Molecular versus Ionic Structures in Adducts of GaX₃ with Monodentate Carbon-Based Ligands

A molecular donor–acceptor adduct has been isolated by the reaction of the N-heterocyclic carbene 1,3-dimethyl imidazol-2-ylidene (diMe-IMD) with GaCl3. In contrast, the structurally related, yet much more nucleophilic, 1,3-dimethyl-2-methylene-2,3-dihydro-1H-imidazole (diMe-MDI) gave rise to ion pairs of type [L2GaX2]­[GaX4], where X = Cl, Br, or I. With IBioxMe4, a N-heterocyclic carbene that is more nucleophilic than diMe-IMD, the outcome of the reaction was dependent on the nature of the halide. Ionic 1:1 adducts between monodentate ligands and GaX3 salts have only one precedent in the literature. The peculiar behavior of carbon-based ligands was explained on the basis of their electronic properties and reaction kinetics.