Synthesis and structure of four-coordinate gallium aminophenolate complexes and studies of their reactivity toward B(C6F5)3

The Ga dimethyl complexes {6-(CH2NMe2)-2-R-C6H3O}GaMe2 (2a, R = Me; 2b, R = Ph; 2c, R = Bu-t) are readily accessible via a classical alkane elimination reaction between the corresponding aminophenol ligand and GaMe3. In the case of 2a, X-ray crystallographic studies clearly establish this species as monomeric and with the Ga center being eta(2)-chelated by one aminophenolate moiety. The ionization reaction of complexes 2a-c with B(C6F5)(3) affords the corresponding dinuclear Ga cationic adducts {6-(CH2NMe2)-2-R-C6H3O} GaMe center dot {6-(CH2NMe2)-2-R-C6H3O}GaMe2+(3a(+), R = Me; 3b(+), R = Ph; 3c(+), R = Bu-t) as fully dissociated MeB(C6F5)(3)(-) salts. On the basis of thorough 1D and 2D NMR studies, the Ga cations 3a-c(+) appear to be structurally similar to their Al analogs, which were previously X-ray characterized. The ionization reaction of 2c by B(C6F5)(3) (room temperature, CH2Cl2) yields a thermodynamic equilibrium (with the Ga cation 3c(+) as the major product under the studied conditions) as deduced from low temperature NMR experiments, which shows that the Me- abstraction reaction performed by B(C6F5)(3) at a Ga center may occur in a reversible way. The reaction of compounds 2a-c with 1 equiv. of PhOH provides access to the corresponding mono-methyl Ga complexes {6-(CH2NMe2)-2-R-C6H3O}Ga(Me)(OPh) (4a, R = Me; 4b, R = Ph; 4c, R = Bu-t), which, unlike 2a-c, do not undergo any ionization reaction when reacted with [Ph3C][B(C6F5)(4)] or B(C6F5)(3).