Method for purifying a crude pnpnh compound

A method for purifying a crude PNPNH compound of the general structure

• R1R2P—N(R3)—P(R4)—N(R5)—H
• wherein R1, R2, R3, R4 and R5 are independently halogen, amino, trimethylsilyl, C1-C10-alkyl, substituted C1-C10-alkyl, C6-C20-aryl and substituted C6-C20-aryl, or any cyclic derivative wherein at least one of the P or N atoms of the PNPN-H structure is a member of a ring system, the ring system being formed from one or more constituent compounds of the PNPNH-structure by substitution,
• comprising:
• a) dissolving the PNPNH-compound in a first solvent;
• b) metalating the PNPNH-compound,
• c) isolating the metalated compound obtained in step b),
• d) re-protonating the metalated compound in a second solvent, and
• e) optionally removing the solvent and optionally recrystallizing the re-protonated PNPNH ligand.