Indium Trichloride

Indium(III) chloride is the chemical compound with the formula In Cl₃. This salt is a white, flaky solid with applications in organic synthesis as a Lewis acid. It is also the most available soluble derivative of indium.

Synthesis and structure

Being a relatively electropositive metal, indium reacts quickly with chlorine to give the trichloride. Indium trichloride is very soluble and deliquescent. A synthesis has been reported using an electrochemical cell in a mixed methanol-benzene solution.

Like AlCl₃ and TlCl₃, InCl₃ crystallizes as a layered structure consisting of a close-packed chloride arrangement containing layers of octahedrally coordinated In(III) centers,Egon Wiberg, Arnold Frederick Holleman (2001) ''Inorganic Chemistry'', Elsevier a structure akin to that seen in YCl₃.Wells, A.F. Structural Inorganic Chemistry, Oxford: Clarendon Press, 1984. . In contrast, GaCl₃ crystallizes as dimers containing Ga₂Cl₆. Molten InCl₃ conducts electricity, whereas AlCl₃ does not as it converts to the molecular dimer, Al₂Cl₆.

Reactions

InCl₃ is a Lewis acid and forms complexes with donor ligands, L, InCl₃L, InCl₃L₂, InCl₃L₃. For example, with the chloride ion it forms tetrahedral InCl₄⁻, trigonal bipyramidal InCl₅²⁻, and octahedral InCl₆³⁻.

In diethyl ether solution, InCl₃ reacts with lithium hydride, LiH, to form LiInH4. This unstable compound decomposes below 0 °C, and is reacted ''in situ'' in organic synthesis as a reducing agent and to prepare tertiary amine and phosphine complexes of InH₃.

Trimethylindium, InMe₃, can be produced by reacting InCl₃ in diethyl ether solution either with the Grignard reagent MeMgI or methyllithium, LiMe. Triethylindium can be prepared in a similar fashion but with the grignard reagent EtMgBr.

: + 3LiMe -> + 3LiCl
: + 3MeMgI -> + 3MgClI
: + 3EtMgBr -> + 3MgBr2

InCl₃ reacts with indium metal at high temperature to form the lower valent indium chlorides In₅Cl₉, In₂Cl₃ and InCl.

Catalyst in chemistry

Indium chloride is a Lewis acid catalyst in organic reactions such as Friedel-Crafts acylations and Diels-Alder reactions. As an example of the latter,''An efficient synthesis of novel pyrano ,3-d and furopyrano ,3-dyrimidines via Indium-Catalyzed Multicomponent Domino Reaction'' Prajapati, D. Mukut Gohain, M. Beilstein Journal of Organic Chemistry 2006, 2:11 the reaction proceeds at room temperature, with 1 mole% catalyst loading in an acetonitrile-water solvent mixture. The first step is a Knoevenagel condensation between the barbituric acid and the aldehyde; the second step is a reverse electron-demand Diels-Alder reaction, which is a multicomponent reaction of N,N'-dimethyl-barbituric acid, benzaldehyde and ethyl vinyl ether. With the catalyst, the reported chemical yield is 90% and the percentage trans isomer is 70%. Without the catalyst added, the yield drops to 65% with 50% trans product.

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References

{{Chlorides

Chlorides
Metal halides
Indium compounds