| Abstract
| - Geometries, aromatic character, Mulliken charge distribution, and MO diagrams of 1,2-aza-, 1,3,2-diaza-, 1,3-aza-, and 1,3,5-diazaphosphinines have been calculated and compared to those ofphosphinine and pyridine. This study reveals that the introduction of nitrogen atoms at the positionadjacent to phosphorus significantly reduces the aromatic delocalization and induces a [1,4] dipolarcharacter through an increase of the positive charge on the P atom. This phenomenon does notoccur in 1,3-aza- and 1,3,5-diazaphosphinines, which exhibit a poor dipolar character. Thiscomparison confirms the high reactivity of 1,3,2-diazaphosphinines toward alkynes. A [4 + 2]cycloaddition reaction between these two types of diazaphosphinines and acetylene has beenmodelized. Calculated geometries of the resultant [4 + 2] diazabarrelene cycloadducts and that oftheir respective transition states reveal that, especially with 1,3,2-diaza isomers, the cycloadditionproceeds via a disymmetrical pathway that involves the preliminary formation of the P−C bond.
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