Remarkable improvement of cyclic stability in Li–O2 batteries using ruthenocene as a redox mediator

Nonaqueous Li–O₂ batteries attract attention for their theoretical specific energy density. However, due to the difficulty of decomposition of Li₂O₂, Li–O₂ batteries have high charge overpotential and poor cycling life. So all kinds of catalysts have been studied on the cathode. Compared to heterogeneous solid catalysts, soluble catalysts achieve faster and more effective transport of electrons by reversible redox pairs. Here, we first report ruthenocene (Ruc) as a mobile redox mediator in a Li–O₂ battery. 0.01 mol/L Ruc in the electrolyte effectively reduces the charging voltage by 610 mV. Additionally, Ruc greatly increases the cycling life by four-fold (up to 83 cycles) with a simple ketjen black (KB) cathode. The results of SEM, XPS and XRD confirm that less discharge product residue accumulated after recharge. To verify the reaction mechanisms of the mediator, free energy profiles of the possible reaction pathways based on DFT are provided.     

Trimetallic complexes containing 1,1′-Rc′(CC)2 units [Rc′ = ruthenocene-1,1′-diyl, Ru(η-C5H4-)2]

Reactions between 1,1′-(Me₃SiCC)₂Rc′ [Rc′ = ruthenocen-1,1′-diyl, Ru(η-C₅H₄-)₂] and RuCl(PP)Cp′ in the presence of KF gave 1,1′-{Cp(PP)RuCC}₂Rc′ [Cp′ = Cp, PP = PPh₃1, P(m-tol)₃2, dppe 3, dppf 4; Cp′ = Cp^∗, PP = dppe 5]. Compounds 1 and 2 react with tcne to give two diastereomers a/b of the allylic (vinylcarbene) complexes 6 and 7, while methylation of 5 gave the bis-vinylidene [1,1′-{Cp^∗(dppe)RuCCMe}₂Rc′](BPh₄)₂ (8). The X-ray structures of 4, 6b and 8 have been determined. Cyclic voltammograms indicate that there is some electronic communication between the ruthenium end-groups through the Rc′ centre.     

Anodic oxidation of organometallic sandwich complexes using [Al(OC(CF3)3)4] or [AsF6] as the supporting electrolyte anion

Anodic voltammetry and electrolysis of the metallocenes ferrocene, ruthenocene, and nickelocene have been studied in dichloromethane containing two different fluorine-containing anions in the supporting electrolyte. The perfluoroalkoxyaluminate anion [Al(OC(CF₃)₃)₄]⁻ has very low nucleophilicity, as shown by its inertness towards the strong electrophile [RuCp₂]⁺ and by computation of its electrostatic potential in comparison to other frequently used electrolyte anions. The low ion-pairing ability of this anion was shown by the large spread in E_1/2 potentials (ΔE_1/2 = 769 mV) for the two one-electron oxidations of bis(fulvalene)dinickel. The hexafluoroarsenate anion [AsF₆]⁻, on the other hand, reacts rapidly with the ruthenocenium ion and is much more strongly ion-pairing towards oxidized bis(fulvalene)dinickel (ΔE_1/2 = 492 mV). In terms of applications of these two anions to the anodic oxidation of organometallic sandwich complexes, the behavior of [Al(OC(CF₃)₃)₄]⁻ is similar to that of other weakly-coordinating anions such as [B(C₆F₅)₄]⁻, whereas that of [AsF₆]⁻ is similar to the more traditional electrolyte anions such as [PF₆]⁻ and [BF₄]⁻. Additionally, the synthesis and crystal structure of [Cp₂Fe][Al(OC(CF₃)₃)₄] are reported.     

Synthesis, structures and reactions of some metallocene alcohols

E-1-Ferrocenyl-4,4-dimethylpent-2-ene-1-one has been synthesised from the Friedel-Crafts acylation of ferrocene with E-3-tert-butylacryloylchloride and converted to 1-ferrocenyl-3-chloro-4,4-dimethylpentan-1-one using ethereal hydrogen chloride. This new chloro ketone has been converted into three new ferrocene alcohols: 1-ferrocenyl-3,4-dimethyl-4-hydroxypentan-1-one, 1-ferrocenyl-3-chloro-4,4-dimethylpentan-1-ol, and 2,2,6,6-tetramethyl-3-ferrocenyl-5-chloroheptan-3-ol. A new dinuclear ferrocene derivative, E,E-2,2,9,9-tetramethyl-5,6-diferrocenyl-deca-3,7-diene, was isolated after treatment of 1-ferrocenyl-3-chloro-4,4-dimethylpentan-1-ol with acidic alumina; its structure was confirmed by X-ray crystallography, whilst electrochemistry revealed metal-metal interactions of similar magnitude to those seen for other 1,2-bis(ferrocenyl)ethane derivatives. Crystal structures have also been determined for 2,2,6,6-tetramethyl-3-ferrocenyl-5-chloroheptan-3-ol, rac-1-hydroxy[3]ferrocenophane, rac-1S,3S-1,3-diphenyl-1-hydroxy[3]ferrocenophane, and of rac-1,1^′-diphenyl-1,1^′-(1,1^′- ruthenocenediyl)dimethanol and show an intramolecular Cl?H-O hydrogen bond, a tetramer based on O?H-O hydrogen bonds, no hydrogen bonding, and a dimer with inter- and intramolecular O?H-O hydrogen bonds, respectively.     

