Reactions of the Complexes ReNCl2(PMe2Ph)3, [ReNCl4]—, [OsO3N]—, and Cl3VNCl with Metal Halides

The nitrido complexes ReNCl₂(PMe₂Ph)₃ and [OsO₃N]^— have strong basic terminal nitrido ligands which can react with Lewis acidic metal halides to form nitrido bridges. The synthesis and structure of complexes with ReNCl₂(PMe₂Ph)₃ and nitrido bridges Re≡N‐M (M = B, Ga, Sn, Ti, Zr, V, Nb, Ta, Mo, Re, Pd, Au, and Zn) as well as of complexes with [OsO₃N]^— and nitrido bridges Os≡N‐M (M = Pd and Pt) are reported. Strong Lewis acids can also remove phosphine or chloro ligands from ReNCl₂(PMe₂Ph)₃. The resulting complex fragments subsequently combine to yield oligomeric complexes with nitrido bridges Re≡N‐Re. If the reaction with strong Lewis acids is carried out in a chlorinated solvent the solvent can be decomposed to form HCl which then protonates the nitrido ligand affording an imido complex. [ReNCl₄]^— is able to form nitrido bridges to electrophilic halides if a donor ligand is coordinated in trans position to the nitrido ligand to enhance its basicity sufficiently. The synthesis and structure of examples with nitrido bridges Re≡N‐M (M = Pd, Pt, Ta) are reported. The chloro imido complex Cl₃V≡N‐Cl can act as a nitride ion transfer reagent. Its reaction with MoCl₅ yields Mo₂NCl₈ whereas with MoCl₃ the nitride chlorides Mo₃N₂Cl₁₁ and MoNCl₃ are obtained. Cl₃VNCl can also act as an reactive intermediate by the reaction of VN with a halide as was shown by the reaction of MoCl₅ with VN yielding Mo₂NCl₇. The structures of these molybdenum nitride chlorides are discussed.     

A Terminal Iron Nitrilimine Complex: Accessing the Terminal Nitride through Diazo N−N Bond Cleavage

A novel method for the N?N bond cleavage of trimethylsilyl diazomethane is reported for the synthesis of terminal nitride complexes. The lithium salt of trimethylsilyl diazomethane was used to generate a rare terminal nitrilimine transition metal complex with partially occupied d‐orbitals. This iron complex 2 was characterized by CHN combustion analysis, ¹H and ¹³C NMR spectroscopic analysis, single‐crystal X‐ray crystallography, SQUID magnetometry, ⁵⁷Fe Mössbauer spectroscopy, and computational analysis. The combined results suggest a high‐spin d ⁶ (S=2) electronic configuration and an allenic structure of the nitrilimine ligand. Reduction of 2 results in release of the nitrilimine ligand and formation of the iron(I) complex 3 , which was characterized by CHN combustion analysis, ¹H NMR spectroscopic analysis, and single‐crystal X‐ray crystallography. Treatment of 2 with fluoride salts quantitatively yields the diamagnetic Fe^IV nitride complex 4 , with concomitant formation of cyanide and trimethylsilyl fluoride through N?N bond cleavage.     

Controlled Expansion of a Strong‐Field Iron Nitride Cluster: Multi‐Site Ligand Substitution as a Strategy for Activating Interstitial Nitride Nucleophilicity

Multimetallic clusters have long been investigated as molecular surrogates for reactive sites on metal surfaces. In the case of the μ₄‐nitrido cluster [Fe₄(μ₄‐N)(CO)₁₂]^?, this analogy is limited owing to the electron‐withdrawing effect of carbonyl ligands on the iron nitride core. Described here is the synthesis and reactivity of [Fe₄(μ₄‐N)(CO)₈(CNAr^Mes2)₄]^?, an electron‐rich analogue of [Fe₄(μ₄‐N)(CO)₁₂]^?, where the interstitial nitride displays significant nucleophilicity. This characteristic enables rational expansion with main‐group and transition‐metal centers to yield unsaturated sites. The resulting clusters display surface‐like reactivity through coordination‐sphere‐dependent atom rearrangement and metal–metal cooperativity.     

Room‐Temperature Functionalization of N2 to Borylamine at a Molybdenum Complex

Intermolecular, stepwise functionalization by BH bonds of a (triphosphine)Mo^IV–nitrido complex generated by N₂ splitting is reported. The imido–hydride and di‐hydride–amido Mo^IV complexes have been isolated and characterized. Addition of PinBH to the [Mo(H)₂(N(BPin)₂)]⁺ complex at room temperature results in the liberation of borylamines from the metal center.     

CH Activation of Benzene by a Photoactivated NiII(azide): Formation of a Transient Nickel Nitrido Complex

Photochemical activation of nickel‐azido complex 2 [Ni(N₃)(PNP)] (PN^HP=2,2′‐di(isopropylphosphino)‐4,4′‐ditolylamine) in neat benzene produces diamagnetic complex 3 [Ni(Ph)(PN^PN^H)], which is crystallographically characterized. DFT calculations support photoinitiated N₂‐loss of the azido complex to generate a rare, transient Ni^IV nitrido species, which bears significant nitridyl radical character. Subsequent trapping of this nitrido through insertion into the Ni? P bond generates a coordinatively unsaturated Ni^II imidophosphorane P?N donor. This species shows unprecedented reactivity toward 1,2‐addition of a C? H bond of benzene to form 3 . The structurally characterized chlorido complex 4 [Ni(Cl)(PN^PN^H)] is generated by reaction of 3 with HCl or by direct photolysis of 2 in chlorobenzene. This is the first report of aromatic C? H bond activation by a trapped transient nitrido species of a late transition metal.     

C?H Activation of Benzene by a Photoactivated NiII(azide): Formation of a Transient Nickel Nitrido Complex

Photochemical activation of nickel‐azido complex 2 [Ni(N₃)(PNP)] (PN^HP=2,2′‐di(isopropylphosphino)‐4,4′‐ditolylamine) in neat benzene produces diamagnetic complex 3 [Ni(Ph)(PN^PN^H)], which is crystallographically characterized. DFT calculations support photoinitiated N₂‐loss of the azido complex to generate a rare, transient Ni^IV nitrido species, which bears significant nitridyl radical character. Subsequent trapping of this nitrido through insertion into the Ni P bond generates a coordinatively unsaturated Ni^II imidophosphorane PN donor. This species shows unprecedented reactivity toward 1,2‐addition of a C H bond of benzene to form 3 . The structurally characterized chlorido complex 4 [Ni(Cl)(PN^PN^H)] is generated by reaction of 3 with HCl or by direct photolysis of 2 in chlorobenzene. This is the first report of aromatic C H bond activation by a trapped transient nitrido species of a late transition metal.     

Counterion Dependence of Dinitrogen Activation and Functionalization by a Diniobium Hydride Anion

We report the synthesis of anionic diniobium hydride complexes with a series of alkali metal cations (Li⁺, Na⁺, and K⁺) and the counterion dependence of their reactivity with N₂. Exposure of these complexes to N₂ initially produces the corresponding side‐on end‐on N₂ complexes, the fate of which depends on the nature of countercations. The lithium derivative undergoes stepwise migratory insertion of the hydride ligands onto the aryloxide units, yielding the end‐on bridging N₂ complex. For the potassium derivative, the N?N bond cleavage takes place along with H₂ elimination to form the nitride complex. Treatment of the side‐on end‐on N₂ complex with Me₃SiCl results in silylation of the terminal N atom and subsequent N?N bond cleavage along with H₂ elimination, giving the nitride‐imide‐bridged diniobium complex.     

Conversion of a Fleeting Open‐Shell Iron Nitride into an Iron Nitrosyl

Terminal metal nitrides have been proposed as key intermediates in a series of pivotal chemical transformations. However, exploring the chemical activity of transient tetragonal iron(V) nitrides is largely impeded by their facile dimerization in fluid solutions. Herein, in situ EPR and Mössbauer investigations are presented of unprecedented oxygenation of a paramagnetic iron(V) nitrido intermediate, [Fe^VN(cyclam‐ac)]⁺ ( 2 , cyclam‐ac^?=1,4,8,11‐tetraazacyclotetradecane‐1‐acetate anion), yielding an iron nitrosyl complex, [Fe(NO)(cyclam‐ac)]⁺ ( 3 ). Further theoretical studies suggest that during the reaction a closed‐shell singlet O atom is transferred to 2 . Consequently, the N?O bond formation does not follow a radical coupling mechanism proposed for the N?N bond formation but is accomplished by three mutual electron‐transfer pathways between 2 and the O atom donor, thanks to the ambiphilic nature of 2 .     

