Organomanganese chemistry
Encyclopedia
Organomanganese chemistry is the chemistry
of organometallic compounds containing a carbon
to manganese
chemical bond
. In a recent review Cahiez et al. argue that as manganese is cheap and benign (only iron
performs better in these aspects), organomanganese compounds have potential as chemical reagents, although currently they are not widely used as such despite extensive research.
The first organomanganese compounds were synthesised in 1937 by Gilman and Bailee who reacted phenyllithium
with manganese(II) iodide
to form phenylmanganese iodide (PhMnI) and diphenylmanganese (Ph2Mn).
The reactivity of organomanganese compounds can be compared to that of organomagnesium compounds and organozinc compound
s. The electronegativity
of Mn (1.55) is comparable to that of Mg (1.55) and Zn (1.65) making the carbon atom (EN = 2,55) nucleophilic. The reduction potential
of Mn is also intermediate between Mg and Zn. Key disadvantage of organomanganese compounds is that they can be obtained directly from the metal only with difficulty.
Organomanganese halides can be obtained by reaction of manganese halides (manganese(II) bromide
, manganese(II) bromide
) with organolithium or organomagnesium compounds in transmetallation:
Manganese iodide can be prepared in situ from manganese and iodine
in ether
. Further reaction gives the symmetrical diorganomanganese compound.
Organomanganates (the ate complex
) are the most stable compounds:
The organomanganese compounds are usually prepared in THF
where they are the most stable (via complexation) even though many of them must be handled at low temperatures. Simple dialkylmanganese decompose by beta-hydride elimination
to a mixture of alkanes and alkenes.
, Mn2(CO)10. Bromination and reduction affords BrMn(CO)5 and LiMn(CO)5. These species are precursors to alkyl, aryl, and acyl derivatives:
The general pattern of reactivity is analogous to that for the more popular cyclopentadienyliron dicarbonyl dimer
.
The Mn(I) compound BrMn(CO)5 is also the precursor to many pi-arene complexes:
These cationic half-sandwich complexes are susceptible to nucleophilic additions to give cyclohexadienyl derivatives and ultimated functionalized arenes.
s and ketone
s to the alcohol
, with carbon dioxide
to the carboxylic acid
(tolerating higher operating temperature
than corresponding RLi or RMgBr counterparts), sulfur dioxide
and isocyanate
s behaving like soft Grignard reagents. They do not react with ester
s, nitrile
s, or amide
s. They are more sensitive to steric than to electronic effects.
With acyl halide
s RMnX compounds form the corresponding ketones. This reaction is chemoselective
and has been applied in organic synthesis
for this reason.
Certain manganese amides of the type RR1NMnR2 are used for the deprotonation of ketones forming manganese enolates. Just like lithium enolates they can further react with silyl chlorides to silyl enol ether
s, with alkyl halides in alpha-alkylation and with aldehydes and ketones to beta-keto-alcohols. Manganese enolates can also be obtained by transmetalation
of manganese halides with Li, Mg, K or Na enolates.
Manganese halides are catalysts in several homo- and crosscoupling reactions
involving stannanes and Grignards in which organomanganese intermediates play a part. Likewise coupling reactions involving organomanganese halides are catalysed by Pd, Ni, Cu and Fe compounds
with lithium
metal in a solution of a catalytic amount of naphthalene
in THF. Other reducing agents are potassium graphite and magnesium. Activated manganese facilitates the Mn version of the Barbier reaction
and the pinacol coupling .
Mn(IV)(Me)6−2 complex was reported in 1992, obtained by reaction of MnMe4(PMe3), with methyllithium followed by addition of TMED..
is a half-sandwich compound used as a gasoline additive.
is a radioactive synthetic element and little explored. Organorhenium compounds can be found with oxidation states +4 and +5. An important starting material is dirhenium decacarbonyl
, which can be synthesized by carbonylation of rhenium(VII) oxide
. Methylrhenium trioxide
is used as a catalyst .
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
of organometallic compounds containing a 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...
to manganese
Manganese
Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...
chemical bond
Chemical bond
A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction...
