Trimethylaluminium

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Trimethylaluminium
Trimethylaluminium-from-xtal-3D-bs-17-25.png
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Names
IUPAC name
Trimethylalumane
Other names
Trimethylaluminum; aluminium trimethyl; aluminum trimethyl
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.000.776 OOjs UI icon edit-ltr-progressive.svg
PubChem CID
UNII
  • InChI=1S/3CH3.Al/h3*1H3; Yes check.svgY
    Key: JLTRXTDYQLMHGR-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/3CH3.Al/h3*1H3;/rC3H9Al/c1-4(2)3/h1-3H3
    Key: JLTRXTDYQLMHGR-MZZUXTGEAJ
Properties
C6H18Al2
Molar mass 144.17 g/mol
72.09 g/mol (C3H9Al)
AppearanceColorless liquid
Density 0.752 g/cm3
Melting point 15 °C (59 °F; 288 K)
Boiling point 125–130 °C (257–266 °F; 398–403 K) [1] [2]
Reacts
Vapor pressure
  • 1.2 kPa (20 °C)
  • 9.24 kPa (60 °C) [1]
Viscosity
  • 1.12 cP (20 °C)
  • 0.9 cP (30 °C)
Thermochemistry
155.6 J/mol·K [2]
Std molar
entropy (S⦵298)
209.4 J/mol·K [2]
−136.4 kJ/mol [2]
−9.9 kJ/mol [2]
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
Pyrophoric
GHS labelling:
GHS-pictogram-flamme.svg GHS-pictogram-acid.svg [1]
Danger
H250, H260, H314 [1]
P222, P223, P231+P232, P280, P370+P378, P422 [1]
NFPA 704 (fire diamond)
NFPA 704.svgHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 4: Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Flash point below 23 °C (73 °F). E.g. propaneInstability 3: Capable of detonation or explosive decomposition but requires a strong initiating source, must be heated under confinement before initiation, reacts explosively with water, or will detonate if severely shocked. E.g. hydrogen peroxideSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g. sodium, sulfuric acid
3
4
3
W
Flash point −17.0 °C (1.4 °F; 256.1 K) [1]
Related compounds
Related compounds
 Triethylaluminium
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

Trimethylaluminium is one of the simplest examples of an organoaluminium compound. Despite its name it has the formula Al 2(CH3)6 (abbreviated as Al2Me6 or TMA), as it exists as a dimer. This colorless liquid is pyrophoric. It is an industrially important compound, closely related to triethylaluminium. [3] [4]

Contents

Structure and bonding

The structure and bonding in Al2R6 and diborane are analogous (R = alkyl). In Al2Me6, the Al-C(terminal) and Al-C(bridging) distances are 1.97 and 2.14 Å, respectively. The Al center is tetrahedral. [5] The carbon atoms of the bridging methyl groups are each surrounded by five neighbors: three hydrogen atoms and two aluminium atoms. The methyl groups interchange readily intramolecularly. At higher temperatures, the dimer cracks into monomeric AlMe3. [6]

Synthesis

TMA is prepared via a two-step process that can be summarized as follows:

2 Al + 6 CH3Cl + 6 Na → Al2(CH3)6 + 6 NaCl

Applications

Catalysis

Starting with the invention of Ziegler-Natta catalysis, organoaluminium compounds have a prominent role in the production of polyolefins, such as polyethylene and polypropylene. Methylaluminoxane, which is produced from TMA, is an activator for many transition metal catalysts.

Semiconductor applications

TMA is also used in semiconductor fabrication to deposit thin film, high-k dielectrics such as Al2O3 via the processes of chemical vapor deposition or atomic layer deposition. TMA is the preferred precursor for metalorganic vapour phase epitaxy (MOVPE) of aluminium-containing compound semiconductors, such as AlAs, AlN, AlP, AlSb, AlGaAs, AlInGaAs, AlInGaP, AlGaN, AlInGaN, AlInGaNP, etc. Criteria for TMA quality focus on (a) elemental impurities, (b) oxygenated and organic impurities.

