The Reduction of Sterically Hindered o-Quinone and o-Iminoquinone with Gallium and "GaI"

Metallic gallium reacts with 3,6-di-tert-butyl-o-benzoquinone (3,6-Q) in THF to produce a gallium tris-o-semiquinolate complex, whereas the same interaction with 4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-iminobenzoquinone (imQ) does not proceed. The reduction of imQ is possible with amalgamed gallium in THF and produces a gallium complex that contains two o-iminobenzoquinone ligands in different redox states. In the case of 3,6-Q, the analogous reaction leads to dimeric derivative [Cat2Ga(Et2O)2][CatGa] (in which Cat is the dianion of 3,6-Q). The structure of this compound was determined by X-ray diffraction analysis. The gallium(III) amidophenolate derivative can only be obtained by exchange reaction of APNa2 with GaI3 (in which AP is the dianion of imQ). The reduction of 3,6-Q and imQ with GaI results in the formation of corresponding compounds that contain redox-active ligands in the dianionic state. The structure of [AP2Ga][GaI2] was determined by X-ray diffraction analysis.