M.Sc Student | Molev Victoria |
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Subject | Silyl Radicals Preparation and Reactivity of Novel Conpounds with Si=C Bond |
Department | Department of Chemistry |
Supervisor | ? 18? Yitzhak Apeloig |
This thesis studied two main topics: silyl radicals and silenes.
Silyl radicals
We studied the homolytic cleavage of polysilanes R_{2}R’Si-SiR_{2}R’, with R = R’ = (Me_{3}Si)_{3}Si (3a), (Me_{3}SiMe_{2}Si)_{3}Si (4a), and (t-Bu_{2}HSi)(Me_{3}Si)_{2}Si (5a), and with R = t-Bu, R’ = Me_{3}Si (6a), and R = t-Bu_{ }R’ = Me_{3}SiMe_{2}Si (7a), All polysilanes were successfully crystallized and their structures were determined by X-ray crystallography. By following the rates of decay of the produced radicals of type R_{2}R’Si• we could determine their dimerization rates. The dimerization rate constants span over a range of six orders of magnitude. A Me_{3}SiMe_{2}Si substituent kinetically stabilizes the radical by a factor of 100 relative to a b-Me_{3}Si substituent. Two Me_{3}SiMe_{2}Si substituents kinetically stabilize the radical by a factor of 40 relative to two t-Bu groups. The bulky silyl substituents are responsible for the significant kinetic stabilization of (Me_{3}SiMe_{2}Si)_{3}Si• (4b) and Bu_{2}HSi(Me_{3}Si)_{2}Si• (5b) relative to (Me_{3}Si)_{3}Si• (3b). In two pairs of oligosilanes: [(Me_{3}Si)_{3}Si]_{2} vs. [(Me_{3}SiMe_{2}Si)_{3}Si]_{2} and [t-Bu_{2}(Me_{3}Si)Si]_{2} vs. [t-Bu_{2}(Me_{3}SiMe_{2}Si)Si]_{2} the b-silyl substituents do not cause elongation of the central Si-Si bond, being 2.41Å and 2.54Å respectively, but in [(t-BuMe_{2}Si)_{3}Si]_{2} it is calculated to be very long, 2.63Å, and the central Si-Si bond energy is estimated to be only 8 kcal/mol.Silenes
Three novel silenes, RR’Si=2-Ad (2-Ad = 2-adamantantyl), with RR’Si with R = R’ = (Me_{3}SiMe_{2}Si)_{2}Si (1) and R = R’ = (t-BuMe_{2}Si)_{2}Si (3), and with R = (t-BuMe_{2}Si), R’ = (Me_{3}SiMe_{2}Si)Si, (2) were synthesized using the silaolefination reaction (reaction of 2-adamantanone with the corresponding lithiosilane). The following order was found for the relative rate of elimination of the R_{3}SiOLi group as a function of R, from the intermediate silanolate: Me_{3}Si (120) > t-BuMe_{2}Si (6) > Me_{3}SiMe_{2}Si (1).