Periodinane
Encyclopedia
Periodinanes are chemical compound
s containing hypervalent iodine. These iodine
compounds are hypervalent because the iodine atom in it contains more than the 8 electrons in the valence shell required for the octet rule
. When iodine is complexed with a monodentate electronegative ligand
such as chlorine
, iodine compounds occur with a +3 oxidation number
as iodine(III) or λ
3-iodanes or as a +5 oxidation number
as iodine(V) or λ
5-iodanes. Iodine itself contains 7 valence electrons and in a λ3-iodane three more are donated by the ligands making it a decet structure. λ5-iodanes are dodecet molecules. In an ordinary iodine compound such as iodobenzene the number of valence electrons is eight as expected. In order to get from iodine to a hypervalent iodine compound it gets oxidized with removal of first 3 electrons and then 5 electrons. The ligands in turn contribute electrons pairs and form coordinate covalent bond
s by adding a total of 6 or 10 electrons back to iodine. In the L-I-N notation L stands for the number of electrons donated by ligands and N the number of ligands.
The first hypervalent iodine compound, (dichloroiodo)benzene
(C6H5Cl2I) was prepared in 1886 by the German chemist Conrad Willgerodt
by passing chlorine
gas through iodobenzene
in a cooled solution of chloroform
.
λ3-iodanes such as diarylchloroiodanes have a pseudotrigonal bipyramidal
geometry displaying apicophilicity
with a phenyl group and a chlorine group at the apical positions and other phenyl group with two lone pair
electrons in the equatorial positions. The λ5-iodanes such as the Dess-Martin periodinane
have square pyramidal
geometries with 4 heteroatoms in basal positions and one apical phenyl group.
Classical organic procedures exist for the preparation of iodosobenzene diacetate from peracetic acid and acetic acid
.
Phenyliodine bis(trifluoroacetate), PIFA, or (bis(trifluoroacetoxy)iodo)benzene
is a related compound based on trifluoroacetic acid
Phenyliodine diacetate, PIDA, is an organic reagent used as an oxidizing agent. This is suitable for cleaving glycols and alpha-hydroxy ketones in ring opening and Mannich reaction.
The acetate can be hydrolysed with water to iodoxybenzene or iodylbenzene C6H5O2I
This compound was first prepared by Willgerodt by disproportionation
of iodosylbenzene under steam distillation
to iodylbenzene and iodobenzene
is a known oxidizing agent
.
Iodosobenzene diacetate can also be hydrolyzed to iodosylbenzene with sodium hydroxide which is actually a polymer
with the molecular formula (C6H5OI)n . Iodosylbenzene is used in organic oxidations. Dess-Martin periodinane
(1983) is another powerful oxidant and an improvement of the IBX acid already in existence in 1893. The IBX acid is prepared from 2-iodobenzoic acid and potassium bromate
and sulfuric acid
and is insoluble in most solvents whereas the Dess-Martin reagent prepared from reaction of the IBX acid with acetic anhydride
is very soluble. The oxidation mechanism ordinarily consists of a ligand exchange reaction followed by a reductive elimination.
is misleading and IUPAC prefers diaryl-λ3-iodane. The first such compound was synthesised in 1894 (Meyer and Hartmann reaction) . With halogen counterions diaryliodonium salts show poor solubility in many organic solvents but solubility is improved with triflate
and tetrafluoroborate
counterions.
Diaryliodonium salts can be prepared in a number of ways. In one method an aryl iodide is first oxidized to an aryliodine(III) compound (ArIO, ArIO2) with as a second step a ligand exchange with an arene (AES
), an arylstannane or an arylsilane. In another method diaryliodonium salts a prepared from preformed hypervalent iodine compounds such as iodic acid
, iodosyl sulfate or iodosyl triflate.
diaryliodonium salts react with nucleophile
s at iodine replacing one ligand and then form the substituted arene ArNu and iodobenzen ArI by reductive elimination or by substitution by ligand. diaryliodonium salts also react with metals M through ArMX intermediates in cross-coupling reactions.
Current research focuses on their use in carbon-carbon
and carbon-heteroatom bond forming reactions. In one study such reaction, an intramolecular
C-N coupling of an alkoxyhydroxylamine to its anisole
group is accomplished with a catalytic amount of aryliodide in trifluoroethanol:
In this reaction the periodinane (depicted as intermediate A) is formed by oxidation of the aryliodide with the sacrificial catalyst mCPBA which in turn converts the hydroxylamine group to a nitrenium ion
B. This ion is the electrophile
in ipso
addition to the aromatic ring forming a lactam
with a enone
group.
