Reactivity of boranes with a titanium(iv) amine tris(phenolate) alkoxide complex; formation of a Ti(iv) tetrahydroborate complex, a Ti(iii) dimer and a Ti(iv) hydroxide Lewis acid adduct

Abstract

Treatment of the titanium(IV) alkoxide complex [Ti(OⁱPr)(OC₆Me₂H₂CH₂)₃N] (2) with BH₃·THF, as part of a study into the utility and reactivity of (2) in the metal mediated borane reduction of acetophenone, results in alkoxide–hydride exchange and formation of the structurally characterised titanium(IV) tetrahydroborate complex [Ti{BH₄}(OC₆Me₂H₂CH₂)₃N] (3). Complex (3) readily undergoes reduction to form the isolable titanium(III) species [Ti(OC₆Me₂H₂CH₂)₃N]₂ (4). Reaction of (2) with B(C₆F₅)₃ results in formation of the Lewis acid adduct [Ti(OC₆Me₂H₂CH₂)₃N][HO·B(C₆F₅)₃] (5). In comparison, treatment of the less sterically encumbered alkoxide Ti(OⁱPr)₄ with B(C₆F₅)₃ results in alkoxide–aryl exchange and formation of the organometallic titanium complex [Ti(OⁱPr)₃(C₆F₅)]₂ (6). The molecular structures of 3, 4, 5 and 6 have been determined by X-ray diffraction.