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.

Aromatic heterocycles XII. Semiempirical PM3 study of Diels-Alder cycloaddition reaction of substituted phosphabenzenes

“…Nucleus independent chemical shift criteria (NICS) calculated at B3LYP/6-31G* level showed a value of -10.2 for phosphabenzene, which is close to NICS calculated for benzene: -11.5 [14].…”

Aromaticity in heterocyclic analogues of benzene: comprehensive analysis of structural aspects, electron delocalization and magnetic characteristics

“…3,45 The presence of heavier heteroatoms leads to different consequences. Phosphorus, arsenic and antimony analogues of pyridine exhibit lower aromaticity than benzene 3 and pyridine 46,47 . However, according to values of the resonance energy 48 and the delocalization enthalpy 49 they remain clearly aromatic.…”

Recent Developments in the Chemistry of Pyridyl-functionalized, Low-coordinate Phosphorus Heterocycles

“…The nucleus-independent chemical shift values (NICS) of phosphinines lead to the same conclusion. 20 Theoretical calculations indicate that the parent phosphinine C 5 H 5 P possesses 8890% of the aromaticity of benzene, whereas pyridine is totally aromatic. 21 The lone pair at the phosphorus atom in λ 3 -phosphinines has a high 3s orbital character (63.8% versus 29.1% in pyridine).…”