Flash Communication: Electronic Frustration in Stibine–Borane Lewis Pairs

Triaryl stibine–borane Lewis pairs remain poorly understood because of their weak Sb→B donor–acceptor interactions. Herein, we report the first single-crystal structure of Ph3Sb·B(C6F5)3 (1) together with two related triarylstibine–borane Lewis pairs. Despite retaining classical Lewis adduct characteristics, all three compounds exhibit reactivity consistent with the lability of their weakened Sb→B donor–acceptor interactions. NBO and DLPNO-CCSD(T)-based LED analyses reveal a systematic weakening of the Pn→B interaction from P to As to Sb, with the Sb→B interaction retaining a genuine two-center, two-electron donor–acceptor bond but being ∼12 kcal mol–1 weaker than its phosphine analog. These results provide structural and electronic insight into the weakened Sb→B donor–acceptor interaction in triarylstibine–borane Lewis adducts and its relationship to their observed dissociative reactivity.