Trimethylphosphine is the organophosphorus compound with the formula P(CH3)3, commonly abbreviated PMe3. This colorless liquid has a strongly unpleasant odour, which is characteristic of alkylphosphines. It is a pyramidal molecule with C3v symmetry
Symmetry group
The symmetry group of an object is the group of all isometries under which it is invariant with composition as the operation...

, similar to ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

 (NH3) and phosphine
Phosphine is the compound with the chemical formula PH3. It is a colorless, flammable, toxic gas. Pure phosphine is odourless, but technical grade samples have a highly unpleasant odor like garlic or rotting fish, due to the presence of substituted phosphine and diphosphine...

 (PH3). As a ligand, its cone angle
Ligand cone angle
The ligand cone angle is a measure of the size of a ligand. It is defined as the solid angle formed with the metal at the vertex and the hydrogen atoms at the perimeter of the cone . Tertiary phosphine ligands are commonly classified using this parameter, but the method can be applied to any...

 is 118°. This angle, close to the optimal angles for sp2-hybridisation, is an indication for the hybridisation of the phosphorus atom. The lone pair is left in an almost straight p-orbital
Atomic orbital
An atomic orbital is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom. This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus...

, so it points rather localized outward, in contrast to the higher members of the nitrogen group
Nitrogen group
The nitrogen group is a periodic table group consisting of nitrogen , phosphorus , arsenic , antimony , bismuth and ununpentium ....

, to open the route to the rather hard basic
HSAB theory
The HSAB concept is an acronym for 'hard and soft acids and bases. Also known as the Pearson acid base concept, HSAB is widely used in chemistry for explaining stability of compounds, reaction mechanisms and pathways....

 properties of the compound.

PMe3 is prepared using Grignard reagents:
3 CH3MgCl
Methylmagnesium chloride
Methylmagnesium chloride is a commercially available Grignard reagent. Like methyllithium, it is the synthetic equivalent to the methyl carbanion synthon. It is usually sold as a solution in tetrahydrofuran. The model of the molecule shows methylmagnesium chloride with the magnesium atom in the...

 + P(OC6H5)3  → P(CH3)3 + 3 C6H5OMgBr

The synthesis is conducted in a dibutyl ether, from which the more volatile PMe3 can be distilled.

Coordination chemistry

Trimethylphosphine is a highly basic ligand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...

 that forms complexes with most metals. The synthesis of an illustrative example is shown:
PMe3 + Fe(CO)5
Iron pentacarbonyl
Iron pentacarbonyl, also known as iron carbonyl, is the compound with formula 5. Under standard conditions Fe5 is a free-flowing, straw-colored liquid with a pungent odour. This compound is a common precursor to diverse iron compounds, including many that are useful in organic synthesis. Fe5 is...

  → Fe(CO)4PMe3 + CO

Its complex with silver iodide, AgI(PMe3) is a weighable, air stable solid that releases PMe3 upon heating.


PMe3 is potentially pyrophoric as well as toxic. PMe3 can be converted to non-pyrophoric phosphine oxide
Phosphine oxide
Phosphine oxides are either inorganic phosphorus compounds such as phosphoryl trichloride or organophosphorus compounds with the formula OPR3, where R = alkyl or aryl...

 by treatment with dilute bleach
Bleach refers to a number of chemicals that remove color, whiten, or disinfect, often via oxidation. Common chemical bleaches include household chlorine bleach , lye, oxygen bleach , and bleaching powder...

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