Enhanced Reactivity of N‐heterocyclic Halophosphines and Phosphenium Cations: The Activation of Carbon─Heteroatom and Boron─Heteroatom Bonds

N ‐heterocyclic phosphines (NHPs), and especially their ionic derivatives, phosphenium cations, have gained significant attention not only as isoelectronic species to N ‐heterocyclic carbenes (NHCs) but mainly, as highly Lewis acidic, active organocatalysts. A novel type of saturated NHPs has been introduced, with the nitrogen atoms substituted by phosphoramidothioates–{[κ 2 ‐ O , O ‐(OCH 2 C(Me) 2 CH 2 O)P(= S)] 2 ‐μ‐[NCH 2 CH 2 N]}PX, where X = F, Cl, Br, I, H, Ph, and their derivatives. Thanks to an increased positive charge at the P(III) atom, these compounds are prone to activate C─O, B─H, B─C, or B─F bonds and open cyclic ethers through the formation of intermediate species–phosphenium cations. The hydrido derivative can effectively catalyze the transfer hydrogenation of azobenzene by ammonia borane when irradiated by UV light at room temperature. The self‐ionization of the iodido derivative promoted by the coordination of less sterically demanding N ‐heterocyclic carbene enables the isolation of a phosphenium cation.