Master of Science
Baines, Kim M.
The stereochemistry of the addition of HX (X = OH, NH2, Cl, Br, I) to the stereoisomers of 1,2-di-tert-butyl-1,2-bis(2,4,6-triisopropylphenyl)disilene (3E or 3Z) was found to be 100 % stereospecific resulting in the syn-isomer, except for HCl which resulted in the anti-isomer. Kinetic studies on the reaction of tetramesityldisilene (1) with isopropyl amine (iPrNH2) revealed that the order in both amine and disilene was 1, indicating that the proton is transferred in the rate determining step with KIE of 3.06, and that the addition is nucleophilic. Computational studies of the mechanism revealed nucleophilic addition gives the anti-oriented donor adduct which is independent of the substituents on the disilene. Inversion or rotation in the anti-donor adduct relies on the twist of the disilene. Depending on the substituents on the disilene, the rate-determining step might be inversion or proton transfer. The hydrolysis of the synthesized adducts occurs with inversion of stereochemistry.
Summary for Lay Audience
Silicon, with 27.7 % abundance, is the second most abundant element on earth after oxygen and thus, it is of interest to investigate applications of silicon-based chemicals. Just like alkenes, molecules with a carbon-carbon double bond (C=C), disilenes, with a silicon-silicon double bond (Si=Si), can be synthesized. These species have been shown to be capable of reacting with and activating important small molecules such as water and ammonia. However, the understanding of the mechanism of these disilene reactions is shallow, although such an understanding is critical for the development of applications of disilene chemistry. Thus, in this work, the spatial characteristics of the addition of HX (X = OH, NH2, Cl, Br, I) to 1,2-di-tert-butyl-1,2-bis(2,4,6-triisopropylphenyl)disilene (3E or 3Z), were investigated. The results of these studies will be used along with mechanistic studies and computational studies, done in collaboration, to refine the understanding of the mechanisms of these fundamental reactions.
The experimental studies of the addition of HX to 3E or 3Z revealed that the reactions formed a single and unique product for each disilene. The reaction conditions, such as solvent, concentration of reagent, and temperature, had no influence on the outcome of the reaction. The ability to generate exclusively one product in HX additions is very advantageous. Thus, understanding the factors affecting the mechanism will allow for control of the reactivity of disilenes in future applications.
Sharif, Zahra M., "Insight into the Stereochemistry and Mechanism of σ-Addition to Disilenes" (2022). Electronic Thesis and Dissertation Repository. 9020.