| Sumario: | We report the synthesis of a niobium cyclopropyl complex, TpNbMe(c-CH)(MeCCMe), and show that thermal loss of methane from this compound generates an intermediate that is capable of activating both aliphatic and aromatic C-H bonds. Isotopic labeling, trapping studies, a detailed kinetic analysis, and density functional theory all suggest that the active intermediate is an η-cyclopropene complex formed via β-hydrogen abstraction rather than an isomeric cyclopropylidene species. C-H activation chemistry of this type represents a rather unusual reactivity pattern for η-alkene complexes but is favored in this case by the strain in the C ring which prevents the decomposition of the key intermediate via loss of cyclopropene.
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