Iodine(III)‐Catalyzed Rearrangements of Imides: A Versatile Route to α,α‐Dialkylated α‐Hydroxy Carboxylamides

A tertiary hydroxy group α to a carboxyl moiety comprises a key structural motif in many bioactive substances. With the herein presented metal‐free rearrangement of imides triggered by hypervalent λ³‐iodane, an easy and selective way to gain access to such a compound class, namely α,α‐disubstituted‐α‐hydroxy carboxylamides, was established. Their additional methylene bromide side chain constitutes a useful handle for rapid diversification, as demonstrated by a series of further functionalizations. Moreover, the in situ formation of an iodine(III) species under the reaction conditions was proven. Our findings clearly corroborate that hypervalent λ³‐benziodoxolones are involved in these organocatalytic reactions.     

Minimizing Side Product Formation in Alkyne Functionalization of Ruthenium Complexes by Introduction of Protecting Groups

The synthesis of alkyne functionalized bipyridine ruthenium complexes are reported. The improved synthetic approach through application of stable protecting groups prevents formation of possible side products while facilitating purification. By applying copper-catalysed azide-alkyne cycloaddition reactions (CuAAC) pyrene units with flexible alkyl linkers are introduced at the periphery of the complex, opening up various applications including surface immobilization and DNA intercalation. All complexes are characterized structurally as well as photophysically, especially regarding the influence of the introduced alkyne and triazolyl substituents on their photophysical behavior.     

Formation and Reactivity of Organo‐Functionalized Tin Selenide Clusters

Reactions of R¹SnCl₃ (R¹=CMe₂CH₂C(O)Me) with (SiMe₃)₂Se yield a series of organo‐functionalized tin selenide clusters, [(SnR¹)₂SeCl₄] ( 1 ), [(SnR¹)₂Se₂Cl₂] ( 2 ), [(SnR¹)₃Se₄Cl] ( 3 ), and [(SnR¹)₄Se₆] ( 4 ), depending on the solvent and ratio of the reactants used. NMR experiments clearly suggest a stepwise formation of 1 through 4 by subsequent condensation steps with the concomitant release of Me₃SiCl. Furthermore, addition of hydrazines to the keto‐functionalized clusters leads to the formation of hydrazone derivatives, [(Sn₂(μ‐R³)(μ‐Se)Cl₄] ( 5 , R³=[CMe₂CH₂CMe(NH)]₂), [(SnR²)₃Se₄Cl] ( 6 , R²=CMe₂CH₂C(NNH₂)Me), [(SnR⁴)₃Se₄][SnCl₃] ( 7 , R⁴=CMe₂CH₂C(NNHPh)Me), [(SnR²)₄Se₆] ( 8 ), and [(SnR⁴)₄Se₆] ( 9 ). Upon treatment of 4 with [Cu(PPh₃)₃Cl] and excess (SiMe₃)₂Se, the cluster fragments to form [(R¹Sn)₂Se₂(CuPPh₃)₂Se₂] ( 10 ), the first discrete Sn/Se/Cu cluster compound reported in the literature. The derivatization reactions indicate fundamental differences between organotin sulfide and organotin selenide chemistry.     

Control of reaction mechanisms in cationically polymerized epoxy resins facilitates the adjustment of morphology and mechanical properties

Structure–property relations of cationically polymerized epoxy thermosets with different morphologies are examined. The morphology adjustment of amorphous epoxy based copolymers and partially crystalline polymer alloys is carried out with star‐shaped poly(ε‐caprolactone) (SPCL) bearing various numbers of hydroxyl end groups. These hydroxyl groups are known for their reactivity toward epoxides following the activated monomer (AM) mechanism. For this reason, four‐armed SPCL was synthesized with four hydroxyl end groups (SPCL‐tetraol) and, in addition, with successively esterified ones down to a SPCL with four ester end groups (SPCL‐tetraester). SPCL species bearing fewer or no hydroxyl end groups segregate into needle‐like nanodomains within the epoxy networks and, if the concentration is high enough, also into crystalline domains. The stronger phase separation of SPCL‐tetraester within the epoxy network compared with SPCL‐tetraol is due to a reduction of the AM mechanism. The mechanical properties resulting from different morphologies lead to a trade‐off between higher storage moduli and T_g values in the case of the more phase separated (and partially crystalline) polymer alloys and higher strain at break in the case of the amorphous copolymers. Nevertheless, in both cases toughness is improved or at least kept on the same level as for the pure epoxy resin. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2188–2199     

Efficient and accurate two-scale simulation of non-linear heterogeneous microstructures

This work is concerned with the development of an efficient two-scale numerical scheme for the prediction of the local and effective mechanical response of heterogeneous materials with non-linear constitutive behavior. In order to ensure both, accurate micromechanical fields and feasible overall CPU-times, an efficient but rather simple solution scheme is proposed. Its capabilities are demonstrated using the FE-FFT method [2,3] for the solution of simple two-scale problems. As an example, two-dimensional polycrystalline microstructures with an elasto-viscoplastic constitutive law are considered. (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Scorpio-Ligand: Synthesis of Biphenyl-Dihydroazepine Phosphoramidite Ligands for Asymmetric Hydrogenation

A novel dihydroazepine-bridged BIPHEP phosphoramidite ligand with an amino acid moiety in the backbone was synthesized and evaluated in the Rh-catalyzed asymmetric hydrogenation. The scorpion tail-like amino acid backbone is capable of hydrogen bond formation and able to shift the rotamer composition of the biphenyl axis with the two scissor-like arms. Pivaloyl-l -valine was studied as chiral selector unit and compared with pivaloylglycine as the achiral reference substance. The enantiomerization barrier of the pivaloylglycine-modified biphenylamide was determined to be ΔG^≠=110 kJ/mol. In the case of pivaloyl-l -valine, the (S_ax) isomer is thermodynamically favored. Due to the relatively high barrier, the ligand is atropisomeric at room temperature and allows the preparative separation of the stereoisomers. The obtained phosphoramidite ligands were separated by chiral HPLC. For the first eluting rotamer, Rh complex ([Rh(cod)(L)₂]BF₄) was generated in situ and examined in the enantioselective hydrogenation of 2-acetamidoacrylate and methyl 2-acetamido-3-phenylacrylate, achieving enantiomeric excesses of up to 94 %.     

Stability and Conversion of Tin Zintl Anions in Liquid Ammonia Investigated by NMR Spectroscopy

Homoatomic polyanions of post‐transition main‐group metals, namely, Zintl anions, are precast in analogous Zintl phases and can react in solution to form new materials. Despite comprehensible reaction approaches, the formed products cannot be planned in advance, as hitherto undetected and therefore disregarded side reactions take place. The outcomes and interpretations of the reactions of Zintl anions are so far based mainly on crystal structures, which only allow characterization of the product that has the lowest solubility. Here we present the results of our investigation of the stability of highly charged tin Zintl anions in liquid ammonia, which is not exclusively based on solution effects but also on the oxidative influence of the solvent. This allows for a deeper understanding of the ongoing processes in solution and opens doors to the directed synthesis of transition metal complexes of Sn₄^4?, here shown by its reactivity towards MesCu.