Fulvalenediyl-bridged heterobimetallic complexes consisting of sandwich and half-sandwich compounds with early-late transition metals

A straightforward synthesis methodology for the preparation of heterobimetallic [(η⁵-C₅H₅)(η⁵-C₅H₄-C₅Me₄)M] (3a, M = Fe; 3b, M = Ru) and [(η⁵-C₅H₅)((μ-η⁵:η⁵-C₅H₄-C₅Me₄)TiCl₃)M] (4a, M = Fe; 4b, M = Ru) in which early and late transition metals are connected by a fulvalenediyl bridge is reported.The structures of molecules 3b and 4a in the solid state are discussed. Most noteworthy in 4a is the exo arrangement of the iron and titanium atoms coordinated by the fulvalenediyl unit which itself is twisted with a dihedral angle between the joined cyclopentadienyl rings of 19.33(9)°. Electrochemical, UV/Vis/NIR spectroscopic and spectroelectrochemical experiments on 4a and Cp∗TiCl₃, for comparison, provide evidence for some transfer of electronic information between the conjoined ferrocene and half-sandwich titanocene trichloride subunits of 4a. Evidence comes from systematic potential shifts and the presence of a fairly intense Fe → Ti charge-transfer absorption band that vanishes upon oxidation and reduction of 4a.     

Tri-, penta-, and hexa-phospha ruthenocenes

Synthesis and structural studies of the ruthenium(II) ‘sandwich’ complexes [Ru(η⁵-P₃C₂^tBu₂)₂], [Ru(η⁵-P₃C₂C₂^tBu₂)(η⁵-P₂C₃^tBu₃)], [Ru(η⁵-C₅R₅)(η⁵-P₃C₂^tBu₂)] (R=H, Me) are described. The results of a single crystal X-ray structural study of [Ru(η⁵-P₃C₂^tBu₂)₂] are discussed.     

Ruthenocene as a new donor fragment in [60]fullerene-donor dyads

Four novel fullerene derivatives containing ruthenocene as the donor fragment have been synthesized and their electrochemical and fluorescence properties have been studied. Steady state fluorescence studies suggest the existence of photoinduced electron transfer in these dyads.     

二茂钌共轭大环氮杂冠醚的合成及结构

合成并表征了质子化的N-(二茂钌基甲基)-1,4,7-三氮杂-9-冠-3(1)和N,N′,N″-三-(二茂钌基甲基)-1,4,7-三氮杂-9-冠-3(2).用X射线衍射法测定了化合物2的结构.化合物2的晶体属P₂₁/a空间群.晶胞参数a=1.4285(3)nm,b=1.9888(3)nm,c=1.9133(3)nm;β=109.12(2)°;V=5.1358(1.0)nm³;Z=4.D_c=1.665g/cm³.1和2的核磁共振谱表明,化合物中取代Cp环上质子的共振吸收较二茂钌Cp环上质子的吸收向低场移动.这表明质子化的1,4,7-三氮杂-9冠-3对Cp环上质子具有去屏蔽作用.化合物2的电位扫描曲线在0.84V处出现一个氧化波.     

An Electrochemical Study of Immobilized Ruthenocene in Aqueous Media

The voltammetric exploration of ruthenocene RuCp₂ in aqueous solution via abrasive modification on a basal plane pyrolytic graphite electrode is reported. It is found that ruthenocene undergoes a one‐electron electrochemically irreversible oxidation to ruthenocenium, which then rapidly dimerizes to form [RuCp₂] . Then, depending on the anion in solution, either disproportionates to [RuCp₂]²⁺ and subsequently decomposes to ruthenium oxide, or is anion stabilized. SEM images and cyclic voltammetry of the electrode surface indicates that in the presence of smaller anions the dimer is not stabilized, whereas for larger anions, such as sodium toluene sulfonate, the dimer is stabilized and decomposition is inhibited.     

Synthesis and electrochemistry of novel heteronuclear Fe-Ru bi- and quatermetallocenes, conjugatively connected by ethene and thiophene bridges

(E)-2-(1′-Formylruthenocenyl)ethenyl-1′,2,2′,3,3′,4,4′,5-octamethylferrocene (1) and (all-E)-2,5-bis[2-[1′-[2-(1′,2,2′,3,3′,4,4′,5-octamethylferrocenyl)ethenyl]ruthenocenyl]ethenyl]thiophene (2) were synthesized by a sequence of Wittig olefinations. The X-ray structure of 1 is reported. The cyclic voltammogram of compound 1 shows the irreversible one-electron transfer expected for ruthenocene and a reversible wave for the octamethylferrocene moiety. Both waves occur at about the same potential as observed for the parent metallocenes. Compound 2, however, exhibits completely unusual redox properties. In contrast to most ruthenocene-containing compounds, a reversible two-electron transfer is observed at a significantly lower potential than found usually for ruthenocenes that can be attributed unambiguously to the independent oxidation/reduction of the two ruthenocene moieties. The unexpected stability of the oxidation products must be due to the presence of the thiophene-ethene bridge, which facilitates the oxidation reaction and stabilizes the reaction products by delocalization of the valence electrons.