# Aminophosphine

In organophosphorus chemistry, aminophosphines are compounds with the formula R$_{3−n}$P(NR$_2$)$_n$ where R is a hydrogen or organic substituent, and n = 0, 1, or 2. At one extreme, the parents H$_2$PNH$_2$ and P(NH$_2$)$_3$ are lightly studied and fragile. At the other extreme, tris(dimethylamino)phosphine (P(NMe$_2$)$_3$) is commonly available. Intermediate members are known, such as Ph$_2$PN(H)Ph. Aminophosphines are typically colorless and reactive to oxygen. Aminophosphines are pyramidal geometry at phosphorus.

## Parent members

The fundamental aminophosphines have the formulae PH$_{3−n}$(NH$_2$)$_n$ (n = 1, 2, or 3). Fundamental aminophosphines can not be isolated in a practical quantities but have been examined theoretically. H$_2$NPH$_2$ is predicted to be more stable than the P(V) tautomer HN=PH$_3$.
Secondary amines are more straightforward. Trisaminophosphines are made by treating phosphorus trichloride with secondary amines:
    PCl$_3$ + 6 HNMe$_2$ → (Me$_2$N)$_3$P + 3 [H$_2$NMe$_2$]Cl

## Aminophosphine chlorides

The amination of phosphorus trihalides occur sequentially, with each amination proceeding slower than before:
    PCl$_3$ + 2 HNMe$_2$ → Me$_2$NPCl$_2$ + [H$_2$NMe$_2$]Cl
    Me$_2$NPCl$_2$ + 2 HNMe$_2$ → (Me$_2$N)$_2$PCl + [H$_2$NMe$_2$]Cl
    (Me$_2$N)$_2$PCl + 2 HNMe$_2$ → (Me$_2$N)$_3$P + [H$_2$NMe$_2$]Cl
    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 the diphosphine MeN(PF$_2$)$_2$:
    2 PF$_3$ + 3 MeNH$_2$ → MeN(PF$_2$)$_2$ + 2 [MeNH$_3$]F
Me(PF$_2$)$_2$ is a bridging ligand in organometallic chemistry.
Aminophosphines can also made from organophosphorus chlorides and amines. Chlorodiphenylphosphine and diethylamine react to give an aminophosphine:
    Ph$_2$PCl + 2 HNEt$_2$ → Ph$_2$PNEt$_2$ + [H$_2$NEt$_2$]Cl
Primary amines react with phosphorus(III) chlorides to give aminophosphines with acidic α-NH centers:
    Ph$_2$PCl + 2 H$_2$NR → Ph$_2$PN(H)R + [H$_3$NR]Cl

## Reactions
### Protonolysis

Protic reagents attack the P-N bond. Alcoholysis readily occurs:
    Ph$_2$PNEt$_2$ + ROH → Ph$_2$POR + HNEt$_2$
The P-N bond reverts to the chloride when treated with anhydrous hydrogen chloride:
    Ph$_2$PNEt$_2$ + HCl → Ph$_2$PCl + HNEt$_2$
Transamination similarly converts one aminophosphine to another:
    P(NMe$_2$)$_3$ + R$_2$NH ⇌ P(NR$_2$)(NMe$_2$)$_2$ + HNMe$_2$
With tris(dimethylamino)phosphine, dimethylamine evaporation can drive the equilibrium.
Since Grignard reagents do not attack P-NR$_2$ bond, aminophosphine chlorides are useful reagents in preparing unsymmetrical tertiary phosphines. Illustrative is converting dimethylaminophosphorus dichloride to chlorodimethylphosphine:
    2 MeMgBr + Me$_2$NPCl$_2$ → Me$_2$NPMe$_2$ + 2 MgBrCl
    Me$_2$NPMe$_2$ + 2 HCl → ClPMe$_2$ + Me$_2$NH$_2$Cl
Also, illustrative is the synthesis of 1,2-bis(dichlorophosphino)benzene using (Et$_2$N)$_2$PCl (Et = ethyl). This route gives C$_6$H$_4$[P(NEt$_2$)$_2$]$_2$, which is treated with hydrogen chloride:
    C$_6$H$_4$[P(NEt$_2$)$_2$]$_2$ + 8 HCl → C$_6$H$_4$(PCl$_2$)$_2$ + 4 Et$_2$NH$_2$Cl

### Conversion to phosphenium salts

Diaminophosphorus chlorides and tris(dimethylamino)phosphine are precursors to phosphenium ions of the type [(R$_2$N)$_2$P]$^+$:
    R$_2$PCl + AlCl$_3$ → [R$_2$P$^+$]AlCl$_4$$^−$
    P(NMe$_2$)$_3$ + 2 HOTf → [P(NMe$_2$)$_2$]OTf + [H$_2$NMe$_2$]OTf

### 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.