Insights into the Factors Controlling the Origin of Activation Barriers in the [2 + 2] Cycloaddition Reactions of Heavy Imine-like Molecules Featuring a Ge=Group 15 Double Bond with Heterocumulenes

• Published in: Molecules (Basel, Switzerland) Vol. 30; no. 9; p. 1905
• Main Authors: Zhang, Zheng-Feng, Su, Ming-Der
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 25.04.2025; MDPI
• Subjects: [2 + 2] cycloaddition; Analysis; Chemists; Density functionals; donor–acceptor interaction; electron-sharing; Energy; heavy imine; heterocumulene; Ligands; Molecules; heavy imine; [2 + 2] cycloaddition; heterocumulene; electron-sharing; donor–acceptor interaction
• DOI: 10.3390/molecules30091905
• ISSN: 1420-3049

The [2 + 2] cycloaddition reactions of the heterocumulene (N=C=N) with the heavy imine-like molecule Ge=G15-Rea (G15 = Group 15 element) were examined using density functional theory (M06-2X-D3/def2-TZVP). The theoretical findings indicate that the doubly bonded Ge=G15 moiety in Ge=G15-Rea (L1L2Ge=G15L3) is characterized by electron-sharing bonding between the triplet L1L2Ge and triplet G15–L3 fragments. All five Ge=G15-based heavy imine analogues readily undergo [2 + 2] cycloaddition reactions with N=C=N. Energy decomposition analysis (EDA–NOCV) suggests that the [2 + 2] cycloaddition reaction between Ge=G15-Rea and N=C=N involves a donor–acceptor (singlet–singlet) interaction instead of an electron-sharing (triplet–triplet) interaction. Frontier molecular orbital (FMO) theory and the energy decomposition analysis–natural orbitals for chemical valence (EDA–NOCV) findings emphasize that the key bonding interaction involves the occupied p-π orbital of Ge=G15-Rea and the vacant p-π* orbital of C=N=C. Based on the activation strain model results, the activation barrier of the [2 + 2] cycloaddition reaction is predominantly controlled by the deformation energies of Ge=G15-Rea and N=C=N.