Synthesis and structure of four-coordinate gallium aminophenolate complexes and studies of their reactivity toward B(C 6 F 5 ) 3

Abstract

The Ga dimethyl complexes {6-(CH₂NMe₂)-2-R-C₆H₃O}GaMe₂ (2a, R = Me; 2b, R = Ph; 2c, R = ^tBu) 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 η²-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·{6-(CH₂NMe₂)-2-R-C₆H₃O}GaMe₂⁺ (3a⁺, R = Me; 3b⁺, R = Ph; 3c⁺, R = ^tBu) 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 = ^tBu), which, unlike 2a – c, do not undergo any ionization reaction when reacted with [Ph₃C][B(C₆F₅)₄] or B(C₆F₅)₃.