Insight into the Stereochemistry and Mechanism of σ-Addition to Disilenes

Zahra M. Sharif, The University of Western Ontario

Abstract

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.