Selective functionalization of unactivated C-H bonds and ammonia production are extremely important industrial processes. A range of metalloenyzmes achieve these challenging tasks in biology by ...activating dioxygen and dinitrogen using cheap and abundant transition metals, such as iron, copper and manganese. High-valent iron-oxo and -nitrido complexes act as active intermediates in many of these processes. The generation of well-described model compounds can provide vital insights into the mechanism of such enzymatic reactions. Advances in the chemistry of model high-valent iron-oxo and -nitrido systems can be related to our understanding of the biological systems.
Catalysis remains
one of the final frontiers in molecular uranium
chemistry. Depleted uranium is mildly radioactive, continuously generated
in large quantities from the production and consumption of ...nuclear
fuels and accessible through the regeneration of “uranium waste”.
Organometallic complexes of uranium possess a number of properties
that are appealing for applications in homogeneous catalysis. Uranium
exists in a wide range of oxidation states, and its large ionic radii
support chelating ligands with high coordination numbers resulting
in increased complex stability. Its position within the actinide series
allows it to involve its
f
-orbitals in partial covalent
bonding; yet, the U–L bonds remain highly polarized. This causes
these bonds to be reactive and, with few exceptions, relatively weak,
allowing for high substrate on/off rates. Thus, it is reasonable that
uranium could be considered as a source of metal catalysts. Accordingly,
uranium complexes in oxidation states +4, +5, and +6 have been studied
extensively as catalysts in sigma-bond metathesis reactions, with
a body of literature spanning the past 40 years. High-valent species
have been documented to perform a wide variety of reactions, including
oligomerization, hydrogenation, and hydrosilylation. Concurrently,
electron-rich uranium complexes in oxidation states +2 and +3 have
been proven capable of performing reductive small molecule activation
of N
2
, CO
2
, CO, and H
2
O. Hence, uranium’s
ability to activate small molecules of biological and industrial relevance
is particularly pertinent when looking toward a sustainable future,
especially due to its promising ability to generate ammonia, molecular
hydrogen, and liquid hydrocarbons, though the advance of catalysis
in these areas is in the early stages of development. In this Perspective,
we will look at the challenges associated with the advance of new
uranium catalysts, the tools produced to combat these challenges,
the triumphs in achieving uranium catalysis, and our future outlook
on the topic.
A facile method for the electrodeposition of amorphous nickel oxyhydroxide is described and discussed in which well‐defined nickel complexes with pyridinedimethanol ligands are employed as ...single‐source molecular precursors. No buffering agent is required to assist the anodic deposition process. The deposited nickel oxyhydroxide shows high robustness and efficiency for electrocatalytic water oxidation.
NiOx for ox: Upon the application of an anodic potential, molecular nickel cubane 1 with 2,6‐pyridinedimethanol ligands is converted into amorphous nickel oxyhydroxide, which catalyzes water oxidation efficiently.
Electron-rich uranium coordination complexes display a pronounced reactivity toward small molecules. In this Feature article, the exciting chemistry of trivalent uranium ions coordinated to classic ...Werner-type ligand environments is reviewed. Three fundamentally important reactions of the (((R)ArO)3tacn)U-system are presented that result in alkane coordination, CO/CO2 activation, and nitrogen atom-transfer chemistry.
We investigated the surface tension and surface composition of various mixtures of the two ionic liquids (ILs) 1-methyl-3-octyl-imidazolium hexafluorophosphate C
C
ImPF
and 1,3-
(polyethylene ...glycol)imidazolium iodide (mPEG
)
ImI in the temperature range from 230 to 370 K under ultraclean vacuum conditions. The surface tension was measured using a newly developed apparatus, and the surface composition was determined by angle-resolved X-ray photoelectron spectroscopy (ARXPS). In the pure ILs, the alkyl chains of C
C
ImPF
and the PEG chains of (mPEG
)
ImI are enriched at the IL/vacuum interface. In the mixtures, a strong selective surface enrichment of the alkyl chains occurs, which is most pronounced at low C
C
ImPF
contents. For the surface tension, strong deviations from an ideal mixing behaviour take place. By applying a simple approach based on the surface composition of the mixtures as deduced from ARXPS, we are able to predict and reproduce the experimentally measured temperature-dependent surface tension values with astonishingly high accuracy.
A Pair of Cobalt(III/IV) Terminal Imido Complexes Mao, Weiqing; Fehn, Dominik; Heinemann, Frank W. ...
