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Although phosphorine and [[pyridine]] are structurally similar, phosphorines are far less basic. The p''K''<sub>a</sub> of C<sub>5</sub>H<sub>5</sub>PH<sup>+</sup> and C<sub>5</sub>H<sub>5</sub>NH<sup>+</sup> are respectively −16.1 and +5.2. The P-oxides are extremely unstable, rapidly adding nucleophiles to a species tetracoordinate at phosphorus. Strongly backbonding Lewis acids (e.g. [[tungsten pentacarbonyl]]) can stabilize a [[dative bond]] from phosphorus.<ref name=Mathey>Mathey, François (2011). "Phosphorus Heterocycles" in ''Modern Heterocyclic Chemistry'',
Both [[electrophile]]s and strong, hard [[nucleophile]]s preferentially attack at phosphorus, but the ring aromaticity is sufficiently weak that the result is an [[addition reaction]], and not aromatic substitution.<ref name=Mathey/> Thus for example [[methyllithium]] adds to phosphorus in phosphorine whereas it adds to the 2-position of pyridine.<ref>Ashe III, Arthur J.; Smith, Timothy W. "The reaction of phosphabenzene, arsabenzene and stibabenzene with methyllithium." Tetrahedron Letters 1977, volume 18, pp. 407–410. {{doi|10.1016/S0040-4039(01)92651-6}}</ref> Halophosphorines do undergo noble-metal- or [[zirconocene]]-catalyzed substitution, and λ<sup>5</sup>-phosphorines exhibit [[electrophilic aromatic substitution|a much more traditional substitution chemistry]].<ref name=Mathey/>
Unlike [[arsabenzene]], phosphorine rarely participates in [[Diels-Alder]]-type cycloadditions; when it does, the coupling partner must be an extremely electron-poor alkyne. Phosphorine ''complexes'' are tolerable Diels-Alder reactants.<ref name=Mathey/>
===Coordination chemistry===
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