Synthesis and molecular structure of Cr(salen)(μ‐N)RhCl(COD): the first example of a heterobimetallic nitride‐bridged complex containing chromium

Five‐coordinate Cr(N)(salen) {salen is 2,2′‐[ethane‐1,2‐diylbis(nitrilomethylidyne)]diphenolate} reacts with [RhCl(COD)]₂ (COD is 1,5‐cyclooctadiene) to yield the heterobimetallic nitride‐bridged title compound, namely chlorido‐2κCl‐[2(η⁴)‐1,5‐cyclooctadiene]{2,2′‐[ethane‐1,2‐diylbis(nitrilomethylidyne)]diphenolato‐1κ⁴O,N,N′,O′}‐μ‐nitrido‐1:2κ²N:N‐chromium(V)rhodium(I), [CrRh(C₁₆H₁₄N₂O₂)ClN(C₈H₁₂)]. The Cr—N bond of 1.5936 (14) Å is elongated by only 0.035 Å compared to the terminal Cr—N bond in the precursor. The nitride bridge is close to being linear [173.03 (9)°] and the Rh—N bond of 1.9594 (14) Å is very short for a monodentate nitrogen‐donor ligand, indicating significant π‐acceptor character of the Cr[triple‐bond]N group.     

Redox‐Active‐Ligand‐Mediated Formation of an Acyclic Trinuclear Ruthenium Complex with Bridging Nitrido Ligands

Coordination of a redox‐active pyridine aminophenol ligand to Ru^II followed by aerobic oxidation generates two diamagnetic Ru^III species [ 1 a (cis) and 1 b (trans)] with ligand‐centered radicals. The reaction of 1 a / 1 b with excess NaN₃ under inert atmosphere resulted in the formation of a rare bis(nitrido)‐bridged trinuclear ruthenium complex with two nonlinear asymmetrical Ru‐N‐Ru fragments. The spontaneous reduction of the ligand centered radical in the parent 1 a / 1 b supports the oxidation of a nitride (N^3?) to half an equivalent of N₂. The trinuclear omplex is reactive toward TEMPO‐H, tin hydrides, thiols, and dihydrogen.     

Two‐Electron Reductive Carbonylation of Terminal Uranium(V) and Uranium(VI) Nitrides to Cyanate by Carbon Monoxide

Two‐electron reductive carbonylation of the uranium(VI) nitride [U(Tren^TIPS)(N)] ( 2 , Tren^TIPS=N(CH₂CH₂NSiiPr₃)₃) with CO gave the uranium(IV) cyanate [U(Tren^TIPS)(NCO)] ( 3 ). KC₈ reduction of 3 resulted in cyanate dissociation to give [U(Tren^TIPS)] ( 4 ) and KNCO, or cyanate retention in [U(Tren^TIPS)(NCO)][K(B15C5)₂] ( 5 , B15C5=benzo‐15‐crown‐5 ether) with B15C5. Complexes 5 and 4 and KNCO were also prepared from CO and the uranium(V) nitride [{U(Tren^TIPS)(N)K}₂] ( 6 ), with or without B15C5, respectively. Complex 5 can be prepared directly from CO and [U(Tren^TIPS)(N)][K(B15C5)₂] ( 7 ). Notably, 7 reacts with CO much faster than 2 . This unprecedented f‐block reactivity was modeled theoretically, revealing nucleophilic attack of the π* orbital of CO by the nitride with activation energy barriers of 24.7 and 11.3 kcal mol^?1 for uranium(VI) and uranium(V), respectively. A remarkably simple two‐step, two‐electron cycle for the conversion of azide to nitride to cyanate using 4 , NaN₃ and CO is presented.     