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
s containing hypervalent iodine. These iodine
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
compounds are hypervalent because the iodine atom in it contains more than the 8 electrons in the valence shell required for the octet rule
Octet rule
The octet rule is a chemical rule of thumb that states that atoms of low The octet rule is a chemical rule of thumb that states that atoms of low The octet rule is a chemical rule of thumb that states that atoms of low (The octet rule is a chemical rule of thumb that states that atoms of low (...
. When iodine is complexed with a monodentate electronegative 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...
such as chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
, iodine compounds occur with a +3 oxidation number
Oxidation number
In coordination chemistry, the oxidation number of a central atom in a coordination compound is the charge that it would have if all the ligands were removed along with the electron pairs that were shared with the central atom. Oxidation numbers are often confused with oxidation states.The...
as iodine(III) or λ
Lambda
Lambda is the 11th letter of the Greek alphabet. In the system of Greek numerals lambda has a value of 30. Lambda is related to the Phoenician letter Lamed . Letters in other alphabets that stemmed from lambda include the Roman L and the Cyrillic letter El...
3-iodanes or as a +5 oxidation number
Oxidation number
In coordination chemistry, the oxidation number of a central atom in a coordination compound is the charge that it would have if all the ligands were removed along with the electron pairs that were shared with the central atom. Oxidation numbers are often confused with oxidation states.The...
as iodine(V) or λ
Lambda
Lambda is the 11th letter of the Greek alphabet. In the system of Greek numerals lambda has a value of 30. Lambda is related to the Phoenician letter Lamed . Letters in other alphabets that stemmed from lambda include the Roman L and the Cyrillic letter El...
5-iodanes. Iodine itself contains 7 valence electrons and in a λ3-iodane three more are donated by the ligands making it a decet structure. λ5-iodanes are dodecet molecules. In an ordinary iodine compound such as iodobenzene the number of valence electrons is eight as expected. In order to get from iodine to a hypervalent iodine compound it gets oxidized with removal of first 3 electrons and then 5 electrons. The ligands in turn contribute electrons pairs and form coordinate covalent bond
Coordinate covalent bond
A dipolar bond, also known as dative covalent bond or coordinate bond is a kind of 2-centre, 2-electron covalent bond in which the two electrons derive from the same atom. Typically, a dipolar bond is formed when a Lewis base donates a pair of electrons to a Lewis acid. This description of bonding...
s by adding a total of 6 or 10 electrons back to iodine. In the L-I-N notation L stands for the number of electrons donated by ligands and N the number of ligands.
Periodinane compounds
The concept of hypervalent iodine was developed by J.J. Musher in 1969. In order to accommodate the excess of electrons in hypervalent compounds the 3-center-4-electron bond was introduced in analogy with the 3-center-2-electron bond observed in electron deficient compounds. One such bond exists in iodine(III) compounds and two such bonds reside in iodine(V) compounds.The first hypervalent iodine compound, (dichloroiodo)benzene
Iodobenzene dichloride
Iodobenzene dichloride is a complex of iodobenzene with chlorine. It is used as an oxidant.Single-crystal X-ray crystallography has been used to determine its structure; as can be predicted by VSEPR theory, it adopts a T-shaped geometry about the central iodine atom.-Preparation:Iodobenzene...
(C6H5Cl2I) was prepared in 1886 by the German chemist Conrad Willgerodt
Conrad Willgerodt
Conrad Heinrich Christoph Willgerodt was a German chemist and discovered of the Willgerodt reaction. He was also the discoverer of Iodosobenzene.Willgerodt was a professor at the University of Freiburg.-References:...
by passing chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
gas through iodobenzene
Iodobenzene
Iodobenzene is an organic compound consisting of a benzene ring substitituted with one iodine atom. It is useful as a synthetic intermediate in organic chemistry.-Preparation:...
in a cooled solution of chloroform
Chloroform
Chloroform is an organic compound with formula CHCl3. It is one of the four chloromethanes. The colorless, sweet-smelling, dense liquid is a trihalomethane, and is considered somewhat hazardous...
.
