Trimethylaluminium

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Trimethylaluminium
Trimethylaluminium-from-xtal-3D-bs-17-25.png
Trimethylaluminium-from-xtal-3D-sf.png
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)
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

In the chemical sciences, methylation denotes the addition of a methyl group on a substrate, or the substitution of an atom by a methyl group. Methylation is a form of alkylation, with a methyl group replacing a hydrogen atom. These terms are commonly used in chemistry, biochemistry, soil science, and the biological sciences.

<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.

<span class="mw-page-title-main">Manganese(II) chloride</span> Chemical compound

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.

<span class="mw-page-title-main">Iron(II) chloride</span> Chemical compound

Iron(II) chloride, also known as ferrous chloride, is the chemical compound of formula FeCl2. It is a paramagnetic solid with a high melting point. The compound is white, but typical samples are often off-white. FeCl2 crystallizes from water as the greenish tetrahydrate, which is the form that is most commonly encountered in commerce and the laboratory. There is also a dihydrate. The compound is highly soluble in water, giving pale green solutions.

<span class="mw-page-title-main">Amidine</span> Organic compounds

Amidines are organic compounds with the functional group RC(NR)NR2, where the R groups can be the same or different. They are the imine derivatives of amides (RC(O)NR2). The simplest amidine is formamidine, HC(=NH)NH2.

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

Trimethylsilyl chloride, also known as chlorotrimethylsilane is an organosilicon compound (silyl halide), with the formula (CH3)3SiCl, often abbreviated Me3SiCl or TMSCl. It is a colourless volatile liquid that is stable in the absence of water. It is widely used in organic chemistry.

Boron trichloride is the inorganic compound with the formula BCl3. This colorless gas is a reagent in organic synthesis. It is highly reactive toward 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">Mercury(II) acetate</span> Chemical compound

Mercury(II) acetate is the chemical compound with the formula Hg(O2CCH3)2. Commonly abbreviated Hg(OAc)2, this compound is employed as a reagent to generate organomercury compounds from unsaturated organic precursors. It is a white water-soluble solid, but samples appear yellowish with time owing to decomposition.

<span class="mw-page-title-main">Organomercury chemistry</span> Group of chemical compounds containing mercury

Organomercury chemistry refers to the study of organometallic compounds that contain mercury. Typically the Hg–C bond is stable toward air and moisture but sensitive to light. Important organomercury compounds are the methylmercury(II) cation, CH3Hg+; ethylmercury(II) cation, C2H5Hg+; dimethylmercury, (CH3)2Hg, diethylmercury and merbromin ("Mercurochrome"). Thiomersal is used as a preservative for vaccines and intravenous drugs.

Chloramines refer to derivatives of ammonia and organic amines wherein one or more N-H bonds have been replaced by N-Cl bonds. Two classes of compounds are considered: inorganic chloramines and organic chloramines.

<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">4-Bromoanisole</span> Chemical compound

4-Bromoanisole is the organobromine compound with the formula CH3OC6H4Br. It is colorless liquid with a pleasant smell similar to that of anise seed. It is one of three isomers of bromoanisole, the others being 3-bromoanisole and 2-bromoanisole. It is the precursor to many 4-anisyl derivatives.

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

Diethylaluminum cyanide ("Nagata's reagent") is the organoaluminum compound with formula ((C2H5)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">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.

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

Diethyl phosphite is the organophosphorus compound with the formula (C2H5O)2P(O)H. It is a popular reagent for generating other organophosphorus compounds, exploiting the high reactivity of the P-H bond. Diethyl phosphite is a colorless liquid. The molecule is tetrahedral.

Hydroxymethylation is a chemical reaction that installs the CH2OH group. The transformation can be implemented in many ways and applies to both industrial and biochemical processes.

In organic chemistry, methylenation is a chemical reaction that inserts a methylene group into a chemical compound:

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.
  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. Inorganic Syntheses. Vol. 15. pp. 203–207. doi:10.1002/9780470132463.ch45. ISBN   9780470132463.
  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.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  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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