טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentYuzefovich Michael
SubjectBranched Polysilyl Radicals and Polysilanes -
Generation, Structure and Reaction Mechanisms
DepartmentDepartment of Chemistry
Supervisor ? 18? Yitzhak Apeloig


Abstract

The main goal of this thesis is to broaden our mechanistic and structural knowledge and understanding of silyl radicals, in particular of branched polysilyl radicals, and to develop their synthetic potential and applications, with special emphasis on  polysilanes - a novel group of important materials. We have concentrated our efforts on the development of synthetic methods for the preparation of novel branched "hypersilyl" radicals, i.e., silyl radicals containing several silicon atoms, such as (Me3Si)3Si, and to study their structures, their spectroscopic and electronic properties and their reactions. The following are the main results: (1) The novel star polysilyl radical (Me3SiMe2Si)3SiŸ was produced from a variety of precursors by both photolytic and thermal reactions and its EPR spectrum was recorded and analysed. (2) (Me3SiMe2Si)3SiŸ is kinetically significantly more stable than the parent (Me3Si)3SiŸ radical. Density-functional quantum mechanical calculations show that the b-silyl groups do not stabilize (Me3SiMe2Si)3SiŸ  thermodynamically relative to (Me3Si)3SiŸ. (3) Photolysis of [(Me3SiMe2Si)3Si]2 leads to (Me3SiMe2Si)4Si while its thermolysis leads to an isomer, (Me3SiMe2Si)3Si-SiMe2-Si(SiMe2SiMe3)2SiMe3, which is thermodynamically more stable. (4) We synthesized the first chain-type, silyltrimercurial compound, [t-Bu-Hg-(i-Pr3Si)2Si]2Hg. (5) Lithiation of [t-Bu-Hg-(i-Pr3Si)2Si]2Hg leads to the preparation of the first known dilithium silylmercurial reagent [Li(i-Pr3Si)2Si]2Hg. (6) By photolysis of [t-Bu-Hg-(i-Pr3Si)2Si]2Hg we generated and observed the EPR spectrum of the first two functionalized silyl radicals: H(i-Pr3Si)2SiŸ  having an a-hydrogen and (i-Pr3Si)2LiSiŸ  having an a-Li substituent. (7) We also prepared the first monocyclic silyl mercury compound, [(Me3Si)2Si(SiMe2)2]2Hg2 and the first bicyclic silyl mercury compound, [(MeSi)Si(SiMe2)3]2Hg3. These compounds are potential precursors to vicinal polysilyl radicals, 1,3-sila biradical and possibly also to sila triradicals.