Unlike ferrocene, bis(η -cyclopentadienyl)magnesium (magnesocene, MgCp ) is slightly dissociated in solvents, such as ethers, resulting in electrolyte solutions with low conductivity. MgCp /tetrahydrofuran solutions make possible reversible magnesium plating and stripping with low over-potentials for many cycles. The Mg deposits appear with a cauliflower-like morphology. IR and NMR spectroscopy confirm that the electrolyte is stable and not decomposed during prolonged cycling. The anodic stability limit is in the range of 1.5 V (at platinum) and 1.8 V versus Mg/Mg (at stainless steel), which may be sufficient for low-voltage cathode materials. MgCp is a first example of a completely new class of halide-free electrolytes, which may open up a new research direction for future magnesium metal and magnesium-ion batteries.

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Solvent-free polymerisation of vinyl terephthalate was used to obtain high molecular weight polymers, whose corresponding Li-salts underlined the superiority of polymers regarding long term stability in battery tests compared to their monomeric counterparts.

The 1-tetrahydropyranyl-(THP-)protected pyrazoles 4-R-pz(THP) (R=pinacolatoboryl=Bpin (3a(THP)), Me3Si (4a(THP)), Me3Sn (5a(THP)), and 4-R-3,5-Ph2pz (R=Bpin (3b(THP)), Me3Si (4b(THP)), Me3Sn (5b(THP)) were obtained by the following syntheses: i) In a first step, 4-X-pz (X=Br (1a), I (2a)) and 4-X-3,5-Ph2pz (X=Br (1b), I (2b)) were reacted with 3,4-dihydro-2Hpyran (DHP) to give the related THP-protected bromo- or iodopyrazole derivatives. ii) In a second step these THP derivatives were metalated by treatment with nBuLi or iPrMgCl. Subsequent reactions of the THP-protected metallopyrazoles 4-M-pz(THP) and 4-M-3,5-Ph2pz(THP) (M=Li, MgBr) with Bpin(OiPr), Me3SiCl, and Me3SnCl yielded the pyrazole derivatives 3a(THP), 3b(THP), 4a(THP), 4b(THP), 5a(THP), and 5b(THP). In contrast to the stannylated pyrazoles 5a(THP) and 5b(THP), the corresponding borylated and silylated derivatives could be easily deprotected: treatment of 3a(THP), 3b(THP), and 4a(THP) with HCl yielded the parent pyrazoles 3a, 3b and 4a. The microwave-assisted C-C cross-coupling reactions of these pyrazoles with aryl halides were examined, e. g. Suzuki reactions of 3a with p-pentylphenylbromide, p-hexylphenylbromide, and p- (2-ethylhexyl)phenylbromide. Similar reactions were also performed with 1a, 1b, 2a, and 2b and aryl-substituted pinacolatoboranes or boronic acids. Crystals of 5b(THP) suitable for X-ray diffraction were grown (monoclinic P21/c) and their structure determined. The crystal structures of 1a·HBr (monoclinic P21/n), 1b (triclinic P̄1̄), (1c)2·HBr (monoclinic P2/c), 1c·HBr·(Br2)0.5 (triclinic P̄1̄), (2a)3·H2SO4 (triclinic P̄1̄), 3a (orthorhombic P212121), (3a)3·H2O (trigonal R3c), 3b (orthorhombic Pna21), and 4a (monoclinic Pc) reveal interesting hydrogen bonding networks.

Unlike ferrocene,b is(h 5 -cyclopentadienyl)magnesium (magnesocene,MgCp 2 )isslightly dissociated in solvents, such as ethers,r esulting in electrolyte solutions with low conductivity.M gCp 2 /tetrahydrofuran solutions make possible reversible magnesium plating and stripping with low overpotentials for many cycles.T he Mg deposits appear with ac auliflower-like morphology.I Ra nd NMR spectroscopy confirm that the electrolyte is stable and not decomposed during prolonged cycling. The anodic stability limit is in the range of 1.5 V( at platinum) and 1.8 Vv ersus Mg/Mg 2+ (at stainless steel), whichmay be sufficient for low-voltage cathode materials.MgCp 2 is afirst example of acompletely new class of halide-free electrolytes,w hich may open up an ew research direction for future magnesium metal and magnesium-ion batteries.Withtheadventofthedigitalage,theelectrificationofnonstationary devices puts up an ever-growing demand on energy storage-challenging todaystechnology.Since the end of the 20th century,l ithium-ion batteries have been predominantly used in non-stationary devices.H owever,f uture needs for efficiency,c apacity and availability of energy-storage solutions exceed the current state-of-the-art technology by far. [1,2] Alternatives such as sodium-or magnesium-based secondary batteries are still in the research stage.Magnesium offers ag ood match to those future needs-a divalent ion with ac omparatively small ionic radius of 86 pm, af easible magnesium metal anode with at heoretical capacity of 2205 mAh g À1 ,a bundancy( magnesium is the 5th most abundant element in the earth crust) and significant commercial edge. [3,4] Despite these promising properties,m agnesium-based batteries still face major roadblocks until their commercialization. Thef avored, high energy density,m agnesium metal anode is at the current state of research only compatible with af ew different classes of magnesium salts or complexes dissolved in ethereal solution. Reversible magnesium deposition and stripping was first demonstrated in av ariety of different magnesium-organic compounds,including Grignard compounds and magnesium organoborates. [5] This approach saw agreat improvement in anodic stability by reacting strong chloroaluminate Lewis acids with the magnesium-organic Lewis bases. [6,7] It led to the recent development of ab road variety of different organo-halo-aluminate complexes with greatly enhanced anodic stabilities up to 3.5 Vv ersus Mg/ Mg 2+ ,l ower oxygen sensitivity and low nucleophilicity, [8] as well as of inorganic chloroaluminate complexes. [9,10] Most of these electrolytes contain chlorine.Itappears that they act as as ource for Cl À ions which helps to depassivate the Mg electrode and to facilitate the Mg deposition process. [11,12] Ad ifferent approach, pursuing ah alide-free electrolyte, uses ethereal solutions of Mg(BH 4 ) 2 , [13] the electrochemical properties of which can be further enhanced by using mixtures of Mg(BH 4 ) 2 and LiBH 4 . [13,14] Thereupon magnesium-carboranyl salts have been developed, whi...