Organogallium chemistry

Trimethylgallium

Organogallium chemistry is the chemistry of organometallic compounds containing a carbon to gallium (Ga) chemical bond. Despite their high toxicity ^{[citation needed]}, 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:

Ga(CH₃)₃ + AsH₃ → GaAs + 3CH₄

Gallium trichloride is an important reagent for the introduction of gallium into organic compounds.

The main gallium oxidation state is Ga(III), as in all lower group 13 elements (such as aluminium).^[1][2]

Organogallium(I) chemistry

Organometallic complexes of gallium(I) are significantly rarer than that of gallium(III). Some common species include arene-gallium(I) complexes and sterically hindered aryl gallium(I) complexes.^[3][4]

An example of an aryl organogallium(I) compound, note its reversible dimerization

Organogallium(III) chemistry

Compounds of the type R₃Ga are monomeric. Lewis acidity decreases in the order Al > Ga > In and as a result organogallium compounds do not form bridged dimers as organoaluminum compounds do. Organogallium compounds are also less reactive than organoaluminum compounds. They do form stable peroxides.^[5]

Organogallium compounds can be synthesized by transmetallation, for example the reaction of gallium metal with dimethylmercury:

2Ga + 3Me₂Hg → 2Me₃Ga + 3 Hg

or via organolithium compounds or Grignards:

GaCl₃ + 3MeMgBr → Me₃Ga + 3MgBrCl

The electron-deficient nature of gallium can be removed by complex formation, for example

Me₂GaCl + NH₃ → [Me₂Ga(NH₃)Cl]⁺Cl⁻

Pi complex formation with alkynes is also known.

Organogallium compounds are reagents or intermediates in several classes of organic reactions:

• Barbier-type reactions with elemental gallium, allylic substrates and carbonyl compounds
• Carbometallation (carbogallation) reactions ^[6]

See also

• Organoindium chemistry
• Organothallium chemistry

References

1. C. Elschenbroich, A. Salzer Organometallics : A Concise Introduction (2nd Ed) (1992) from Wiley-VCH: Weinheim. ISBN 3-527-28165-7
2. Chemistry of aluminium, gallium, indium, and thallium Anthony John Downs (Ed.) ISBN 978-0-7514-0103-5, 1993
3. Greenwood (2001). Chemistry of the Elements (2nd ed.). Elsevier. pp. 262–265. ISBN 0-7506-3365-4.
4. Housecroft, Catherine E. (2018). Inorganic chemistry (Fifth ed.). Harlow, England ; New York: Pearson. pp. 887–892. ISBN 978-1-292-13414-7.
5. W, Uhl and M. R. Halvagar; et al. (2009). "Reducing Ga-H and Ga-C Bonds in Close Proximity to Oxidizing Peroxo Groups: Conflicting Properties in Single Molecules". Chemistry: A European Journal. 15 (42): 11298–11306. doi:10.1002/chem.200900746. PMID 19780106.
6. Amemiya Ryo, Yamaguchi Masahiko (2005). "GaCl₃ in Organic Synthesis". Eur. J. Org. Chem. 2005 (24): 5145–5150. doi:10.1002/ejoc.200500512.