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In this Forum Article, we discuss the use of redox-active pincer-type ligands to enable multielectron reactivity, specifically nitrene group transfer, at the electron-poor metals tantalum and zirconium. Two analogous ligand platforms, ONO and NNN, are discussed with a detailed examination of their similarities and differences and the structural and electronic constraints they impose upon coordination to early transition metals. The two-electron redox capabilities of these ligands enable the transfer of organic nitrenes to tantalum(V) and zirconium(IV) metal centers despite formal d(0) electron counts. Under the correct conditions, the resulting metal imido complexes can participate in further multielectron reactions such as imide reduction, nitrene coupling, or formal nitrene transfer to an isocyanide.
Heyduk et al. (Wed,) studied this question.