Chemical Oxidation of a Coordinated PNP-Pincer Ligand Forms Unexpected Re-Nitroxide Complexes with Reversal of Nitride Reactivity.

Because of the thermodynamic demands of N cleavage, N-derived nitride complexes are often unreactive. The development of multistep N functionalization reactions hinges on methods for modulating nitride reactivity with supporting ligands. Here, we describe the reactions of N-derived Re-nitride complexes, including the first Re nitrides supported by a nitroxide-containing pincer ligand, and unusual examples of Re-nitride complexes. The previously reported N-derived complex (PNP)Re(N)(Cl) (PNP = N(CHCHPBu)) can be oxidized by O atom transfer to the backbone amide to form a novel nitroxide-pincer complex or by 1e to form a rare = 1/2 Re-nitride complex. The Re-nitrido interaction in a series of Re- and ligand-oxidized complexes is characterized using N NMR spectroscopy, IR spectroscopy, and DFT calculations, and shows changes in the Re-N bond order from both ligand- and metal-centered oxidations. Chemical oxidation of the supporting ligand to form a nitroxide-pincer ligand results in subtle electronic changes at Re and a more electron-deficient nitride ligand. Combined ligand- and metal-centered oxidation to form a Re-nitroxide complex results in a reversal of reactivity at the nitride ligand from nucleophilic to electrophilic. These systematic electronic structure and reactivity studies demonstrate methods for inducing reactivity in N-derived nitride complexes.