Organomanganese chemistry is the chemistry of organometallic compounds containing a carbon to manganese chemical bond. In a 2009 review, Cahiez et al. argued 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. [1]
Organomanganese compounds were first reported in 1937 by Gilman and Bailee who described the reaction of phenyllithium and manganese(II) iodide to form phenylmanganese iodide (PhMnI) and diphenylmanganese (Ph2Mn). [1]
Following this precedent, other organomanganese halides can be obtained by alkylation of manganese(II) chloride, manganese(II) bromide, and manganese(II) iodide. Manganese iodide is attractive because the anhydrous compound can be prepared in situ from manganese and iodine in ether. Typical alkylating agents are organolithium or organomagnesium compounds:
A variety of organomanganates (the ate complex) are isolable:
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 compounds decompose by beta-hydride elimination to a mixture of alkanes and alkenes.
Many organomanganese complexes are derived from dimanganese decacarbonyl, Mn2(CO)10. Bromination and reduction with lithium affords BrMn(CO)5 and LiMn(CO)5, respectfully. 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: [2]
These cationic half-sandwich complexes are susceptible to nucleophilic additions to give cyclohexadienyl derivatives and ultimated functionalized arenes.
The chemistry of organometallic compounds of Mn(II) are unusual among the transition metals due to the high ionic character of the Mn(II)-C bond. [3] The reactivity of organomanganese compounds can be compared to that of organomagnesium and organozinc compounds. The electronegativity of Mn (1.55) is comparable to that of Mg (1.31) and Zn (1.65), making the carbon atom (EN = 2.55) nucleophilic. The reduction potential of Mn is also intermediate between Mg and Zn.
Organomanganese halides react with aldehydes and ketones to the alcohol, with carbon dioxide to the carboxylic acid (tolerating higher operating temperature than corresponding RLi or RMgBr counterparts), sulfur dioxide and isocyanates behaving like soft Grignard reagents. They do not react with esters, nitriles, or amides. They are more sensitive to steric than to electronic effects.
With acyl halides 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 ethers, 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.
Manganese chloride is a precursor to organomanganese reagents in organic chemistry. [4] [5]
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) chloride 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. [6]
Several organomanganese compounds with valency +3 or +4 are known. The first one discovered (1972) was Mn(nor)4 with four norbornyl units. [7] An octahedral [MnIVMe6]−2 complex was reported in 1992, obtained by reaction of MnMe4(PMe3), with methyllithium followed by addition of TMED. [8]
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 to the substrates in synthetic steps, through nucleophilic addition or simple deprotonation. Organolithium reagents are used in industry as an initiator for anionic polymerization, which leads to the production of various elastomers. They have also been applied in asymmetric synthesis in the pharmaceutical industry. Due to the large difference in electronegativity between the carbon atom and the lithium atom, the C−Li bond is highly ionic. Owing to the polar nature of the C−Li bond, organolithium reagents are good nucleophiles and strong bases. For laboratory organic synthesis, many organolithium reagents are commercially available in solution form. These reagents are highly reactive, and are sometimes pyrophoric.
Francois Auguste Victor Grignard was a French chemist who won the Nobel Prize for his discovery of the eponymously named Grignard reagent and Grignard reaction, both of which are important in the formation of carbon–carbon bonds.
The Stille reaction is a chemical reaction widely used in organic synthesis. The reaction involves the coupling of two organic groups, one of which is carried as an organotin compound (also known as organostannanes). A variety of organic electrophiles provide the other coupling partner. The Stille reaction is one of many palladium-catalyzed coupling reactions.
Manganese(II) chloride is the dichloride salt of manganese, MnCl2. This inorganic chemical exists in the anhydrous form, as well as the dihydrate (MnCl2·2H2O) and tetrahydrate (MnCl2·4H2O), with the tetrahydrate being the most common form. Like many Mn(II) species, these salts are pink, with the paleness of the color being characteristic of transition metal complexes with high spin d5 configurations.
Metalation is a chemical reaction that forms a bond to a metal. This reaction usually refers to the replacement of a halogen atom in an organic molecule with a metal atom, resulting in an organometallic compound. In the laboratory, metalation is commonly used to activate organic molecules during the formation of C—X bonds, which are necessary for the synthesis of many organic molecules.
