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Molecularly‐modified electrode materials that maintain stability over a broad pH range are rare. Typically, each electrochemical transformation necessitates a specifically tuned system to achieve strong binding and high activity of the catalyst. Here, we report the functionalisation of mesoporous indium tin oxide (mITO) electrodes with the macrocyclic host molecule pillar[6]arene (PA[6]). These electrodes are stable within the pH range of 2.4–10.8 and can be equipped with electrochemically active ruthenium complexes through host–guest interactions to perform various oxidation reactions. Benzyl alcohol oxidation serves as a model reaction in acidic media, while ammonia oxidation is conducted to assess the systems performance under basic conditions. PA[6]‐modified electrodes demonstrate catalytic activity for both reactions when complexed to different guest molecules and can be reused by reabsorption of the catalyst after its degradation. Furthermore, the system can be employed to perform subsequent reactions in electrolyte with varying pH, enabling the same electrode to be utilised in multiple different electrocatalytic reactions. [ABSTRACT FROM AUTHOR]

Abundantly available biomass‐based platform chemicals, including 5‐hydroxymethylfurfural (HMF), are essential stepping stones in steering the chemical industry away from fossil fuels. The efficient catalytic oxidation of HMF to its diacid derivative, 2,5‐furandicarboxylic acid (FDCA), is a promising research area with potential applications in the polymer industry. Currently, the most encouraging approaches are based on solid‐state catalysts and are often conducted in basic aqueous media, conditions where HMF oxidation competes with its decomposition. Efficient molecular catalysts are practically unknown for this reaction. In this study, we report on the synthesis and electrocatalysis of surface‐bound molecular ruthenium complexes for the transformation of HMF to FDCA under acidic conditions. Catalyst immobilisation on mesoporous indium tin oxide electrodes is achieved through the incorporation of phosphonic acid anchoring groups. Screening experiments with HMF and further reaction intermediates revealed the catalytic route and bottlenecks in the catalytic synthesis of FDCA. Utilising these immobilised electrocatalysts, FDCA yields of up to 85 % and faradaic efficiencies of 91 % were achieved, without any indication of substrate decomposition. Surface analysis by X‐ray photoelectron spectroscopy (XPS) post‐electrocatalysis unveiled the desorption of the catalyst from the electrode surface as a limiting factor in terms of catalytic performance. [ABSTRACT FROM AUTHOR]

Artificial photosynthesis with respect to water splitting is usually divided into water oxidation catalysis (WOC) and the hydrogen evolution reaction (HER). Though in the combined redox dissociation of water into oxygen and hydrogen no protons and electrons occur, both half reactions show photoinduced proton coupled electron transfer (PCET). Regarding a classical approach, photosensitizers (PS) deliver electrons and protons that are accepted by water reduction catalysts (WRC) containing suitable basic atoms like nitrogen working as proton relays. However, the mechanisms of PCET reactions differ, where concerted proton electron transfer (CPET) is an elementary step. In CPET simultaneous electron and proton transfer occurs in the femtoseconds range, being rapid when compared to the periods for coupled vibrations and solvent modes. This has to be distinguished from stepwise electron and proton transfer, leading to underlying thermodynamics of the intermediates. DFT calculations based on X‐ray diffraction (XRD) data help to specify the different reaction pathways. A plethora of experimental procedures are used in order to verify the theoretical predictions. Among them femtosecond pump‐probe spectroscopic measurements play an important role. Furthermore, cyclic voltammetry (CV) has proven to be also a powerful tool. In the case of electrochemical PCET rotating‐disk electrode voltammetry, electrochemical impedance spectroscopy and spectroelectrochemistry complete the experimental tools. In this minireview a selection of examples, where PCET occurs is discussed with respect to possible mechanisms and used methods. [ABSTRACT FROM AUTHOR]

Azobenzene macrocycles are widely investigated as potential drug delivery systems and as part of molecular machines due to their photo-responsive properties. Herein, we detect the formation of a series of new azobenzene macrocycles that feature up to eight switchable repeating units. High-resolution mass spectrometry and ion mobility (IM) mass spectrometry experiments and 1H and diffusion-ordered spectroscopy (DOSY) NMR are used to detect the presence of the macrocycles that contain 10 to 40 aromatic rings in the gas phase and solution, respectively. The responsiveness of the Z-to-E photo-switching of the smallest of the macrocycles, exhibiting two azobenzene units and in total 10 aromatic rings, separated with column chromatography, is studied with irradiation experiments, using both UV-Vis light and thermal excitation and relaxation, and monitoring the sample with UV-Vis absorption and 1H NMR spectroscopy. DFT calculations are used to understand the conformation of this isolated species in solution. [ABSTRACT FROM AUTHOR]

Several PNP‐type ligands of the form bis(dianisylphosphanylmethyl)alkylamine, where alkyl is methyl, ethyl, isopropyl, and benzyl (1–4), have been coordinated to Co(II), Ni(II), Pd(II), and Pt(II) (5–26). This series of water reduction catalysts (WRC) has been characterized by single‐crystal X‐ray structure analysis, multinuclear and 2D NMR spectroscopy, mass spectrometry and a computational study. Intramolecular contact approaches show differences depending on hetero‐ or homoleptic complexes. Both solid state and solution structures indicate an enhancement of steric pressure for the latter. As a consequence CH/M as well as CH/π interactions appear in the X‐ray structures and 1H NMR spectra. They can also be clearly identified by quantum mechanical calculations on a B3LYP level. Since these WRC contain proton relays due to the used PNP‐ligands, they are prone to proton coupled electron transfer (PCET) during photocatalysis. The different steric pressure influences their reorganisation energy. Obviously, the observed intramolecular contact approaches should be regarded as a tool for the design of future WRC. [ABSTRACT FROM AUTHOR]

Inspired by natural photosynthesis, features such as proton relays have been integrated into water reduction catalysts (WRC) for effective production of hydrogen. Research by DuBois et al. showed the crucial influence of these relays, largely in the form of pendant amine functions. In this work catalysts are presented containing innovative diphosphinoamine ligands: [M(ii)Cl2(PNP-C1)], [M(ii)(MeCN)2(PNP-C1)]2+, [M(ii)(PNP-C1)2]2+, and [M(ii)Cl(PNP-C2)]+ (M = Pt2+, Pd2+, Ni2+, Co2+; PNP-C1 = N,N-bis{(di(2-methoxyphenyl)phosphino)methyl}-N-alkylamine, PNP-C2 = N,N-bis{(di(2-methoxyphenyl)phosphino)ethyl}-N-alkylamine and alkyl = Me, Et, iso-Pr, Bz). Synthetic strategies and detailed characterisation are covered, including 1H-, 13C-, and 31P-NMR analysis, mass spectroscopy and single crystal X-ray diffractometry (XRD). The catalytic properties have been explored by changing the pendant amines and auxiliary methoxy coordination sites, as well as enlarging the ligand backbone. Moreover, confirmed by density functional theory (DFT) calculations based on XRD data in vacuo and solvent environment, two very different catalytic cycles are proposed. PNP-C1 shows a classical proton relay, whereas PNP-C2 allows an additional coordination of nitrogen, acting optionally like a pincer. Through new insights into efficiency and stability-increasing influences of proton relays in general, their number per metal centre, an enlarged ligand backbone and the use of solvato instead of halogenido complexes, substantial improvements have been made in catalytic performance over the DuBois et al. catalysts and recently self-made WRCs. The turnover number (TON) related to the single site of cost-efficient nickel WRCs is increased from 11.4 to 637, whereas a corresponding palladium catalyst gives TON as high as 2289. [ABSTRACT FROM AUTHOR]

The new bis(bidentate) tetraphosphane cis,trans,cis‐1,2,3,4‐tetrakis(diphenylphosphanyl)buta‐1,3‐diene (dppbd) (7) was obtained by applying a photochemical synthetic protocol. The key step of the photochemical reaction consisted of an intramolecular [2+2] cycloaddition involving a C–C double and triple bond of the Pt‐dimer species of the formula [Pt2Cl4(dppa)(trans‐dppen)] (2) {dppa = 1,2‐bis(diphenylphosphanyl)acetylene and dppen = 1,2‐bis(diphenylphosphanyl)ethene} leading to [Pt2Cl4(dppbd)] (5). The asymmetrically bridged precursor complex 2 was obtained by combinatorial chemistry. Single crystal X‐ray structure analyses of 2 and 5 proved that the intramolecular photochemical reaction occurred. Cyanolysis of 5 gave 7, which was oxidized to dppbdO4 (8). Compounds 7, 8, and the PdII dimer complex [Pd2Cl4(dppbd)] (9) were characterized in the solid state by a single‐crystal X‐ray structure analysis. Interesting photophysial properties emerged from the UV/Vis spectra acquired for 7 and the dimer Os complexes meso‐Δ,Λ/Λ,Δ‐[Os2(bpy)4(dppbd)](PF6)4 (10) and rac‐Δ,Δ/Λ,Λ‐[Os2(bpy)4(dppbd)](PF6)4 (11). An intramolecular photochemical reaction between 1,2‐trans‐bis(diphenylphosphanyl)ethene and 1,2‐bis(diphenylphosphanyl)acetylene within a dimetallic PtII complex gave selectively cis,trans,cis‐1,2,3,4‐tetra‐kis(diphenylphosphanyl)buta‐1,3‐diene. Its bis‐chelating nature makes it suitable to access bimetallic chromophores applicable for photochemical hydrogen production. [ABSTRACT FROM AUTHOR]

The Front Cover shows the important steps of the synthesis of dppbd. After the formation of the initial intermediate, comes the second and key step, which is a light induced pericyclic cycloaddition, immediately followed by a thermally induced ring opening reaction. The third step is the removal of platinum, which was used as a template. The last step shows two examples of the coordination of metal centers. In the background is an excitation/emission spectrum of a compound consisting of osmium and the title compound, demonstrating its application as a photosensitizer. More information can be found in the Full Paper by W. Oberhauser, G. Knör, P. Brüggeller et al. For more on the story behind the cover research, see the Cover Profile. [ABSTRACT FROM AUTHOR]

Molybdenum sulfide serves as an effective nonprecious metal catalyst for hydrogen evolution, primarily active at edge sites with unsaturated molybdenum sites or terminal disulfides. To improve the activity at a low loading density, two molybdenum sulfide clusters, [Mo 3 S 4 ] 4+ and [Mo 3 S 13 ] 2- , were investigated. The Mo 3 S x molecular catalysts were heterogenized on Sb 2 Se 3 with a simple soaking treatment, resulting in a thin catalyst layer of only a few nanometers that gave up to 20 mA cm -2 under one sun illumination. Both [Mo 3 S 4 ] 4+ and [Mo 3 S 13 ] 2- exhibit catalytic activities on Sb 2 Se 3 , with [Mo 3 S 13 ] 2- emerging as the superior catalyst, demonstrating enhanced photovoltage and an average faradaic efficiency of 100% for hydrogen evolution. This superiority is attributed to the effective loading and higher catalytic activity of [Mo 3 S 13 ] 2- on the Sb 2 Se 3 surface, validated by X-ray photoelectron and Raman spectroscopy., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)