Trimethylaluminium

Trimethylaluminium
Trimethylaluminium
Identifiers
CAS number 75-24-1 YesY
PubChem 16682925
ChemSpider 10606585 YesY
Jmol-3D images Image 1
Properties
Molecular formula C6H18Al2
Molar mass 144.18 g/mol
Appearance Colorless liquid
Density 0.752 g/mL
Melting point

15 °C

Boiling point

125 °C

Hazards
Main hazards Pyrophoric
NFPA 704
NFPA 704.svg
4
3
3
W
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Trimethylaluminium is the chemical compound with the formula Al2(CH3)6, abbreviated as Al2Me6, (AlMe3)2 or the abbreviation TMA. This pyrophoric, colorless liquid is an industrially important organoaluminium compound. It evolves white smoke (aluminium oxides) when the vapor is released into the air.

Contents

Structure and bonding

Al2Me6 exists as a dimer, analogous in structure and bonding to diborane. As with diborane, the metalloids are connected by a 3-center-2-electron bond: the shared methyl groups bridge between the two aluminium atoms. The Al-C(terminal) and Al-C(bridging) distances are 1.97 and 2.14 Å, respectively.[1] 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 and intermolecularly.

3-Centered-2-electron bonds are an utterance of "electron-deficient" molecules and tend to reactions with Lewis bases that would give products consisting of 2-centered-2-electron bonds. For example upon treatment with amines gives adducts R3N-AlMe3. Another reaction that gives products that follow the octet rule is the reaction of Al2Me6 with aluminium trichloride to give (AlMe2Cl)2.

The species AlMe3, which would feature an aluminium atom bonded to three methyl groups is unknown. VSEPR Theory predicts that such a molecule would have idealized threefold symmetry, as observed in BMe3.

Synthesis and applications

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

TMA is mainly used for the production of methylaluminoxane, an activator for Ziegler-Natta catalysts for olefin polymerisation. TMA is also employed as a methylation agent. Tebbe's reagent, which is used for the methylenation of esters and ketones, is prepared from TMA. TMA is often released from sounding rockets as a tracer in studies of upper atmospheric wind patterns.

TMA is also used in semiconductor fabrication to grow thin film, high-k dielectrics such as Al2O3 via the processes of Chemical Vapor Deposition or Atomic Layer Deposition.

TMA forms a complex with the tertiary amine DABCO, which is safer to handle than TMA itself.[2]

In combination with 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.[3]

Semiconductor grade TMA

TMA is the preferred metalorganic source 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 impurites, (b) oxygenated and organic impurities.

References

  1. ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
  2. ^ Biswas, K.; Prieto, O.; Goldsmith, P. J.Woodward, S. (2005). "Remarkably Stable (Me3Al)2DABCO and Stereoselective Nickel-Catalyzed AlR3 (R = Me, Et) Additions to Aldehydes". Angewandte Chemie International Edition 44 (15): 2232–2234. doi:10.1002/anie.200462569. PMID 15768433. 
  3. ^ Negishi, E.; Matsushita, H., "Palladium-Catalyzed Synthesis of 1,4-Dienes by Allylation of Alkenyalane: α-Farnesene [1,3,6,10-Dodecatetraene, 3,7,11-trimethyl-]", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv7p0245 ; Coll. Vol. 7: 245 

External links


Wikimedia Foundation. 2010.

Игры ⚽ Поможем решить контрольную работу

Look at other dictionaries:

  • Trimethylaluminium — Strukturformel Allgemeines Name Trimethylaluminium S …   Deutsch Wikipedia

  • trimethylaluminium — trimetilaliuminis statusas T sritis chemija formulė (CH₃)₃Al atitikmenys: angl. trimethylaluminium rus. триметилалюминий …   Chemijos terminų aiškinamasis žodynas

  • Methylaluminoxane — Identifiers Properties Molecular formula (Al(CH3)xOy)n Appearance white solid Hazards Main hazards …   Wikipedia

  • Trimethylborane — IUPAC name Trimethylborane …   Wikipedia

  • Organoaluminium chemistry — is the study of compounds containing bonds between carbon and aluminium bond. It is one of the major themes within organometallic chemistry.[1] [2] Illustrative organoaluminium compounds are the dimer trimethylaluminium, the monomer… …   Wikipedia

  • Aluminium — Infobox aluminiumAluminium (Audio IPA|En uk aluminium1.ogg|ˌæljʊˈmɪniəm, IPA|/ˌæljəˈmɪniəm/) or aluminum (Audio IPA|En uk aluminum.ogg|/əˈluːmɪnəm/, see spelling below) is a silvery white and ductile member of the boron group of chemical elements …   Wikipedia

  • Chemikalienliste — Die Chemikalienliste stellt eine alphabetisch sortierte Liste von Chemikalien dar, ohne Anspruch auf Vollständigkeit. Elemente sind fett gekennzeichnet, Stoffgruppen kursiv. Der Haupteintrag zu einer Chemikalie ist gleichzeitig der Name des… …   Deutsch Wikipedia

  • E173 — Eigenschaften …   Deutsch Wikipedia

  • E 173 — Eigenschaften …   Deutsch Wikipedia

  • Liste chemischer Verbindungen — Die Chemikalienliste stellt eine alphabetisch sortierte Liste von Chemikalien dar, ohne Anspruch auf Vollständigkeit. Elemente sind fett gekennzeichnet, Stoffgruppen kursiv. Der Haupteintrag zu einer Chemikalie ist gleichzeitig der Name des… …   Deutsch Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”