Reversible Single Electron Redox Steps Convert Polycycles with a C3P3 Core to a Planar Triphosphinine

Reaction of the imidazolium-stabilized diphosphete-diide IDP with trityl phosphaalkyne affords a mixture which contains the molecules 1 a and 1 b with a central C₃P₃ core, which formally carries a two-fold negative charge. In order to avoid the formation of an antiaromatic 8π electron system within a conjugated dianionic six-membered [C₃P₃]²⁻ ring, 1 a adopts a bicyclic [3.1.0] and 1 b a tricyclic [2.2.0.0] structure which are in a dynamic equilibrium. 1 a , b can be reversibly oxidized to a triphosphinine dication [ 5 ]²⁺ with a central flat aromatic six-membered C₃P₃ ring. This two-electron redox reaction occurs in two single-electron transfer steps via the 7π-radical cation [ 4 ]⋅⁺, which could also be isolated and fully characterized. The profound reversible structural change observed for the two-electron redox couple [ 5 ]²⁺/ 1 a , b is in sharp contrast to the C₆H₆/[C₆H₆]²⁻ couple, which undergoes only a modest structural deformation.     

Reduction of Na+ within a {Mg2Na2} Assembly

Ionic compounds containing sodium cations are notable for their stability and resistance to redox reactivity unless highly reducing electrical potentials are applied. Here we report that treatment of a low oxidation state {Mg₂Na₂} species with non-reducible organic bases induces the spontaneous and completely selective extrusion of sodium metal and oxidation of the Mg^I centers to the more conventional Mg^II state. Although these processes are also characterized by a structural reorganisation of the initially chelated diamide spectator ligand, computational quantum chemical studies indicate that intramolecular electron transfer is abetted by the frontier molecular orbitals (HOMO/LUMO) of the {Mg₂Na₂} ensemble, which arise exclusively from the 3s valence atomic orbitals of the constituent sodium and magnesium atoms.     

DOPA Residues Endow Collagen with Radical Scavenging Capacity**

Here we uncover collagen, the main structural protein of all connective tissues, as a redox-active material. We identify dihydroxyphenylalanine (DOPA) residues, post-translational oxidation products of tyrosine residues, to be common in collagen derived from different connective tissues. We observe that these DOPA residues endow collagen with substantial radical scavenging capacity. When reducing radicals, DOPA residues work as redox relay: they convert to the quinone and generate hydrogen peroxide. In this dual function, DOPA outcompetes its amino acid precursors and ascorbic acid. Our results establish DOPA residues as redox-active side chains of collagens, probably protecting connective tissues against radicals formed under mechanical stress and/or inflammation.     

Substrate-Mediator Duality of 1,4-Dicyanobenzene in Electrochemical C(sp2)−C(sp3) Bond Formation with Alkyl Bromides

Electrochemical approaches to form C(sp²)−C(sp³) bonds have focused on coupling C(sp³) electrophiles that form stabilized carbon-centered radicals upon reduction or oxidation. Whereas alkyl bromides are desirable C(sp³) coupling partners owing to their availability and cost-effectiveness, their tendency to undergo radical-radical homocoupling makes them challenging substrates for electroreductive cross-coupling. Herein, we disclose a metal-free regioselective cross-coupling of 1,4-dicyanobenzene, a useful precursor to aromatic nitriles, and alkyl bromides. Alkyl bromide reduction is mediated directly by 1,4-dicyanobenzene radical anions, leading to negligible homocoupling and high cross-selectivity to form 1,4-alkyl cyanobenzenes. The cross-coupling scheme is compatible with oxidatively sensitive and acidic functional groups such as amines and alcohols, which have proven difficult to incorporate in alternative electrochemical approaches using carboxylic acids as C(sp³) precursors.     

