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Metal atom lability from a well-defined bimetallic cluster was canvassed as a function of ligand substitution, redox chemistry, and group transfer processes. 

A dipyrrin-supported copper complex mediates C–H bond amination and aziridination of exogenous substrates using electron-deficient arylazides, proceeding through copper-nitrene adducts. 

Despite the myriad Cu-catalyzed nitrene transfer methodologies to form new C–N bonds (e.g.,amination, aziridination), the critical reaction intermediates have largely eluded direct characterization due to their inherent reactivity. Herein, we report the synthesis of dipyrrin-supported Cu nitrenoid adducts, investigate their spectroscopic features, and probe their nitrene transfer chemistry through detailed mechanistic analyses. Treatment of the dipyrrin CuI complexes with substituted organoazides affords terminally ligated organoazide adducts with minimal activation of the azide unit as evidenced by vibrational spectroscopy and single crystal X-ray diffraction. The Cu nitrenoid, with an electronic structure most consistent with a triplet nitrene adduct of CuI, is accessed following geometric rearrangement of the azide adduct from k1-N terminal ligation to k1-N internal ligation with subsequent expulsion of N2. For perfluorinated arylazides, stoichiometric and catalytic C–H amination and aziridination was observed. Mechanistic analysis employing substrate competition reveals an enthalpically-controlled, electrophilic nitrene transfer for primary and secondary C–H bonds. Kinetic analyses for catalytic amination using tetrahydrofuran as a model substrate reveal pseudo-first order kineticsunderrelevantaminationconditionswithafirst-orderdependenceonbothCuandorganoazide. Activation parameters determined from Eyring analysis(DH‡=9.2(2)kcalmol−1,DS‡=−42(2)calmol−1 K−1, DG‡ 298K =21.7(2) kcal mol−1) and parallel kinetic isotope effect measurements (1.10(2)) are consistent with rate-limiting Cu nitrenoid formation, followed by a proposed stepwise hydrogen-atom abstraction and rapid radical recombination to furnish the resulting C–N bond. The proposed mechanism and experimental analysis are further corroborated by density functional theory calculations. Multiconfigurational calculations provide insight into the electronic structure of the catalytically relevant Cu nitrene intermediates. The findings presented herein will assist in the development of future methodology for Cu-mediated C–N bond forming catalysis. 

In polynuclear biological active sites, multiple electrons are needed for turnover, and the distribution of these electrons among the metal sites is affected by the structure of the active site. However, the study of the interplay between structure and redox distribution is difficult not only in biological systems but also in synthetic polynuclear clusters since most redox changes produce only one thermodynamically stable product. Here, the unusual chemistry of a sterically hindered trichromium complex allowed us to probe the relationship between structural and redox isomerism. Two structurally isomeric trichromium imides were isolated: asymmetric terminal imide ( tbs L)Cr 3 (NDipp) and symmetric, μ 3 -bridging imide ( tbs L)Cr 3 (μ 3 –NBn) (( tbs L) 6− = (1,3,5-C 6 H 9 (NC 6 H 4 - o -NSi t BuMe 2 ) 3 ) 6− ). Along with the homovalent isocyanide adduct ( tbs L)Cr 3 (CNBn) and the bisimide ( tbs L)Cr 3 (μ 3 –NPh)(NPh), both imide isomers were examined by multiple-wavelength anomalous diffraction (MAD) to determine the redox load distribution by the free refinement of atomic scattering factors. Despite their compositional similarities, the bridging imide shows uniform oxidation of all three Cr sites while the terminal imide shows oxidation at only two Cr sites. Further oxidation from the bridging imide to the bisimide is only borne at the Cr site bound to the second, terminal imido fragment. Thus, depending on the structural motifs present in each [Cr 3 ] complex, MAD revealed complete localization of oxidation, partial localization, and complete delocalization, all supported by the same hexadentate ligand scaffold. 

Abstract Metalation of the polynucleating ligand^F,tbsLH₆(1,3,5‐C₆H₉(NC₆H₃−4‐F−2‐NSiMe₂^tBu)₃) with two equivalents of Zn(N(SiMe₃)₂)₂affords the dinuclear product (^F,tbsLH₂)Zn₂(1), which can be further deprotonated to yield (^F,tbsL)Zn₂Li₂(OEt₂)₄(2). Transmetalation of2with NiCl₂(py)₂yields the heterometallic, trinuclear cluster (^F,tbsL)Zn₂Ni(py) (3). Reduction of3with KC₈affords [KC₂₂₂][(^F,tbsL)Zn₂Ni] (4) which features a monovalent Ni centre. Addition of 1‐adamantyl azide to4generates the bridging μ³‐nitrenoid adduct [K(THF)₃][(^F,tbsL)Zn₂Ni(μ³‐NAd)] (5). EPR spectroscopy reveals that the anionic cluster possesses a doublet ground state (S=). Cyclic voltammetry of5reveals two fully reversible redox events. The dianionic nitrenoid [K₂(THF)₉][(^F,tbsL)Zn₂Ni(μ³‐NAd)] (6) was isolated and characterized while the neutral redox isomer was observed to undergo both intra‐ and intermolecular H‐atom abstraction processes. Ni K‐edge XAS studies suggest a divalent oxidation state for the Ni centres in both the monoanionic and dianionic [Zn₂Ni] nitrenoid complexes. However, DFT analysis suggests Ni‐borne oxidation for5.