. In a recent review Cahiez et al. argue that as manganese is cheap and benign (only iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
performs better in these aspects), organomanganese compounds have potential as chemical reagents, although currently they are not widely used as such despite extensive research.
The first organomanganese compounds were synthesised in 1937 by Gilman and Bailee who reacted phenyllithium
Phenyllithium
Phenyllithium is an organometallic agent with the empirical formula C6H5Li. It is most commonly used as a metalating agent in organic syntheses and a substitute for Grignard reagents for introducing phenyl groups in organic syntheses...
with manganese(II) iodide
Manganese(II) iodide
Manganese iodide is the chemical compound composed of manganese and iodine with the formula MnI2.It can be used as a pink pigment or as a source of the manganese ion or iodide ion. It is often used in the lighting industry....
to form phenylmanganese iodide (PhMnI) and diphenylmanganese (Ph2Mn).
The reactivity of organomanganese compounds can be compared to that of organomagnesium compounds and organozinc compound
Organozinc compound
Organozinc compounds in organic chemistry contain carbon to zinc chemical bonds. Organozinc chemistry is the science of organozinc compounds describing their physical properties, synthesis and reactions....
s. The 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 Mn (1.55) is comparable to that of Mg (1.55) and Zn (1.65) making the carbon atom (EN = 2,55) nucleophilic. The reduction potential
Reduction potential
Reduction potential is a measure of the tendency of a chemical species to acquire electrons and thereby be reduced. Reduction potential is measured in volts , or millivolts...
of Mn is also intermediate between Mg and Zn. Key disadvantage of organomanganese compounds is that they can be obtained directly from the metal only with difficulty.
Synthesis
General methods for the synthesis of organomanganese compounds exist.Organomanganese halides can be obtained by reaction of manganese halides (manganese(II) bromide
Manganese(II) bromide
Manganese bromide is the chemical compound composed of manganese and bromine with the formula MnBr2.It can be used in place of palladium in the Stille reaction, which couples two carbon atoms using an organotin compound....
, manganese(II) bromide
Manganese(II) bromide
Manganese bromide is the chemical compound composed of manganese and bromine with the formula MnBr2.It can be used in place of palladium in the Stille reaction, which couples two carbon atoms using an organotin compound....
) with organolithium or organomagnesium compounds in transmetallation:
Manganese iodide can be prepared in situ from manganese and 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....
in ether
Ether
Ethers are a class of organic compounds that contain an ether group — an oxygen atom connected to two alkyl or aryl groups — of general formula R–O–R'. A typical example is the solvent and anesthetic diethyl ether, commonly referred to simply as "ether"...
. Further reaction gives the symmetrical diorganomanganese compound.
Organomanganates (the ate complex
Ate complex
An ate complex in chemistry is a salt formed by reaction of a Lewis acid with a base whereby the central atom increases its valence . Often in chemical nomenclature the phrase ate is suffixed to the element in question. For example, the ate complex of a boron compound is called a borate...
) are the most stable compounds:
The organomanganese compounds are usually prepared in THF
ThF
Follicular B helper T cells , are antigen-experienced CD4+ T cells found in the B cell follicles of secondary lymphoid organs such as lymph nodes, spleens and Peyer's patches, and are identified by their constitutive expression of the B cell follicle homing receptor CXCR5...
where they are the most stable (via complexation) even though many of them must be handled at low temperatures. Simple dialkylmanganese decompose by beta-hydride elimination
Beta-hydride elimination
Beta-hydride elimination is a reaction in which an alkyl group bonded to a metal centre is converted into the corresponding metal-bonded hydride and an alkene. The alkyl must have hydrogens on the beta carbon. For instance butyl groups can undergo this reaction but methyl groups cannot...
to a mixture of alkanes and alkenes.
Derivatives of Mn2(CO)10
Many organomanganese complexes are derived from dimanganese decacarbonylDimanganese decacarbonyl
Dimanganese decacarbonyl is the chemical compound with the formula Mn210. This metal carbonyl is an important reagent in the organometallic chemistry of manganese.-Synthesis:...