Photovoltaic applications

In deposition processes very similar to semiconductor processing, TMA is used to deposit thin film, low-k (non-absorbing) dielectric layer stacks with Al2O3 via the processes of chemical vapor deposition or atomic layer deposition. The Al2O3 provides excellent surface passivation of p-doped silicon surfaces. The Al2O3 layer is typically the bottom layer with multiple silicon nitride (SixNy) layers for capping.

Reactions

Trimethylaluminium is hydrolyzed readily, even dangerously:

Al2Me6 + 3 H2O → Al2O3 + 6 CH4

Under controlled conditions, the reaction can be stopped to give methylaluminoxane:

AlMe3 + H2O → 1/n [AlMeO]n + 2 CH4

Alcoholysis and aminolysis reactions proceed comparably. For example, dimethylamine gives the dialuminium diamide dimer: [7]

2 AlMe3 + 2 HNMe2 → [AlMe2NMe2]2 + 2 CH4

Reactions with metal chlorides

TMA reacts with many metal halides to install alkyl groups. When combined with gallium trichloride, it gives trimethylgallium. [8] Al2Me6 reacts with aluminium trichloride to give (AlMe2Cl)2.

TMA/metal halide reactions have emerged as reagents in organic synthesis. Tebbe's reagent, which is used for the methylenation of esters and ketones, is prepared from TMA and titanocene dichloride. [9] In combination with 20 to 100 mol % Cp2ZrCl2 (zirconocene dichloride), the (CH3)2Al-CH3 adds "across" alkynes to give vinyl aluminium species that are useful in organic synthesis in a reaction known as carboalumination. [10]

Adducts

As for other "electron-deficient" compounds, trimethylaluminium gives adducts R3N.AlMe3. The Lewis acid properties of AlMe3 have been quantified. [11] The enthalpy data show that AlMe3 is a hard acid and its acid parameters in the ECW model are EA =8.66 and CA = 3.68.

These adducts, e.g. the complex with the tertiary amine DABCO, are safer to handle than TMA itself. [12]

The NASA ATREX mission (Anomalous Transport Rocket Experiment) employed the white smoke that TMA forms on air contact to study the high altitude jet stream.

Synthetic reagent

TMA is a source of methyl nucleophiles, akin to methyl lithium, but less reactive. It reacts with ketones to give, after a hydrolytic workup, tertiary alcohols.

Safety

Trimethylaluminium is pyrophoric, reacting violently with air and water.

Related Research Articles

<span class="mw-page-title-main">Ketone</span> Organic compounds of the form >C=O

In organic chemistry, a ketone is an organic compound with the structure R−C(=O)−R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group −C(=O)−. The simplest ketone is acetone, with the formula (CH3)2CO. Many ketones are of great importance in biology and industry. Examples include many sugars (ketoses), many steroids, and the solvent acetone.

<span class="mw-page-title-main">Aluminium chloride</span> Chemical compound

Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula AlCl3. It forms a hexahydrate with the formula [Al(H2O)6]Cl3, containing six water molecules of hydration. Both the anhydrous form and the hexahydrate are colourless crystals, but samples are often contaminated with iron(III) chloride, giving them a yellow colour.

Methylaluminoxane, commonly called MAO, is a mixture of organoaluminium compounds with the approximate formula (Al(CH3)O)n. It is usually encountered as a solution in (aromatic) solvents, commonly toluene but also xylene, cumene, or mesitylene, Used in large excess, it activates precatalysts for alkene polymerization.

<span class="mw-page-title-main">Trimethylsilyldiazomethane</span> Chemical compound

Trimethylsilyldiazomethane is the organosilicon compound with the formula (CH3)3SiCHN2. It is classified as a diazo compound. Trimethylsilyldiazomethane, which is a commercially available, reagent used in organic chemistry as a methylating agent of carboxylic acids. Its behavior is akin to the reagent diazomethane, but the trimethylsilyl (TMS) analog is nonexplosive.

<i>tert</i>-Butyllithium Chemical compound

tert-Butyllithium is a chemical compound with the formula (CH3)3CLi. As an organolithium compound, it has applications in organic synthesis since it is a strong base, capable of deprotonating many carbon molecules, including benzene. tert-Butyllithium is available commercially as solutions in hydrocarbons (such as pentane); it is not usually prepared in the laboratory.

