The aromatic stabilization of cyclic phosphenium cations compound (tBuN-CH 2 -CH 2 -NtBu)P-Cl (2) is covalent. The two chloro-phosphanes 1 and 2 differ sharply in their (general type C 2 N 2 P + ) was studied by experimental methods (synthesis, multinuclear NMR, single crystal X-ray volatility and solubility in organic solvents. Compound 2 is soluble in hydrocarbons and sublimes readily at 90 ยฐC/0.1 crystallography) and quantum chemical calculations (ab initio methods). The structures of the 1,3,2-diazaphosphole Torr but 1 is insoluble in hexanes and not volatile below 180 ยฐC/0.1 Torr. The degree of aromatic stabilization in the derivatives [(tBuN-CH=CH-NtBu)P + ]Cl -(1), (tBuN-CH 2 -CH 2 -NtBu)P-Cl (2), [(tBuN-CH=CH-NtBu)P] + PF 6 -(3) and phosphenium cation 1 was investigated by ab initio methods. For the model cations [RN-CH 2 -CH 2 -NR]P + and [(RN-CH= [(tBuN-CH 2 -CH 2 -NtBu)]P + PF 6 -(4) were examined by single crystal X-ray diffraction. The chloro phosphane [(tBuN-CH= CH-NR)P] + , thermochemical stabilization energies of 25.8 kcal โข mol -1 (R = H) and 28.1 kcal โข mol -1 (R = Me) were CH-NtBu)P] + Cl -(1) has an ionic P-Cl bond and contains an aromatically stabilized phosphenium cation [shortest obtained from isodesmic hydrogenation reactions at the RHF/MP2/6-31G*//RHF/6-31G* level. distance PโขโขโขCl = 275.9(2) pm], while the CC-saturated ment. For some elements, the experimental comparison of