Aminophosphine

In organophosphorus chemistry, aminophosphines are compounds with the formula R_3−nP_n where R is a hydrogen or organic substituent, and n = 0, 1, or 2. At one extreme, the parents H₂PNH₂ and are lightly studied and fragile. At the other extreme, tris(dimethylamino)phosphine is commonly available. Intermediate members are known, such as Ph₂PNPh. Aminophosphines are typically colorless and reactive to oxygen. Aminophosphines are pyramidal geometry at phosphorus.

Parent members

The fundamental aminophosphines have the formulae PH_3−n_n. Fundamental aminophosphines can not be isolated in a practical quantities but have been examined theoretically. H₂NPH₂ is predicted to be more stable than the P tautomer HN=PH₃.
Secondary amines are more straightforward. Trisaminophosphines are made by treating phosphorus trichloride with secondary amines:
where Me = methyl.

Aminophosphine chlorides

The amination of phosphorus trihalides occur sequentially, with each amination proceeding slower than before:
Monosubstitution selectivity improves with bulky amines such as diisopropylamine. Commercially available aminophosphine chlorides include dimethylaminophosphorus dichloride and bisphosphorus chloride.
Methylamine and trifluorophosphine react to give MeN₂:
MeN₂ is a bridging ligand in organometallic chemistry.
Aminophosphines can also made from organophosphorus chlorides and amines. Chlorodiphenylphosphine and diethylamine react to give an aminophosphine:
Primary amines react with phosphorus chlorides to give aminophosphines with acidic α-NH centers:

Reactions

Protonolysis

Protic reagents attack the P-N bond. Alcoholysis readily occurs:
The P-N bond reverts to the chloride when treated with anhydrous hydrogen chloride:
Transamination similarly converts one aminophosphine to another:
With trisphosphine, dimethylamine evaporation can drive the equilibrium.
Since Grignard reagents do not attack P-NR₂ bond, aminophosphine chlorides are useful reagents in preparing unsymmetrical tertiary phosphines. Illustrative is converting dimethylaminophosphorus dichloride to chlorodimethylphosphine:
Also, illustrative is the synthesis of 1,2-bis(dichlorophosphino)benzene using (Et₂N)₂PCl. This route gives C₆H₄₂, which is treated with hydrogen chloride:

Conversion to phosphenium salts

Diaminophosphorus chlorides and tris(dimethylamino)phosphine are precursors to phosphenium ions of the type ⁺:

Oxidation and quaternization

Typical aminophosphines oxidize. Alkylation, such as by methyl iodide, gives the phosphonium cation.

Addition to carbonyls

In diazaphospholenes the polarity of the P-H bond is inverted compared to traditional secondary phosphines. They have some hydridic character. One manifestation of this polarity is their reactivity toward benzophenone in yet another way.