Department of Applied Chemistry, National Chiayi University, Chiayi 60004, Taiwan.
Department of Medicinal and Applied Chemistry, Kaohsiung Medical University, Kaohsiung 80708, Taiwan.
Phys Chem Chem Phys. 2023 Mar 8;25(10):7423-7435. doi: 10.1039/d2cp05135d.
The element effects of Lewis acid (LA) and Lewis base (LB) on the potential energy surfaces of [2+5] cycloaddition reactions of norbornene-based G14/P-based (G14 = group 14 element) and Si/G15-based (G15 = group 14 element) frustrated Lewis pair (FLP)-type molecules with benzaldehyde were theoretically examined density functional theory and several sophisticated methods. The theoretical findings indicated that among the above nine norbornene-linked G14/G15-based FLPs, only the Si/N-Rea, Si/P-Rea, and Si/As-Rea FLP-assisted compounds can readily undergo cycloaddition reactions with doubly bonded organic systems from kinetic and thermodynamic viewpoints. The energy decomposition analysis showed that the bonding interactions between the norbornene-based G14/G15-FLPs and benzaldehyde are better described in terms of the singlet-singlet model (donor-acceptor model) rather than the triplet-triplet model (electron-sharing model). In particular, natural orbitals for chemical valence findings revealed that the forward bonding is the lone pair (G15) → p-π*(C) interaction, which is a significantly strong FLP-to-benzaldehyde interaction. However, the back-bonding is the p-π*(G14) ← lone-pair orbital(O) interaction, which is a weak benzaldehyde-to-FLP interaction. The analyses based on the activation strain model showed that the larger the atomic radius of either the G14(LA) or the G15(LB) atom, the greater the G14⋯G15 separation distance in the norbornene-based G14/G15-FLP molecule, the smaller the orbital overlaps between G14/G15-FLP and Ph(H)CO, and the higher the activation barrier during its cycloaddition reaction with benzaldehyde.
采用密度泛函理论和几种精细方法，从理论上考察了路易斯酸（LA）和路易斯碱（LB）对基于降冰片烯的 G14/P 基（G14 = 第 14 族元素）和 Si/G15 基（G15 = 第 14 族元素）受阻路易斯对（FLP）型分子与苯甲醛的[2+5]环加成反应势能面的元素效应。理论研究结果表明，在所研究的九种基于降冰片烯的 G14/G15-FLP 中，只有 Si/N-Rea、Si/P-Rea 和 Si/As-Rea FLP 辅助化合物从动力学和热力学的角度来看，容易与双键有机体系发生环加成反应。能量分解分析表明，基于降冰片烯的 G14/G15-FLP 与苯甲醛之间的成键相互作用可以更好地用单重态-单重态模型（给体-受体模型）而不是三重态-三重态模型（电子共享模型）来描述。特别是自然轨道化学价键分析结果表明，正向成键是孤对电子（G15）→p-π*（C）相互作用，这是一种很强的 FLP-苯甲醛相互作用。然而，反向成键是 p-π*（G14）←孤对轨道（O）相互作用，这是一种弱的苯甲醛-FLP 相互作用。基于活化应变模型的分析表明，G14（LA）或 G15（LB）原子的原子半径越大，基于降冰片烯的 G14/G15-FLP 分子中 G14⋯G15 分离距离越大，G14/G15-FLP 与 Ph（H）C≡O 的轨道重叠越小，与苯甲醛环加成反应的活化能垒越高。
