The first example of rare earth metal-catalyzed cycloaddition of terminal alkynes to azides resulting in the formation of 1,5-disubstituted 1,2,3-triazoles is described. Preliminary studies revealed that the present cycloaddition shows unprecedented mechanistic features involving a tandem anionic cascade cyclization and anti-addition across the C≡C triple bond.

The treatment of [(Me(3)Si)(2)NC(NCy)(2)](2)Ln(mu-Cl)(2)Li(THF)(2) with 1 equiv of BnK (Bn = benzyl) in toluene affords [(Me(3)Si)(2)NC(NCy)(2)](2)LnBn [Ln = Er (1-Er), Y (1-Y)] in good yields. Similarly, [(Me(3)Si)(2)NC(NCy)(2)](2)Ln(t)Bu [Ln = Er (2-Er), Yb (2-Yb)] are obtained in satisfactory yields by the reaction of [(Me(3)Si)(2)NC(NCy)(2)](2)Ln(mu-Cl)(2)Li(THF)(2) with (t)BuLi in hexane. 1 reacts with 1/8 equiv of S(8) in toluene to form the sulfur insertion products {[(Me(3)Si)(2)NC(NCy)(2)](2)Ln(mu-SBn)}(2) [Ln = Er (3-Er), Y (3-Y)], while the reaction of 2 with elemental sulfur under the same conditions affords the oxidation products {[(Me(3)Si)(2)NC(NCy)(2)](2)Ln}(2)(mu-eta(2):eta(2)-S(2)) [Ln = Er (4-Er), Yb (4-Yb)] regardless of the equivalency of S(8) employed. Disulfide complexes 4 can also be obtained by the reaction of 3 with (1)/(4) equiv of S(8). Furthermore, the treatment of [(Me(3)Si)(2)NC(NCy)(2)](2)Ln(mu-Cl)(2)Li(THF)(2) with 1 equiv of (n)BuLi in hexane, followed by reaction with (1)/(8) equiv of S(8), affords the dinuclear thiolate complexes {[(Me(3)Si)(2)NC(NCy)(2)](2)Ln(mu-S(n)Bu)}(2) [Ln = Y (5-Y), Er (5-Er)] in good yields. However, under the same conditions, [(Me(3)Si)(2)NC(NCy)(2)](2)Yb(mu-Cl)(2)Li(THF)(2) reacts with (n)BuLi and S(8) to give {[(Me(3)Si)(2)NC(NCy)(2)](2)Yb}(2)(mu-eta(2):eta(2)-S(2)) (4-Yb) as the main metal-containing product. [(Me(3)Si)(2)NC(NCy)(2)](2)LnPh (generated in situ from [(Me(3)Si)(2)NC(NCy)(2)](2)Ln(mu-Cl)(2)Li(THF)(2) and PhLi) also undergoes sulfur insertion, affording {[(Me(3)Si)(2)NC(NCy)(2)](2)Ln(mu-SPh)}(2) [Ln = Er (6-Er), Yb (6-Yb)] in good yields. All of the complexes were characterized by spectroscopic and elemental analyses. The structures of all of these compounds, except 3-Y, are also determined by single-crystal X-ray diffraction analysis. Surprisingly, 3, 5, and 6 bear the same space group and very similar cell parameters, despite the different thiolate ligands.

