Benzoxaborolate ligands in group 13 metal complexes

A series of group 13 metal benzoxaborolates [R2MOB(o-CH2O)(C6H4)]2 [R = tBu, M = Al (2), R = Me, M = Ga (3), R = tBu, M = Ga (4), R = tBu, M = In (5)] were synthesized in reactions of 1,3-dihydro-1-hydroxy-2,1-benzoxaborole (1) with group 13 metal trialkyls. The compounds were characterized by elemental analysis, melting point measurements, 1H, 13C NMR, and IR spectroscopy. The molecular structure of 2–5 was determined by single-crystal X-ray diffraction. The structure of the compounds depends on the kind of metallic center. Reaction of tBu3Al with the benzoxaborole 1 leads to the aluminum derivative 2, similar to typical dialkylaluminum carboxylates, with a central eight-membered B2Al2O4 ring, in which two oxygen atoms of the benzoxaborolate unit are bonded to aluminum atoms. In the presence of gallium and indium trialkyls, the benzoxaborole 1 acts as an alcohol yielding complexes 3–5, similar to dialkylmetal alkoxides, with a central M2O2 (where M = Ga, In) ring. Thermal decomposition of compounds 2 and 4 revealed the liberation of a mixture of organoboron compounds.