Diphosphorus

    Diphosphorus, P₂, is the diatomic form of phosphorus. Unlike its nitrogen group neighbour nitrogen which forms a stable N₂ molecule with a nitrogen to nitrogen triple bond, phosphorus prefers a tetrahedral form P₄ because P-P pi-bonds are high in energy. Diphosphorus is therefore very reactive with a bond dissociation energy (117 kcal/mol or 490 kJ/mol) half that of dinitrogen.

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Traditionally diphosphorus can be generated by heating white phosphorus at 1100 kelvins. The compound attracted attention in 2006 when a new method for its synthesis at milder temperatures emerged ^[1].

This method is a variation on nitrogen expulsion in azides with formation of a nitrene. The synthesis of the diphosphorus precursor consists of reacting a terminal niobium phosphide with a chloroiminophosphane:

Heating this compound at 50 °C in 1,3-cyclohexadiene serving as a solvent and as a trapping reagent, expulses diphosphorus which reactive as it is forms a double Diels-Alder adduct and the niobium imido compound:

The same imido compound also forms when the thermolysis is performed in toluene but then the fate of diphosphorus in unknown.

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