Computation and Simulation Unit (Analytical & Environmental Science Division and Centralized Instrument Facility), CSIR-Central Salt & Marine Chemicals Research Institute, Bhavnagar, Gujarat, India, 364 002; Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India.
J Mol Graph Model. 2024 Dec;133:108866. doi: 10.1016/j.jmgm.2024.108866. Epub 2024 Sep 14.
This study presents a computational investigation into the mechanistic pathway and the linker units involved in forming the zwitterionic 1,2-anti-addition product of non-conjugated diacetylenes, di(propargyl)ether (DPE), di(prop-2yn-1yl)sulfane (DPS) and 1,6-Heptadiyne (HD) catalyzed by the inter-molecular phosphine/borane frustrated Lewis pairs (FLPs), i.e., PPhCH(CF)/B(CF) and P(o-tolyl)(P-tol)/B(CF). The potential energy surface (PES) calculations reveal that the anti-addition of P-CF to the internal C-atoms of acetylene units is energetically more favored than that of the addition of P-tol in DPE, DPS, and HD by ∼10.0, ∼9.2, and ∼6.0 kcal/mol, respectively. The calculations performed with DPE contain "-O-," linker unit exhibits superior reactivity than DPS and HD, which suggests the electronegativity of linkers plays a significant role and facilitates the addition of Lewis bases. The higher electronegativity of linker units enables the 1,2-addition reaction by lowering the free energy activation barriers, as observed in the DFT calculations. The Molecular Electrostatic Potential (MESP) study shows that the electrostatic interactions favor the addition of P-CF to the active acetylene positions (C5/C4/C4) of [B]-DPE/DPS/HD-π complexes than the P-tol. The Distortion/Interaction (D/I) analysis reveals that transition states involving P-CF (TS1, TS3, and TS5) exhibit more interaction energy (ΔE) and less distortion energies (ΔE) than that of the P-tol (TS2, TS4, and TS6). Further, the Energy Decomposition Analysis (EDA) also rationalizes the preferential approach of the electron-deficient Lewis base over the electron-rich one on the basis of the significant contribution of orbital interaction energies (ΔE) in the cases of P-CF; TS1, TS3, and TS5. This study suggests that the electronic effects of substrates and the FLPs are crucial to facilitate the desired products formed with non-conjugated terminal alkynes.
本研究通过分子间膦/硼受阻路易斯对（FLP），即 PPhCH(CF)/B(CF)和 P(o-tolyl)(P-tol)/B(CF)，对非共轭二炔、二丙炔醚（DPE）、二丙炔硫醚（DPS）和 1,6-庚二炔（HD）的 1,2-反式加成产物形成的机械途径和连接基单元进行了计算研究。势能面（PES）计算表明，P-CF 对内乙炔单元的 C 原子的反加成比 DPE、DPS 和 HD 中 P-tol 的加成更有利，分别约为 10.0、9.2 和 6.0 kcal/mol。用 DPE 进行的计算含有“-O-”连接基单元，比 DPS 和 HD 表现出更高的反应性，这表明连接基的电负性起着重要作用，并促进路易斯碱的加成。DFT 计算表明，连接基单元的较高电负性通过降低自由能活化势垒，使 1,2-加成反应更容易发生。分子静电势（MESP）研究表明，静电相互作用有利于 P-CF 加成到 [B]-DPE/DPS/HD-π 复合物中活性乙炔位置（C5/C4/C4），而不是 P-tol。扭曲/相互作用（D/I）分析表明，涉及 P-CF（TS1、TS3 和 TS5）的过渡态比涉及 P-tol（TS2、TS4 和 TS6）的过渡态具有更多的相互作用能（ΔE）和更少的扭曲能（ΔE）。此外，能量分解分析（EDA）也基于轨道相互作用能（ΔE）在 P-CF 情况下的显著贡献，从电子缺路易斯碱优先接近电子富路易斯碱的角度合理地解释了优先方法。本研究表明，底物和 FLP 的电子效应对于促进非共轭末端炔烃形成所需产物至关重要。
