Übergangsmetallkomplexe von N-geankerten N-heterozyklischen Carben-Liganden: Synthese, Charakterisierung und Reaktivität

Our laboratory recently developed a nitrogen-anchored ligand series with donor functionalities ranging from tris(carbene) to tris(phenolate), including two new mixed ligands, (BIMPNMes,Ad,Me)– and (MIMPNMes,Ad,Me)2–, combining NHC carbene and phenolate donors. The new bis(carbene) mono(phenolate) ligand (BIMPNMes,Ad,Me)– was coordinated to manganese and the resulting complexes [(BIMPNMes,Ad,Me)MnII(Cl)], [(BIMPNMes,Ad,Me)MnII(N3)], and [(BIMPNMes,Ad,Me)MnII](BPh4), were synthesized and characterized in detail. SQUID magnetization studies confirmed high-spin ground states for all complexes. The molecular structures of the full complex series including the corresponding iron and cobalt complexes verified the desired ease of the steric strain compared to the tris(carbene) ligand TIMENR. Accordingly, the accessibility of the reactive metal center for small molecules is increased as intended; thus. promising a higher reactivity of the corresponding nitrido complexes. By photolysis of the cobalt(II) azido complex [(BIMPNMes,Ad,Me)CoII(N3)] at low temperatures (T = 10 K), the transient low-spin cobalt(IV) nitrido complex [(BIMPNMes,Ad,Me)CoIV(N)] was generated. This is the first example for a cobalt(IV) nitrido complex reported in the literature. At higher temperatures, the complex undergoes N-migratory insertion, yielding the stable cobalt(II) imino species [(NHBIMPNMes, Ad,Me)CoII](BPh4). It is a rare example of a trigonal pyramidal complex with four different donor ligands of a tetradentate chelate – an N-heterocyclic carbene, a phenolate, an imine, and an amine – binding to a high-spin cobalt(II) ion. This renders the complex chiral-at-metal. The reaction mechanism was studied by computational analysis and experimentally supported by CW X-band EPR spectroscopy studies. The N-migratory insertion product was isolated and fully characterized. Inspired by the tetracoordinate ligand, the tridentate analogue was synthesized. The flexible nitrogen-anchored bis(carbene) ligand (HBIMENMes) was coordinated to manganese, iron, and cobalt. The resulting chlorido complexes were characterized in detail as well. SQUID magnetization and zero-field 57Fe Mössbauer spectroscopy, where applicable, confirm high-spin ground states for all complexes in the solid state. The reactivity of cobalt(II) chlorido complex [(HBIMENMes)CoII(Cl)](PF6) towards a variety of reagents, including potassium, carbon monoxide, and sodium triethylborohydride was studied. The results are demonstrating the remarkable flexibility of the ligand to adopt trigonal, tetragonal, as well as square planar coordination geometries, the latter enforced by the deprotonation of the anchoring amine to the amide. Synthesis and photolysis experiments of the cobalt(II) azido complex [(HBIMENMes)CoII(N3)](PF6) at low temperatures (10 K) indicate the formation of a transient cobalt(IV) nitrido complex remarkably stable at liquid nitrogen temperature, but undergoes N-migratory insertion at higher temperatures. The reaction of the cobalt chlorido complex with potassium resulted in the cyclometallation of the metal center, generating [(Cyclo-BIMENMes)CoII]. The addition of one atmosphere of carbon monoxide to a solution of the cobalt chlorido complex led to the initial formation of the carbonyl complex [(HBIMENMes)CoII(Cl)(CO)](PF6). The hydrogen chloride adduct of the precursor complex, [(H2BIMENMes)CoII(Cl)2](PF6), was generated over time in a subsequent reaction. The subjection of the cobalt chlorido complex to two equivalents of sodium triethylborohydride yielded [(BIMENMes)CoII(H)]. To the best of our knowledge, this is the first cobalt(II) hydrido complex reported in the literature.Unser Labor entwickelte kürzlich