|M.Sc Student||Yosi Kratish|
|Subject||Reactions of Si-H Bonds with Organosilyl-Zinc and|
|Department||Department of Chemistry||Supervisors||? 18? Apeloig Yitzhak|
|Dr. Bravo-Zhivotovs Dmitry|
|Full Thesis text|
We developed a new single step method for the synthesis of zinciosilanes. Reaction of Me3SiMe2SiH or of (Me3Si)3SiH with R2Zn (R=tBu, Et) or with (tBuMe2Si)2Zn is very sluggish yielding low yields of the corresponding silylzincs (Me3SiMe2Si)2Zn and ((Me3Si)3Si)2Zn, respectively. In contrast, in the presence of catalytic amounts of radical initiators, such as AIBN or tBu2Hg, the corresponding zinciosilanes are produced in good yields. (Me3Si)3SiH gives higher yields of the zinciosilanes than Me3SiMe2SiH.
Using this reaction our group synthesized the silylenoid-type compound [Cl(tBuMe2Si)2Si]2Zn, which upon lithiation yields the interesting zinc-bridged bis(silyllithium) [(thf)2Li(tBuMe2Si)2Si]2Zn (1), the first known compound with lithium and zinc bonded to the same Group 14 atom. 1 was successfully characterized and its structure was determined by X-ray crystallography. The novel tetrametallic bis(zinciosilyllithium) silane [(thf)3Li(tBuMe2Si)2SiZn]2Si(SiMe2tBu)2 was also synthesized and was characterized by X-ray crystallography.
In addition we investigated the cooperative chemistry of platinum(0) complexes with zinciosilanes and silylmercury compounds. Zinciosilanes and silylmercurials are poor precursors for thermal radical reactions because of their relatively high thermal stability. We now report that (R3Si)2M (M=Zn, Hg) easily generate R3Si radicals under mild conditions (60-80°C) in the presence of Pt(0) complexes. Thus, addition of (dmpe)Pt(PEt3)2 to bis(silyl)zinc or bis(silyl)mercury leads to the generation of the corresponding silyl radicals under mild conditions whose presence can be shown by trapping reactions. The activating effect of the Pt(0) complex is due to the easy reaction of (R3Si)2M with (dmpe)Pt(PEt3)2 to form the thermally unstable Pt(IV) octahedral complexes which we isolated and characterized by X-ray crystallography. Upon irradiation of the Pt(IV) complexes we observe by EPR spectroscopy a Pt(III) paramagnetic species which we believe, based on the spectrum and supporting calculations, to be a novel platinum centered radical.
Using the cooperative chemistry of Pt(0) complexes and bis(silyl)zinc or bis(silyl)mercury we succeeded to catalytically hydrogenate (using H2 gas) Si-Zn and Si-Hg bonds. In the case of ((Me3Si)3Si)2Zn the hydrogenation products are the corresponding silane (Me3Si)3SiH and the silicon zinc hydride (Me3Si)3SiZnH. The reaction is reversible and upon heating yields H2 and bis(silyl)zinc. Thus, this is a hydrogen “storage-release” process.