Oxidation of [M(η-C5H5)2], M = Cr, Fe or Co, by the new Brønsted acid H2O·B(C6F5)3 yielding the salts [M(η-C5H5)2]+A–, where A– = [(C6F5)3B(µ-OH)B(C6F5)3]– or [(C6F5)3BOH· · ·H2OB(C6F5)3]–†

Abstract

The Brønsted acids H₂O·B(C₆F₅)₃ and D₂O·B(C₆F₅)₃ have been synthesized. Reaction of neutral divalent metallocenes [M(η-C₅H₅)₂], M = Cr, Fe or Co, with two equivalents of H₂O·B(C₆F₅)₃ 2a resulted in metallocene oxidation and formation of salts containing [M(η-C₅H₅)₂]⁺ cations together with the hydroxoborate anion [HOB(C₆F₅)₃]^– which is hydrogen bonded to the second acid equivalent, namely [M(η-C₅H₅)₂][(F₅C₆)₃BOH· · ·H₂OB(C₆F₅)₃], M = Cr 3a, Fe 4a or Co 5a. Treatment of one equivalent of 2a and one equivalent of B(C₆F₅)₃ 1 with [M(η-C₅H₅)₂] yielded salts containing the same metallocene cations but now with µ-OH bridged anions, as in [M(η-C₅H₅)₂][(F₅C₆)₃B(µ-OH)B(C₆F₅)₃], where M = Cr 3b or Co 5b. All products have been characterised by NMR spectroscopy, elemental analysis, and the single-crystal structures of 2a, 3a, 4a, and 5a have been determined.