In organophosphorus chemistry, aminophosphines are compounds with the formula R<sub>3âÂÂn</sub>P(NR<sub>2</sub>)<sub>n</sub> where R is a hydrogen or organic substituent, and n = 0, 1, or 2. At one extreme, the parents H<sub>2</sub>PNH<sub>2</sub> and are lightly studied and fragile. At the other extreme, tris(dimethylamino)phosphine (P(NMe<sub>2</sub>)<sub>3</sub>) is commonly available. Intermediate members are known, such as Ph<sub>2</sub>PN(H)Ph. Aminophosphines are typically colorless and reactive to oxygen. Aminophosphines are pyramidal geometry at phosphorus.
The fundamental aminophosphines have the formulae PH<sub>3âÂÂn</sub>(NH<sub>2</sub>)<sub>n</sub> (n = 1, 2, or 3). Fundamental aminophosphines can not be isolated in a practical quantities but have been examined theoretically. H<sub>2</sub>NPH<sub>2</sub> is predicted to be more stable than the P(V) tautomer HN=PH<sub>3</sub>.
Secondary amines are more straightforward. Trisaminophosphines are made by treating phosphorus trichloride with secondary amines:
where Me = methyl.
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 bis(dimethylamino)phosphorus chloride.
Methylamine and trifluorophosphine react to give MeN(PF<sub>2</sub>)<sub>2</sub>:
MeN(PF<sub>2</sub>)<sub>2</sub> 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(III) chlorides to give aminophosphines with acidic ñ-NH centers:
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 tris(dimethylamino)phosphine, dimethylamine evaporation can drive the equilibrium.
Since Grignard reagents do not attack P-NR<sub>2</sub> 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 (Et<sub>2</sub>N)<sub>2</sub>PCl (Et = ethyl). This route gives C<sub>6</sub>H<sub>4</sub>[P(NEt<sub>2</sub>)<sub>2</sub>]<sub>2</sub>, which is treated with hydrogen chloride:
Diaminophosphorus chlorides and tris(dimethylamino)phosphine are precursors to phosphenium ions of the type [(R<sub>2</sub>N)<sub>2</sub>P]<sup>+</sup>:
Typical aminophosphines oxidize. Alkylation, such as by methyl iodide, gives the phosphonium cation.
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.