Tributylphosphine
Encyclopedia
Tributylphosphine, formula
P(CH) or PBu, is a tertiary phosphine, most commonly encountered as a ligand
in transition metal
complex
es. It is an oily liquid at room temperature, with a nauseating odor. It reacts slowly with atmospheric oxygen
, and rapidly with other oxidizing agent
s, to give the corresponding phosphine oxide
. It is usually handled using air-free technique
s.
to butene: the addition proceeds by a free radical mechanism, and so the Markovnikov rule is not followed.
Tributylphosphine can be prepared in the laboratory by reaction of the appropriate Grignard reagent with phosphorus trichloride
although, as it is commercially available at reasonable prices, it is rare to have to perform the small-scale preparation.
in the cobalt
-catalyzed hydroformylation
of alkene
s, where it greatly increases the ratio of straight-chain aldehyde
s to branched-chain aldehydes in the product mixture. However, tricyclohexylphosphine
is even more effective for this purpose (although more expensive) and, in any case, rhodium catalysts are usually preferred to cobalt catalysts for the hydroformylation of alkenes.
Tributylphosphine is also a common ligand
for the preparation of complex
es of transition metal
s in relatively low oxidation state
s, as it is cheap and less air-sensitive. It has a conveniently low volatility, which makes it easier to handle than other trialkylphosphines. Although its complexes are generally highly soluble, they are often more difficult to crystallize compared to complexes of more rigid phosphines. Furthermore, the 1H NMR properties are less easily interpreted and can mask signals for other ligands. Compared to other tertiary phosphines, it is compact (cone angle: 136°) and basic (χ-parameter: 5.25 cm–1)
, and glassware which has come into contact with the compound must be decontaminated before leaving the hood. Because tributylphosphine must be protected from the atmosphere, it is usually handled using syringe techniques. The manipulation of large quantities requires specific precautions to prevent the release of the vapour into the environment. For transport purposes, it is classified as a "spontaneously flammable liquid" (group 4.2), although this is rarely a significant problem in the laboratory use of small quantities: it may not be transported by air.
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
P(CH) or PBu, is a tertiary phosphine, most commonly encountered as a ligand
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...
in transition metal
Transition metal
The term transition metal has two possible meanings:*The IUPAC definition states that a transition metal is "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." Group 12 elements are not transition metals in this definition.*Some...
complex
Complex (chemistry)
In chemistry, a coordination complex or metal complex, is an atom or ion , bonded to a surrounding array of molecules or anions, that are in turn known as ligands or complexing agents...
es. It is an oily liquid at room temperature, with a nauseating odor. It reacts slowly with atmospheric oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
, and rapidly with other oxidizing agent
Oxidizing agent
An oxidizing agent can be defined as a substance that removes electrons from another reactant in a redox chemical reaction...
s, to give the corresponding 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...
. It is usually handled using air-free technique
Air-free technique
Air-free techniques refer to a range of manipulations in the chemistry laboratory for the handling of compounds that are air-sensitive. These techniques prevent the compounds from reacting with components of air, usually water and oxygen; less commonly carbon dioxide and nitrogen...
s.
Preparation
Tributylphosphine is prepared industrially by the addition of phosphinePhosphine
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...
to butene: the addition proceeds by a free radical mechanism, and so the Markovnikov rule is not followed.
-
- PH + 3CH=CHCHCH → P(CHCHCHCH)
Tributylphosphine can be prepared in the laboratory by reaction of the appropriate Grignard reagent with phosphorus trichloride
Phosphorus trichloride
Phosphorus trichloride is a chemical compound of phosphorus and chlorine, having chemical formula PCl3. Its shape is trigonal pyramidal. It is the most important of the three phosphorus chlorides. It is an important industrial chemical, being used for the manufacture of organophosphorus compounds...
although, as it is commercially available at reasonable prices, it is rare to have to perform the small-scale preparation.
-
- 3BuMgCl + PCl → PBu + 3MgCl
Use
Tributylphosphine finds some industrial use as a catalyst modifierCatalysis
Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations....
in the cobalt
Cobalt
Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....
-catalyzed hydroformylation
Hydroformylation
Hydroformylation, also known as oxo synthesis or oxo process, is an important industrial process for the production of aldehydes from alkenes. This chemical reaction entails the addition of a formyl group and a hydrogen atom to a carbon-carbon double bond...
of alkene
Alkene
In organic chemistry, an alkene, olefin, or olefine is an unsaturated chemical compound containing at least one carbon-to-carbon double bond...
s, where it greatly increases the ratio of straight-chain aldehyde
Aldehyde
An aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl center bonded to hydrogen and an R group....
s to branched-chain aldehydes in the product mixture. However, tricyclohexylphosphine
Tricyclohexylphosphine
Tricyclohexylphosphine is the tertiary phosphine with the formula P3. Commonly used as a ligand in organometallic chemistry, it is often abbreviated to PCy3, where Cy stands for cyclohexyl...
is even more effective for this purpose (although more expensive) and, in any case, rhodium catalysts are usually preferred to cobalt catalysts for the hydroformylation of alkenes.
Tributylphosphine is also a common ligand
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...
for the preparation of complex
Complex (chemistry)
In chemistry, a coordination complex or metal complex, is an atom or ion , bonded to a surrounding array of molecules or anions, that are in turn known as ligands or complexing agents...
es of transition metal
Transition metal
The term transition metal has two possible meanings:*The IUPAC definition states that a transition metal is "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." Group 12 elements are not transition metals in this definition.*Some...
s in relatively low oxidation state
Oxidation state
In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...
s, as it is cheap and less air-sensitive. It has a conveniently low volatility, which makes it easier to handle than other trialkylphosphines. Although its complexes are generally highly soluble, they are often more difficult to crystallize compared to complexes of more rigid phosphines. Furthermore, the 1H NMR properties are less easily interpreted and can mask signals for other ligands. Compared to other tertiary phosphines, it is compact (cone angle: 136°) and basic (χ-parameter: 5.25 cm–1)
Hazards
The main laboratory inconvenience of tributylphosphine is its extremely strong and unpleasant smell. All manipulations must be carried out in an efficient fume hoodFume hood
A fume hood or fume cupboard is a type of local ventilation device that is designed to limit exposure to hazardous or noxious fumes, vapors or dusts. A fume hood is typically a large piece of equipment enclosing five sides of a work area, the bottom of which is most commonly located at a standing...
, and glassware which has come into contact with the compound must be decontaminated before leaving the hood. Because tributylphosphine must be protected from the atmosphere, it is usually handled using syringe techniques. The manipulation of large quantities requires specific precautions to prevent the release of the vapour into the environment. For transport purposes, it is classified as a "spontaneously flammable liquid" (group 4.2), although this is rarely a significant problem in the laboratory use of small quantities: it may not be transported by air.