Anion stability in stannylium, oxonium, and silylium salts of the weakly coordinating anion [C6F4-1,2-{B(C6F5)2} 2(μ-OCH3)]-

Article abstract of DOI:10.1021/om010750x

Reaction of [Ph₃C]+[C₆F₄-1,2-({B(C₆F₅ )₂}₂(μ-OCH₃)]^-, 1, with Bu₃SnH gives the solvated stannylium ion [Bu₃Sn(arene)]⁺[C₆F₄-l,2-{B(C₆ F₅)₂}₂(μ-OCH₃)]-, 2, as a light brown oil (δ ¹¹⁹Sn = 434 ppm). This material is thermodynamically stable toward transfer of the chelated OMe^- anion to "Bu₃Sn⁺" as evidenced by the reaction of free diborane C₆F₄-1,2-[B(C₆F₅)₂]₂ with 2 equiv of Bu₃SnOMe. This reaction produces the stannyloxonium complex [(Bu₃Sn)₂OCH₃]⁺[C₆F₄ -1,2-{B(C₆F₅)₂}₂(μ-OCH ₃)]^-, 3 (δ ¹⁹⁹Sn = 277 ppm), which is stable at -60 °C. Upon warming, the cation in 3 undergoes decomposition to unidentified products, while the anion remains intact. Ion pair 2 reacts rapidly with ethereal HCl in CH₂Cl₂ to generate Bu₃SnCl and the oxonium acid [(Et₂O)₂H]⁺[C₆F₄-1,2-{B(C ₆F₅)₂}₂(μ-OCH₃)]^- , 4, isolated in 76% yield as a white, crystalline solid. Acid 4 is thermally stable in solution and was characterized crystallographically. The C₂B₂OMe core of the anion in 4 deviates from planarity due to intermolecular interactions in the crystal, in contrast to the structures found in other ion pairs with this anion. Reaction of 2 with anhydrous HCl gives the unsymmetrical MeOH adduct of C₆F₄-1,2-[B(C₆F₅)₂]₂ , 5, which was separately synthesized by direct reaction of methanol with the free diborane. The anion [C₆F₄-l,2-{B(C₆F₅)₂} ₂(μ-OCH₃)]^- is not stable in the presence of the triethylsilylium ion, generated from 1 and Et₃SiH.