On the σ-complex character of bis(gallyl)/digallane transition metal species

Abstract

σ-complexes of homoatomic E–E bonds are key intermediates in catalytically relevant oxidative addition reactions, but are as yet unknown for the group 13 elements. Here, stable species best described as σ-complexes of a 1,2-dichlorodigallane derivative with Ni and Pd are reported. They are readily accessed through the combination of a 1,2-dichlorodigallane derivative, which features chelating phosphine functionalities, with Ni⁰ and Pd⁰ synthons. In-depth computational analyses of these complexes importantly reveal considerable Ga–Ga bonding interactions in both Ni and Pd complexes, despite the expected elongation of the Ga–Ga bond upon complexation, suggestive of σ-complex character as opposed to more commonly described bis(gallyl) character. Finally, the well-defined disproportion of the Ni complex is described, leading to a unique Ga^I–nickel complex, with concomitant expulsion of uncomplexed Ga^III species.