Organoboron chemistry or organoborane chemistry studies organoboron compounds, also called organoboranes. These chemical compounds combine boron and carbon; typically, they are organic derivatives of borane (BH3), as in the trialkyl boranes.
n-Butyllithium C4H9Li (abbreviated n-BuLi) is an organolithium reagent. It is widely used as a polymerization initiator in the production of elastomers such as polybutadiene or styrene-butadiene-styrene (SBS). Also, it is broadly employed as a strong base (superbase) in the synthesis of organic compounds as in the pharmaceutical industry.
The Corey–House synthesis (also called the Corey–Posner–Whitesides–House reaction and other permutations) is an organic reaction that involves the reaction of a lithium diorganylcuprate () with an organic halide or pseudohalide () to form a new alkane, as well as an ill-defined organocopper species and lithium (pseudo)halide as byproducts.
The Reformatsky reaction is an organic reaction which condenses aldehydes or ketones with α-halo esters using metallic zinc to form β-hydroxy-esters:
Grignard reagents or Grignard compounds are chemical compounds with the general formula R−Mg−X, where X is a halogen and R is an organic group, normally an alkyl or aryl. Two typical examples are methylmagnesium chloride Cl−Mg−CH3 and phenylmagnesium bromide (C6H5)−Mg−Br. They are a subclass of the organomagnesium compounds.
The Finkelstein reaction, named after the German chemist Hans Finkelstein, is an SN2 reaction that involves the exchange of one halogen atom for another. It is an equilibrium reaction, but the reaction can be driven to completion by exploiting the differential solubility of halide salts, or by using a large excess of the halide salt.
Methyllithium is the simplest organolithium reagent, with the empirical formula CH3Li. This s-block organometallic compound adopts an oligomeric structure both in solution and in the solid state. This highly reactive compound, invariably used in solution with an ether as the solvent, is a reagent in organic synthesis as well as organometallic chemistry. Operations involving methyllithium require anhydrous conditions, because the compound is highly reactive toward water. Oxygen and carbon dioxide are also incompatible with MeLi. Methyllithium is usually not prepared, but purchased as a solution in various ethers.
Organozinc chemistry is the study of the physical properties, synthesis, and reactions of organozinc compounds, which are organometallic compounds that contain carbon (C) to zinc (Zn) chemical bonds.
Organocopper chemistry is the study of the physical properties, reactions, and synthesis of organocopper compounds, which are organometallic compounds containing a carbon to copper chemical bond. They are reagents in organic chemistry.
In organic chemistry, the Buchwald–Hartwig amination is a chemical reaction for the synthesis of carbon–nitrogen bonds via the palladium-catalyzed coupling reactions of amines with aryl halides. Although Pd-catalyzed C–N couplings were reported as early as 1983, Stephen L. Buchwald and John F. Hartwig have been credited, whose publications between 1994 and the late 2000s established the scope of the transformation. The reaction's synthetic utility stems primarily from the shortcomings of typical methods for the synthesis of aromatic C−N bonds, with most methods suffering from limited substrate scope and functional group tolerance. The development of the Buchwald–Hartwig reaction allowed for the facile synthesis of aryl amines, replacing to an extent harsher methods while significantly expanding the repertoire of possible C−N bond formations.
Organotitanium chemistry is the science of organotitanium compounds describing their physical properties, synthesis, and reactions. Organotitanium compounds in organometallic chemistry contain carbon-titanium chemical bonds. They are reagents in organic chemistry and are involved in major industrial processes.
Group 2 organometallic chemistry refers to the chemistry of compounds containing carbon bonded to any group 2 element. By far the most common group 2 organometallic compounds are the magnesium-containing Grignard reagents which are widely used in organic chemistry. Other organometallic group 2 compounds are rare and are typically limited to academic interests.
Tetramethyltin is an organometallic compound with the formula (CH3)4Sn. This liquid, one of the simplest organotin compounds, is useful for transition-metal mediated conversion of acid chlorides to methyl ketones and aryl halides to aryl methyl ketones. It is volatile and toxic, so care should be taken when using it in the laboratory.
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In organometallic chemistry, metal–halogen exchange is a fundamental reaction that converts an organic halide into an organometallic product. The reaction commonly involves the use of electropositive metals and organochlorides, bromides, and iodides. Particularly well-developed is the use of metal–halogen exchange for the preparation of organolithium compounds.
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