title: The CH by N Replacement Effects on the Aromaticity and Reactivity of Phosphinines.
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 of phosphinine and pyridine. This study reveals that the introduction of nitrogen atoms at the position adjacent to phosphorus significantly reduces the aromatic delocalization and induces a [1,4] dipolar character through an increase of the positive charge on the P atom. This phenomenon does not occur in 1,3-aza- and 1,3,5-diazaphosphinines, which exhibit a poor dipolar character. This comparison 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 been modelized. Calculated geometries of the resultant [4 + 2] diazabarrelene cycloadducts and that of their respective transition states reveal that, especially with 1,3,2-diaza isomers, the cycloaddition proceeds via a disymmetrical pathway that involves the preliminary formation of the P-C bond.
authors.affiliation: Laboratoire de Chimie Théorique, UMR CNRS 7616, Université Pierre et Marie Curie, T 22-23, Case 137, 4 Place Jussieu, 75252 Paris Cedex 05, France, and Laboratoire "Héteroéléments et Coordination", UMR CNRS 7653, Ecole Polytechnique, 91128 Palaiseau Cedex, France.
authors.forename: Gilles
authors.initials: G
authors.lastname: Frison
authors.forename: Alain
authors.initials: A
authors.lastname: Sevin
authors.forename: Narcis
authors.initials: N
authors.lastname: Avarvari
authors.forename: François
authors.initials: F
authors.lastname: Mathey
authors.forename: Pascal
authors.initials: P
authors.lastname: Le Floch