Indium(III) chloride

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 close-packed chloride arrangement containing layers of octahedrally coordinated In(III) centers. The motif is akin to that seen for YCl₃. 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 chloride ion it forms tetrahedral, InCl₄⁻; trigonal bipyramidal, InCl₅²⁻ and octahedral InCl₆³⁻.

In diethyl ether solution InCl₃ reacts with lithium hydride, LiH, to form LiInH 4 , an unstable compound decomposing below 0 °C, which 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.

InCl₃ reacts with indium metal at high temperature to form 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 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 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.