CH Bond Activation of Methane by a Transient η²‑Cyclopropene/Metallabicyclobutane Complex of Niobium

This study challenges the problem of the activation of a CH bond of methane by soluble transition metal complexes. High pressure solution NMR, isotopic labeling studies, and kinetic analyses of the degenerate exchange of methane in the methyl complex [Tp^Me2NbCH₃(<i>c</i>-C₃H₅)­(MeCCMe)] (<b>1</b>) are reported. Stoichiometric methane activation by the mesitylene complex [Tp^Me2Nb­(CH₂-3,5-C₆H₃Me₂)­(<i>c</i>-C₃H₅) (MeCCMe)] (<b>2</b>) giving <b>1</b> is also realized. Evidence is provided that these reactions proceed via an intramolecular abstraction of a β-H of the cyclopropyl group to form either methane or mesitylene from <b>1</b> or <b>2</b>, respectively, yielding the transient unsaturated η²-cyclopropene/metallabicyclobutane intermediate [Tp^Me2Nb­(η²-<i>c</i>-C₃H₄) (MeCCMe)] <b>A</b>. This is followed by its mechanistic reverse 1,3-CH bond addition of methane yielding the product