Unravelling Molecular Aspects of the Migratory Insertion Step in Cp*Co^III Metallacyclic Systems

This Forum Article describes the reactivity and regioselectivity of the insertion of electrophiles, such as alkynes and alkenes, into Co-C bonds in the context of Cp*Co-catalyzed C-H functionalization reactions. The mechanistic investigation, using diphenylacetylene as the model system, reveals that the rate-determining step of the insertion process depends on the temperature. The reaction of a catalytically relevant cobaltacycle, [Cp*Co^III(2-ppy)(MeCN)](BF₄), with selected terminal electrophiles, such as phenylacetylene, styrene, and vinyl acetate, unravels different insertion modes depending on the nature of the unsaturated molecule. The inserted products were fully characterized by NMR spectroscopy, electrospray ionization mass spectrometry, and single-crystal X-ray diffraction. In addition, we performed a kinetic study to establish their relative reactivity.