Trimethylphosphine is an

organophosphorus compound Organophosphorus chemistry is the scientific study of the synthesis and properties of organophosphorus compounds, which are organic compounds containing phosphorus. They are used primarily in pest control as an alternative to chlorinated hydrocarbo ...

with the formula P(CH₃)₃, commonly abbreviated as PMe₃. This colorless liquid has a strongly unpleasant odor, characteristic of alkylphosphines. The compound is a common

ligand In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's el ...

coordination chemistry A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of chemical bond, bound molecules or ions, that are in turn known as ' ...

Structure and bonding

It is a

pyramidal A pyramid () is a structure whose visible surfaces are triangular in broad outline and converge toward the top, making the appearance roughly a pyramid in the geometric sense. The base of a pyramid can be of any polygon shape, such as triangu ...

molecule with approximate ''C''_3''v''

symmetry Symmetry () in everyday life refers to a sense of harmonious and beautiful proportion and balance. In mathematics, the term has a more precise definition and is usually used to refer to an object that is Invariant (mathematics), invariant und ...

. The C–P–C bond angles are approximately 98.6°. The C–P–C bond angles are consistent with the notion that phosphorus predominantly uses the 3p orbitals for forming bonds and that there is little sp hybridization of the phosphorus atom. The latter is a common feature of the chemistry of phosphorus. As a result, the lone pair of trimethylphosphine has predominantly s-character as is the case for phosphine, PH₃. PMe₃ can be prepared by the treatment of

triphenyl phosphite Triphenyl phosphite is the organophosphorus compound with the formula P(OC6H5)3. It is a colourless viscous liquid. Preparation Triphenylphosphite is prepared from phosphorus trichloride and phenol in the presence of a catalytic amount of base: :P ...

with

methylmagnesium chloride Methylmagnesium chloride is an organometallic compound with the general formula . This highly flammable, colorless, and moisture sensitive compound is the simplest Grignard reagent and is commercially available, usually as a solution in tetrahydro ...

: : 3 CH₃MgCl + P(OC₆H₅)₃ → P(CH₃)₃ + 3 C₆H₅OMgCl The synthesis is conducted in

dibutyl ether Dibutyl ether is a chemical compound belonging to the ether family with the molecular formula of . It is colorless, volatile, and flammable liquid and has peculiar ethereal smell. Liquid dibutyl ether is lighter than water. On the other hand, the ...

, from which the more volatile PMe₃ can be distilled.

Reactions

With a pK_a of 8.65, PMe₃ reacts with strong acids to give salts PMe₃. This reaction is reversible. With strong bases, such as

alkyl lithium compound In organometallic chemistry, organolithium reagents are chemical compounds that contain carbon–lithium (C–Li) bonds. These reagents are important in organic synthesis, and are frequently used to transfer the organic group or the lithium atom ...

s, a methyl group undergoes deprotonation to give PMe₂CH₂Li. PMe₃ is easily oxidised to the phosphine oxide with oxygen. It reacts with

methyl bromide Bromomethane, commonly known as methyl bromide, is an organobromine compound with chemical formula, formula Carbon, CHydrogen, H3Bromine, Br. This colorless, odorless, nonflammable gas is Bromine cycle, produced both industrially and biologically ...

to give

tetramethylphosphonium bromide Tetramethylphosphonium bromide is an organophosphorus compound with the formula (CH3)4PBr. It is a white, water-soluble solid, the salt of the cation tetramethylphosphonium and the bromide anion. It is prepared by treating trimethylphosphine with ...

Coordination chemistry

Trimethylphosphine is a highly basic

that forms complexes with most metals. As a ligand, trimethylphosphine's Tolman cone angle is 118°. This angle is an indication of the amount of steric protection that this ligand provides to the metal that to which it is bound. Being a relatively compact phosphine, several can bind to a single transition metal, as illustrated by the existence of Pt(PEt₃)₄. Its complex with silver iodide, AgI(PMe₃) is an air-stable solid that releases PMe₃ upon heating.

Safety

PMe₃ is toxic and

pyrophoric A substance is pyrophoric (from , , 'fire-bearing') if it ignites spontaneously in air at or below (for gases) or within 5 minutes after coming into contact with air (for liquids and solids). Examples are organolithium compounds and triethylb ...

. It converts to a much safer

phosphine oxide Phosphine oxide is the inorganic compound with the formula H3PO. Although stable as a dilute gas, liquid or solid samples are unstable. Unlike many other compounds of the type POxHy, H3PO is rarely discussed and is not even mentioned in major so ...

upon treatment with

sodium hypochlorite Sodium hypochlorite is an alkaline inorganic chemical compound with the formula (also written as NaClO). It is commonly known in a dilute aqueous solution as bleach or chlorine bleach. It is the sodium salt of hypochlorous acid, consisting of ...

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...

References

{{Reflist Tertiary phosphines Foul-smelling chemicals Methyl compounds