To be competitive with other electrically rechargeable large scale energy storage, the range of active materials for redox flow batteries is currently expanded by organic compoundsthis holds especially for the redox active material class of quinones that can be derived from naturally abundant resources at low cost. Here we propose the modified quinone 2,3-diaza-anthracenedione, and two of its derivatives, as a promising active material for aqueous redox flow batteries. We systematically study the electrochemical performance (redox potentials, rate constants, diffusion coefficients) for these three compounds at different pH values experimentally and complement the results with density functional calculations: A positive redox potential shift of about 300 mV is achieved by the incorporation of a diaza moiety into the anthraquinone base structure. Our experiments at low pH show that the addition of a methoxy group to the base structure of the 2,3-diaza-anthracenedione strongly increases the electrochemical stability in aqueous acidic mediaalthough the impact of the conjugate base is not clear yet. Furthermore, a functionalization with two hydroxyl groups evokes a negative redox potential shift of 54 mV in acidic and 264 mV in alkaline solution. This demonstrates that this novel class of compounds is very versatile and can be tailor-made for use as active material in redox flow batterieseither in alkaline or acidic media. The 2,3-diaza-anthracenediones presented in this study were used as anolyte active materials in a full redox flow cell as a proof of concept; best cycling stability was achieved with 2,3-diaza-anthracenediones functionalized with a methoxy group as active material. Transferring our findings to other quinone base structures, such as naphthoquinones, could lead to even better performing catholyte and anolyte active materials for future redox flow batteries with organic active material.

The synthesis, structure, and reactivity of organoyttrium phosphides toward phenyl isocyanate (PhNCO) and phenyl isothiocyanate (PhNCS) are described. Reaction of (TpMe2)CpYCH2Ph(THF) (TpMe2 = tris(3,5-dimethylpyrazolyl)borate; Cp = C5H5) with 1 equiv of HPPh2 in THF at ambient temperature gives an organoyttrium phosphide (TpMe2)CpYPPh2(THF) (1). Treatment of 1 with 1 equiv of PhNCO in THF at ambient temperature results in monoinsertion of PhNCO into the Y–P σ-bond to yield complex (TpMe2)CpY[OC(PPh2)NPh](THF) (2), whereas reaction of 1 with 2 equiv of PhNCO affords the PhNCO diinsertion product (TpMe2)CpY[OC(PPh2)N(Ph)C(O)NPh] (4). However, reaction of 1 with PhNCS under the same conditions is independent of the stoichiometric ratio and gives only the monoinsertion product (TpMe2)CpY[SC(PPh2)NPh] (3). Moreover, 1 can effectively catalyze the cyclotrimerization of PhNCO under mild conditions, but does not catalyze the cyclotrimerization of PhNCS. In addition, the reaction of Cp2LnPPh2(THF) with PhNCS affords the insertion products Cp2Ln[SC(PPh2)NPh](THF) (Ln = Y (6), Er (7), Dy (8)). All new complexes were characterized by elemental analysis, IR, and/or 1H, 13C and 31P NMR, and their solid-state structures, except 4, were determined through single-crystal X-ray diffraction analysis. These reactions represent the first example of isocyanate and isothiocyanate insertions into the Ln–P σ-bond and provide an efficient method for the construction of phosphaureido, phosphadiureido, and phosphathioureido ligands.

To enable cost-efficient stationary energy storage, organic active materials are the subject of current investigations with regard to their application in aqueous redox flow batteries. Especially quinones with their beneficial electrochemical properties and natural abundance pose a promising class of compounds for this challenging endeavor. Yet, there are not many active materials available for the catholyte side to realize solely quinone-based systems. Herein we introduce the novel hydroquinone 5,8dihydroxy-2,3-phthalazine together with two of its derivatives and propose it as a promising active material for the catholyte side of aqueous redox flow batteries. We systematically investigate the electrochemical properties as well as the structure−property relationship of this class of compounds. The unmodified dihydroxyphthalazine exhibits a favorably high redox potential of 796 mV vs SHE in acidic solution that is competitive with benzoquinone compounds. Moreover, the introduced dihydroxyphthalazines feature a high electron transfer rate surpassing benzoquinone species by almost one order of magnitude. With regard to stable cycling performance, we further achieved a high resilience against detrimental side reactions such as Michael addition by adding methyl substituents to the base structure. Our experimental findings are supported and extended by theoretical considerations in terms of density functional theory calculations. With this combined approach we outline further promising dihydroxyphthalazine-based materials with regard to performance-relevant quantities like redox potential, cycling stability, and water solubility. This study aims to propel further research in the field of quinone-based active materials for the catholyte of future aqueous redox flow batteries.