eine stickstoff-geankerte Ligandenserie mit Donorfunktionalitäten von Tris(carben) bis Tris(phenolat), einschließlich zwei neuer gemischter Liganden, (BIMPNMes,Ad,Me)– und (MIMPNMes,Ad,Me)2–, in welchen NHC Carben und Phenolat-Donoren kombiniert werden. Der neue Bis(carben) Mono(phenolat)-Ligand (BIMPNMes,Ad,Me)– wurde an Mangan koordiniert und die resultierenden Komplexe [(BIMPNMes,Ad,Me)MnII(Cl)], [(BIMPNMes,Ad,Me)MnII(N3)] und [(BIMPNMes,Ad,Me)MnII](BPh4) wurden isoliert und detailliert charakterisiert. SQUID-magnetometrische Studien ergaben high-spin Grundzustände für alle Komplexe. Die molekularen Strukturen der vollständigen Komplexreihe mit den entsprechenden Eisen- und Kobaltkomplexen bestätigten die gewünschte Reduktion des sterischen Drucks gegenüber dem Tris(Carben) Liganden TIMENR. Dementsprechend wird die Zugänglichkeit des reaktiven Metallzentrums wie beabsichtigt erhöht, was eine höhere Reaktivität der korrespondierenden Nitridokomplexe verspricht. Durch die Photolyse des Kobalt(II)-Azidokomplexes [(BIMPNMes,Ad,Me)CoII(N3)] bei niedrigen Temperaturen (T = 10 K) wurde der flüchtige low-spin Kobalt(IV)- Nitridokomplex [(BIMPNMes,Ad,Me)CoIV(N)] erzeugt. Dies ist das erste Beispiel für einen Kobalt(IV)-Nitridokomplex, von dem in der Literatur berichtet wird. Bei höheren Temperaturen findet eine Insertionsreaktion des Nitrido-Stickstoffatoms in eine Metall-Carben-Bindung statt, was die stabile Kobalt(II) Iminospezies [(NH-BIMPNMes,Ad,Me)CoII](BPh4) ergibt. Dieser Komplex stellt ein seltenes Beispiel eines trigonal-pyramidalen Komplexes mit vier verschiedenen Donoren eines tetradentaten Chelatliganden dar (ein N-heterocyclisches Carben, ein Phenolat, ein Imin und ein Amin), wodurch der Komplex an seinem Metallzentrum chiral ist. Der Reaktionsmechanismus wurde durch theoretische computerchemische Analysen und experimentelle CW X-band EPRspektroskopische Studien unterstützt. Das Produkt der Insertionsreaktion wurde isoliert und voll charakterisiert. Angeregt durch den vierzähnigen Liganden wurde der analoge dreizähnige Ligand synthetisiert. Der flexible stickstoff-geankerte Bis(Carben)-Ligand (HBIMENMes) wurde an Mangan, Eisen und Kobalt koordiniert. Die erhaltenen Chloridkomplexe wurden ebenfalls detailreich charakterisiert. SQUIDmagnetochemische Studien und Nullfeld 57Fe Mössbauer-Spektroskopie, wenn anwendbar, bestätigten high-spin Grundzustände für alle Komplexe im Festkörper. Die Reaktivität des Kobalt(II)-Chloridokomplexes [(HBIMENMes)CoII(Cl)](PF6) gegenüber einer Vielzahl von Reagenzien, einschließlich Kalium, Kohlenmonoxid und Natriumtriethylborhydrid, wurde untersucht. Die Ergebnisse zeigen die bemerkenswerte Flexibilität des Liganden, trigonale, tetragonale sowie quadratisch planare Koordinationsgeometrien anzunehmen, wobei letztere durch die Deprotonierung des ankernden Amins zum Amid erzwungen wird. Synthese und Photolyseexperimente des Kobalt(II)-Azidokomplexes [(HBIMENMes)CoII(N3)](PF6) bei niedrigen Temperaturen (10 K) deuten auf die BIldung eines flüchtigen Kobalt(IV)-Nitridokomplexes hin, der bei 77 K bemerkenswert stabil ist und dessen Nitridoligand bei höheren Temperaturen insertiert. Die Reaktion des Kobalt(II)-Chloridokomplexes mit Kalium führte zur Cyclometallierung des Metallzentrum, wodurch [(Cyclo-BIMENMes)CoII] erzeugt wurde. Die Zugabe von Kohlenmonoxid zu einer Lösung des Kobalt(II)- Chloridokomplexes führte zur anfänglichen Bildung des Carbonylkomplexes [(HBIMENMes)CoII(Cl)(CO)](PF6), der im Laufe der Zeit in einer Folgereaktion das Chlorwasserstoff-Addukt des Vorläuferkomplexes, [(H2BIMENMes)CoII(Cl)2](PF6), erzeugt. Bei Zugabe von zwei Äquivalenten Natriumtriethylborhydrid zum Kobalt(II)-Chloridokomplex entsteht [(BIMENMes)CoII(H)], welcher nach unserem besten Wissen der erste in der Literatur beschriebene Kobalt(II)-Hydridokomplex ist

