Reactivity of B(C₆F₅)₃ with Simple Early Transition Metal Alkoxides: Alkoxide-Aryl Exchange, THF Ring-Opening, or Acetonitrile CC Coupling

Treatment of the titanium(IV) and vanadium(IV) alkoxide complexes M(OPrⁱ)₄ [M = Ti, V] with B(C₆F₅)₃ results in alkoxide−aryl exchange and formation of the organometallic dimer complexes [M(OPrⁱ)₂(μ-OPrⁱ)(C₆F₅)]₂ (M = Ti (1), V (2)). In comparison, the reaction between B(C₆F₅)₃ and Zr(OBu^t)₄ in pentane, followed by recrystallization in acetonitrile−THF solutions, affords the unexpected trimeric zirconium salt [Zr₃(OBu^t)₆(μ₂-OBu^t)₃(μ₃-OBu^t)(μ₃-OCH₂CH₂CH₂CH₃)][B(C₆F₅)₄] (3), which proceeds through a redox reaction involving the borane and the THF solvent. In the presence of CH₃CN, a tetranuclear complex formulated as [Zr₂(OBu^t)₅(μ-OBu^t)₂(μ-N,N′-N(H)C(CH₃)C(H)CN)]₂ (5) is obtained, which results from a C,C coupling reaction between two acetonitrile molecules. When Zr(OBu^t)₄ is treated with (HO)B(C₆F₅)₂, a dimer complex formulated as [Zr(OBu^t)₂{μ-O-OB(OBu^t)(C₆F₅)₂-κ²-O,O}]₂ (7) is formed that contains an unusual ligand bonding mode. The molecular structures of 1, 2, 3, 5, and 7 as well as the adduct B(C₆F₅)₃·THF (4) and [Zr(OBu^t)₃(μ-OBu^t)]₂(μ-NCCH₃) (6) have been determined by X-ray diffraction.