Boron trichloride is the inorganic compound with the formula BCl3. This colorless gas is a reagent in organic synthesis. It is highly reactive towards water.

<span class="mw-page-title-main">Tebbe's reagent</span> Chemical compound

Tebbe's reagent is the organometallic compound with the formula (C5H5)2TiCH2ClAl(CH3)2. It is used in the methylidenation of carbonyl compounds, that is it converts organic compounds containing the R2C=O group into the related R2C=CH2 derivative. It is a red solid that is pyrophoric in the air, and thus is typically handled with air-free techniques. It was originally synthesized by Fred Tebbe at DuPont Central Research.

<span class="mw-page-title-main">Neopentyl alcohol</span> Chemical compound

Neopentyl alcohol is a compound with formula (CH3)3CCH2OH. It is a colorless solid. The compound is one of the eight isomers of pentyl alcohol.

<span class="mw-page-title-main">Organotitanium chemistry</span>

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.

<span class="mw-page-title-main">Trimethylindium</span> Chemical compound

Trimethylindium, often abbreviated to TMI or TMIn, is the organoindium compound with the formula In(CH3)3. It is a colorless, pyrophoric solid. Unlike trimethylaluminium, but akin to trimethylgallium, TMI is monomeric.

<span class="mw-page-title-main">Trimethylgallium</span> Chemical compound

Trimethylgallium, often abbreviated to TMG or TMGa, is the organogallium compound with the formula Ga(CH3)3. It is a colorless, pyrophoric liquid. Unlike trimethylaluminium, TMG adopts a monomeric structure. When examined in detail, the monomeric units are clearly linked by multiple weak Ga---C interactions, reminiscent of the situation for trimethylindium.

<span class="mw-page-title-main">Organoaluminium chemistry</span>

Organoaluminium chemistry is the study of compounds containing bonds between carbon and aluminium. It is one of the major themes within organometallic chemistry. Illustrative organoaluminium compounds are the dimer trimethylaluminium, the monomer triisobutylaluminium, and the titanium-aluminium compound called Tebbe's reagent. The behavior of organoaluminium compounds can be understood in terms of the polarity of the C−Al bond and the high Lewis acidity of the three-coordinated species. Industrially, these compounds are mainly used for the production of polyolefins.

<span class="mw-page-title-main">Triethylaluminium</span> Chemical compound

Triethylaluminium is one of the simplest examples of an organoaluminium compound. Despite its name the compound has the formula Al2(C2H5)6 (abbreviated as Al2Et6 or TEA). This colorless liquid is pyrophoric. It is an industrially important compound, closely related to trimethylaluminium.

<span class="mw-page-title-main">Diethylaluminium cyanide</span> Chemical compound

Diethylaluminium cyanide is the organoaluminium compound with formula ( 2AlCN)n. This colorless compound is usually handled as a solution in toluene. It is a reagent for the hydrocyanation of α,β-unsaturated ketones.

<span class="mw-page-title-main">Bis(trimethylsilyl)acetamide</span> Chemical compound

Bis(trimethylsilyl)acetamide (BSA) is an organosilicon compound with the formula MeC(OSiMe3)NSiMe3 (Me = CH3). It is a colorless liquid that is soluble in diverse organic solvents, but reacts rapidly with moisture and solvents containing OH and NH groups. It is used in analytical chemistry to increase the volatility of analytes, e.g., for gas chromatography. It is also used to introduce the trimethylsilyl protecting group in organic synthesis. A related reagent is N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA).

<span class="mw-page-title-main">Dichlorophenylphosphine</span> Chemical compound

Dichlorophenylphosphine is an organophosphorus compound with the formula C6H5PCl2. This colourless viscous liquid is commonly used in the synthesis of organophosphines.

Silylation is the introduction of one or more (usually) substituted silyl groups (R3Si) to a molecule. Silylations are core methods for production of organosilicon chemistry. Silanization involves similar methods but usually refers to attachment of silyl groups to solids.

