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 [TpMe2NbCH3(c-C3H5)­(MeCCMe)] (1) are reported. Stoichiometric methane activation by the mesitylene complex [TpMe2Nb­(CH2-3,5-C6H3Me2)­(c-C3H5) (MeCCMe)] (2) giving 1 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 1 or 2, respectively, yielding the transient unsaturated η2-cyclopropene/metallabicyclobutane intermediate [TpMe2Nb­(η2-c-C3H4) (MeCCMe)] A. This is followed by its mechanistic reverse 1,3-CH bond addition of methane yielding the product.