- C6H5I + Cl2 → C6H5ICl2
λ3-iodanes such as diarylchloroiodanes have a pseudotrigonal bipyramidal
Trigonal bipyramid molecular geometry
In chemistry a trigonal bipyramid formation is a molecular geometry with one atom at the center and 5 more atoms at the corners of a triangular dipyramid...
geometry displaying apicophilicity
Apicophilicity
Apicophilicity is the phenomenon in which electronegative substituents of trigonal bipyramidal pentacoordinate compounds prefer to occupy apical positions ....
with a phenyl group and a chlorine group at the apical positions and other phenyl group with two lone pair
Lone pair
In chemistry, a lone pair is a valence electron pair without bonding or sharing with other atoms. They are found in the outermost electron shell of an atom, so lone pairs are a subset of a molecule's valence electrons...
electrons in the equatorial positions. The λ5-iodanes such as the Dess-Martin periodinane
Dess-Martin periodinane
Dess–Martin periodinane is a chemical reagent used to oxidize primary alcohols to aldehydes and secondary alcohols to ketones. This periodinane has several advantages over chromium- and DMSO-based oxidants that include milder conditions , shorter reaction times, higher yields, simplified workups,...
have square pyramidal
Square pyramidal molecular geometry
In molecular geometry, square based pyramidal geometry describes the shape of certain compounds with the formula ML5 where L is a ligand. If the ligand atoms were connected, the resulting shape would be that of a pyramid with a square base. The geometry is common for certain main group compounds...
geometries with 4 heteroatoms in basal positions and one apical phenyl group.
Classical organic procedures exist for the preparation of iodosobenzene diacetate from peracetic acid and acetic acid
Acetic acid
Acetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell...
.
- C6H5I + CH3COOOH → C6H5I(OOCCH3)2
Phenyliodine bis(trifluoroacetate), PIFA, or (bis(trifluoroacetoxy)iodo)benzene
(Bis(trifluoroacetoxy)iodo)benzene
benzene, C10H5F6IO4, is a hypervalent iodine compound used as a reagent in organic chemistry. The reagent is used in an acidic modification of the Hofmann rearrangement. One example is the conversion of cyclobutanecarboxamine to cyclobutylamine hydrochloride...
is a related compound based on trifluoroacetic acid
Trifluoroacetic acid
Trifluoroacetic acid is the simplest stable perfluorinated carboxylic acid chemical compound, with the formula CF3CO2H. It is a strong carboxylic acid due to the influence of the electronegative trifluoromethyl group. TFA is almost 100,000-fold more acidic than acetic acid...
Phenyliodine diacetate, PIDA, is an organic reagent used as an oxidizing agent. This is suitable for cleaving glycols and alpha-hydroxy ketones in ring opening and Mannich reaction.
The acetate can be hydrolysed with water to iodoxybenzene or iodylbenzene C6H5O2I
This compound was first prepared by Willgerodt by disproportionation
Disproportionation
Disproportionation, also known as dismutation is used to describe a specific type of redox reaction in which a species is simultaneously reduced and oxidized so as to form two different products....
of iodosylbenzene under steam distillation
Steam distillation
Steam distillation is a special type of distillation for temperature sensitive materials like natural aromatic compounds....
to iodylbenzene and iodobenzene
- 2 PhIO → PhIO2 + PhI
is a known oxidizing agent
Oxidizing agent
An oxidizing agent can be defined as a substance that removes electrons from another reactant in a redox chemical reaction...
.
Iodosobenzene diacetate can also be hydrolyzed to iodosylbenzene with sodium hydroxide which is actually a polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
with the molecular formula (C6H5OI)n . Iodosylbenzene is used in organic oxidations. Dess-Martin periodinane
Dess-Martin periodinane
Dess–Martin periodinane is a chemical reagent used to oxidize primary alcohols to aldehydes and secondary alcohols to ketones. This periodinane has several advantages over chromium- and DMSO-based oxidants that include milder conditions , shorter reaction times, higher yields, simplified workups,...
(1983) is another powerful oxidant and an improvement of the IBX acid already in existence in 1893. The IBX acid is prepared from 2-iodobenzoic acid and potassium bromate
Bromate
The bromate anion, BrO, is a bromine-based oxoanion. A bromate is a chemical compound that contains this ion. Examples of bromates include sodium bromate, , and potassium bromate, .Bromates are formed many different ways in municipal drinking water...
and sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
and is insoluble in most solvents whereas the Dess-Martin reagent prepared from reaction of the IBX acid with acetic anhydride
Acetic anhydride
Acetic anhydride, or ethanoic anhydride, is the chemical compound with the formula 2O. Commonly abbreviated Ac2O, it is the simplest isolatable acid anhydride and is a widely used reagent in organic synthesis...
is very soluble. The oxidation mechanism ordinarily consists of a ligand exchange reaction followed by a reductive elimination.
