Frustrated Lewis Trios and Long-Range Hole Interactions: A Combined Structural and Theoretical Study of LB−AX₃⋅⋅⋅LB and LB⋅⋅⋅AX₃⋅⋅⋅LB (A=B, Al, Ga, In) Systems

Herein, we present a theoretical study of systems with long-range Lewis acid–base interactions that involve a triel center and two electron donor species. These intermediate situations, between LB−AX₃ and LB−AX₃−LB (LB=Lewis base, A=group 13 element), exist experimentally and their interaction topologies obey precise geometrical rules, such that they show a marked directionality and a clear dependence between the two A–LB distances. Despite the relatively long acid⋅⋅⋅base distances of up to 4 Å, the interaction energies calculated at the M06-2X/aug-cc-pVTZ level are considerably large (5–25 kcal mol⁻¹). A significant contribution to the interaction is related to the lone-pair-containing species that interacts with the π hole of the acid center, as revealed by the natural bond order, atoms in molecules, and molecular electrostatic potential analyses. Remarkably, this n(N)→σ_Al−N* interaction persists even at distances greater than the sum of the van der Waals radii.