The dependence of the protolytic decomposition rate of triphenylmethylphosphonous dichloride 1 was allowed to react with 3 equivalents of HTMG, forming the stable phosphorus amides on the substituents at phosphorus is decribed. On treatment with HCl, the NЈ,NЈ,NЉ,NЉ-phosphonium salt 19, soluble in water, which was converted to the bicationic species 20c upon treatment with HCl. -The tetramethylguanidine(= TMG)-substituted σ 4 (P) compounds 5 and 9 formed salts that were protonated at the imino basicity of the tritylated phosphorus compounds was found to increase in the order 5 Ͻ 2 Ͻ 19 Ͻ 13 Ͻ HTMG Ͻ 21; nitrogen atoms and were completely stable in the solid state, and surprisingly stable in solution. Even with a large excess the basic centre is the phosphorus atom in 21 and the imino nitrogen atom in all other compounds. The fluorinating agent of HCl, only the imino nitrogen atom underwent protonation, with formation of HCl 2 -as a counter anion, without cleavage Et 3 N • 3 HF caused rapid conversion of compound 6 to 25, the nucleophilic attack of fluoride ion at phosphorus could of the P-N bond. The basicity of the imino nitrogen atom also protected σ 3 (P) species from electrophilic attack, and the not be prevented by the stabilizing effects mentioned. -All compounds were investigated by 1 H-and 31 P-NMR spec-ionic compounds 12, 14, and 20c were formed, providing examples of the first stable σ 3 (P) amides with one or two troscopy. The crystal structures of compounds 5, Ph 3 CP(=O)-(H)TMG,and 6, [5 • 2 HCl], were determined; 6 is protonated protonated P-N bonds. Such unusual stability is associated with steric protection by the Ph 3 C (= trityl) group and charge at the imino nitrogen, leading to a longer P-N bond [5: 161.6(2), 6: 168.7(2) pm], and the counterion is HCl 2 -. In the delocalization over the TMG-moiety. In contrast, MeP(TMG) 2 was unstable towards HCl, whereas treatment with HSbF 6 structure of 20c, [Ph 3 CP(TMG) 2 ] • 3 HCl, the cation is protonated at both imino N atoms and the counterions are led to the phosphonium salt 24, where protonation had occurred at phosphorus. The same result was obtained when Cl -and HCl 2 -(one of each).