A comparative study of frustration in Al/P and B/P-based intramolecular frustrated Lewis pairs

Intramolecular frustrated Lewis pairs (IFLPs) have emerged as versatile systems for small molecule activation, with their reactivity critically influenced by the nature of the bridging unit and the intrinsic properties of the Lewis acid and base. In this work, we present a comparative computational analysis of AlP- and BP-based IFLPs featuring a series of structurally analogous linkers. Using H₂ activation as a unified metric, we evaluate the degree of frustration encoded within each system by examining transition state energetics, adduct stability, and electronic structure features. Our findings reveal that while AlP-IFLPs often exhibit masked behavior due to partial Al-P interactions, their BP counterparts remain classical FLPs with greater spatial separation. The geminal-bridged AlP_Gem system exhibits the most favorable energetic profile, whereas rigid systems like AlP_Nap incur substantial strain. This study underscores the role of both electronic and geometric parameters in dictating FLP behavior and provides valuable insights for the rational design of future IFLPs with enhanced reactivity and tunability.