1.2.3- Diazaphospholenium ions

Keywords 1,3,2-diazaphospholes 1,3,2-diazaphospholenes 1,3,2-diazaphosphinines 2,3-dihydro-l,3,2-diazaphosplinines diketiminto-phosphenium ions N-heterocyclic phosphines N-heterocyclc phosphenium ions 1,2,3-diazaphospholenium ions... 

Scheme 4 Direct synthesis of 1,3,2-diazaphospholenium ions via redox reactions (Ar=Dipp R=t-Bu, Dipp)... 

Quantitative assessment of the electrophilic character of various types of phosphenium ions has been attempted using computational studies on hydride and halide exchange reactions, and the results attribute to 1,3,2-diazaphospholenium ions a lower electrophilicity (and thus higher stability) than other types of phosphenium ions [20, 66], The gain in stability due to aromatic -delocalization is predicted to be somewhat larger than inductive stabilization resulting from exhaustive A-alkylation of the parent diaminophosphenium ion, [P(NH2)2]+. 

Ab initio calculations carried out on three 1,3,2-diazaphosphole derivatives, eg., 1, at the MP2/6-31 lG(d,p) level, gave rise to structural and energy data that are interpreted in context of its aromaticity. The 1,3,2-diazaphospholenium ion 2 also has a substantial degree of aromatic stabilisation energy (24.0 kcal mol ) in fact it is comparable to that of pyrrole. Cyclic delocalisation is supported by an analysis of computed charge distribution data, natural bond orbital data, bond... 

Reactions of P-halogen-NHPs with Lewis acids leading to halide abstraction, or metathetic replacement of the halide by a nucleofugic, noncoordinating anion form by far the most important routes to access phosphenium ions in general [51, 52] and also 1,3,2-diazaphospholenium cations in particular. As Lewis acid assisted P-X... 

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