Generation of a π-Bonded Isomer of [P4]4− by Aluminyl Reduction of White Phosphorus and its Ammonolysis to PH3

By employing the highly reducing aluminyl complex [K{(NON)Al}]<sub>2</sub> (NON=4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene), we demonstrate the controlled formation of P<sub>4</sub> <sup>2-</sup> and P<sub>4</sub> <sup>4-</sup> complexes from white phosphorus, and chemically reversible inter-conversion between them. The tetra-anion features a unique planar π-bonded structure, with the incorporation of the K<sup>+</sup> cations implicit in the use of the anionic nucleophile offering additional stabilization of the unsaturated isomer of the P<sub>4</sub> <sup>4-</sup> fragment. This complex is extremely reactive, acting as a source of P<sup>3-</sup> : exposure to ammonia leads to the release of phosphine (PH<sub>3</sub> ) under mild conditions (room temperature and pressure), which contrast with those necessitated for the direct combination of P<sub>4</sub> and NH<sub>3</sub> (>5 kbar and >250 °C)