Making and breaking of phosphorus–phosphorus bonds

In contrast to their mostly unstable isolobal carbon counterparts, oligophosphanide anions, such as M( cyclo -P 5 t Bu 4 ) (M=Li, Na) and M 2 (P 4 R 4 ) [M=Na, K; R=Ph, t Bu, 2,4,6-Me 3 C 6 H 2 (Mes)], have unique features, depending on their composition and structure, and are highly suitable building blocks for the synthesis of phosphorus-rich metal compounds. However, alkali metal oligophosphanediides are highly reactive and highly reducing, and a major problem is their tendency for disproportionation in reactions with electrophiles. This, however, can also give rise to a fascinating chemistry of making and breaking of P–P bonds. On the other hand, neutral cyclooligophosphines, such as cyclo -(P 5 Ph 5 ), are suitable stable ligands for the formation of phosphorus-rich metal complexes.