Abstract: | Stable acyclic arsenium cations R2As+, isoelectronic analogues of germylenes, are rare in comparison to the corresponding phosphenium cations. The first example of a diphosphaarsenium salt, {(Dipp)2P}2As]Al{OC(CF3)3}4]?1 PhMe, is described. This salt exhibits remarkable stability due to the delocalisation of a lone pair from a planar phosphorus centre into the vacant p‐orbital at arsenic; the bonding in 2 has been probed by DFT calculations. An attempt to synthesise an analogous diphosphaphosphenium salt unexpectedly generated the cyclic phosphonium salt cyclo‐{(Mes)P}2P(Mes)2]BArF4]?CyMe through the cyclisation of a putative phosphine‐substituted diphosphene cation intermediate. |