<span class="mw-page-title-main">2,2,4,4-Tetramethylcyclobutanedione</span> Chemical compound

2,2,4,4-Tetramethylcyclobutanedione is the organic compound with the formula (CH3)4C4O2. The compound is a diketone of cyclobutane, bearing four methyl groups. It is a white solid that is used as a precursor to diverse industrial products.

<i>tert</i>-Butyldimethylsilyl chloride Chemical compound

tert-Butyldimethylsilyl chloride is an organosilicon compound with the formula (Me3C)Me2SiCl (Me = CH3). It is commonly abbreviated as TBSCl or TBDMSCl. It is a chlorosilane containing two methyl groups and a tert-butyl group. As such it is more bulky that trimethylsilyl chloride. It is a colorless or white solid that is soluble in many organic solvents but reacts with water and alcohols. The compound is used to protect alcohols in organic synthesis.

<span class="mw-page-title-main">Dimethylaluminium chloride</span> Chemical compound

Dimethylaluminium chloride is an organoaluminium compound with the chemical formula [(CH3)2AlCl]2. It behaves similarly to diethylaluminium chloride but is more expensive. Hence, it is less commonly used.

References

  1. 1 2 3 4 5 6 Sigma-Aldrich Co., Trimethylaluminum. Retrieved on 2014-05-05.
  2. 1 2 3 4 5 "Trimethyl aluminum".
  3. ↑ Krause, Michael J.; Orlandi, Frank; Saurage, Alfred T.; Zietz, Joseph R. (2000). "Aluminum Compounds, Organic". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. doi:10.1002/14356007.a01_543. ISBN   978-3527306732.
  4. ↑ C. Elschenbroich (2006). Organometallics. VCH. ISBN   978-3-527-29390-2.
  5. ↑ Holleman, A. F.; Wiberg, E. (2001). Inorganic Chemistry. San Diego: Academic Press. ISBN   0-12-352651-5.
  6. ↑ Vass, Gábor; Tarczay, György; Magyarfalvi, Gábor; Bödi, András; Szepes, László (2002). "HeI Photoelectron Spectroscopy of Trialkylaluminium and Dialkylaluminium Hydride Compounds and Their Oligomers". Organometallics. 21 (13): 2751–2757. doi:10.1021/om010994h.
  7. ↑ Lipton, Michael F.; Basha, Anwer; Weinreb, Steven M. (1979). "Conversion of Esters to Amides with Dimethylaluminium Amides: N,N-Dimethylcyclohexanecarboxamide". Organic Syntheses. 59: 49. doi:10.15227/orgsyn.059.0049.
  8. ↑ Gaines, D. F.; Borlin, Jorjan; Fody, E. P. (1974). "Trimethylgallium". Inorganic Syntheses. Vol. 15. pp. 203–207. doi:10.1002/9780470132463.ch45. ISBN   978-0-470-13246-3.
  9. ↑ Pine, S. H.; Kim, V.; Lee, V. (1990). "Enol ethers by methylenation of esters: 1-Phenoxy-1-phenylethene and 3,4-dihydro-2-methylene-2H-1-benzopyran". Org. Synth. 69: 72. doi:10.15227/orgsyn.069.0072.
  10. ↑ Negishi, E.; Matsushita, H. (1984). "Palladium-Catalyzed Synthesis of 1,4-Dienes by Allylation of Alkenyalane: α-Farnesene [1,3,6,10-Dodecatetraene, 3,7,11-trimethyl-]". Organic Syntheses. 62: 31. doi:10.15227/orgsyn.062.0031.
  11. ↑ Henrickson, C. H.; Duffy, D.; Eyman, D. P. (1968). "Lewis acidity of Alanes. Interactions of Trimethylalane with Amines, Ethers, and Phosphines". Inorganic Chemistry. 7 (6): 1047–1051. doi:10.1021/ic50064a001.
  12. ↑ Vinogradov, Andrej; Woodward, S. (2010). "Palladium-Catalyzed Cross-Coupling Using an Air-Stable Trimethylaluminium Source. Preparation of Ethyl 4-Methylbenzoate". Organic Syntheses. 87: 104. doi: 10.15227/orgsyn.087.0104 .
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