, Mn2(CO)10. Bromination and reduction affords BrMn(CO)5 and LiMn(CO)5. These species are precursors to alkyl, aryl, and acyl derivatives:
- BrMn(CO)5 + RLi → RMn(CO)5 + LiBr
- LiMn(CO)5 + RC(O)Cl → RC(O)Mn(CO)5 + LiCl
- RMn(CO)5 + CO → RC(O)Mn(CO)5
The general pattern of reactivity is analogous to that for the more popular cyclopentadienyliron dicarbonyl dimer
Cyclopentadienyliron dicarbonyl dimer
Cyclopentadienyliron dicarbonyl dimer is an organometallic compound with the formula 2Fe24, also abbreviated Cp2Fe24. It is called Fp2 or "fip dimer." It is a dark reddish-purple crystalline solid, which is readily soluble in moderately polar organic solvents such as chloroform and pyridine, but...
.
The Mn(I) compound BrMn(CO)5 is also the precursor to many pi-arene complexes:
-
- BrMn(CO)5 + Ag+ + C6R6 → [Mn(CO)3(C6R6)]+ + AgBr + 2 CO
These cationic half-sandwich complexes are susceptible to nucleophilic additions to give cyclohexadienyl derivatives and ultimated functionalized arenes.
Reactions
Organomanganese halides react with aldehydeAldehyde
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 and ketone
Ketone
In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...
s to the alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
, with carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
to the carboxylic acid
Carboxylic acid
Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...
(tolerating higher operating temperature
Operating temperature
An operating temperature is the temperature at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the device function and application context, and ranges from the minimum operating temperature to the...
than corresponding RLi or RMgBr counterparts), sulfur dioxide
Sulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...
and isocyanate
Isocyanate
Isocyanate is the functional group of elements –N=C=O , not to be confused with the cyanate functional group which is arranged as –O–C≡N or with isocyanide, R-N≡C. Any organic compound which contains an isocyanate group may also be referred to in brief as an isocyanate. An isocyanate may have more...
s behaving like soft Grignard reagents. They do not react with ester
Ester
Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
s, nitrile
Nitrile
A nitrile is any organic compound that has a -C≡N functional group. The prefix cyano- is used interchangeably with the term nitrile in industrial literature. Nitriles are found in many useful compounds, one example being super glue .Inorganic compounds containing the -C≡N group are not called...
s, or amide
Amide
In chemistry, an amide is an organic compound that contains the functional group consisting of a carbonyl group linked to a nitrogen atom . The term refers both to a class of compounds and a functional group within those compounds. The term amide also refers to deprotonated form of ammonia or an...
s. They are more sensitive to steric than to electronic effects.
With acyl halide
Acyl halide
An acyl halide is a chemical compound derived from an oxoacid by replacing a hydroxyl group with a halide group....
s RMnX compounds form the corresponding ketones. This reaction is chemoselective
Chemoselectivity
Chemical reactions are defined usually in small contexts , such generalizations are a matter of utility. The preferential outcome of one instance of a generalized reaction over a set of other plausible reactions, is defined as chemoselectivity...
and has been applied in organic synthesis
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
for this reason.
Certain manganese amides of the type RR1NMnR2 are used for the deprotonation of ketones forming manganese enolates. Just like lithium enolates they can further react with silyl chlorides to silyl enol ether
Silyl enol ether
Silyl enol ethers in organic chemistry are a class of organic compounds that share a common functional group composed of an enolate bonded through its oxygen terminus to an organosilicon group....
s, with alkyl halides in alpha-alkylation and with aldehydes and ketones to beta-keto-alcohols. Manganese enolates can also be obtained by transmetalation
Transmetalation
Transmetalation is a general chemical reaction type in organometallic chemistry describing the exchange of ligands between two metal centers....
of manganese halides with Li, Mg, K or Na enolates.
