Lewis Base Activation of Lewis Acid: A Detailed Bond Analysis

The effect of a Lewis
base (LB) on the nucleophilic attack on chalcogeniranium
(chalcogen = sulfur and selenium) cations, the so-called LB activation
of a Lewis acid, has been studied coupling natural orbital for chemical
valence decomposition of the orbital interaction energy with charge
displacement analysis. This methodology provides a detailed and accurate
description of all the interactions (LB···chalcogen,
chalcogen···olefin and olefin···ammonia)
present in the system and leads to a deeper understanding of how they
influence each other at all stages of the reaction: reactant complex,
transition state, and product complex. In particular, the bond between
the chalcogen and the olefin has been decomposed in terms of σ
donation/π back-donation and the bond components quantified.
This allowed determination of a linear relationship between the activation
barrier of the nucleophilic attack and the net amount of charge donated
by the olefin to the chalcogen.

本研究针对路易斯碱（Lewis base, LB）对硫杂环丙鎓与硒杂环丙鎓阳离子的亲核进攻过程产生的影响，即所谓的路易斯酸（Lewis acid）的LB活化效应，采用轨道相互作用能的化学价自然轨道分解（natural orbital for chemical valence decomposition）与电荷位移分析相结合的方法展开探究。该方法可对体系中存在的LB···硫族元素、硫族元素···烯烃以及烯烃···氨三类相互作用提供详尽且精准的描述，并有助于深入理解各相互作用在反应全阶段——包括反应物复合物、过渡态与产物复合物——间的相互影响机制。特别地，本研究将硫族元素与烯烃之间的化学键按照σ给体/π反馈作用进行分解，并量化了各键组分的贡献。据此明确了亲核进攻的活化能垒与烯烃向硫族元素转移的净电荷之间存在线性相关关系。