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While N2O2 tetraanionic ligands containing a strong N-amidate σ-donor are generally assumed to stabilise metal high valence states, we herein have shown that, in dianionic ...Cu(II)-diamido-diphenoxo complexes, H-bonding and electronic effects on the phenolate groups may modulate the electronic structure of their oxidised species from Cu(III) to Cu(II)-phenoxyl radical complexes; and so in the negative potential range. We observe that electron-poor phenolate complexes 22− and 32− oxidise to Cu(III) species, whereas electron rich phenolate complex 12− oxidises to a Cu(II)-phenoxyl radical. Our DFT results suggest that π-electron-rich phenolate rings in 12− are responsible for an increase of the HOMO orbital energy, bringing the HOMO-SOMO gap small enough to favour a ligand-based oxidation process. Further DFT-calculations have also shown that upon changing the o,p-phenol substituent from electron-widthdrawing groups (NO2) to electron-donating ones (OMe), the favoured oxidised state switches from Cu(III) to Cu(II)-radical. These results emphasize the use of the versatile diamido-diphenoxo backbone asa promising way to novel GO-chemical models, as well as molecular switches.
Small‐molecule catalysts as mimics of biological systems illustrate the chemists’ attempts at emulating the tantalizing abilities displayed by nature's metalloenzymes. Among these innate behaviors, ...spin multistate reactivity is used by biological systems as it offers thermodynamic leverage towards challenging chemical reactivity but this concept is difficult to translate into the realm of synthetic organometallic catalysis. Here, we report a rare example of molecular spin catalysis involving multistate reactivity in a small‐molecule biomimetic copper catalyst applied to aziridination. This behavior is supported by spin state flexibility enabled by the redox‐active ligand.
Putting a (molecular) spin on copper catalysis: Metalloenzymes routinely perform multielectronic transformations using multistate reactivity and redox cofactors but this behavior is difficult to emulate in synthetic systems. We report a rare example of molecular spin catalysis in the context of copper‐catalyzed aziridination. The molecular spin fluxionality enabled by the redox‐active ligands is central to this behavior.
In their Full Paper on page 8779 ff., V. Artero, M. Orio et al. report the experimental and theoretical study of an original dinuclear cobalt complex exhibiting a significant catalytic activity for ...hydrogen production in organic solvents. A detailed analysis of its electrocatalytical behavior allowed the quantification of the rates of both protonation steps in the proposed ECEC catalytic pathway and to show that our complex compares pretty‐well with other benchmark molecular catalysts. This system also displays a peculiar type of hydrogen evolution reaction (HER) reactivity that can be defined as ligand‐assisted metal‐centered in which, with the help of DFT calculations, the authors are able to propose a catalytic mechanism involving first ligand‐based reduction and protonation steps followed by metal‐centered processes for subsequent hydrogen evolution.
Ultrafast photoisomerization reactions generally start at a higher excited state with excess of internal vibrational energy and occur via conical intersections. This leads to ultrafast dynamics which ...are difficult to investigate with a single transient absorption spectroscopy technique, be it in the ultraviolet–visible (UV–vis) or infrared (IR) domain. On one hand, the information available in the UV–vis domain is limited as only slight spectral changes are observed for different isomers. On the other hand, the interpretation of vibrational spectra is strongly hindered by intramolecular relaxation and vibrational cooling. These limitations can be circumvented by fusing UV–vis and IR transient absorption spectroscopy data in a multiset multivariate curve resolution analysis. We apply this approach to describe the spectrodynamics of the ultrafast cis–trans photoisomerization around the C–N double bond observed for aromatic Schiff bases. Twisted intermediate states could be elucidated, and isomerization was shown to occur through a continuous complete rotation. More broadly, data fusion can be used to rationalize a vast range of ultrafast photoisomerization processes of interest in photochemistry.
The reaction between p-nitrosonitrobenzene and the tetramethylpropylenediamine-copper(i) complex yields a dinuclear complex that is structurally and electronically similar to side-on peroxo species ...known in Cu/O2 chemistry. The complex reacts with di-tert-butylphenolate via nitrene transfer, as observed through an intermediate and the aminophenol product obtained upon reductive work-up.
This work reports on the synthesis and characterization of a dinuclear bis-(thiosemicarbazone) cobalt complex Co2L2(NCS)2 that exhibits a significant catalytic activity for hydrogen production in DMF ...using triethylammonium (Et3NHBF4) as the proton source. Cyclic voltammetry data allowed a maximum turnover frequency of 130 s-1 for 1 M proton concentration to be determined. The catalytic nature of the process and the production of dihydrogen were confirmed by gas analysis during controlled potential electrolysis experiments. Quantum chemical calculations show that the complex displays a ligand-assisted metal-centered reactivity and support a catalytic mechanism involving ligand-based reduction and protonation steps followed by metal-centered processes.
We report on the electrochemical alteration of a nickel( ii ) bis-glyoximato complex into nickel-based nanoparticles at a glassy carbon electrode under acid reducing conditions. These particles show ...electrocatalytic activity towards hydrogen production at +410 mV compared to the bare glassy carbon electrode. Mechanistic insights are discussed based on DFT calculations.
We have investigated the charge ordering phase of the quasi-one-dimensional quantum antiferromagnet (TMTTF)
X (X = SbF
, AsF
, and PF
) using high-fields/frequency electron paramagnetic resonance. In ...addition to the uniform displacement of the counteranions involved in the charge-order phase, we report the existence of a superlattice between the spin chains in the direction c, caused by the space modulation of the charge order. When the field is high enough, the magnetic decoupling of the spin chains allows us to estimate the interaction between the chains, J
< 1 mK, three orders of magnitude lower than expected from the mean field theory.
A series of polypyridyl ruthenium(II) complexes has been synthesized and characterized by 1H‐NMR, electronic absorption and voltammetric techniques. Among this series, hexafluorophosphate salts of ...eight ruthenium(II) complexes were newly prepared. Due to the well‐known ability of this class of compounds to assist electro‐ and photocatalytic reductive processes (such as the reduction of CO2, H+ and NAD(P)+ models), particular attention has been paid to investigate the nature of their one‐ and two‐electron reduced species through computational and spectroscopic techniques.
Identifying key intermediates in catalytic processes involving Ru(tpy)(bpy)X‐type complexes is of great importance to understand mechanisms better. We provide a full set of spectroscopic and computational characterizations of the first two reduced states of a series of these complexes.
We report here two copper complexes as first functional models for lytic polysaccharide monooxygenases, mononuclear copper-containing enzymes involved in recalcitrant polysaccharide breakdown. These ...complexes feature structural and spectroscopic properties similar to those of the enzyme. In addition, they catalyze oxidative cleavage of the model substrate p-nitrophenyl-β-d-glucopyranoside. More importantly, a particularly stable copper(II) hydroperoxide intermediate is detected in the reaction conditions.
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