氧化还原活性碳纤维的研究进展

就氧化还原碳纤维的制备及其结构、影响氧化还原容量的因素、氧化还原机理等方面进行了综述，并做了研究前景展望。     

Electroreductive Radical Borylation of Unactivated (Hetero)Aryl Chlorides Without Light by Using Cumulene-Based Redox Mediators**

Single-electron transfer (SET) plays a critical role in many chemical processes, from organic synthesis to environmental remediation. However, the selective reduction of inert substrates (E_p/2<−2 V vs Fc/Fc⁺), such as ubiquitous electron-neutral and electron-rich (hetero)aryl chlorides, remains a major challenge. Current approaches largely rely on catalyst photoexcitation to reach the necessary deeply reducing potentials or suffer from limited substrate scopes. Herein, we demonstrate that cumulenes–organic molecules with multiple consecutive double bonds–can function as catalytic redox mediators for the electroreductive radical borylation of (hetero)aryl chlorides at relatively mild cathodic potentials (approximately −1.9 V vs. Ag/AgCl) without the need for photoirradiation. Electrochemical, spectroscopic, and computational studies support that step-wise electron transfer from reduced cumulenes to electron-neutral chloroarenes is followed by thermodynamically favorable mesolytic cleavage of the aryl radical anion to generate the desired aryl radical intermediate. Our findings will guide the development of other sustainable, purely electroreductive radical transformations of inert molecules using organic redox mediators.     

Os(Ⅱ)配合物的电化学性质及其电子能级结构

采用电化学循环伏安法和荧光光谱研究了系列Ｏｓ配合物的电化学性质及分子结构对其电子能级结构的影响。     

Fine-Tuning Redox Properties of Heteroleptic Molybdenum Complexes through Ligand-Ligand-Cooperativity

Heteroleptic molybdenum complexes bearing 1,5-diaza-3,7-diphosphacyclooctane (P₂N₂) and non-innocent dithiolene ligands were synthesized and electrochemically characterized. The reduction potentials of the complexes were found to be fine-tuned by a synergistic effect identified by DFT calculations as ligand-ligand cooperativity via non-covalent interactions. This finding is supported by electrochemical studies combined with UV/Vis spectroscopy and temperature-dependent NMR spectroscopy. The observed behavior is reminiscent of enzymatic redox modulation using second ligand sphere effects.     

Conjugated and Non-conjugated Polymers Containing Two-Electron Redox Dihydrophenazines for Lithium-Organic Batteries

Organic p-type cathode materials have recently attracted increasing attention due to their higher redox potentials and rate capabilities in comparison to n-type cathodes. However, most of the p-type cathodes based on one-electron redox still suffer from limited stability and low specific capacity (<150 mAh g⁻¹). Herein, two polymers, conjugated poly(diethyldihydrophenazine vinylene) ( CPP ) and non-conjugated poly(diethyldihydrophenazine ethylidene) ( NCPP ) containing two-electron redox dihydrophenazine, have been developed as p-type cathode materials. It is experimentally and theoretically found that the conjugated linkage among the redox centers in polymer CPP is more favorable for the effective charge delocalization on the conjugated polymer backbone and the sufficient oxidation in the higher potential region (3.3–4.2 V vs. Li/Li⁺). Consequently, the CPP cathode displays a higher reversible specific capacity of 184 mAh g⁻¹ with excellent cycling stability.     

Electrochemistry of redox-active Group 15/16 heterocyles

This review is a critical overview of the literature on electrochemistry of unsaturated ring-compounds containing bonds between Group 15 and Group 16 elements (principally S and N), including metallacycles. It contains a detailed compilation of measured redox potentials and the conditions under which these were obtained for over 200 compounds. An introduction to the application of solution electrochemistry to this class of compounds is provided, and the relevance of such measurements to materials design is discussed.     

基于氧化还原循环信号放大技术的单分子电化学研究进展

现代分析科学的整体发展对分析方法的灵敏度、选择性以及快速响应等有了更高的要求。在单分子水平上实现对目标分子的检测及控制是化学家们长期以来梦寐以求的一项富有挑战性的前沿领域,也是近年来分析科学很重要的前沿发展方向。用电化学方法直接检测单分子面临的一项挑战是单个分子在氧化还原过程中得失电子产生的电流变化太小,现代仪器无法对如此小的电流进行识别。使电极表面氧化还原过程中的电子交换实现多次循环可以放大产生的电流,从而实现单分子水平的直接电化学分析。本文对近期通过循环电子交换过程放大电流信号的技术和装置进行了综述,将各类方法进行对比,并对单分子电化学未来的发展方向进行了展望。     

Linear and Bent Cp*2Si: Reversible Phase Transition of a Key Molecule

The solid-state structure of decamethylsilicocene Cp*₂Si with a bent and a linear molecule in the same unit cell was so far considered an exception in relation to the structures of its all-bent heavier analogues Cp*₂E with E=Ge, Sn, Pb. Here, we present the solution to this conundrum by reporting a low-temperature phase, where all three symmetrically independent molecules are present in a bent formation. This reversible enantiotropic phase transition occurs in the temperature range between 80 K and 130 K and provides a rationale for the unexpected linear molecule based in entropy beyond hand-waving explanations such as electronic reasons or packing effects.     

Nano-Impact Electrochemistry Reveals Kinetics Information of Metal-Ion Battery Materials with Multiple Redox Centers

Prussian blue (PB) has emerged as a promising cathode material in aqueous batteries. It possesses two distinct redox centers, and the potassium ions (K⁺) are unevenly distributed throughout the compound, adding complexity to the interpretation of the K⁺ insertion/de-insertion kinetic mechanism. Traditional ensemble-averaged measurements are limited in uncovering the precise kinetic information of the PB particles, as the results are influenced by the construction of the porous composite electrode and the redox behavior from different particles. In this study, the electrochemical processes of individual PB particles were investigated using nano-impact electrochemistry. By varying the potentials, different types of transient current signals were obtained that revealed the kinetic mechanism of each oxidation/reduction reaction in combination with theoretical simulation. Additionally, a partially contradictory conclusion between single-particle analysis and the ensemble-averaged measurement was discussed. These findings contribute to a better understanding of the electrochemical processes of cathode materials with multiple redox centers, which facilitates the development of effective strategies to optimize these materials.     

Aggregation of Electrochemically Active Conjugated Organic Molecules and Its Impact on Aqueous Organic Redox Flow Batteries

Molecule aggregation in solution is acknowledged to be universal and can regulate the molecule's physiochemical properties, which however has been rarely investigated in electrochemistry. Herein, an electrochemical method is developed to quantitatively study the aggregation behavior of the target molecule methyl viologen dichloride. It is found that the oxidation state dicationic ions stay discrete, while the singly-reduced state monoradicals yield a concentration-dependent aggregation behavior. As a result, the molecule's energy level and its redox potential can be effectively regulated. This work does not only provide a method to investigate the molecular aggregation, but also demonstrates the feasibility to tune redox flow battery's performance by regulating the aggregation behavior.     

Electrochemistry of Supramolecular Systems

What is the role of electrochemistry in supramolecular chemistry? On one hand, it provides information on energy and kinetics that is not available with spectroscopic and mass spectrometric techniques; on the other, it can be used to alter the electronic states and thus the interactions between molecules, resulting in new compounds and materials. A typical cyclic voltammogram of the complex shown is depicted on the right; only the first three reductions are presented, although a total of six electrons can be transferred to the bipyridine units sequentially (E in V vs. ferrocene/ferrocenium).     

Antimony(III) Halide-Assisted Stereospecific Coordination of Thione

The antimony halide-aided stereospecific coordination of a cyclic thiourea-type of ligand is observed for the first time. The antimony(III) imidazole thione complexes syn-[( L¹ )SbCl₃] ( syn- 1 ) and anti-[( L¹ )SbBr₃] ( anti- 2 ) have been synthesized in very good yield by the reaction between the spatially defined steric impact ligand [(IPaul)S] ( L¹ ) ([(IPaul)S]=1,3-bis(2,4-methyl-6-diphenyl phenyl)imidazole thione) and corresponding antimony halide. The stereoselective formation of complexes syn- 1 and anti- 2 has been confirmed by both NMR and single-crystal X-ray diffraction studies. Interestingly the stereospecific nature of syn- 1 and anti- 2 remains intact in solution. Furthermore, the thermal stability of antimony(III) imidazole thione complexes were examined by TGA analysis.     

