Organoindium chemistry is the chemistry of compounds containing In-C bonds. The main application of organoindium chemistry is in the preparation of semiconducting components for microelectronic applications. The area is also of some interest in organic synthesis. Most organoindium compounds feature the In(III) oxidation state, akin to its lighter congeners Ga(III) and B(III). [1]
Monovalent In is relatively more common than Ga(I) or B(I). One example is cyclopentadienylindium(I).
![Structure of [InC(tms)3]4, an In(I) tetrahedrane (dark gray = In) YUZZOI.svg](http://upload.wikimedia.org/wikipedia/commons/thumb/e/ec/YUZZOI.svg/222px-YUZZOI.svg.png)
Trimethylindium is a colorless, volatile solid. It is the preferred source of indium for metalorganic vapour phase epitaxy (MOVPE) of indium-containing compound semiconductors, such as InP, InAs, AlInGaNP, etc. InMe3 is pyrophoric.
To obtain the trialkyl derivatives, alkylation of indium trihalides with organolithium reagents is typical. [4]
OrganoIn(III) compounds are also prepared by treating In metal with alkyl halides. This reaction gives mixed organoindium halides. Illustrative is the reaction of allyl bromide with a THF suspension of indium. Both monoallylindium dibromide and diallylindium bromide are produced. [5]
A variety of organoindium(III) species such as InRX3− and solvates of RXIn+, R2In+, and X2In+ are thought to rapidly interconvert at room temperature. [6]
IMAs proceed in two steps: first, indium reacts with the allyl halide, give an allyl-In(III) intermediate, second, this allyl indide reacts with an electrophile:
The reaction is conducted under the conditions of a Barbier reaction where the indium, allyl halide, and electrophile are all mixed in a one-pot process. Indium alkylates more readily than other metals, such as Mg, Pb, Bi, or Zn and does not require a promoter or organic solvent. IMAs have advantages over other carbon bond forming reactions because of their ability to be carried out in water (see Green chemistry). [7] [8] Although indium mediated allylations can be carried out in aqueous media, a variety of other solvents may be used including THF (tetrahydrofuran), DMF (dimethylformamide), room temperature ionic liquids, NMF (n-methylformamide), and others. [9] [10] Solvent often affects the solubility, rate of the reaction, yield, stability, regioselectivity, and stereoselectivity. Indium mediates the allylation of a wide variety of electrophiles. The examples in the following scheme illustrate the breadth of applications of IMA.
Organoindium intermediates do not react with –OH or –CO2H groups. Reactions with carbonyls, however, give high yields. Research has shown that in reactions of an indium intermediate with an electrophilic compound of both aldehyde and ketone, the reaction proceeded with the aldehyde. The electrophilic compound is shown below. [11]
The regioselectivity of allylation mediated by indium in water is dependent on the steric effects of the substituents on both the intermediate and carbonyl. An α-attack from the nucleophile (at the position bearing the halogen) is distinguishable from a γ-attack (at the double bond) by inspecting the products. The scheme below gives an example of two different products formed from the same nucleophile under α-regioselectivity (α) and γ-regioselectivity (γ). This regioselectivity does not appear to depend on conjugation or the degree of substitution. [12]
The addition of allylindium reagents to aldehydes substituted at α or β carbons can be very diastereoselective in aqueous systems. For example, if chelation control is present in an α-oxy aldehyde, the product is expected to be the syn diastereomer. A sample reaction of chelation versus non-chelation control is illustrated below.
Numerous investigations have found an explanation for this effect. The oxygens of the carbonyl and the hydroxyl group chelate the indium of the organoindium intermediate as illustrated below on the left by the two green bonds. The incipient C-C bond, illustrated in red, creates a six-member ring in a chair conformation. Under chelation control, the allyl group attacks the carbonyl carbon from the less hindered side opposite to that of the R group. Once the C-C bond is fully formed, the indium is released, producing the syn diol. A similar chelated structure is relevant to the allylation of β-oxy aldehydes results in anti diols. [13] [14]
The addition of allylindium reagents to electrophilic hydrazones, illustrated below, has been reported to synthesize only one enantiomer of the chiral product with up to 97% selectivity using binol as a chiral additive. [15] Similarly, a chiral amino alcohol allows for extremely high enantioselectivity in the allylation of ketones. [16] The indium-mediated allylation in water is especially useful in carbohydrate synthesis (such as sialic acids), without using protecting groups. [17]
The Grignard reaction is an organometallic chemical reaction in which alkyl, allyl, vinyl, or aryl-magnesium halides is added to a carbonyl group in an aldehyde or ketone. This reaction is important for the formation of carbon–carbon bonds. The reaction of an organic halide with magnesium is not a Grignard reaction, but provides a Grignard reagent.
In organic chemistry, a nucleophilic addition reaction is an addition reaction where a chemical compound with an electrophilic double or triple bond reacts with a nucleophile, such that the double or triple bond is broken. Nucleophilic additions differ from electrophilic additions in that the former reactions involve the group to which atoms are added accepting electron pairs, whereas the latter reactions involve the group donating electron pairs.
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.
Organoboron chemistry or organoborane chemistry is the chemistry of organoboron compounds or organoboranes, which are chemical compounds of boron and carbon that are organic derivatives of borane (BH3), for example trialkyl boranes..
