A simple high-yield synthesis of gallium(I) tetrachlorogallate(III) and the reaction of digallium tetrachloride tetrahydrofuran solvate with 1,2-diols

Gallium(I) tetrachlorogallate(III) Ga[GaCl₄] was prepared in quantitative yield by thermal decomposition of dichlorogallane [HGaCl₂]₂, which is readily available from Et₃SiH and [GaCl₃]₂. The reaction of catechol with solutions of this gallium(I) tetrachlorogallate(III) in tetrahydrofuran leads to the evolution of hydrogen gas and affords a dinuclear gallium(III) complex with penta-coordinate metal atoms chelated and bridged by mono-deprotonated catechol ligands. In the crystalline phase tetrahydrofuran molecules are hydrogen-bonded to the hydroxy groups: [Ga(1,2-OC₆H₄OH)Cl₂(C₄H ₈O)]₂. The reaction with pinacol also gives hydrogen and the analogous product [Ga(OCMe₂CMe₂OH)Cl₂(C₄H ₈O)]₂. The structures of the two compounds have been determined by X-ray diffraction. A mechanism of the new reaction has been proposed which involves oxidative addition of the diol to the solvate (THF)Cl₂Ga-GaCl₂(THF) present in the tetrahydrofuran solution to give a gallium hydride intermediate.