Nontrigonal pnictogen compounds

By virtue of their geometric constraint, these compounds exhibit distinct electronic structures and reactivities, which bestow on them potential to provide unique nonmetal platforms for bond cleavage reactions.

The first examples of nontrigonal pnictogen compound were synthesized by Arduengo and co-workers in 1984,[1] through condensation of a diketoamine with a phosphorus trihalide in the presence of base.

[3] Other synthetic methods involve deprotonation of OH or NH groups in the presence of ECl3 (E=P,[4] As, Sb[5] and Bi[6]), salt metathesis[7] or reduction of pentavalent pnictogen compounds.

The flattened geometry of these molecules influences the relatively low energetic barriers for inversion of the configuration via planar coordinated pnictogen atoms in the transition state.

[4] Results of quantum chemical calculations confirm that in these compounds, the lone pair of electrons at the pnictogen atoms is localized in orbitals with relatively high s-character.

[4] The LUMO is delocalized but has important contributions from pnictogen empty p orbitals, which should favor a nucleophilic attack of substrates at this position in accordance with experimental findings.

These easily available and sterically constrained compounds are potentially suitable for an application in a wide variety of secondary processes such as small molecule activation or the generation of new catalysts based on main-group and transition-metal elements.

[13] These sterically constrained phosphorus compounds show remarkable reactivity towards protic reagents such as primary amines and alcohols, which results in intermolecular oxidative addition of these O−H and N−H bonds.