Aminophosphine


In organophosphorus chemistry, an aminophosphine is a compound with the formula R3−nPn where R = H or an organic substituent, and n = 0, 1, 2. At one extreme, the parent H2PNH2 is lightly studied and fragile, but at the other extreme trisphosphine is commonly available. Intermediate members are known, such as Ph2PNPh. These compounds are typically colorless and reactive toward oxygen. They have pyramidal geometry at phosphorus.

Parent members

The fundamental aminophosphines have the formulae PH2−nn. These species cannot be isolated in a practical quantities, although they have been examined theoretically. H2NPH2 is predicted to be more stable than the P tautomer HN=PH3.
With secondary amines, the chemistry is more straightforward. Trisaminophosphines are prepared by treatment of phosphorus trichloride with secondary amines:

Aminophosphine chlorides

The amination of phosphorus trihalides occur sequentially, with each amination proceeding more slowly than the preceding:
The mixed aminophosphine chlorides are readily isolated and are a versatile reagents. Commercially available derivatives include dimethylaminophosphorus dichloride and bisphosphorous chloride.
Related aminophosphine fluorides compounds are available from trifluorophosphine. Notable is the diphosphine MeN2 prepared from methylamine:
Me2 is used as a bridging ligand in organometallic chemistry.
Substituted aminophosphines are generally prepared from organophosphorus chlorides and amines. The method is used to prepare ligands for homogeneous catalysis. Chlorodiphenylphosphine and diethylamine react to give an aminophosphine:
Primary amines react with phosphorus chlorides give aminophosphines with acidic α-NH centers:

Reactions

Protonolysis

The P-N bond is susceptible to attack by protic reagents. Alcoholysis occurs readily:
The P-N bond reverts to the chloride upon treatment with anhydrous hydrogen chloride:
Similarly, transamination is used in the conversion of one aminophosphine to another.
Since the P-NR2 bond is not attacked by Grignard reagents, aminophosphine chlorides are useful reagents in the preparation of unsymmetrical tertiary phosphines. Illustrative is the conversion of dimethylaminophosphorus dichloride to chlorodimethylphosphine:
Illustrative is the chemistry of 1,2-bisbenzene, a versatile precursor to diphosphine ligands, is prepared using aminophosphine reagents. It is prepared from 1,2-dibromobenzene via lithiation and treatment with 2PCl. This route gives C6H42, which is treated with hydrogen chloride:

Conversion to phosphenium salts

Diaminophosphorus chlorides and trisphosphine are precursors to phosphenium ions of the type +:

Oxidation and quaternization

Typical aminophosphines undergo oxidation to the oxide. Alkylation, e.g. by methyl iodide, gives the phosphonium cation.