טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentKaushansky Alexander
SubjectFunctional Silyl Radicals and Attempts toward Silanones
DepartmentDepartment of Chemistry
Supervisors ? 18? Yitzhak Apeloig
Dr. Dmitry Bravo-Zhivotovs
Full Thesis textFull thesis text - English Version


Abstract

This thesis is divided into two main parts: (1) Synthesis and characterization of novel functional silyl radicals; (2) Synthesis of a coordinated silanone.

(1) Synthesis and characterization of novel functional silyl radicals

Silyl radicals are of significant importance in diverse areas, such as organic synthesis, silicon chemistry and material sciences. Silyl radicals are usually highly reactive short-lived species and therefore their direct characterization is difficult. It is therefore desirable to stabilize them kinetically by using bulky substituents. The synthesis and study of persistent and stable silyl radicals is at the center of this part of the research. The novel stable (tBu3Si)(tBu2MeSi)2Si radical (1) is prepared (70 % yield) by a reaction of di-chlorosilane (tBu3Si)Cl2SiH with tBu2MeSiLi.  1 was studied by EPR spectroscopy and its X-ray molecular structure was determined, showing that it has a planar geometry around the central silicon atom.

Reactions of aminochlorosilanes (Me2N)Cl2SiH, ((Me3Si)2N)Cl2SiH and (Me2N)(tBu3Si)Cl2SiH with tBu2MeSiLi yield several novel persistent (up to several weeks) and stable silyl radicals carrying amino substituents: (tBu2MeSi)2(Me2N)Si, (tBu2MeSi)2((Me3Si)2N)Si, (tBu3Si)(tBu2MeSi)(Me2N)Si. The EPR spectra of these radicals were recorded and electron spin delocalization was analyzed.

(2) Synthesis of a coordinated silanone

No stable genuine silanones,R2Si=O, are known and currently silanone chemistry is limited to transient intermediates and to compounds having a SiO moiety with a partial double bond character stabilized by donors and acceptors. Bromosilanolate  Br(R3Si)2SiOLi (2) was synthesized in reaction of bromosilanol Br(R3Si)2SiOH with tBu2MeSiLi in hexane. 2 crystallize as a trimer. Analysis of the X-ray molecular structure of 2 and in particular the short Si-O distance of 1.58 Å and comparison to known silanone complexes leads us to conclude that 2 is best described as a silanone complex coordinated to  LiBr, where Br- serves as the donor interacting with the electrophilic silicon atom and Li serves as the acceptor interacting with the negatively charged oxygen atom.

Theoretical calculations predict that elimination of MX from Br(R3Si)2SiOM and Cl(R3Si)2SiOM (M = Li, Na, K) requires (DG) 5-16 kcal/mol and therefore these compounds can serve as potential precursors for the generation of silanones. Studies along these lines will continue.