 | |
 | |
| Names | |
|---|---|
| IUPAC name Trimethylalumane | |
Other names
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| Identifiers | |
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3D model (JSmol) | |
| ChemSpider |
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| ECHA InfoCard | 100.000.776 |
| UNII | |
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| Properties | |
| Al2(CH3)6 | |
| Molar mass | 144.17 g/mol 72.09 g/mol (Al(CH3)3) |
| Appearance | Colorless liquid |
| Density | 0.752 g/cm3 (20 °C)[1] |
| Melting point | 15.4 °C (59.7 °F; 288.5 K)[1] |
| Boiling point | 125–130 °C (257–266 °F; 398–403 K)[1][2] |
| Reacts | |
| Vapor pressure |
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| Viscosity |
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| Thermochemistry | |
| 155.6 J/(mol·K)[2] | |
Std molar entropy(S⦵298) | 209.4 J/(mol·K)[2] |
Std enthalpy of formation(ΔfH⦵298) | −136.4 kJ/mol[2] |
Gibbs free energy(ΔfG⦵) | −9.9 kJ/mol[2] |
| Hazards | |
| Occupational safety and health (OHS/OSH): | |
Main hazards | Pyrophoric, severe skin burns and eye damage |
| GHS labelling: | |
  [1] | |
| Danger | |
| H250,H260,H314[1] | |
| P222,P223,P231+P232,P280,P370+P378,P422[1] | |
| NFPA 704 (fire diamond) | |
| Flash point | −17.0 °C (1.4 °F; 256.1 K)[1] |
| Related compounds | |
Related compounds | |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Trimethylaluminium orTMA is one of the simplest examples of anorganoaluminium compound. Despite its name it has theformulaAl2(CH3)6 (abbreviated asAl2Me6, where Me stands formethyl), as it exists as adimer. This colorless liquid ispyrophoric. It is an industrially important compound, closely related totriethylaluminium.[3][4]
The structure and bonding inAl2R6 anddiborane are analogous (R = alkyl). InAl2Me6, the Al-C(terminal) and Al-C(bridging) distances are 1.97 and 2.14Å, respectively. The Al center istetrahedral.[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, thedimerAl2Me6cracks intomonomericAlMe3.[6]
TMA is prepared via a two-step process that can be summarized as follows:
Starting with the invention ofZiegler-Natta catalysis,organoaluminium compounds have a prominent role in the production ofpolyolefins, such aspolyethylene andpolypropylene.Methylaluminoxane, which is produced from TMA, is an activator for many transition metal catalysts.
TMA is also used in semiconductor fabrication to deposit thin film, high-kdielectrics such asAl2O3 via the processes ofchemical vapor deposition oratomic layer deposition. TMA is the preferred precursor formetalorganic vapour phase epitaxy (MOVPE) of aluminium-containingcompound semiconductors, such asAlAs,AlN,AlP,AlSb,AlGaAs,AlInGaAs,AlInGaP,AlGaN,AlInGaN,AlInGaNP, etc. Criteria for TMA quality focus on (a) elemental impurities, (b) oxygenated and organic impurities.
In deposition processes very similar to semiconductor processing, TMA is used to deposit thin film, low-k (non-absorbing) dielectric layer stacks withAl2O3 via the processes ofchemical vapor deposition oratomic layer deposition. TheAl2O3 provides excellent surface passivation of p-doped silicon surfaces. TheAl2O3 layer is typically the bottom layer with multiple silicon nitride (SixNy) layers for capping.
Trimethylaluminium is hydrolyzed readily, even dangerously:
Under controlled conditions, the reaction can be stopped to givemethylaluminoxane:
Alcoholysis and aminolysis reactions proceed comparably. For example,dimethylamine gives the dialuminium diamide dimer:[7]
TMA reacts with many metal halides to install alkyl groups. When combined with gallium trichloride, it givestrimethylgallium.[8]Al2Me6 reacts withaluminium trichloride to give(AlMe2Cl)2.
TMA/metal halide reactions have emerged as reagents inorganic synthesis.Tebbe's reagent, which is used for the methylenation ofesters andketones, is prepared from TMA andtitanocene 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 inorganic synthesis in a reaction known as carboalumination.[10]
As for other "electron-deficient" compounds, trimethylaluminium givesadductsR3N·AlMe3. The Lewis acid properties ofAlMe3 have been quantified.[11] The enthalpy data show thatAlMe3 is ahard acid and its acid parameters in theECW model are EA = 8.66 and CA = 3.68.
These adducts, e.g. the complex with thetertiary amineDABCO, are safer to handle than TMA itself.[12]
TheNASA ATREX mission (Anomalous Transport Rocket Experiment) employed the white smoke that TMA forms on air contact to study the high altitude jet stream.
TMA is a source of methyl nucleophiles, akin tomethyl lithium, but less reactive. It reacts with ketones to give, after a hydrolytic workup, tertiary alcohols.
Trimethylaluminium ispyrophoric, reacting violently with air and water, releasing gases which can spontaneously ignite. Violent reactions are also possible withacids,oxygen,alcohols,halogens andoxidizing agents. May cause severe skin burns and serious eye damage.[1]