Manganese halides are catalysts in several homo- and crosscoupling reactions
Coupling reaction
A coupling reaction in organic chemistry is a catch-all term for a variety of reactions where two hydrocarbon fragments are coupled with the aid of a metal catalyst...
involving stannanes and Grignards in which organomanganese intermediates play a part. Likewise coupling reactions involving organomanganese halides are catalysed by Pd, Ni, Cu and Fe compounds
Activated manganese
Commercial manganese powder is not suited for the synthesis of organomanganese compounds. In 1996 Rieke introduced activated manganese (see Rieke metal) obtained by reaction of anhydrous manganese(II) chlorideManganese(II) chloride
Manganese chloride describes a series of compounds with the formula MnCl2x, where the value of x can be 0, 2, or 4. The tetrahydrate is the most common form of "manganese chloride". MnCl2·4H2O, but the anhydrous form and dihydrate MnCl2·2H2O are also known...
with lithium
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...
metal in a solution of a catalytic amount of naphthalene
Naphthalene
Naphthalene is an organic compound with formula . It is a white crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 ppm by mass. As an aromatic hydrocarbon, naphthalene's structure consists of a fused pair of benzene rings...
in THF. Other reducing agents are potassium graphite and magnesium. Activated manganese facilitates the Mn version of the Barbier reaction
Barbier reaction
The Barbier reaction is an organic reaction between an alkyl halide and a carbonyl group as an electrophilic substrate in the presence of magnesium, aluminium, zinc, indium, tin or its salts. The reaction product is a primary, secondary or tertiary alcohol...
and the pinacol coupling .
High-valent compounds
Several organomanganese compounds with valency +3 or +4 are known. The first one discovered (1972) was Mn(nor)4 with four norbornyl units . An octahedralOctahedral molecular geometry
In chemistry, octahedral molecular geometry describes the shape of compounds where in six atoms or groups of atoms or ligands are symmetrically arranged around a central atom, defining the vertices of an octahedron...
Mn(IV)(Me)6−2 complex was reported in 1992, obtained by reaction of MnMe4(PMe3), with methyllithium followed by addition of TMED..
Applications
Methylcyclopentadienyl manganese tricarbonylMethylcyclopentadienyl manganese tricarbonyl
Methylcyclopentadienyl manganese tricarbonyl is an organomanganese compound with the formula Mn3. Marketed initially in 1958 as a supplement to the gasoline additive tetraethyl lead to increase the fuel's octane rating, MMT was later used in unleaded gasoline...
is a half-sandwich compound used as a gasoline additive.
Higher group 7 organometallics
In the same group 7 elements technetiumTechnetium
Technetium is the chemical element with atomic number 43 and symbol Tc. It is the lowest atomic number element without any stable isotopes; every form of it is radioactive. Nearly all technetium is produced synthetically and only minute amounts are found in nature...
is a radioactive synthetic element and little explored. Organorhenium compounds can be found with oxidation states +4 and +5. An important starting material is dirhenium decacarbonyl
Dirhenium decacarbonyl
Dirhenium decacarbonyl is an inorganic compound with the formula Re210. Commercially available, it is used as a starting point for the synthesis of many rhenium carbonyl complexes. It was first reported in 1941 by Walter Hieber who prepared it by carbonylation of Re2O7. The compound consists of a...
, which can be synthesized by carbonylation of rhenium(VII) oxide
Rhenium(VII) oxide
Rhenium oxide is the chemical compound with the formula Re2O7. It is the anhydride of the hypothetical acid . Perrhenic acid, Re2O7·2H2O, however is closely related structurally to Re2O7. Solid Re2O7 is polymeric consisting, unusually, of the metal centers in two coordination environments...
. Methylrhenium trioxide
Methylrhenium trioxide
Methylrhenium trioxide, also known as methyltrioxorhenium, is an organometallic compound with the formula CH3ReO3. It is a volatile, colourless solid has been used as a catalyst in some laboratory experiments. In this compound, Re has a tetrahedral coordination environment with one methyl and...
is used as a catalyst .
See also
- Chemical bonds of carbon with other elements in the periodic table: