Thermal nitrogen fixation relies on strong reductants to overcome the extraordinarily large N À Nb ond energy. Photochemical strategies that drive N 2 fixation are scarcely developed. Here,t he synthesis of ad inuclear N 2 -bridged complex is presented upon reduction of arhenium(III) pincer platform. Photochemical splitting into terminal nitride complexes is triggered by visible light. Clean nitrogen transfer with benzoyl chloride to free benzamide and benzonitrile is enabled by cooperative 2H + /2 e À transfer of the pincer ligand. Athreestep cycle is demonstrated for N 2 to nitrile fixation that relies on electrochemical reduction, photochemical N 2 -splitting and thermal nitrogen transfer. Figure 3. Left:CVof7 in presence of 0-15 equiv.b enzoic acid.Right: CV of 7 with 10 equiv 2,6-dichlorophenol under N 2 before CPE (orange), after 8hCPE at À1.65 V( pink) and after subsequent 5h CPE at À1.85 V(blue).Scheme 3. Optimized, three-steps ynthetic cycle. Angewandte ChemieCommunications 833

The coupling of electron- and proton-transfer steps provides a general concept to control the driving force of redox reactions. N splitting of a molybdenum dinitrogen complex into nitrides coupled to a reaction with Brønsted acid is reported. Remarkably, our spectroscopic, kinetic, and computational mechanistic analysis attributes N-N bond cleavage to protonation in the periphery of an amide pincer ligands rather than the {Mo-N -Mo} core. The strong effect on electronic structure and ultimately the thermochemistry and kinetic barrier of N-N bond cleavage is an unusual case of a proton-coupled metal-to-ligand charge transfer process, highlighting the use of proton-responsive ligands for nitrogen fixation.

The redox series [Irn(NHx)(PNP)] (n = II–IV, x = 3–0; PNP = N(CHCHPtBu2)2) was examined with respect to electron, proton, and hydrogen atom transfer steps. The experimental and computational results suggest that the IrIII imido species [Ir(NH)(PNP)] is not stable but undergoes disproportionation to the respective IrII amido and IrIV nitrido species. N–H bond strengths are estimated upon reaction with hydrogen atom transfer reagents to rationalize this observation and are used to discuss the reactivity of these compounds toward E–H bond activation.

The combination of well-established meridionally coordinating, tridentate pincer ligands with group 15 elements affords geometrically constrained non-trigonal pnictogen pincer compounds. These species show remarkable activity in challenging element–hydrogen bond scission...

ational synthetic method development is driven by the ability to relate reactivity to the electronic structures of key transient intermediates. For example, organic nitrenes (R-N) are generally highly reactive monovalent nitrogen species and detailed spectroscopic studies have enabled the assignment of their diverse reaction pathways, such as C-H insertion or N-N coupling, to the accessibility of triplet versus (open shell) singlet spin states 1,2 . In comparison, the well-established class of nitrido complexes (L n MN) commonly features trivalent nitrogen with significant covalent components of M-N σand π-bonding (Fig. 1a) 3 . Increased radical and electrophilic nitrogen character can be formally represented by divalent nitridyl all the way to monovalent metallonitrene contributions 4 . Formal nitrido complexes with predominant subvalent metallonitrene (L n M-N) character, which can be regarded as metal analogues of organic nitrenes, have been proposed as key intermediates in stoichiometric intramolecular [5][6][7][8][9] and intermolecular 10-15 nitrogen atom transfer reactions. However, in contrast to organic nitrenes 16 , authentic metallonitrenes with a monovalent atomic nitrogen ligand remain elusive, which impedes the development of new nitrogen transfer reactions based on electronic structure/reactivity relationships.The emergence of C-H amination and amidation via nitrene transfer as a powerful synthetic tool was fuelled by the development of group 9-11 transition metal catalysts that facilitate selective insertion of coordinated nitrene fragments (Fig. 1b) [17][18][19] . Late transition metals are also instrumental as anode materials in electrocatalytic amine oxidation for synthetic and fuel cell applications [20][21][22] . The dominance of late transition metals in redox transformations of nitrogenous species stimulated fundamental interest in M-N(R) bonding 3 . C-H insertion by L n M-NR species has been associated with electrophilic subvalent nitrene ( 3 NR) 23 or imidyl ( 2 NR − ) [24][25][26] character that arises from low lying d orbitals of late transition met-als. This strongly reduces the imido ( 1 NR 2− ) contribution 27,28 . Similar considerations might apply for metallonitrene (L n M-N) or nitridyl (L n M=N • ) versus nitrido (L n M≡N) species (Fig. 1a). However, intermolecular C-H activation has not been reported for the few known late transition metal nitrido or nitridyl complexes [29][30][31] . The exploitation of nitrogen atom insertion reactivity (Fig. 1b) is still in its infancy; as of yet, catalytic protocols are not known and systematic advances suffer from the lack of well-defined metallonitrene platforms.In this contribution, a formal nitrido complex beyond group 9 is reported. Crystallographic, spectroscopic, magnetic and computational characterization shows a triplet electronic ground state with a predominantly single-bonded metallonitrene (L n Pt ii -N) and nitrogen-centred diradical character. Facile N-atom insertion into C-H, B-H and B-C bonds is demonstrated. In contrast to the...