Investigation of a series of oxidized nitridomanganese (V) salen complexes with different para-ring substituents (R = CF 3 , tBu and NMe 2 ) demonstrates that nitride activation is dictated by remote ligand electronics. For R = CF 3 and tBu, oxidation affords a Mn(VI) species and nitride activation, with dinitrogen homocoupling accelerated by the more electron withdrawing CF 3 substituent. Employing an electron-donating substituent (R = NMe 2 ) results in a localized ligand radical species that is resistant to N-coupling of the nitrides, and is stable in solution at both 195 and 298 K.Transition metal complexes bearing terminal nitride (N 3-) ligands are of significant interest due to the key role they may play in the nitrogen fixation process, 1 their importance in stoichiometric nitrene transfer reactions, 2 and their utility as catalysts. 3 In the context of industrial (and biological) nitrogen fixation, 4 there have been a number of important reports of Fe nitride complexes in oxidation states IV, 5 V, 6 and VI, 7 and their reactivities are well documented. 8 In many cases the reactivity of terminal nitride complexes can be rationalized by the nucleophilicity (or electrophilicity) of the nitride ligand, which is determined by both metal and oxidation state, as well as ancillary ligands. 9 Group 8 nitrides of Ru(VI) and Os(VI) react with a variety of nucleophiles 10 due to population of MN  * -antibonding orbitals in the transition state. In addition, reactive electrophilic group 9 terminal nitride complexes of Co, 11 Rh,12 and Ir 13 have been reported, and a transient terminal nitride of Ni has recently been described. 14 In contrast to the reactivity of late metal nitrides, early metal nitrides are generally more stable, and are often a product of N 2 activation reactions. 15 In some cases, early transition metal nitrides react as nucleophiles. 16 Terminal nitrides of Mn(V) exhibit intermediate reactivity between their early and late transition metal analogues, and have found utility as nitrene transfer reagents. 2b Early work by Groves demonstrated nitrene transfer from a nitridomanganese(V) porphyrin complex to cyclooctene upon activation with trifluoroacetic anhydride (TFAA). 17 This reactivity was extended to nitridomanganese(V) salen complexes as a means of nitrene transfer to other electron rich alkenes, as well as silyl enol ethers. 18 Despite their synthetic utility, all examples require the addition of Lewis acids such as TFAA or tosic anhydride; likely to activate the nitride by conversion to the corresponding imide before group transfer to the substrate. 19 Nitridomanganese(V) salen complexes have also been employed as a reagent in the synthesis of other metalnitrido fragments. 20 Herein, we investigate the oxidative activation of a series of Mn(V) nitrides in which the resulting reactivity is tuned by the electronic properties of the ancillary ligand (Scheme 1). We employ the tetradentate salen due to its facile and highly modular synthesis, allowing for changes in the electr...

A dipyrrin-supported nickel catalyst (AdFL)­Ni­(py) (AdFL: 1,9-di­(1-adamantyl)-5-perfluorophenyldipyrrin; py: pyridine) displays productive intramolecular C–H bond amination to afford N-heterocyclic products using aliphatic azide substrates. The catalytic amination conditions are mild, requiring 0.1–2 mol% catalyst loading and operational at room temperature. The scope of C–H bond substrates was explored and benzylic, tertiary, secondary, and primary C–H bonds are successfully aminated. The amination chemoselectivity was examined using substrates featuring multiple activatable C–H bonds. Uniformly, the catalyst showcases high chemoselectivity favoring C–H bonds with lower bond dissociation energy as well as a wide range of functional group tolerance (e.g., ethers, halides, thioetheres, esters, etc.). Sequential cyclization of substrates with ester groups could be achieved, providing facile preparation of an indolizidine framework commonly found in a variety of alkaloids. The amination cyclization reaction mechanism was examined employing nuclear magnetic resonance (NMR) spectroscopy to determine the reaction kinetic profile. A large, primary intermolecular kinetic isotope effect (KIE = 31.9 ± 1.0) suggests H–atom abstraction (HAA) is the rate-determining step, indicative of H–atom tunneling being operative. The reaction rate has first order dependence in the catalyst and zeroth order in substrate, consistent with the resting state of the catalyst as the corresponding nickel iminyl radical. The presence of the nickel iminyl was determined by multinuclear NMR spectroscopy observed during catalysis. The activation parameters (ΔH‡ = 13.4 ± 0.5 kcal/mol; ΔS‡= −24.3 ± 1.7 cal/mol·K) were measured using Eyring analysis, implying a highly ordered transition state during the HAA step. The proposed mechanism of rapid iminyl formation, rate-determining HAA, and subsequent radical recombination was corroborated by intramolecular isotope labeling experiments and theoretical calculations.

Nickel-supported nitrenoids exhibit iminyl character, as determined by multi-edge XAS and TDDFT analysis, demonstrate efficacy for C–H activation and nitrene transfer chemistry.