Dual Lewis Acid-Base Molecular Cages Facilitate Cooperative N2 Activation: Insights from Theory.

Activating molecular nitrogen (N2) under ambient conditions remains a major challenge. Dual Lewis acid-base molecular cages are investigated to cooperatively activate N2 using computational chemistry. Cages composed of Lewis acids (LA) and Lewis bases (LB) connected by a linker chain ([LA,LB]C) are analyzed via binding free energies, interaction and deformation energies, bond lengths, angles, and Wiberg bond indices and charge distributions. Two interaction arrangements emerge: 1) rigid systems with strong LA-LB dative bonds that deform substantially upon N2 binding and do not act as frustrated Lewis pairs (FLPs), and 2) flexible cages with extended LA-LB separations displaying typical FLP behavior. Borylene donors enable strong, stable N2 interactions, particularly in systems 6a and 7c, whereas Verkade's base is less effective. Structural flexibility and electronic tuning of LA/LB centers are fundamental for efficient activation. Natural bond orbital and quantum theory of atoms in molecules analyses reveal partially covalent electrostatic interactions at the acidic site and covalent interactions at the basic site. These results provide design principles for molecular cages for N2 activation.