The Challenging P‐Alkylation of Aromatic Phosphorus Heterocycles and Follow‐Up Reactions

In contrast to the simple and straightforward generation of pyridinium cations, the P‐alkylation of the heavier homolog λ 3 σ 2 ‐phosphinines is more challenging due to their weak nucleophilicity, as demonstrated only by a handful of examples. The previously reported methods to such species either apply multistep syntheses or make use of extreme electrophiles. As a consequence, detailed studies on their reactivity are underexplored due to their limited synthetic availability. Herein, it is reported that the labile Lewis pair of 3,5‐bis(trimethylsilyl)‐phosphinine and B(C 6 F 5 ) 3 serves as a platform for the facile generation of 1‐R‐phosphininium salts, utilizing esters or iso(thio)cyanates as alkylating reagents. With this new approach in hand, the reactivity of 1‐R‐phosphininium salts toward isolobal and valence‐isoelectronic substrates exhibiting C≡C, C≡N, or C≡P multiple bonds has been explored systematically. To gain a deeper understanding of reactivity trends, the stability of the newly accessed phosphininium cations and the mechanisms of their follow‐up reactions are explored using density functional theory (DFT) calculations.