Indium(III) chloride is the chemical compound with the formula InCl3 which forms a tetrahydrate. 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.[2] This is one of three known indium chlorides.
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 . 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 or methyllithium, LiMe. Triethylindium can be prepared in a similar fashion but with the grignard reagent EtMgBr.[11]
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.