Cameron Jones and his colleagues at Monash University, Melbourne and Cardiff University, Wales have shown the solubility of an indium(I) bromide complex in tmeda/toluene mixtures [InBr(tmeda)]. In solution the compound is metastable and disproportionates above -20°C. 

Indium(I) halides, InX (X = Cl, Br or I), are commercially available and have found numerous uses as reagents for organic transformations and in synthetic organometallic chemistry. Despite this, these salt-like compounds have almost no solubility in non-coordinating organic solvents and they normally decompose in coordinating solvents. 

Jones has achieved solubility of these compounds and also obtained a crystal structure of the indium(I) bromide complex, which shows the compound is monomeric in the solid state. This differs to the remarkable oligomeric, metastable aluminium(I) and gallium(I) halide complexes developed by Schnöckels group in Kahlsruhe.

'I have always been a great admirer of Schnöckels work with metastable aluminium(I) and gallium(I) halide complexes, and have wondered, for some time, why no similar indium(I) halide complexes had been isolated and structurally authenticated.   A number of years ago I stumbled across some elegant work by Dennis Tuck from the early 80's.   He reported that indium(I) halides can dissolve in solvents containing the bidentate ligand, tmeda, without undergoing disproportionation.   This intrigued me and I was very keen to find out what the nature of the dissolved indium(I) species were,' explains Jones.

Jones' future plans for this work is 'to develop easy to prepare, soluble complexes of indium(I) halides that are stable at room temperature.   If this can be achieved, such compounds could prove commercially viable as specialist reagents for organic and organometallic chemists.' 

In the meantime, Jones suggests that chemists requiring a well defined, soluble indium(I) halide reagent should consider using solutions of InBr in 10% tmeda/toluene below -20°C!

Emma Shiells