טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentSheberla Dennis
SubjectStable Silyl Radicals - Preparation and Properties
DepartmentDepartment of Chemistry
Supervisors ? 18? Yitzhak Apeloig
Dr. Dmitry Bravo-Zhivotovs
Full Thesis textFull thesis text - English Version


Abstract

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. Therefore, their direct structural characterization is very difficult. This problem can be solved by their kinetic stabilization, for example by using bulky polysilyl substituents. The synthesis, characterization and study of stable and persistent radicals are at the center of this research.

(a) Synthesis of stable radicals

In this work, we study in some detail a new reaction recently discovered by our group which leads to high yields of persistent and stable silyl radicals (equation 1). The effect of the size of the substituents )R. a ndR3Si), type of halogen (X) and solvent on the radicals. yields were studied. 

(1)


Was found that stable silyl radicals can be synthesized and isolated if

R3Si=t-Bu2MeSi, R.= Mes or t-Bu2MeSi. Either an hydridochlorosilane or a dichlorosilane precursor (X=Cl) and a non-solvated silyllithium (e.g., t-Bu2MeSiLi) in hydrocarbons are required for a one-step preparation of stable silyl radicals, according to equation 1.

The first stable α-carbon substituted silyl radical 1 was prepared by this reaction (equation 2). EPR spectroscopy and DFT calculations show that the spin density is not delocalized into the aryl ring. This is attributed to the fact that the aryl ring is perpendicular to the singly occupied 3p-orbital.

                   (2)


Persistent ferrocenyl substituted silyl radicals were observed in the reaction of [1]silaferrocenophane with tBu2MeSiLi (equation 3). In contrast to the aryl substituted silyl radicals, EPR spectroscopy and DFT calculations show that in the ferrocenyl silyl radical 10% of the spin density is transferred to the Fe atom.

improvement in the accuracy of predicted hfcc. sva lueswhich allows easier and more precise identification of the obtained radicals. 

(d) Reactions of phosphonyl radical with stable N-heterocyclic metallylenes

The first systematic study of phosphonyl radical (i-PrO)2(O)P(generated by photolysis of [(i-PrO)2(O)P]2Hg) adducts of N-heterocyclic stable carbenes, silylenes and germylenes 3 by EPR spectroscopy and DFT calculations is presented.

EPR spectroscopy and DFT calculations show that spin delocalization to the 5-membered heterocyclic ring in 3 follows the order: C << Si < Ge.