Diamidonaphthalene-Stabilized N-Heterocyclic Pnictogenium Cations and Their Cation−Cation Solid-State Interactions

The synthesis and comprehensive characterization of a new series of N-heterocyclic phosphine, arsine, and stibine compounds is presented. The diamidochloropnictines ClPn(NR)2C10H6 (Pn = P, As, Sb) were prepared via the dehydrohalide coupling reactions of N,N‘-diisopropyl-1,8-diaminonaphthalene, ( i PrNH)2C10H6, or N,N‘-diphenyl-1,8-diaminonaphthalene, (PhNH)2C10H6, with the appropriate pnictogen trichloride. Reaction of these pnictines with appropriate halide abstraction agents yielded the corresponding phosphenium and arsenium salts. These planar pnictogenium cations {Pn(NR)2C10H6}+ (Pn = P, As; R = i Pr, Ph) display dicoordinate pnictogen centers that are stabilized by an electron-rich diamidonaphthalene framework and represent rare examples of six-membered N-heterocyclic pnictogenium cations possessing a π-conjugated carbon backbone. The related stibenium salts could not be prepared via this route; however, the reaction of the new heteroleptic triamidostibene, (Me2N)Sb( i PrN)2C10H6, with triflic acid does generate the base-stabilized stibenium cation, [Sb( i PrN)2C10H6·(Me2NH)]+. The phosphenium and arsenium salts exhibit different modes of packing in their solid-state structures depending upon the identity of the nitrogen substituents. The two phenyl substituted compounds display an interaction between the pnictogen center and the π-system of an adjacent naphthyl moiety. In contrast, the isopropyl substituted species undergo metastable dimerization through naphthyl π-stacking. These dimers are bound by strong dipole−dipole and dispersion interactions as revealed through computational studies.