Influence of the nacnac Ligand in Iron(I)-Mediated P4 Transformations

A study of P-4 transformations at low-valent iron is presented using -diketiminato (L) Fe-I complexes [LFe(tol)] (tol=toluene; L=L-1 (1a), L-2 (1b), L-3 (1c)) with different combinations of aromatic and backbone substituents at the ligand. The products [(LFe)(4)((4)-(2):(2):(2):(2)-P-8)] (L=L-1 (2a), L-2 (2b)) containing a P-8 core were obtained by the reaction of 1a,b with P-4 in toluene at room temperature. Using a slightly more sterically encumbered ligand in 1c results in the formation of [((LFe)-Fe-3)(2)(-(4):(4)-P-4)] (2c), possessing a cyclo-P-4 moiety. Compounds 2a-c were comprehensively characterized and their electronic structures investigated by SQUID magnetization and Fe-57 Mossbauer spectroscopy as well as by DFT methods

An Intermediate Cobalt(IV) Nitrido Complex and its N-Migratory Insertion Product

International audienceLow-temperature photolysis experiments (T = 10 K) on the tripodal azido complex [(BIMPNMes,Ad,Me)CoII(N3)] (1) were monitored by EPR spectroscopy and support the formation of an exceedingly reactive, high-valent Co nitrido species [(BIMPNMes,Ad,Me)CoIV(N)] (2). Density functional theory calculations suggest a low-spin d5, S = 1/2, electronic configuration of the central cobalt ion in 2 and, thus, are in line with the formulation of complex 2 as a genuine, low-spin Co(IV) nitride species. Although the reactivity of this species precludes handling above 50 K or isolation in the solid state, the N-migratory insertion product [(NH-BIMPNMes,Ad,Me)CoII](BPh4) (3) is isolable and was reproducibly synthesized as well as fully characterized, including CHN elemental analysis, paramagnetic 1H NMR, IR, UV–vis, and EPR spectroscopy as well as SQUID magnetization and single-crystal X-ray crystallography studies. A computational analysis of the reaction pathway 2 → 3 indicates that the reaction readily occurs via N-migratory insertion into the Co–C bond (activation barrier of 2.2 kcal mol–1). In addition to the unusual reactivity of the nitride 2, the resulting divalent cobalt complex 3 is a rare example of a trigonal pyramidal complex with four different donor ligands of a tetradentate chelate—an N-heterocyclic carbene, a phenolate, an imine, and an amine—binding to a high-spin Co(II) ion. This renders complex 3 chiral-at-metal

An Intermediate Cobalt(IV) Nitrido Complex and its N-Migratory Insertion Product

International audienceLow-temperature photolysis experiments (T = 10 K) on the tripodal azido complex [(BIMPNMes,Ad,Me)CoII(N3)] (1) were monitored by EPR spectroscopy and support the formation of an exceedingly reactive, high-valent Co nitrido species [(BIMPNMes,Ad,Me)CoIV(N)] (2). Density functional theory calculations suggest a low-spin d5, S = 1/2, electronic configuration of the central cobalt ion in 2 and, thus, are in line with the formulation of complex 2 as a genuine, low-spin Co(IV) nitride species. Although the reactivity of this species precludes handling above 50 K or isolation in the solid state, the N-migratory insertion product [(NH-BIMPNMes,Ad,Me)CoII](BPh4) (3) is isolable and was reproducibly synthesized as well as fully characterized, including CHN elemental analysis, paramagnetic 1H NMR, IR, UV–vis, and EPR spectroscopy as well as SQUID magnetization and single-crystal X-ray crystallography studies. A computational analysis of the reaction pathway 2 → 3 indicates that the reaction readily occurs via N-migratory insertion into the Co–C bond (activation barrier of 2.2 kcal mol–1). In addition to the unusual reactivity of the nitride 2, the resulting divalent cobalt complex 3 is a rare example of a trigonal pyramidal complex with four different donor ligands of a tetradentate chelate—an N-heterocyclic carbene, a phenolate, an imine, and an amine—binding to a high-spin Co(II) ion. This renders complex 3 chiral-at-metal

An Intermediate Cobalt(IV) Nitrido Complex and its N‑Migratory Insertion Product

Low-temperature photolysis experiments (<i>T</i> = 10 K) on the tripodal azido complex [(BIMPN^Mes,Ad,Me)­Co^II(N₃)] (<b>1</b>) were monitored by EPR spectroscopy and support the formation of an exceedingly reactive, high-valent Co nitrido species [(BIMPN^Mes,Ad,Me)­Co^IV(N)] (<b>2</b>). Density functional theory calculations suggest a low-spin d⁵, <i>S</i> = 1/2, electronic configuration of the central cobalt ion in <b>2</b> and, thus, are in line with the formulation of complex <b>2</b> as a genuine, low-spin Co­(IV) nitride species. Although the reactivity of this species precludes handling above 50 K or isolation in the solid state, the N-migratory insertion product [(NH-BIMPN^Mes,Ad,Me)­Co^II]­(BPh₄) (<b>3</b>) is isolable and was reproducibly synthesized as well as fully characterized, including CHN elemental analysis, paramagnetic ¹H NMR, IR, UV–vis, and EPR spectroscopy as well as SQUID magnetization and single-crystal X-ray crystallography studies. A computational analysis of the reaction pathway <b>2</b> → <b>3</b> indicates that the reaction readily occurs via N-migratory insertion into the Co–C bond (activation barrier of 2.2 kcal mol^–1). In addition to the unusual reactivity of the nitride <b>2</b>, the resulting divalent cobalt complex <b>3</b> is a rare example of a trigonal pyramidal complex with four different donor ligands of a tetradentate chelatean N-heterocyclic carbene, a phenolate, an imine, and an aminebinding to a high-spin Co­(II) ion. This renders complex <b>3</b> chiral-at-metal

Synthesis and Characterization of Divalent Manganese, Iron, and Cobalt Complexes in Tripodal Phenolate/N-Heterocyclic Carbene Ligand Environments

Two novel tripodal ligands, (BIMPN^Mes,Ad,Me)⁻ and (MIMPN^Mes,Ad,Me)^2–, combining two types of donor atoms, namely, NHC and phenolate donors, were synthesized to complete the series of N-anchored ligands, ranging from chelating species with tris­(carbene) to tris­(phenolate) chelating arms. The complete ligand series offers a convenient way of tuning the electronic and steric environment around the metal center, thus, allowing for control of the complex’s reactivity. This series of divalent complexes of Mn, Fe, and Co was synthesized and characterized by ¹H NMR, IR, and UV/vis spectroscopy as well as by single-crystal X-ray diffraction studies. Variable-temperature SQUID magnetization measurements in the range from 2 to 300 K confirmed <i>high-spin</i> ground states for all divalent complexes and revealed a trend of increasing zero-field splitting |<i>D</i>| from Mn­(II), to Fe­(II), to Co­(II) complexes. Zero-field ⁵⁷Fe Mössbauer spectroscopy of the Fe­(II) complexes <b>3</b>, <b>4</b>, <b>8</b>, and <b>11</b> shows isomer shifts δ that increase gradually as carbenes are substituted for phenolates in the series of ligands. From the single-crystal structure determinations of the complexes, the different steric demand of the ligands is evident. Particularly, the molecular structure of <b>1</b>in which a pyridine molecule is situated next to the Mn–Cl bondand those of azide complexes <b>2</b>, <b>4</b>, and <b>6</b> demonstrate the flexibility of these mixed-ligand derivatives, which, in contrast to the corresponding symmetrical TIMEN^R ligands, allow for side access of, e.g., organic substrates, to the reactive metal center

