Striking Borane Planarization in the Thermal Rearrangement (η⁵‐C₅H₅)Fe(η³‐B₅H₁₀)→(η⁵‐C₅H₅)Fe(η⁵‐B₅H₁₀)

Abstract

In 1977 Weiss and Grimes, by means of mass spectrometry and 1H and 11B NMR spectroscopy, proposed two structures (I and II) for the ferraborane (η5‐C5H5)Fe(B5H10), isoelectronic with ferrocene. In this work, by means of high‐level quantum‐chemical computations, we confirm the experimental structures of the two isomers with their corresponding energies, and assign the reported 1H and 11B NMR chemical shifts. A striking result from this study is the planarization (3D → 2D) of the B5H10– ligand ‐ an unknown isolated anion, isoelectronic with aromatic cyclopentadienyl anion C5H5– ‐ when attached to the (η5‐C5H5)Fe+ moiety, thus resulting in a more stable ferraborane isomer II.