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

Abstract

The mechanism for the photochemical rearrangement of a cyclic divinyldisilane (1-Si) in its first excited state ((1)π → (1)π*) 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.

A model study on the photodecarbonyl reaction of (η5-C5H5)M(CO)2 (M = Co, Rh, Ir)

“…On the basis of the above information, our computations therefore suggest that once the Rh-S 0 -Rea complex has absorbed the light, it will jump from the singlet ground state to the more highly excited singlet state (Rh-S 4 -FC) and then relaxes to the lowest excited singlet state (Rh-S 1 -FC). Accordingly, in this work we use the conical intersection (CI) concept, [57][58][59][60][61][62][63][64][65][66][67] which considers the crossing between states of the same multiplicity (mostly commonly singlet-singlet), to explore the mechanism of the photochemical activation reactions of the Rh-S 0 -Rea system.…”

“…Subsequently, this species relaxes to arrive at a Rh-S 1 /S 0 -CI point, from which the photoexcited rhodium complex decays nonradiatively to the singlet ground state. [57][58][59][60][61][62][63][64][65][66][67] Our MP2-CAS ndings suggest that Rh-S 1 /S 0 -CI is about 22 kcal mol À1 lower in energy than Rh-S 1 -FC. In Fig.…”

“…Considering the dynamic electron correlations, the multireference Møller-Plesset (MP2-CAS) algorithm, [55][56][57][58][59][60][61][62][63][64][65] contained in the GAUSSIAN 09 program package, 43 is carried out. As a result, the relative energies mentioned in this paper are those calculated at the MP2-CAS/Def2-TZVPD level, using the CAS/Def2-SVPD geometry.…”

Quantum Chemistry Calculations on the Mechanism of Isoquinoline Ring-Opening and Denitrogenation in Supercritical Water

“…Quantum chemistry calculations have been used to predict reaction mechanisms at the molecular level. Here, a quantum chemistry study was used to reveal the most reasonable and believable structures and reaction pathway on the potential energy surface (PES). ,,− This paper proposes six potential pathways and four steps for isoquinoline ring-opening and denitrogenation in the SCW system. Detailed reaction paths were established using the intrinsic reaction coordinate method, each stationary point energy on each reaction path was calculated, and finally the best paths were selected via comparison of the energies and configurations.…”