organophosphorus chemistry Organophosphorus compounds are organic compounds containing phosphorus. They are used primarily in pest control as an alternative to chlorinated hydrocarbons that persist in the environment. Some organophosphorus compounds are highly effective ins ...

, an aminophosphine is a compound with the formula R_3−nP(NR₂)_n 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 tris(dimethylamino)phosphine (P(NMe₂)₃) is commonly available. Intermediate members are known, such as Ph₂PN(H)Ph. These compounds are typically colorless and reactive toward oxygen. They have pyramidal geometry at phosphorus.

Parent members

The fundamental aminophosphines have the formulae PH_2−n(NH₂)_n (n = 1, 2, 3). 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(V)

tautomer Tautomers () are structural isomers (constitutional isomers) of chemical compounds that readily interconvert. The chemical reaction interconverting the two is called tautomerization. This conversion commonly results from the relocation of a hyd ...

HN=PH₃. With secondary amines, the chemistry is more straightforward. Trisaminophosphines are prepared by treatment of phosphorus trichloride with

secondary amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent such ...

s: :PCl₃ + 6 HNMe₂ → (Me₂N)₃P + 3 ₂NMe₂l

Aminophosphine chlorides

The amination of phosphorus trihalides occur sequentially, with each amination proceeding more slowly than the preceding: :PCl₃ + 2 HNMe₂ → Me₂NPCl₂ + ₂NMe₂l :Me₂NPCl₂ + 2 HNMe₂ → (Me₂N)₂PCl + ₂NMe₂l With bulky amines like

diisopropylamine Diisopropylamine is a secondary amine with the chemical formula (Me2CH)2NH (Me = methyl). Diisopropylamine is a colorless liquid with an ammonia-like odor. Its lithium derivative, lithium diisopropylamide, known as LDA is a widely used reagent. ...

, the selectivity for the monosubstitution improves. Commercially available aminophosphine chlorides include dimethylaminophosphorus dichloride and bis(dimethylamino)phosphorous chloride. Related aminophosphine fluorides compounds are available from

trifluorophosphine Phosphorus trifluoride (formula P F3), is a colorless and odorless gas. It is highly toxic and reacts slowly with water. Its main use is as a ligand in metal complexes. As a ligand, it parallels carbon monoxide in metal carbonyls, and indeed i ...

. The diphosphine MeN(PF₂)₂ is prepared from

methylamine Methylamine is an organic compound with a formula of . This colorless gas is a derivative of ammonia, but with one hydrogen atom being replaced by a methyl group. It is the simplest primary amine. Methylamine is sold as a solution in methanol, ...

: :2 PF₃ + 3 MeNH₂ → MeN(PF₂)₂ + 2 eNH₃ Me(PF₂)₂ is used as a

bridging ligand In coordination chemistry, a bridging ligand is a ligand that connects two or more atoms, usually metal ions. The ligand may be atomic or polyatomic. Virtually all complex organic compounds can serve as bridging ligands, so the term is usually ...

in organometallic chemistry. ''Substituted'' aminophosphines are generally prepared from organophosphorus chlorides and amines. The method is used to prepare ligands for homogeneous catalysis.

Chlorodiphenylphosphine Chlorodiphenylphosphine is an organophosphorus compound with the formula (C6H5)2PCl, abbreviated Ph2PCl. It is a colourless oily liquid with a pungent odor that is often described as being garlic-like and detectable even in the ppb range. It is u ...

and

diethylamine Diethylamine is an organic compound with the formula (CH3CH2)2NH. It is a secondary amine. It is a flammable, weakly alkaline liquid that is miscible with most solvents. It is a colorless liquid, but commercial samples often appear brown due to im ...

react to give an aminophosphine: :Ph₂PCl + 2 HNEt₂ → Ph₂PNEt₂ + ₂NEt₂l Primary amines react with phosphorus(III) chlorides give aminophosphines with acidic α-NH centers: :Ph₂PCl + 2 H₂NR → Ph₂PN(H)R + ₃NRl

Reactions

Protonolysis

The P-N bond is susceptible to attack by protic reagents.

Alcoholysis In chemistry, solvolysis is a type of nucleophilic substitution (S1/S2) or elimination where the nucleophile is a solvent molecule. Characteristic of S1 reactions, solvolysis of a chiral reactant affords the racemate. Sometimes however, the ster ...

occurs readily: :Ph₂PNEt₂ + ROH → Ph₂POR + HNEt₂ The P-N bond reverts to the chloride upon treatment with anhydrous

hydrogen chloride The compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride g ...

: :Ph₂PNEt₂ + 2 HCl → Ph₂PCl + ₂NEt₂l Similarly, transamination is used in the conversion of one aminophosphine to another: :P(NMe₂)₃ + R₂NH P(NR₂)(NMe₂)₂ + HNMe₂ With tris(dimethylamino)phosphine is a reactant, the equilibrium can be driven by evaporation of dimethylamine. 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: :2 MeMgBr + Me₂NPCl₂ → Me₂NPMe₂ + 2 MgBrCl :Me₂NPMe₂ + 2 HCl → ClPMe₂ + Me₂NH₂Cl Illustrative also is the chemistry of

1,2-bis(dichlorophosphino)benzene 1,2-Bis(dichlorophosphino)benzene is an organophosphorus compound with the formula C6H4(PCl2)2. A viscous colorless liquid, it is a precursor to chelating diphosphines of the type C6H4(PR2)2. It is prepared from 1,2-dibromobenzene by sequential ...

, a versatile precursor to

diphosphine Diphosphane, or diphosphine, is an inorganic compound with the chemical formula P2H4. This colourless liquid is one of several binary phosphorus hydrides. It is the impurity that typically causes samples of phosphine to ignite in air. Propert ...

ligands, is prepared using aminophosphine reagents. It is prepared from 1,2-dibromobenzene via lithiation and treatment with (Et₂N)₂PCl (Et = ethyl). This route gives C₆H₄ (NEt₂)₂sub>2, which is treated with

: :C₆H₄ (NEt₂)₂sub>2 + 8 HCl → C₆H₄(PCl₂)₂ + 4 Et₂NH₂Cl

Conversion to phosphenium salts

Diaminophosphorus chlorides and tris(dimethylamino)phosphine are precursors to

phosphenium Phosphenium ions, not to be confused with phosphonium or phosphirenium, are divalent cations of phosphorus of the form R2sup>+. Phosphenium ions have long been proposed as reaction intermediates. Synthesis Legacy methods The first cyclic phos ...

ions of the type R₂N)₂Psup>+: :R₂PCl + AlCl₃ → ₂P⁺lCl₄⁻ :P(NMe₂)₃ + 2 HOTf → (NMe₂)₂Tf + ₂NMe₂Tf

Oxidation and quaternization

Typical aminophosphines undergo oxidation to the oxide. Alkylation, e.g. by

methyl iodide Iodomethane, also called methyl iodide, and commonly abbreviated "MeI", is the chemical compound with the formula CH3I. It is a dense, colorless, volatile liquid. In terms of chemical structure, it is related to methane by replacement of one ...

, gives the

phosphonium In polyatomic cations with the chemical formula (where R is a hydrogen or an alkyl, aryl, or halide group). These cations have tetrahedral structures. The salts are generally colorless or take the color of the anions. Types of phosphonium c ...

cation.

References

{{Organophosphorus Functional groups Amides