Diamino-substituted phosphenium

According to these consideration the diamino-substituted phosphenium (an alternative suggestion for its nomenclature is phosphanylium) cation, 5, and the phosphanetriylammonium (iminophosphenium) cation, 6, possess the largest intrinsic (gas phase) stabihties. Since in the X-ray structures the molecules are to a first-order isolated, this theoretical stability scale determined for the gas phase should also mimic the various trends of the stabilities of the cations and their chelation behaviour. The methylenephosphenium, 7, and the PjH cations, 8, suffer from poor stabihties. On the other hand the phosphirenium cation, 11, is considered to be fairly well stabilized. It is due to n-electron delocalisation of the positive charge in the phosphirenium cation. Intermediate cases in stabihty are the PO+ (9) and PS+ cations (10). Of further interest are the frontier orbital considerations, as shown in Fig. 2. 

In contrast to 76 cationic phosphenium complexes for which 31P NMR data have been reported, only 7 complexes have been structurally characterized (Table IV). Five of them are diamino-substituted phosphenium complexes, one is a monoaminomonoalkoxy phosphenium complex,32 and one is a dialkoxy phosphenium complex.16,18 The geometry... 

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