Construction of Stable Redox Systems Composed of the Crowded Triarylphosphines

Extremely crowded triarylphosphines were synthesized by the reaction of arylcopper(I) reagents with chlorophosphines, and the relationship between molecular structure and redox properties was studied by X-ray crystallography and cyclic voltammetry. As the substituent on phosphorus became bulkier, bond lengths and angles around phosphorus atom became longer and larger, and oxidation potential was significantly lowered. Especially, tris(2,4,6-triisopropylphenyl)phosphine had an extremely crowded structure and was oxidized to a stable radical cation at an extraordinarily low oxidation potential. Novel redox systems possessing the crowded triarylphosphine structure as one of the redox sites were designed and synthesized.     

Spectroscopic Identification of Diphosphene HPPH and Isomeric Diphosphinyldene PPH2

The simplest diphosphene HPPH and isomeric diphosphinyldene PPH₂ features prototype phosphorus-phosphorus multiple bonding properties that have been of long-standing interest in main-group chemistry. Herein, we report the observation of cis-HPPH, trans-HPPH, and PPH₂ among the respective laser photolysis products of phosphine (PH₃) and diphosphine (P₂H₄) in solid N₂- and Ar-matrices at 10 K. The identification of these P₂H₂ isomers with matrix-isolation IR and UV/Vis spectroscopy is supported by D-isotope labeling and the quantum chemical calculations at the CCSD(T)-F12a/cc-pVTZ-F12 level using configuration-selective vibrational configuration interaction theory (VCI). Bonding analyses suggest that the two conformers of HPPH contain standard PP double bonds, whereas, PPH₂ resembles P₂ in having partial PP triple bond due to the H₂P←P π bonding interaction.     

Divergent Stabilities of Tetravalent Cerium,Uranium, and Neptunium Imidophosphorane Complexes**

The study of the redox chemistry of mid-actinides (U−Pu) has historically relied on cerium as a model, due to the accessibility of trivalent and tetravalent oxidation states for these ions. Recently, dramatic shifts of lanthanide 4+/3+ non-aqueous redox couples have been established within a homoleptic imidophosphorane ligand framework. Herein we extend the chemistry of the imidophosphorane ligand (NPC=[N=P^tBu(pyrr)₂]⁻; pyrr=pyrrolidinyl) to tetrahomoleptic NPC complexes of neptunium and cerium ( 1-M , 2-M , M=Np, Ce) and present comparative structural, electrochemical, and theoretical studies of these complexes. Large cathodic shifts in the M^4+/3+ (M=Ce, U, Np) couples underpin the stabilization of higher metal oxidation states owing to the strongly donating nature of the NPC ligands, providing access to the U^5+/4+, U^6+/5+, and to an unprecedented, well-behaved Np^5+/4+ redox couple. The differences in the chemical redox properties of the U vs. Ce and Np complexes are rationalized based on their redox potentials, degree of structural rearrangement upon reduction/oxidation, relative molecular orbital energies, and orbital composition analyses employing density functional theory.     

Redox cycling in nanofluidic channels using interdigitated electrodes

Amperometric detection is ideally suited for integration into micro- and nanofluidic systems as it directly yields an electrical signal and does not necessitate optical components. However, the range of systems to which it can be applied is constrained by the limited sensitivity and specificity of the method. These limitations can be partially alleviated through the use of redox cycling, in which multiple electrodes are employed to repeatedly reduce and oxidize analyte molecules and thereby amplify the detected signal. We have developed an interdigitated electrode device that is encased in a nanofluidic channel to provide a hundred-fold amplification of the amperometric signal from paracetamol. Due to the nanochannel design, the sensor is resistant to interference from molecules undergoing irreversible redox reactions. We demonstrate this selectivity by detecting paracetamol in the presence of excess ascorbic acid. Figure