A contaminated Group III metal hydrocarbon is purified by providing an adduct of Group III metal hydrocarbon with a Lewis base in a solvent having a boiling point which is up to 200 C., but at least 30 C. higher than the boiling point of the Group III metal hydrocarbon, separating the solvent from the adduct, and heating the adduct for thermal dissociation, thereby releasing the Group III metal hydrocarbon in high purity form.