solvated gem-dilithiosilanes (R3Si)2SiLi2, 2 (R3Si = i-Pr3Si) and 3 (R3Si = t-BuMe2Si) were synthesized by lithiation of the corresponding silyl mercurials. 2 has a unique structure, in which (R3Si)2SiLi2 is aggregated with t-BuLi, as determined by X-ray spectroscopy. Reactions of dilithiosilane 3 with several halosilanes and dihalosilanes were studied.
(c) Reaction of bulky dichlorosilanes with t-Bu2MeSiLi yields stable long-lived silyl radicals of the type (t-Bu2MeSi)2(R3Si)Si•. Radical 4 (R3Si = t-Bu2MeSi) (previously known) and the novel silyl radicals 5 (R3Si = (Me3Si)3Si) and 6 (R3Si = (t-Bu2MeSi)2HSi) were synthesized in high yield using this method. The structures of 4, 5 and 6 were confirmed by their reactions. Radical 6 was isolated as orange crystals, and its molecular structure was determined by X-ray spectroscopy. Radical 6 was found to exhibit interesting photolytic activity.