Terminal Molybdenum Phosphides with d Electrons: Radical Character Promotes Coupling Chemistry

A terminal Mo phosphide was prepared through the group transfer of both P and Cl atoms from chloro‐substituted dibenzo‐7λ³‐phosphanorbornadiene. This compound represents the first structurally characterized terminal transition‐metal phosphide with valence d electrons. In the tetragonal ligand field, these electrons populate an orbital of d_xy parentage, an electronic configuration that accommodates both metal d electrons and a formal M≡P triple bond. Single‐electron oxidation affords a transient open‐shell terminal phosphide cation with significant spin density on P, as corroborated by continuous wave (CW) and pulse electron paramagnetic resonance (EPR) characterization. Facile P−P bond formation occurs from this species through intermolecular phosphide coupling.     

Reactions of Rhenium and Technetium Nitrido Complexes with ER3 Fragments (E = B,Ga, Al,C, P; R = H,Alkyl, Aryl)

Terminal ‘N^3—’ ligands in rhenium and technetium nitrido complexes are sufficiently nucleophilic to react with Lewis acids under formation of nitrido‐bridged compounds. The reactivity of the nucleophilic centre and the nature of the formed compounds are strongly dependent on the Lewis acid and the composition of the metal complex used. Air‐stable compounds with Re≡N‐ER₃ bridges are formed when ER₃ is BR₃ (R = H, Cl, Br, Ethyl, Phenyl, C₆F₅), BCl₂Ph, GaCl₃, CPh₃⁺, or PPh₃. The six‐co‐ordinate rhenium(V) complexes [ReNX₂(PMe₂Ph)₃] (X = Cl, Br), [ReN(X)(Et₂dtc)(PMe₂Ph)₂] (Et₂dtc^— = diethyldithiocarbamate) and [ReN(Et₂dtc)₂(PMe₂Ph)] have been proved to be excellent starting materials for this type of reactions, whereas the five‐co‐ordinate precursors [ReNCl₂(PPh₃)₂], [ReN(Et₂dtc)₂], [ReN{Ph₂P(S)NP(S)Ph₂}₂] or [ReNCl₄]^— only react with the most reactive Lewis bases of the examples mentioned above such as BCl₂Ph or B(C₆F₅)₃. The rhenium‐nitrido bond lengths remain almost unchanged by the adduct formation, whereas a significant decrease of the trans‐influence of the nitrido complexes has been observed as can be seen by a shortening of the corresponding bond lengths or dimerization of five‐co‐ordinate precursors. Electrophilic attack of the Lewis acid to a donor atom of the equatorial co‐ordination sphere of the rhenium complex results in the formation of ‘underco‐ordinate’ metal centres which resemble to di‐, tri or tetrameric units with asymmetric nitrido bridges between each two rhenium atoms. EPR spectroscopy is an excellent tool to reflect the formation of nitrido bridges at the paramagnetic (d¹) [ReNX₄]^— core (X = F, Cl, Br, NCS). The spectral parameters derived for the products of reactions of [ReNCl₄]^— with various boron compounds indicate an increase of the covalency of the equatorial Re‐L bonds as a consequence of the formation of a nitrido bridge. The tendency for the formation of nitrido bridges with Lewis acids is significantly lower for technetium compounds compared to their rhenium analogues. Only a few examples with BH₃ and BPhCl₂ have been established.     

