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

Abstract

The Ga dimethyl complexes {6-(CH₂NMe₂)-2-R-C₆H₃O}GaMe₂ (2a, R = Me; 2b, R = Ph; 2c, R =  ^t Bu) 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 η ²-chelated by one aminophenolate moiety. The ionization reaction of complexes 2a – c with B(C₆F₅)₃ affords the corresponding dinuclear Ga cationic adducts (3a ⁺ , R = Me; 3b ⁺ , R = Ph; 3c ⁺, R =  ^t Bu) as fully dissociated 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 =  ^t Bu), which, unlike 2a – c, do not undergo any ionization reaction when reacted with [Ph₃C][B(C₆F₅)₄] or B(C₆F₅)₃.

Keywords:

• Gallium complexes
• Cations
• Aminophenolate
• Lewis acids

Acknowledgement

The Centre National de la Recherche Scientifique is acknowledged for financial support. We also gratefully thank Dr. A. De Cian for his help in the X-ray structure determination of complexes 2a and 4c.