Probing the origins of activation barriers in nitrous oxide capture reactions by analyzing Lewis acid-base pairs with dimethylxanthene-linked group-13 (P) and group-15 (B) elements

• Published in: New journal of chemistry Vol. 48; no. 26; pp. 11741 - 11756
• Main Authors: Zhang, Zheng-Feng, Su, Ming-Der
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 01.07.2024
• Subjects: Antimony; Bismuth; Bonding strength; Density functional theory; Greenhouse gases; Lewis acid; Lewis base; Molecular orbitals; Nitrogen oxides; Nitrous oxide
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/d4nj02176b

Nitrogen oxides, including nitrous oxide (N 2 O), are undoubtedly classified as greenhouse gases. In this research, we conducted a theoretical investigation into the N 2 O capturing reactions using frustrated Lewis pair (FLP)-assisted molecules based on the intramolecular dimethylxanthene backbone G13/P (G13 = B, Al, Ga, In, and Tl) and B/G15 (G15 = N, P, As, Sb, and Bi). Density functional theory (DFT) along with frontier molecular orbital (FMO) theory, activation strain model (ASM), and energy decomposition analysis-the natural orbitals for the chemical valence (EDA-NOCV) were employed to analyze the molecular reaction barriers and chemical reactivity. From the DFT calculations, it is evident that only B/P-Rea , among the FLP-type molecules utilizing G13/P and B/G15 as Lewis base/Lewis acid sites, exhibits the ability to capture N 2 O in a reversible reaction. The EDA examinations suggest that the bonding nature between the G13/G15-FLP and N 2 O in the G13/G15-TS structure can be elucidated by the donor-acceptor interaction (singlet-singlet bonding) model, instead of the electron-sharing interaction (triplet-triplet bonding) model. FMO and NOCV analyses reveal that the reaction between N 2 O and the G13/G15-based FLP exhibits two distinct bonding properties: one is the forward bonding, the lone pair of G15 → the p-π* orbital of the N-terminus of N 2 O, which is a significantly strong FLP-to-N 2 O interaction. The other is the back-bonding, the empty orbital of G13 ← the filled p-π orbital of the O atom of N 2 O, which is a relatively weak N 2 O-to-FLP interaction. In basic terms, Lewis base interacting with N 2 O is more pivotal than the interaction of Lewis acid with N 2 O. The ASM analytical findings indicate that the deformation energy of the small N 2 O molecule significantly influences the reaction barrier of the N 2 O capture reaction by the intramolecular dimethylxanthene-linked G13/G15-FLPs. The theoretical evidence for N 2 O capture by intramolecular dimethylxanthene-linked G13/G15-based FLPs shows that the relationships between geometrical structures and energetic values are in accordance with the Hammond postulate. The catching reaction with N 2 O can be kinetically and thermodynamically facilitated exclusively by the B/P-based FLP within the intramolecular dimethylxanthene-linked group-13/P and B/group-15 based FLP-type molecules.