A mechanistic study of the addition of alcohol to a five-membered ring silene via a photochemical reaction

作者：Su Ming Der^*

来源：Physical Chemistry Chemical Physics, 2016, 18(11): 8228-8234.

DOI：10.1039/c5cp06857f

The mechanism for the photochemical rearrangement of a cyclic divinyldisilane (1-Si) in its first excited state ((1)pi -> (1)pi*) is determined using the CAS/6-311G(d) and MP2-CAS/6-311++G(3df,3pd) levels of theory. The photoproduct, a cyclic silene, reacts with various alcohols to yield a mixture of cis-and trans-adducts. The two reaction pathways are denoted as the cis- addition path (path A) and the trans-addition path (path B). These model studies demonstrate that conical intersections play a crucial role in the photo-rearrangements of cyclic divinyldisilanes. The theoretical evidence also demonstrates that the addition of alcohol to a cyclic divinyldisilane follows the reaction path: cyclic divinyldisilane -> Franck-Condon region -> conical intersection -> photoproduct (cyclic silene) -> local intermediate (with alcohol) -> transition state -> cis- or trans-adduct. The theoretical studies demonstrate that the steric effects as well as the concentrations of CH3OH must have a dominant role in determining the yields of the final adducts by stereochemistry. The same mechanism for the carbon derivative (1-C) is also considered in this work. However, the theoretical results indicate that 1-C does not undergo a methanol addition reaction via the photochemical reaction pathway, since its energy of conical intersection (S1/S0-CI-C) is more than that of its FC (FC-C). The reason for these phenomena could be that the atomic radius of carbon is much smaller than that of silicon (77 and 117 pm, respectively). As a result, the conformation for 1-C is more sterically congested than that for 1-Si, along the 1,3-silyl-migration pathway.

• 出版日期2016-3-21