Synthese und Struktur von Mo2NCl8 und Mo3N2Cl11

Synthesis and Crystal Structure of Mo_2<>NCl₈ and Mo₃N₂Cl₁₁ The reaction of MoCl₅ with Cl₃VNCl at 140 °C in a sealed glass ampoule yields air sensitive black crystals of the mixed valent molybdenum(V, VI) nitride chloride, Mo₂NCl₈. It crystallizes in the monoclinic space group P2/c with a = 996.1(1), b = 629.4(1), c = 1780.8(3) pm, β = 101.82(2)°, and Z = 4. The crystal structure consists of dinuclear C₂‐symmetrical units [Cl₂(N≡)Mo(μ₂‐Cl)₃Mo(≡N)Cl₂]^— and [Cl₄Mo(μ₂‐Cl)MoCl₄]⁺, connected in an alternating sequence by asymmetric nitrido bridges Mo≡N‐Mo to form chains. The reaction of Cl₃VNCl with MoCl₃ at 140 °C affords Mo₃N₂Cl₁₁, but for the prolonged reaction period, MoNCl₃ is observed in addition. Mo₃N₂Cl₁₁ can also be obtained from MoNCl₃ and MoCl₅ (2:1) at 140 °C. It forms orthorhombic, black crystals with the space group Pca2₁ and a = 1256.1(1), b = 1001.9(1), c = 1330.10(5) pm, and Z = 4. The structure contains the same dinuclear units [Cl₂(N≡)Mo(μ₂‐Cl)₃Mo(≡N)Cl₂]^— as in Mo₂NCl₈, which in this case are connected with MoCl₄⁺ moieties by asymmetric nitrido bridges Mo≡N‐Mo forming chains. In Mo₂NCl₈ the Mo‐N distances in the nearly linear nitrido bridges are 167.6(2), and 214.8(2) pm, whereas in case of Mo₃N₂Cl₁₁ two sets of Mo‐N distances of 166, 8(4) and 214, 0(4) pm as well as 166, 9(4) and 211, 9(4) pm are observed.     

Dinitrogen‐Molybdenum Complex Induces Dinitrogen Cleavage by One‐Electron Oxidation

Reported here is the N₂ cleavage of a one‐electron oxidation reaction using trans‐[Mo(depe)₂(N₂)₂] ( 1 ) (depe=Et₂PCH₂CH₂PEt₂), which is a classical molybdenum(0)‐dinitrogen complex supported by two bidentate phosphine ligands. The molybdenum(IV) terminal nitride complex [Mo(depe)₂N][BArf₄] ( 2 ) (BArf₄=B(3,5‐(CF₃)₂C₆H₃)₄) is synthesized by the one‐electron oxidation of 1 upon addition of a mild oxidant, [Cp₂Fe][BArf₄] (Cp=C₅H₅), and proceeds by N₂ cleavage from a Mo^II‐N=N‐Mo^II structure. In addition, the electrochemical oxidation reaction for 1 also cleaved the N₂ ligand to give 2 . The dimeric Mo complex with a bridging N₂ is detected by in situ resonance Raman and in situ UV‐vis spectroscopies during the electrochemical oxidation reaction for 1 . Density‐functional theory (DFT) calculations reveal that the unstable monomeric oxidized Mo^I species is converted into 2 via the dimeric structure involving a zigzag transition state.     

A Surface‐Oxide‐Rich Activation Layer (SOAL) on Ni2Mo3N for a Rapid and Durable Oxygen Evolution Reaction

The oxygen evolution reaction (OER) is key to renewable energy technologies such as water electrolysis and metal–air batteries. However, the multiple steps associated with proton‐coupled electron transfer result in sluggish OER kinetics and catalysts are required. Here we demonstrate that a novel nitride, Ni₂Mo₃N, is a highly active OER catalyst that outperforms the benchmark material RuO₂. Ni₂Mo₃N exhibits a current density of 10 mA cm^?2 at a nominal overpotential of 270 mV in 0.1 m KOH with outstanding catalytic cyclability and durability. Structural characterization and computational studies reveal that the excellent activity stems from the formation of a surface‐oxide‐rich activation layer (SOAL). Secondary Mo atoms on the surface act as electron pumps that stabilize oxygen‐containing species and facilitate the continuity of the reactions. This discovery will stimulate the further development of ternary nitrides with oxide surface layers as efficient OER catalysts for electrochemical energy devices.     