An Intermediate Cobalt(IV) Nitrido Complex and its N‑Migratory Insertion Product

Low-temperature photolysis experiments (<i>T</i> = 10 K) on the tripodal azido complex [(BIMPN^Mes,Ad,Me)­Co^II(N₃)] (<b>1</b>) were monitored by EPR spectroscopy and support the formation of an exceedingly reactive, high-valent Co nitrido species [(BIMPN^Mes,Ad,Me)­Co^IV(N)] (<b>2</b>). Density functional theory calculations suggest a low-spin d⁵, <i>S</i> = 1/2, electronic configuration of the central cobalt ion in <b>2</b> and, thus, are in line with the formulation of complex <b>2</b> as a genuine, low-spin Co­(IV) nitride species. Although the reactivity of this species precludes handling above 50 K or isolation in the solid state, the N-migratory insertion product [(NH-BIMPN^Mes,Ad,Me)­Co^II]­(BPh₄) (<b>3</b>) is isolable and was reproducibly synthesized as well as fully characterized, including CHN elemental analysis, paramagnetic ¹H NMR, IR, UV–vis, and EPR spectroscopy as well as SQUID magnetization and single-crystal X-ray crystallography studies. A computational analysis of the reaction pathway <b>2</b> → <b>3</b> indicates that the reaction readily occurs via N-migratory insertion into the Co–C bond (activation barrier of 2.2 kcal mol^–1). In addition to the unusual reactivity of the nitride <b>2</b>, the resulting divalent cobalt complex <b>3</b> is a rare example of a trigonal pyramidal complex with four different donor ligands of a tetradentate chelatean N-heterocyclic carbene, a phenolate, an imine, and an aminebinding to a high-spin Co­(II) ion. This renders complex <b>3</b> chiral-at-metal

From an Fe2P3 complex to FeP nanoparticles as efficient electrocatalysts for water-splitting

In large-scale, hydrogen production from water-splitting represents the most promising solution for a clean, recyclable, and low-cost energy source. The realization of viable technological solutions requires suitable efficient electrochemical catalysts with low overpotentials and long-term stability for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) based on cheap and nontoxic materials. Herein, we present a unique molecular approach to monodispersed, ultra-small, and superiorly active iron phosphide (FeP) electrocatalysts for bifunctional OER, HER, and overall water-splitting. They result from transformation of a molecular iron phosphide precursor, containing a [Fe2P3] core with mixed-valence FeIIFeIII sites bridged by an asymmetric cyclo-P(2+1)3− ligand. The as-synthesized FeP nanoparticles act as long-lasting electrocatalysts for OER and HER with low overpotential and high current densities that render them one of the best-performing electrocatalysts hitherto known. The fabricated alkaline electrolyzer delivered low cell voltage with durability over weeks, representing an attractive catalyst for large-scale water-splitting technologies

Transfer Reagent for Bonding Isomers of Iron Complexes

The cothermolysis of As₄ and [Cp″₂Zr­(CO)₂] (Cp″ = η⁵-C₅H₃tBu₂) results in the formation of [Cp″₂Zr­(η^1:1-As₄)] (<b>1</b>) in high yields and the arsenic-rich complex [(Cp″₂Zr)­(Cp″Zr)­(μ,η^2:2:1-As₅)] (<b>2</b>) as a minor product. In contrast to yellow arsenic, <b>1</b> is a light-stable, weighable and storable arsenic source for subsequent reactions. The transfer reaction of <b>1</b> with [Cp‴Fe­(μ-Br)]₂ (Cp‴ = η⁵-C₅H₂tBu₃) yields the unprecedented bond isomeric complexes [(Cp‴Fe)₂(μ,η^4:4-As₄)] (<b>3a</b>) and [(Cp‴Fe)₂(μ,η^4:4-<i>cyclo</i>-As₄)] (<b>3b</b>). In contrast, the analogous reaction with the Cp^Bn derivative [Cp^BnFe­(μ-Br)]₂ (Cp^Bn = η⁵-C₅(CH₂(C₆H₅)₅) leads exclusively to the triple decker complex [(Cp^BnFe)₂(μ,η^4:4-As₄)] (<b>4</b>) possessing the tetraarsabutadiene-type ligand analogous to <b>3a</b>. To elucidate the stability of the bonding isomers <b>3a</b> and <b>3b</b>, DFT calculations were performed. The oxidation of <b>4</b> with AgBF₄ affords [(Cp^BnFe)₂(μ,η^5:5-As₅)]­[BF₄] (<b>5</b>), which is a product expanded by one arsenic atom, instead of the expected complex [(Cp^BnFe)₂(μ,η^4:4-<i>cyclo</i>-As₄)]⁺