Phosphorine
Encyclopedia
Phosphorine is a heavier element
analog of pyridine
, containing a phosphorus
atom instead of an aza-
moiety. It is also called phosphabenzene and belongs to the phosphaalkene
class. Phosphorine is a planar aromatic compound with 88% of the aromaticity of that of benzene
. The P-C bond length
is 173 pm and the C-C bond lengths center around 140 pm and show little variation.
Phosphorine is generally stable against air and moisture and can be handled without special inert
atmosphere equipment, so it is different from silabenzene
, which is usually not only air- and moisture-sensitive but also thermally unstable without extensive steric protection. This stability of phosphorine comes from the close electronegativities
of phosphorus (2.1) and carbon
(2.5). The physical and chemical properties of metal complex
es bearing phosphorine as a ligand
as well as phosphorine itself have been studied extensively.
and phosphorus sources, such as phosphine
, P(CH2OH)3, and P(SiMe3)3.
Unsubstituted phosphorine, which was reported by Arthur J. Ashe III in 1971, is a distillable liquid that is somewhat air-sensitive but stable against hydrolysis
. In 1990s, François Mathey developed a methodology for the synthesis of functionalized phosphorines using transition metal
mediated reactions including palladium
- or nickel
-catalyzed coupling reactions.
More recently, Mathey and Grundy developed a new ring-opening approach, synthesising a six-membered ring phosphabenzene in a one-pot method from a five-membered phosphole
ring.
, the electronic structure is very different from that of pyridine. The lone pair of pyridine is its HOMO
, so pyridine has good σ-donating ability. The HOMO
and LUMO
of phosphorine, on the other hand, are its π and π* orbital
s, respectively, and the lone pair is located at the lower energy level. Thus phosphinines are much better π-acceptor ligands, but less good σ-donors compared to pyridines. Phosphorine with a 0.55 positive charge on phosphorus and pyridine
with a -0.67 negative charge on nitrogen also show different reactivities against nucleophile
s. Pyridine reacts with nucleophile
s at the C-2 position due to the higher electronegativity
of the nitrogen
atom. Nucleophile
s, however, attack the phosphorus
atom of phosphorine, producing λ4-phosphorine anion, which reacts with electrophile
s to give λ5-phosphorine. Lately it was reported that anionic λ4-phosphorine coordinates to transition metals as a π-donor ligand.
Phosphorine undergoes electrophilic substitution reactions like ordinary aromatic compounds: bromination
, acyl
ation, and so on.
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
analog of pyridine
Pyridine
Pyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one C-H group replaced by a nitrogen atom...
, containing a phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
atom instead of an aza-
Aza-
The prefix aza- is used in organic chemistry to form names of organic compounds where a carbon atom is replaced by a nitrogen atom. Sometimes a number between hyphens is inserted before it to state which atom the nitrogen atom replaces...
moiety. It is also called phosphabenzene and belongs to the phosphaalkene
Phosphaalkene
Phosphaalkenes are organophosphorus compounds with double bonds between carbon and phosphorus with the formula R2C=PR. In the compound phosphorine one carbon atom in benzene is replaced by phosphorus...
class. Phosphorine is a planar aromatic compound with 88% of the aromaticity of that of benzene
Benzene
Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....
. The P-C bond length
Bond length
- Explanation :Bond length is related to bond order, when more electrons participate in bond formation the bond will get shorter. Bond length is also inversely related to bond strength and the bond dissociation energy, as a stronger bond will be shorter...
is 173 pm and the C-C bond lengths center around 140 pm and show little variation.
Phosphorine is generally stable against air and moisture and can be handled without special inert
Inert
-Chemistry:In chemistry, the term inert is used to describe a substance that is not chemically reactive.The noble gases were previously known as inert gases because of their perceived lack of participation in any chemical reactions...
atmosphere equipment, so it is different from silabenzene
Silabenzene
A silabenzene is a heteroaromatic compound containing one or more silicon atoms instead of carbon atom in benzene. A single substitution gives silabenzene proper; additional substitutions give a disilabenzene , trisilabenzene , etc.Silabenzenes have been the targets of many theoretical and...
, which is usually not only air- and moisture-sensitive but also thermally unstable without extensive steric protection. This stability of phosphorine comes from the close electronegativities
Electronegativity
Electronegativity, symbol χ , is a chemical property that describes the tendency of an atom or a functional group to attract electrons towards itself. An atom's electronegativity is affected by both its atomic number and the distance that its valence electrons reside from the charged nucleus...
of phosphorus (2.1) and carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
(2.5). The physical and chemical properties of metal 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 bearing phosphorine 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...
as well as phosphorine itself have been studied extensively.
History
The first phosphorine is 2,4,6-triphenylphoshorine, which was synthesized by Gottfried Märkl in 1969 from the corresponding pyrylium saltPyrylium salt
A pyrylium salt is a salt containing a pyrylium cation or a derivative of it. The pyrylium cation is a conjugated 6-membered carbon ring system with one carbon atom replaced by a positively charged oxygen atom. It is, like benzene, an aromatic compound...
and phosphorus sources, such as phosphine
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...
, P(CH2OH)3, and P(SiMe3)3.
Unsubstituted phosphorine, which was reported by Arthur J. Ashe III in 1971, is a distillable liquid that is somewhat air-sensitive but stable against hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
. In 1990s, François Mathey developed a methodology for the synthesis of functionalized phosphorines using 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...
mediated reactions including palladium
Palladium
Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46. It is a rare and lustrous silvery-white metal discovered in 1803 by William Hyde Wollaston. He named it after the asteroid Pallas, which was itself named after the epithet of the Greek goddess Athena, acquired...
