Insights into the Reactivity of the Ring-Opening Reaction of Tetrahydrofuran by Intramolecular Group-13/P- and Al/Group-15-Based Frustrated Lewis Pairs

Abstract

A theoretical study concerning key factors affecting activation energies for ring-opening reactions of tetrahydrofuran (THF) by G13/P-based (G13 = B, Al, Ga, In, and Tl) and Al/G15-based (G15 = N, P, As, Sb, and Bi) frustrated Lewis pairs (FLPs) featuring the dimethylxanthene scaffold was performed using density functional theory. Our theoretical findings indicate that only dimethylxanthene backbone Al/ P-Rea (Rea = reactant) FLP-type molecules can be energetically favorable to undergo the ring-opening reaction with THF. Our theoretical evidence reveals that the shorter the separating distance between Lewis acidic (LA) and Lewis basic (LB) centers of the dimethylxanthene backbone FLP-type molecules, the greater the orbital overlaps between the FLP and THF and the lower the activation barrier for such a ring-opening reaction. Energy decomposition analysis (EDA) evidence suggests that the bonding interaction for such a ring-opening reaction is predominated by the donor−acceptor interaction (singlet−singlet interaction) compared to the electron-sharing interaction (triplet−triplet interaction). In addition, the natural orbitals for chemical valence (NOCV) evidence demonstrate that the bonding situations of such ring-opening reactions can be best described as FLP-to-THF forward bonding (the lone pair (G15) → the empty σ*(C−O)) and THF-to-FLP back bonding (the empty σ*(G13) ← filled pπ(O)). The EDA-NOCV observations show that the former plays a predominant role and the latter plays a minor role in such bonding conditions. The activation strain model reveals that the deformation energy of THF is the key factor in determining the activation energy of their ring-opening reactions. Comparing the geometrical structures of the transition states with their corresponding reactants, a linear relationship between them can be rationally explained by the Hammond postulate combined with the respective activation barriers calculated in this work.

Reactivity of the Intramolecular Vicinal Group-13/P- and B/Group-15-Based Frustrate Lewis Pairs with Sulfur Dioxide: Mechanistic Insight from DFT

“…Thus, we employed the aforementioned experimental results as a template to investigate the effect of the same group of chemical elements on the reactivity of 1,2cyclohexylene-linked intramolecular G13/G15-assisted (G13 = group 13 element and G15 = group 15 element) FLPs to capture SO 2 theoretically. We have employed theoretical research methods to comprehend the chemical reactions and intrinsic bonding properties of various intramolecular FLPtype molecules and small molecules, including H 2 , 64,65 CO 2 , 66,67 CS 2 , 68 tetrahydrofuran, 69 and ketones. 70 The objective of this study was to investigate the physical origin and bonding characteristics of the activation barriers that govern the binding reactions in the chemical interaction between a cyclohexane-linked molecule assisted by FLP and SO 2 .…”

“…Thus, we employed the aforementioned experimental results as a template to investigate the effect of the same group of chemical elements on the reactivity of 1,2-cyclohexylene-linked intramolecular G13/G15-assisted (G13 = group 13 element and G15 = group 15 element) FLPs to capture SO 2 theoretically. We have employed theoretical research methods to comprehend the chemical reactions and intrinsic bonding properties of various intramolecular FLP-type molecules and small molecules, including H 2 , , CO 2 , , CS 2 , tetrahydrofuran, and ketones …”