The Barbier reaction is an organometallic reaction between an alkyl halide, a carbonyl group and a metal. The reaction can be performed using magnesium, aluminium, zinc, indium, tin, samarium, barium or their salts. The reaction product is a primary, secondary or tertiary alcohol. The reaction is similar to the Grignard reaction but the crucial difference is that the organometallic species in the Barbier reaction is generated in situ, whereas a Grignard reagent is prepared separately before addition of the carbonyl compound. Unlike many Grignard reagents, the organometallic species generated in a Barbier reaction are unstable and thus cannot be stored or sold commercially. Barbier reactions are nucleophilic addition reactions that involve relatively inexpensive, water insensitive metals or metal compounds. For this reason it is possible in many cases to run the reaction in water, making the procedure part of green chemistry. In contrast, Grignard reagents and organolithium reagents are highly moisture sensitive and must be used under an inert atmosphere without the presence of water. The Barbier reaction is named after Victor Grignard's teacher Philippe Barbier.
The Shapiro reaction or tosylhydrazone decomposition is an organic reaction in which a ketone or aldehyde is converted to an alkene through an intermediate hydrazone in the presence of 2 equivalents of organolithium reagent. The reaction was discovered by Robert H. Shapiro in 1967. The Shapiro reaction was used in the Nicolaou Taxol total synthesis. This reaction is very similar to the Bamford–Stevens reaction, which also involves the basic decomposition of tosyl hydrazones.
In stereochemistry, asymmetric induction describes the preferential formation in a chemical reaction of one enantiomer or diastereoisomer over the other as a result of the influence of a chiral feature present in the substrate, reagent, catalyst or environment. Asymmetric induction is a key element in asymmetric synthesis.
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 end to an organosilicon group. They are important intermediates in organic synthesis.
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.
The Stork enamine alkylation involves the addition of an enamine to a Michael acceptor or another electrophilic alkylation reagent to give an alkylated iminium product, which is hydrolyzed by dilute aqueous acid to give the alkylated ketone or aldehyde. Since enamines are generally produced from ketones or aldehydes, this overall process constitutes a selective monoalkylation of a ketone or aldehyde, a process that may be difficult to achieve directly.
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.
Organogallium chemistry is the chemistry of organometallic compounds containing a carbon to gallium (Ga) chemical bond. Despite their high toxicity, organogallium compounds have some use in organic synthesis. The compound trimethylgallium is of some relevance to MOCVD as a precursor to gallium arsenide via its reaction with arsine at 700 °C:
Organostannane addition reactions comprise the nucleophilic addition of an allyl-, allenyl-, or propargylstannane to an aldehyde, imine, or, in rare cases, a ketone. The reaction is widely used for carbonyl allylation.
The Abramov reaction is the related conversions of trialkyl to α-hydroxy phosphonates by the addition to carbonyl compounds. In terms of mechanism, the reaction involves attack of the nucleophilic phosphorus atom on the carbonyl carbon. It was named after the Russian chemist Vasilii Semenovich Abramov (1904–1968) in 1957.
Electrophilic amination is a chemical process involving the formation of a carbon–nitrogen bond through the reaction of a nucleophilic carbanion with an electrophilic source of nitrogen.
Electrophilic substitution of unsaturated silanes involves attack of an electrophile on an allyl- or vinylsilane. An allyl or vinyl group is incorporated at the electrophilic center after loss of the silyl group.
Reactions of organocopper reagents involve species containing copper-carbon bonds acting as nucleophiles in the presence of organic electrophiles. Organocopper reagents are now commonly used in organic synthesis as mild, selective nucleophiles for substitution and conjugate addition reactions.
Heteroatom-promoted lateral lithiation is the site-selective replacement of a benzylic hydrogen atom for lithium for the purpose of further functionalization. Heteroatom-containing substituents may direct metalation to the benzylic site closest to the heteroatom or increase the acidity of the ring carbons via an inductive effect.
Hydrogen auto-transfer, also known as borrowing hydrogen, is the activation of a chemical reaction by temporary transfer of two hydrogen atoms from the reactant to a catalyst and return of those hydrogen atoms back to a reaction intermediate to form the final product. Two major classes of borrowing hydrogen reactions exist: (a) those that result in hydroxyl substitution, and (b) those that result in carbonyl addition. In the former case, alcohol dehydrogenation generates a transient carbonyl compound that is subject to condensation followed by the return of hydrogen. In the latter case, alcohol dehydrogenation is followed by reductive generation of a nucleophile, which triggers carbonyl addition. As borrowing hydrogen processes avoid manipulations otherwise required for discrete alcohol oxidation and the use of stoichiometric organometallic reagents, they typically display high levels of atom-economy and, hence, are viewed as examples of Green chemistry.
The Enders SAMP/RAMP hydrazone alkylation reaction is an asymmetric carbon-carbon bond formation reaction facilitated by pyrrolidine chiral auxiliaries. It was pioneered by E. J. Corey and D. Enders in 1976, and was further developed by D. Enders and his group. This method is usually a three-step sequence. The first step is to form the hydrazone between (S)-1-amino-2-methoxymethylpyrrolidine (SAMP) or (R)-1-amino-2-methoxymethylpyrrolidine (RAMP) and a ketone or aldehyde. Afterwards, the hydrazone is deprotonated by lithium diisopropylamide (LDA) to form an azaenolate, which reacts with alkyl halides or other suitable electrophiles to give alkylated hydrazone species with the simultaneous generation of a new chiral center. Finally, the alkylated ketone or aldehyde can be regenerated by ozonolysis or hydrolysis.
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