Ditetrel Bonding from Reactive Strained Propellane and Cyclic Carbocation as an Electron Donor/Acceptor

The binary ditetrel bond (DTB) complexes between separate strained [1.1.1]propellane (Lewis base) and five- or six-membered cyclic carbocations containing chalcogen oxygen and/or sulfur atom (Lewis acid) were first theoretically investigated at the B3LYP(D3)/def2-TZVP level. All of the binary complexes offer substantial thermodynamic advantages with binding energies (<i>E</i>_b) of more or less -10 kcal mol^-1. The five-membered carbocation complexes are more stable, with -<i>E</i>_b values larger by 2-4 kcal mol^-1 than those of the six-membered ones. A comparison between the ternary and the more saturated complexes shows that the saturation of the cyclic carbocation species favors complexation. The ultralong bridgehead C1-C2 bond also influences the DTB interaction; the binary systems, wherein the wing -CH₂ group of [1.1.1]propellane is substituted by SiH₂ with a C1-C2 bond of 2.0 Å, serving as a Lewis base, are predicted to have -<i>E</i>_b values more than ∼1-3 kcal mol^-1 compared with those of their corresponding [1.1.1]propellane dyads and triads. The energy decomposition analysis (sobEDA), together with the extended transition state combined with natural orbitals for chemical valence (ETS-NOCV), offers in-depth insights into the nature of the interaction. The independent gradient model based on the Hirshfeld partition (IGMH) and the quantum theory of atoms in the molecule (AIM) analyses visualize the existence of substantial DTB interactions.