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...
Metal complexes of 1,2-diamidobenzenes have been long studied because of their intriguing redox properties and electronic structures. We present here a series of such complexes with 1,2-bis(sulfonamido)benzene ligands to probe the utility of these ligands for generating a large zero-field splitting (ZFS, D) in metal complexes that possibly act as single-ion magnets. To this end, we have synthesized a series of homoleptic ate complexes of the form (X) n [M{bis(sulfonamido)benzene} 2 ] (n equals 4 minus the oxidation state of the metal), where M (Fe/Co/Ni), X [K + /(K-18-c-6) + /(HNEt 3 ) + , with 18-c-6 = 18-crown ether 6], and the substituents (methyl and tolyl) on the ligand [bmsab = 1,2-bis(methanesulfonamido)benzene; btsab = 1,2-bis(toluenesulfonamido)benzene] were varied to analyze their effect on the ZFS, possible single-ion-magnet properties, and redox behavior of these metal complexes. A combination of X-ray crystallography, (spectro)electrochemistry, superconducting quantum interference device magnetometry, high-frequency electron paramagnetic resonance spectroscopy, and Mossbauer spectroscopy was used to investigate the electronic/geometric structures of these complexes and the aforementioned properties. These investigations show that the cobalt(II) complexes display very high negative D values in the range of −100 to −130 cm −1 , and the nickel(II) complexes display very high positive D values of 76 and 58 cm −1 . In addition, the cobalt(II) complexes shows barriers of 200−260 cm −1 and slow relaxation of the magnetization in the absence of an external magnetic field, underscoring the robustness of this class of complexes. The iron(II) complex exhibits a D value of −3.29 cm −1 and can be chemically oxidized to an iron(III) complex that has D = −1.96 cm −1 . These findings clearly show that bis(sulfonamido)benzenes are ideally suited to stabilize ate complexes, to generate very high ZFSs at the metal centers with single-ion-magnet properties, and to induce exclusive oxidation at the metal center (for iron) despite the presence of ligands that are potentially noninnocent. Our results therefore substantially enhance the scope for this class of redoxactive ligands.
The chromium(III) complex [CrIII(ddpd)2]3+ (molecular ruby; ddpd=N,N′‐dimethyl‐N,N′‐dipyridine‐2‐yl‐pyridine‐2,6‐diamine) is reduced to the genuine chromium(II) complex [CrII(ddpd)2]2+ with d4 electron configuration. This reduced molecular ruby represents one of the very few chromium(II) complexes showing spin crossover (SCO). The reversible SCO is gradual with T1/2 around room temperature. The low‐spin and high‐spin chromium(II) isomers exhibit distinct spectroscopic and structural properties (UV/Vis/NIR, IR, EPR spectroscopies, single‐crystal XRD). Excitation of [CrII(ddpd)2]2+ with UV light at 20 and 290 K generates electronically excited states with microsecond lifetimes. This initial study on the unique reduced molecular ruby paves the way for thermally and photochemically switchable magnetic systems based on chromium complexes complementing the well‐established iron(II) SCO systems.
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