Angewandte Chemie (International ed.),
July 19, 2021, Letnik:
60, Številka:
30
Journal Article
Recenzirano
Odprti dostop
The reaction of the cobalt(I) complex (TIMMNmes)CoI(BPh4) (2) (TIMMNmes=tris‐2‐(3‐mesitylimidazolin‐2‐ylidene)methylamine) with 1‐adamantylazide yields the cobalt(III) imido complex ...(TIMMNmes)CoIII(NAd)(BPh4) (3) with concomitant release of dinitrogen. The N‐anchor in diamagnetic 3 features an unusual, planar tertiary amine, which results from repulsive electrostatic interaction with the filled d(z2)‐orbital of the cobalt ion and negative hyperconjugation with the neighboring methylene groups. One‐electron oxidation of 3 with FeCp2(OTf) provides access to the rare, high‐valent cobalt(IV) imido complex (TIMMNmes)CoIV(NAd)(OTf)2 (4). Despite a half‐life of less than 1 h at room temperature, 4 could be isolated at low temperatures in analytically pure form. Single‐crystal X‐ray diffractometry and EPR spectroscopy corroborate the molecular structure and the d5 low‐spin, S=1/2
, electron configuration. A computational analysis of 4 suggests high covalency within the CoIV=NAd bond with non‐negligible spin density located at the imido moiety, which translates into substantial triplet nitrene character.
Straightforward access to a cobalt(IV) terminal imido complex was provided by one‐electron oxidation of a cobalt(III) terminal imido precursor. The cobalt(IV) monoimido complex could be isolated at low temperatures in analytically pure form. Single‐crystal X‐ray diffractometry and EPR spectroscopy corroborate the molecular structure and the d5 low‐spin, S=1/2
, electron configuration.
This work reports the design and synthesis of a sterically protected triphenylamine scaffold which undergoes one‐electron oxidation to form an amine‐centered radical cation of remarkable stability. ...Several structural adjustments were made to tame the inherent reactivity of the radical cation. First, the parent propeller‐shaped triphenylamine was planarized with sterically demanding bridging units and, second, protecting groups were deployed to block the reactive positions. The efficiently shielded triphenylamine core can be reversibly oxidized at moderate potentials (+0.38 V, vs. Fc/Fc+ in CH2Cl2). Spectroelectrochemistry and chemical oxidation studies were employed to monitor the evolution of characteristic photophysical features. To obtain a better understanding of the impact of one‐electron oxidation on structural and electronic properties, joint experimental and computational studies were conducted, including X‐ray structural analysis, electron paramagnetic resonance (EPR), and density functional theory (DFT) calculations. The sterically shielded radical cation combines various desirable attributes: A characteristic and unobstructed absorption in the visible region, high stability which enables storage for weeks without spectroscopically traceable degradation, and a reliable oxidation/re‐reduction process due to effective screening of the planarized triphenylamine core from its environment.
Single and happy: Extensive steric shielding of a bridged triphenylamine enabled the generation of a persistent N‐centered radical cation with an intense absorption band in the visible region and a reliable oxidation/re‐reduction process. X‐ray structural analysis, electron paramagnetic resonance (EPR), spectroelectrochemistry, and density functional theory (DFT) calculations were used to disclose the impact of one electron oxidation on the structural and electronic attributes.
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.
Synthesis, Structure, and Reactivity of an Iron(V) Nitride Scepaniak, Jeremiah J; Vogel, Carola S; Khusniyarov, Marat M ...
Science (American Association for the Advancement of Science),
02/2011, Letnik:
331, Številka:
6020
Journal Article
Recenzirano
Despite being implicated as important intermediates, iron(V) compounds have proven very challenging to isolate and characterize. Here, we report the preparation of the iron(V) nitrido complex, ...PhB(tBuIm)₃FeVidentical withNBArF₂₄ (PhB(tBuIm)₃⁻ = phenyltris(3-tert-butylimidazol-2-ylidene)borato, BArF₂₄ = B(3,5-(CF₃)₂C₆H₃)₄⁻), by one electron oxidation of the iron(IV) nitrido precursor. Single-crystal x-ray diffraction of the iron(V) complex reveals a four-coordinate metal ion with a terminal nitrido ligand. Mössbauer and electron paramagnetic resonance spectroscopic characterization, supported by electronic structure calculations, provide evidence for a d³ iron(V) metal center in a low spin (S = 1/2) electron configuration. Low-temperature reaction of the iron(V) nitrido complex with water under reducing conditions leads to high yields of ammonia with concomitant formation of an iron(II) species.
An unprecedented, super oxidized all‐ferric iron–sulfur cubanoid cluster with all terminal thiolates, Fe4S4(STbt)4 (3) Tbt=2,4,6‐tris{bis(trimethylsilyl)methyl}phenyl, has been isolated from the ...reaction of the bis‐thiolate complex Fe(STbt)2 (2) with elemental sulfur. This cluster 3 has been characterized by X‐ray crystallography, zero‐field 57Fe Mössbauer spectroscopy, cyclic voltammetry, and other relevant physico‐chemical methods. Based on all the data, the electronic ground state of the cluster has been assigned to be Stot=0.
Four of a kind: An unprecedented all‐iron(III) thiolate iron–sulfur cubane cluster Fe4S4(STbt)4 with bulky terminal thiolates has been isolated from the reaction of Fe(STbt)2 with S8 Tbt=2,4,6‐tris{bis(trimethylsilyl)methyl}phenyl. Isolation of the cluster raises an interesting possibility that the cuboidal Fe4S4 cluster may exist in nature with the unusual all‐ferric state.
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