Diaryliodonium salts
Diaryliodonium salts are compounds of the type [Ar-I+-Ar]X- . The term saltSalt
In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...
is misleading and IUPAC prefers diaryl-λ3-iodane. The first such compound was synthesised in 1894 (Meyer and Hartmann reaction) . With halogen counterions diaryliodonium salts show poor solubility in many organic solvents but solubility is improved with triflate
Triflate
Trifluoromethanesulfonate, also known by the trivial name triflate, is a functional group with the formula CF3SO3-. The triflate group is often represented by -OTf, as opposed to -Tf...
and tetrafluoroborate
Tetrafluoroborate
Tetrafluoroborate is the anion BF4−. This tetrahedral species is isoelectronic with tetrafluoromethane, CF4 and tetrafluoroammonium NF4+, and is valence isoelectronic with many stable and important species including the closely related anion perchlorate, ClO4−...
counterions.
Diaryliodonium salts can be prepared in a number of ways. In one method an aryl iodide is first oxidized to an aryliodine(III) compound (ArIO, ArIO2) with as a second step a ligand exchange with an arene (AES
Electrophilic aromatic substitution
Electrophilic aromatic substitution EAS is an organic reaction in which an atom, usually hydrogen, appended to an aromatic system is replaced by an electrophile...
), an arylstannane or an arylsilane. In another method diaryliodonium salts a prepared from preformed hypervalent iodine compounds such as iodic acid
Iodic acid
Iodic acid, HIO3, can be obtained as a white solid. It dissolves in water very well, but it also exists in the pure state, as opposed to chloric acid or bromic acid. Iodic acid contains iodine in the oxidation state +5 and it is one of the most stable oxo-acids of the halogens in its pure state....
, iodosyl sulfate or iodosyl triflate.
diaryliodonium salts react 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 iodine replacing one ligand and then form the substituted arene ArNu and iodobenzen ArI by reductive elimination or by substitution by ligand. diaryliodonium salts also react with metals M through ArMX intermediates in cross-coupling reactions.
Periodinane uses
The predominant use of hypervalent iodine compounds is that of oxidizing reagent replacing many toxic reagents based on heavy metals .Current research focuses on their use in carbon-carbon
Carbon-carbon bond
A carbon–carbon bond is a covalent bond between two carbon atoms. The most common form is the single bond: a bond composed of two electrons, one from each of the two atoms. The carbon–carbon single bond is a sigma bond and is said to be formed between one hybridized orbital from each...
and carbon-heteroatom bond forming reactions. In one study such reaction, an intramolecular
Intramolecular
Intramolecular in chemistry describes a process or characteristic limited within the structure of a single molecule, a property or phenomenon limited to the extent of a single molecule.- Examples :...
C-N coupling of an alkoxyhydroxylamine to its anisole
Anisole
Anisole, or methoxybenzene, is the organic compound with the formula CH3OC6H5. It is a colorless liquid with a smell reminiscent of anise seed, and in fact many of its derivatives are found in natural and artificial fragrances...
group is accomplished with a catalytic amount of aryliodide in trifluoroethanol:
In this reaction the periodinane (depicted as intermediate A) is formed by oxidation of the aryliodide with the sacrificial catalyst mCPBA which in turn converts the hydroxylamine group to a nitrenium ion
Nitrenium ion
A nitrenium ion in organic chemistry is a reactive intermediate based on nitrogen with both an electron lone pair and a positive charge and with two substituents . Nitrenium ions are isoelectronic to carbenes, and can exist in either a singlet or a triplet state...
B. This ion is the 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...
in ipso
IPSO
IPSO may refer to:* International Programme on the State of the Ocean IPSO* Les Intellectuels pour la souveraineté — a group of intellectuals studying and promoting Quebec independence....
addition to the aromatic ring forming a lactam
Lactam
A lactam is a cyclic amide. Prefixes indicate how many carbon atoms are present in the ring: β-lactam , γ-lactam , δ-lactam...
with a enone
Enone
An enone is an unsaturated chemical compound or functional group consisting of a conjugated system of an alkene and a ketone. The simplest enone is methyl vinyl ketone or CH2=CHCOCH3....
group.