The Ditetrel Bond between Propellane Derivatives and TH3F

Abstract

Binary and ternary ditetrel bonding complexes of [1.1.1]propellane, [2.1.1]propellane and [2.2.1]propellane as Lewis base interacting with Lewis acid TH₃F (T=C, Si, Ge, Sn, Pb) have been systematically investigated at the wB97XD/def2-TZVP level. With atomic number of T increasing, the binding energies of binary (E_b) within some 9 kcal mol^-1 increase consequently, in which the small E_b values of some 2 kcal mol^-1 are predicted for T=C complexes, and the great ones of about 7 ~ 9 kcal mol-1 are calculated for heavier T=Sn(Pb) ones. Ring size influences binding energy, the -E_b values in the range of 1.9 ~ 6.8 kcal mol^-1 for [1.1.1]-T is smaller some 1~2 kcal mol^-1 than that of [2.1.1]-T and [2.2.1]-T, whereas [2.1.1]-T and [2.2.1]-T have comparable E_b values. Natural bond orbital (NBO) inspection is used for exploring the nature of the noncovalent interaction. The stability of CH₃F complexes mainly stem from the σ(C1-C2)→σ*(C-F) interaction according to natural bond orbital (NBO) inspection. The antibonding interaction of σ*(C1-C2)→σ*(T-F) contributes most to the stability of [1.1.1]-Si(Ge) and [2.1.1]-Ge(Sn,Pb) ones. For [2.2.1]-T complexes, the interaction of σ(T-H)→σ*(C1-C2) contribute more to their stability. In addition, the bulkier the ring of propellanes, the greater the E⁽²⁾ estimate for each σ(T-H)→σ*(C1-C2) interaction. In the T=2C ternary system, a positive cooperativity is found, while the other Si, Ge, Sn and Pb triads exhibit a negative cooperativity. The quantum theory of atoms in molecules (AIM) and energy decomposition analysis (sobEDA) also supply insight for the nature of noncovalent interactions.