- or nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
-catalyzed coupling reactions.
More recently, Mathey and Grundy developed a new ring-opening approach, synthesising a six-membered ring phosphabenzene in a one-pot method from a five-membered phosphole
Phosphole
Phosphole is the organic compound with the chemical formula C4H4PH; it is the phosphorus analog of pyrrole. The term phosphole also refers to substituted derivatives of the parent heterocycle...
ring.
Properties and reactions
Although phosphorine is a heavier element analog of pyridinePyridine
Pyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one C-H group replaced by a nitrogen atom...
, the electronic structure is very different from that of pyridine. The lone pair of pyridine is its HOMO
HOMO/LUMO
HOMO and LUMO are acronyms for highest occupied molecular orbital and lowest unoccupied molecular orbital, respectively. The energy difference between the HOMO and LUMO is termed the HOMO-LUMO gap...
, so pyridine has good σ-donating ability. The HOMO
HOMO/LUMO
HOMO and LUMO are acronyms for highest occupied molecular orbital and lowest unoccupied molecular orbital, respectively. The energy difference between the HOMO and LUMO is termed the HOMO-LUMO gap...
and LUMO
HOMO/LUMO
HOMO and LUMO are acronyms for highest occupied molecular orbital and lowest unoccupied molecular orbital, respectively. The energy difference between the HOMO and LUMO is termed the HOMO-LUMO gap...
of phosphorine, on the other hand, are its π and π* 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...
s, respectively, and the lone pair is located at the lower energy level. Thus phosphinines are much better π-acceptor ligands, but less good σ-donors compared to pyridines. Phosphorine with a 0.55 positive charge on phosphorus and pyridine
Pyridine
Pyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one C-H group replaced by a nitrogen atom...
with a -0.67 negative charge on nitrogen also show different reactivities against nucleophile
Nucleophile
A nucleophile is a species that donates an electron-pair to an electrophile to form a chemical bond in a reaction. All molecules or ions with a free pair of electrons can act as nucleophiles. Because nucleophiles donate electrons, they are by definition Lewis bases.Nucleophilic describes the...
s. Pyridine reacts with nucleophile
Nucleophile
A nucleophile is a species that donates an electron-pair to an electrophile to form a chemical bond in a reaction. All molecules or ions with a free pair of electrons can act as nucleophiles. Because nucleophiles donate electrons, they are by definition Lewis bases.Nucleophilic describes the...
s at the C-2 position due to the higher electronegativity
Electronegativity
Electronegativity, symbol χ , is a chemical property that describes the tendency of an atom or a functional group to attract electrons towards itself. An atom's electronegativity is affected by both its atomic number and the distance that its valence electrons reside from the charged nucleus...
of the nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
atom. Nucleophile
Nucleophile
A nucleophile is a species that donates an electron-pair to an electrophile to form a chemical bond in a reaction. All molecules or ions with a free pair of electrons can act as nucleophiles. Because nucleophiles donate electrons, they are by definition Lewis bases.Nucleophilic describes the...
s, however, attack the phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
atom of phosphorine, producing λ4-phosphorine anion, which reacts with electrophile
Electrophile
In general electrophiles are positively charged species that are attracted to an electron rich centre. In chemistry, an electrophile is a reagent attracted to electrons that participates in a chemical reaction by accepting an electron pair in order to bond to a nucleophile...
s to give λ5-phosphorine. Lately it was reported that anionic λ4-phosphorine coordinates to transition metals as a π-donor ligand.
Phosphorine undergoes electrophilic substitution reactions like ordinary aromatic compounds: bromination
Bromine
Bromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826...
, acyl
Acyl
An acyl group is a functional group derived by the removal of one or more hydroxyl groups from an oxoacid, including inorganic acids.In organic chemistry, the acyl group is usually derived from a carboxylic acid . Therefore, it has the formula RCO-, where R represents an alkyl group that is...
ation, and so on.
See also
- 6-membered aromatic rings with one carbon replaced by another group: borabenzeneBorabenzeneA borabenzene is a heteroaromatic compound that has a boron atom instead of the carbon atom of a benzene molecule. A free borabenzene, which has no donor ligand on the boron atom, has not yet been isolated despite its simple structure and the chemical robustness of boron-carbon bonds...
, silabenzeneSilabenzeneA silabenzene is a heteroaromatic compound containing one or more silicon atoms instead of carbon atom in benzene. A single substitution gives silabenzene proper; additional substitutions give a disilabenzene , trisilabenzene , etc.Silabenzenes have been the targets of many theoretical and...
, germanabenzeneGermanabenzeneGermabenzene is the parent representative of a group of chemical compounds containing in their molecular structure a benzene ring with a carbon atom replaced by a germanium atom. Germabenzene itself has been studied theoretically, but has not been synthesized...
, stannabenzeneStannabenzeneStannabenzene is the parent representative of a group of organotin compounds that are related to benzene with a carbon atom replaced by a tin atom. Stannabenzene itself has been studied by computational chemistry, but has not been isolated....
, pyridinePyridinePyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one C-H group replaced by a nitrogen atom...
, phosphorine, arsabenzeneArsabenzeneArsabenzene is an organoarsenic heterocyclic compound with the chemical formula C5H5As. It belongs to a group of compounds called heteroarenes that have the general formula C5H5E ....
, pyrylium saltPyrylium saltA pyrylium salt is a salt containing a pyrylium cation or a derivative of it. The pyrylium cation is a conjugated 6-membered carbon ring system with one carbon atom replaced by a positively charged oxygen atom. It is, like benzene, an aromatic compound...