Method for purifying a crude PNPNH compound

A method for purifying a crude PNPNH compound comprising a ligand 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, wherein the substitution is by formally eliminating per constituent compound either two whole groups R1-R5 or H, one atom from each of two groups R1-R5 or a whole group R1-R5 or H and an atom from another group R1-R5, and joining the formally so created valence-unsaturated sites by one covalent bond per constituent compound to provide the same valence as initially present at a given site,
• the method comprising:
• A.
• a) dissolving the crude PNPNH-compound in a C1-C10 alcohol or mixture thereof under heating, wherein an alcohol/ligand weight ratio is from 1.0-0.3;
• b) cooling the solution obtained in step a);
• and
• c) isolating the PNPNH compound;
• or
• B.
• (i) washing the crude PNPNH compound with C1-C10 alcohol or a mixture thereof;
• (ii) separating the PNPNH compound;
• and optionally drying thereof.