Cyclometallation reactions of a three-coordinate cobalt(i) complex bearing a nonsymmetric N-heterocyclic carbene ligand†
The reactions of a three-coordinate cobalt(I) complex [(IAdMes)(PPh3)CoCl] (1) (IAdMes = 1-mesityl-3-adamantyl-4,5-dimethylimidazol-2-ylidene) with LiCH3, LiCH2SiMe3 and NaCp gave ligand-based C(sp3)–H bond activation products [(IAd′Mes)Co(η6-C6H5PPh2)] (2), [(IAdMes′)(PPh3)Co(CH2SiMe3)] (4) and [(IAd′Mes)Co(η5-Cp)] (5), respectively (IAd′Mes and IAdMes′ denote adamantyl- and mesityl-cyclometallated N-heterocyclic carbene (NHC) ligands, respectively). All the cobalt–NHC complexes have been characterized by various spectroscopic methods, and their structures have been established by single-crystal X-ray diffraction studies. These cyclometallation reactions are among the rare examples of C(sp3)–H bond activation reactions observed in structurally well-defined low-valent cobalt complexes. Different cyclometallated NHC ligands ([IAd′Mes]1−versus [IAdMes′]1−) and different oxidation states of the metal center (cobalt(I) versus cobalt(II)) in the resultant cobalt complexes hint at different mechanisms for these cobalt-mediated C(sp3)–H bond activation reactions.
- This article is part of the themed collection: The central role of the d-block metals in the periodic table