טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentKosa Monica
SubjectTheoretical Studies of Silicon and Metallasilicon
Compounds
DepartmentDepartment of Chemistry
Supervisor ? 18? Yitzhak Apeloig
Full Thesis textFull thesis text - English Version


Abstract

Theoretical investigations have played a very important role in the study of low-coordination silicon compounds and much of the fundamental knowledge on this class of compounds comes from quantum mechanical calculations. Yet, relatively little is known about their physical and chemical properties, especially the mechanisms which control their chemical reactions and many fundamental issues, such as structure-reactivity relationship.

The research topics studied in the thesis are:

(1) Trisilaallene and the relative stability of Si3H4 isomers.

Published in the Journal of Chemical Theory and Computation, 2006, 2, 956.

In this study, the unique highly bent structure of the yet unknown trisilaallene, H2Si=Si=SiH2, as well as its electronic properties were elucidated. The theoretical prediction was verified recently experimentally by a research group in Japan. 16 minima were located on the Si3H4 potential energy surface.

 (2) How to design linear allenic-type trisilaallenes and trigermaallenes.

Published in the Journal of the American Chemical Society, 2004, 126, 10544.

In this study we provide a theoretical prescription on how to design a linear trisilaallene and trigermaallene. We analyze the electronic and steric factors that control the geometry of trisilaallene, and predict that (R2B)2Si=Si=Si(BR2)2 should have a linear structure similar to that of H2C=C=CH2.

 (3) A theoretical study of ladder polysilanes.

Accepted for publication in Organometallics.

This study rationalizes and provides physical insight into the results of previous experimental studies on ladder polysilanes, which are promising candidates for electronic devices.

(4) Cope rearrangement of 1,5-hexasilahexadiene

Paper in preparation

In this study we investigate the silicon analogue of one of the most studied reactions in organic chemistry - the Cope rearrangement. It reveals unprecedented mechanistic scenario, both in organic and in organosilicon chemistry, where a biradical intermediate is significantly more stable thermodynamically than the starting 1,5-hexasilahexadiene.

 (5) Does the reactivity of silylene indicate its electronic ground state?

Paper in preparation.

We investigate the mechanisms of C-H bond insertion and of 1,4-addition to butadiene of singlet and triplet silylenes. It was believed that insertion of silylenes into a C-H bond occurs preferentially by triplet silylenes, so that if such reaction is observed it provides evidence for their existence. Our study, using DFT and ab initio methods shows that for both reactions the reactivity of singlet silylenes is much greater than that the corresponding triplet silylenes. This reopens the question regarding the existence of triplet state silylenes, and how to prove this experimentally.