This review summarizes the properties of group 9–11 metal–oxo and metal–imido complexes, which have been either isolated or proposed as reactive intermediates in metal‐catalyzed organic transformations. We begin with a general description of the bonding of transition‐metal–oxo and –imido complexes in various geometries, followed by a discussion of complexes from groups 9–11. The focus of this review is to provide a clear picture of the state of the art as well as insight towards potential future synthetic endeavors.

An elusive S=3/2 oxocobalt(IV) complex is stabilized by a Lewis acid interaction with a scandium(III) ion. The {CoIV‐O‐Sc}3+ unit, characterized by spectroscopic and DFT methods, is a stronger electron‐transfer and H‐atom abstraction agent but weaker oxo‐transfer agent than the corresponding {FeIVO} complex (see scheme; L=tris[2‐(N‐tetramethylguanidyl)ethyl]amine).

Ni(III)-intermediates are trapped by EPR and UV/Vis spectroscopy in the reaction of a Ni(II) salt with mCPBA. On the basis of their oxo-transfer and hydrogen-atom abstraction abilities the intermediates are assigned as the elusive terminal Ni(III)-oxo/hydroxo species. The findings suggest that Ni(III)-O(H) moieties are viable reactants in oxidation catalysis.

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