Predicting Nitrogen‐Based Families of Compounds: Transition‐Metal Guanidinates TCN3 (T=V,Nb, Ta) and Ortho‐Nitrido Carbonates T′2CN4 (T′=Ti,Zr, Hf)

Due to its unsurpassed capability to engage in various sp hybridizations or orbital mixings, carbon may contribute in expanding solid‐state nitrogen chemistry by allowing for different complex anions, such as the known NCN^2? carbodiimide unit, the so far unknown CN₃^5? guanidinate anion, and the likewise unknown CN₄^8? ortho‐nitrido carbonate (onc) entity. Because the latter two complex anions have never been observed before, we have chemically designed them using first‐principles structural searches, and we here predict the first hydrogen‐free guanidinates TCN₃ (T=V, Nb, Ta) and ortho‐nitrido carbonates T′₂CN₄ (T′=Ti, Zr, Hf) being mechanically stable at normal pressure; the latter should coexist as solid solutions with the stoichiometrically identical nitride carbodiimides and nitride guanidinates. We also suggest favorable exothermic reactions as useful signposts for eventual synthesis, and we trust that the decay of the novel compounds is unlikely due to presumably large kinetic activation barriers (C?N bond breaking) and quite substantial Madelung energies stabilizing the highly charged complex anions. While chemical‐bonding analysis reveals the novel CN₄^8? to be more covalent compared to NCN^2? and CN₃^5? within related compounds, further electronic‐structure data of onc phases hint at their physicochemical potential in terms of photoelectrochemical water splitting and nonlinear optics.     

Synthese und Struktur von Mo2NCl7

Synthesis and Structure of Mo₂NCl₇ The reaction of VN with MoCl₅ at 175 °C in a sealed glass ampoule yields the molybdenum(V) nitride chloride Mo₂NCl₇ in form of air sensitive black crystals with the triclinic space group P1¯ and a = 905.7(8); b = 975.4((6); c = 1283.4(8) pm, α = 103.13(4)°; β = 109.83(5)° und γ = 98.58(5)°. The crystal structure is built up from dinuclear units [Mo₂N₂Cl₇]^3— and [Mo₂Cl₇]³⁺, which are connected by asymmetric nitrido bridges to form endless chains. Within both dinuclear units the Mo atoms are bridged by three Cl atoms resulting in a Mo‐Mo distance of 349.2(3) pm in the unit [Mo₂N₂Cl₇]^3—. In case of [Mo₂Cl₇]³⁺, however, a shorter Mo‐Mo distance of 289.4(3) pm is observed, which can be interpreted by a single bond. Correspondingly a reduced magnetic moment of 0.95 B.M. per Mo atom is observed.     

catena‐Poly[[[2,4‐dichloro‐6‐(pyridin‐2‐ylmethyl­iminomethyl)phenolato]copper(II)]‐μ‐thio­cyanato]

The title complex, [Cu(C₁₃H₉Cl₂N₂O)(NCS)]_n, is a novel thio­cyanate‐bridged polynuclear copper(II) compound. The Cu^II atom is five‐coordinated in a square‐pyramidal configuration, with one O and two N atoms of one Schiff base ligand and one terminal N atom of a bridging thio­cyanate ligand defining the basal plane, and one terminal S atom of another bridging thio­cyanate ligand occupying the axial position. The [2,4‐dichloro‐6‐(pyridin‐2‐ylmethyl­imino­methyl)­phenolato]­copper(II) moieties are linked by the bridging thio­cyanate ligands, forming polymeric chains running along the a axis.     

catena‐Poly[[{4‐bromo‐2‐[2‐(di­methyl­amino)­ethyl­imino­meth­yl]­phenolato}­copper(II)]‐μ‐thio­cyanato]

The title complex, [Cu(C₁₁H₁₄BrN₂O)(NCS)]_n, is an inter­esting thio­cyanate‐bridged polynuclear copper(II) compound, which crystallizes with two independent mol­ecules in the asymmetric unit. Each Cu^II atom is five‐coordinate in a square‐pyramidal configuration, with one O and two N atoms of one Schiff base ligand and one terminal N atom of a bridging thio­cyanate ligand defining the basal plane, and one terminal S atom of another bridging thio­cyanate ligand occupying the apical position. The {4‐bromo‐2‐[2‐(dimethyl­amino)ethyl­imino­meth­yl]phenolato}copper(II) units are linked by the bridging thio­cyanate ligands, forming polymeric chains running along the a axis. There are weak inter­molecular C—H⋯O and C—H⋯S hydrogen bonds between the chains in the crystal structure.