The ditetrel bond between propellane derivatives and TH3F

Abstract

The binary and ternary ditetrel-bonding complexes of [1.1.1]propellane, [2.1.1]propellane and [2.2.1]propellane as Lewis bases with the Lewis acids TH₃F (T = C, Si, Ge, Sn, Pb) have been systematically investigated at the wB97XD/def2-TZVP level of theory. As the atomic number of T increases, the binding energies of the binary complexes (−E_b) reach up to 9 kcal mol⁻¹, with small −E_b values of around 2 kcal mol⁻¹ being predicted for the TC complexes, and larger values of 7–9 kcal mol⁻¹ being calculated for the heavier TSn(Pb) ones. The ring size influences binding energy; the −E_b values of 1.9–6.8 kcal mol⁻¹ for [1.1.1]-T are about 1–2 kcal mol⁻¹ smaller than those of [2.1.1]-T and [2.2.1]-T; [2.1.1]-T and [2.2.1]-T have comparable E_b values. Natural bond orbital (NBO) analysis was used for exploring the nature of the noncovalent interaction. The stability of the CH₃F complexes mainly stems from the σ(C1–C2) → σ*(C–F) interaction according to NBO. The antibonding interaction σ*(C1–C2) → σ*(T–F) contributes most to the stability of [1.1.1]-Si(Ge) and [2.1.1]-Ge(Sn,Pb). For the [2.2.1]-T complexes, the σ(T–H) → σ*(C1–C2) interaction contributes more to their stability. In addition, the bulkier the propellane ring, the greater the E⁽²⁾ estimated for the σ(T–H) → σ*(C1–C2) interaction. In the T2C ternary system, a positive cooperativity is found, while the Si, Ge, Sn and Pb triads exhibit negative cooperativity. Quantum theory of atoms in molecules (AIM) and energy decomposition analysis (sobEDA) also supply insight into the nature of the noncovalent interactions.