Indium(III) chloride

Being a relatively electropositive metal, indium reacts quickly with chlorine to give the trichloride. Indium trichloride is very soluble and deliquescent.[3] A synthesis has been reported using an electrochemical cell in a mixed methanol-benzene solution.[4]

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,[5] a structure akin to that seen in YCl₃.[6] In contrast, GaCl₃ crystallizes as dimers containing Ga₂Cl₆.[6] Molten InCl₃ conducts electricity,[5] whereas AlCl₃ does not as it converts to the molecular dimer, Al₂Cl₆.[7]

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⁻.[5]

In diethyl ether solution, InCl₃ reacts with lithium hydride, LiH, to form ${\displaystyle {\ce {LiInH4}}}$. This unstable compound decomposes below 0 °C,[8] and is reacted in situ in organic synthesis as a reducing agent[9] and to prepare tertiary amine and phosphine complexes of InH₃.[10]

Trimethylindium, InMe₃, can be produced by reacting InCl₃ in diethyl ether solution either with the Grignard reagent ${\displaystyle {\ce {MeMgI}}}$ or methyllithium, LiMe. Triethylindium can be prepared in a similar fashion but with the grignard reagent EtMgBr.[11]

${\displaystyle {\ce {{InCl3}+ 3LiMe -> {Me3In.OEt2}+ 3LiCl}}}$

${\displaystyle {\ce {{InCl3}+ 3MeMgI -> {Me3In.OEt2}+ 3MgClI}}}$

${\displaystyle {\ce {{InCl3}+ 3EtMgBr -> {Et3In.OEt2}+ 3MgBr2}}}$

InCl₃ reacts with indium metal at high temperature to form the lower valent indium chlorides In₅Cl₉, In₂Cl₃ and InCl.[5]

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,[12] 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.