TY - JOUR A1 - Philipp, Michael S. M. A1 - Radius, Udo T1 - A Versatile Route To Cyclic (Alkyl)(Amino)Carbene–Stabilized Stibinidenes JF - Zeitschrift für Anorganische und Allgemeine Chemie N2 - A convenient route for the synthesis of the cAAC\(^{Me}\) (cAAC=cyclic (alkyl)(amino)carbene, cAAC\(^{Me}\)=1-(2,6-di-iso-propylphenyl)-3,3,5,5-tetramethyl-pyrrolidin-2-ylidene) and cAAC\(^{Cy}\) (cAAC\(^{Cy}\)=2-azaspiro[4.5]dec-2-(2,6-diisopropylphenyl)-3,3-dimethyl-1-ylidene) stabilized stibinidenes cAAC\(^{Me}\)⋅SbMes (2a) (Mes=2,4,6-trimethylphenyl) and cAAC\(^{Cy}\)⋅SbMes (2b) is reported. A mechanism for the formation of [cAAC\(^{R}\)Cl][SbCl\(_{3}\)Mes] 1 and cAAC\(^{R}\)⋅SbMes 2 from the reaction of cAAC with the antimony(III) precursor SbCl\(_{2}\)Mes, which proceeds via the isolable intermediate [cAAC\(^{R}\)SbClMes][SbCl\(_{3}\)Mes] (3), is proposed. KW - stibinidenes KW - antimony KW - cyclic (alkyl)(amino)carbenes KW - lewis acid/base adducts KW - main group element halides Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-318272 SN - 0044-2313 VL - 648 IS - 17 ER - TY - JOUR A1 - Huang, Mingming A1 - Hu, Jiefeng A1 - Shi, Shasha A1 - Friedrich, Alexandra A1 - Krebs, Johannes A1 - Westcott, Stephen A. A1 - Radius, Udo A1 - Marder, Todd B. T1 - Selective, Transition Metal-free 1,2-Diboration of Alkyl Halides, Tosylates, and Alcohols JF - Chemistry-A European Journal N2 - Defunctionalization of readily available feedstocks to provide alkenes for the synthesis of multifunctional molecules represents an extremely useful process in organic synthesis. Herein, we describe a transition metal-free, simple and efficient strategy to access alkyl 1,2-bis(boronate esters) via regio- and diastereoselective diboration of secondary and tertiary alkyl halides (Br, Cl, I), tosylates, and alcohols. Control experiments demonstrated that the key to this high reactivity and selectivity is the addition of a combination of potassium iodide and N,N-dimethylacetamide (DMA). The practicality and industrial potential of this transformation are demonstrated by its operational simplicity, wide functional group tolerance, and the late-stage modification of complex molecules. From a drug discovery perspective, this synthetic method offers control of the position of diversification and diastereoselectivity in complex ring scaffolds, which would be especially useful in a lead optimization program. KW - organic synthesis KW - boronate esters KW - alkyl halides Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-318262 VL - 28 IS - 24 ER - TY - JOUR A1 - Philipp, Michael S. M. A1 - Bertermann, Rüdiger A1 - Radius, Udo T1 - N‐Heterocyclic Carbene and Cyclic (Alkyl)(amino)carbene Adducts of Germanium(IV) and Tin(IV) Chlorides and Organyl Chlorides JF - European Journal of Inorganic Chemistry N2 - A study on the reactivity of N‐heterocyclic carbenes (NHCs) and the cyclic (alkyl)(amino)carbene cAAC\(^{Me}\) with selected germanium(IV) and tin(IV) chlorides and organyl chlorides is presented. The reactions of the NHCs Me\(_{2}\)Im\(^{Me}\), iPr\(_{2}\)Im\(^{Me}\) and Dipp2Im with the methyl chlorides ECl\(_{2}\)Me\(_{2}\) afforded the adducts NHC ⋅ ECl\(_{2}\)Me\(_{2}\) (E=Ge (1), Sn (2)), NHC=Me\(_{2}\)Im\(^{Me}\) (a), iPr\(_{2}\)Im\(^{Me}\) (b), Dipp\(_{2}\)Im (c)). The reaction of Me2Im\(^{Me}\) with GeCl\(_{4}\) led to isolation of Me\(_{2}\)Im\(^{Me}\) ⋅ GeCl\(_{4}\) (3), the reaction of iPr\(_{2}\)Im\(^{Me}\) with SnCl\(_{4}\) in THF afforded the THF adduct iPr\(_{2}\)Im\(^{Me}\) ⋅ SnCl\(_{4}\) ⋅ THF (4). Dipp\(_{2}\)Im ⋅ GeCl\(_{2}\)Me\(_{2}\) (1 c) isomerized into the backbone coordinated imidazolium salt [aDipp\(_{2}\)Im ⋅ GeClMe\(_{2}\)][Cl] (5) upon thermal treatment. The reactions of cAAC\(^{Me}\) with (i) ECl\(_{2}\)R\(_{2}\) (E=Ge, Sn) gave the adducts cAAC\(^{Me}\) ⋅ ECl\(_{2}\)R\(_{2}\) (R=Me: E=Ge (6); Sn (7); Ph: E=Ge (8)), with (ii) GeClMe\(_{3}\) and GeCl\(_{4}\) the salts [cAAC\(^{Me}\) ⋅ GeMe\(_{3}\)][Cl] (9) and [cAACMeCl][GeCl\(_{3}\)] (10), and (iii) with SnCl\(_{4}\) the salt [cAACMeCl][SnCl\(_{3}\)] (11) and the adduct cAAC\(^{Me}\) ⋅ SnCl\(_{4}\) (12). Reduction of 2 a with KC\(_{8}\) afforded the NHC‐stabilized stannylene Me\(_{2}\)Im\(^{Me}\) ⋅ SnMe\(_{2}\) 13, reduction of 7 with either KC8 or 1,4‐bis‐(trimethylsilyl)‐1,4‐dihydropyrazin in the presence of SnCl\(_{2}\)Me\(_{2}\) yielded cAAC\(^{Me}\) ⋅ SnMe\(_{2}\) ⋅ SnMe\(_{2}\)Cl\(_{2}\) (14). Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-293865 VL - 2022 IS - 32 ER - TY - JOUR A1 - Tendera, Lukas A1 - Luff, Martin S. A1 - Krummenacher, Ivo A1 - Radius, Udo T1 - Cationic Nickel d\(^{9}\)‐Metalloradicals [Ni(NHC)\(_{2}\)]\(^{+}\) JF - European Journal of Inorganic Chemistry N2 - A series of five new homoleptic, linear nickel d\(^{9}\)‐complexes of the type [Ni\(^{I}\)(NHC)\(_{2}\)]\(^{+}\) is reported. Starting from the literature known Ni(0) complexes [Ni(Mes\(_{2}\)Im)\(_{2}\)] 1, [Ni(Mes\(_{2}\)Im\(^{H2}\))2] 2, [Ni(Dipp\(_{2}\)Im)\(_{2}\)] 3, [Ni(Dipp\(_{2}\)Im\(^{H2}\))\(_{2}\)] 4 and [Ni(cAAC\(^{Me}\))\(_{2}\)] 5 (Mes\(_{2}\)Im=1,3‐bis(2,4,6‐trimethylphenyl)‐imidazolin‐2‐ylidene, Mes\(_{2}\)Im\(^{H2}\)=1,3‐bis(2,4,6‐trimethylphenyl)‐imidazolidin‐2‐ylidene, Dipp\(_{2}\)Im=1,3‐bis(2,6‐diisopropylphenyl)‐imidazolin‐2‐ylidene, Dipp\(_{2}\)Im\(^{H2}\)=1,3‐bis(2,6‐diisopropylphenyl)‐imidazolidin‐2‐ylidene, cAAC\(^{Me}\)=1‐(2,6‐diisopropylphenyl)‐3,3,5,5‐tetramethylpyrrolidin‐2‐yliden), their oxidized Ni(I) analogues [Ni\(^{I}\)(Mes\(_{2}\)Im)\(_{2}\)][BPh\(_{4}\)] 1\(^{+}\), [Ni\(^{I}\)(Mes\(_{2}\)Im\(^{H2}\))\(_{2}\)][BPh\(_{4}\)] 2\(^{+}\), [Ni\(^{I}\)(Dipp\(_{2}\)Im)\(_{2}\)][BPh\(_{4}\)] 3\(^{+}\), [Ni\(^{I}\)(Dipp\(_{2}\)Im\(^{H2}\))\(_{2}\)][BPh\(_{4}\)] 4\(^{+}\) and [Ni\(^{I}\)(cAAC\(^{Me}\))\(_{2}\)][BPh\(_{4}\)] 5\(^{+}\) were synthesized by one‐electron oxidation with ferrocenium tetraphenyl‐borate. The complexes 1\(^{+}\)–5\(^{+}\) were fully characterized including X‐ray structure analysis. The complex cations reveal linear geometries in the solid state and NMR spectra with extremely broad, paramagnetically shifted resonances. DFT calculations predicted an orbitally degenerate ground state leading to large magnetic anisotropy, which was verified by EPR measurements in solution and on solid samples. The magnetic anisotropy of the complexes is highly dependent from the steric protection of the metal atom, which results in a noticeable decrease of the g‐tensor anisotropy for the N‐Mes substituted complexes 1\(^{+}\) and 2\(^{+}\) in solution due to the formation of T‐shaped THF adducts. KW - Alkyl(amino)carbene KW - EPR spectroscopy KW - Metalloradicals KW - Nickel ComplexCyclic Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-293702 VL - 2022 IS - 31 ER - TY - JOUR A1 - Philipp, Michael S. M. A1 - Bertermann, Rüdiger A1 - Radius, Udo T1 - Activation of Ge−H and Sn−H Bonds with N‐Heterocyclic Carbenes and a Cyclic (Alkyl)(amino)carbene JF - Chemistry – A European Journal N2 - A study of the reactivity of several N‐heterocyclic carbenes (NHCs) and the cyclic (alkyl)(amino)carbene 1‐(2,6‐di‐iso‐propylphenyl)‐3,3,5,5‐tetramethyl‐pyrrolidin‐2‐ylidene (cAAC\(^{Me}\)) with the group 14 hydrides GeH2Mes2 and SnH2Me2 (Me=CH\(_{3}\), Mes=1,3,5‐(CH\(_{3}\))\(_{3}\)C\(_{6}\)H\(_{2}\)) is presented. The reaction of GeH\(_{2}\)Mes\(_{2}\) with cAAC\(^{Me}\) led to the insertion of cAAC\(^{Me}\) into one Ge−H bond to give cAAC\(^{Me}\)H−GeHMes\(_{2}\) (1). If 1,3,4,5‐tetramethyl‐imidazolin‐2‐ylidene (Me\(_{2}\)Im\(^{Me}\)) was used as the carbene, NHC‐mediated dehydrogenative coupling occurred, which led to the NHC‐stabilized germylene Me\(_{2}\)Im\(^{Me}\)⋅GeMes\(_{2}\) (2). The reaction of SnH\(_{2}\)Me\(_{2}\) with cAAC\(^{Me}\) also afforded the insertion product cAAC\(^{Me}\)H−SnHMe\(_{2}\) (3), and reaction of two equivalents Me\(_{2}\)Im\(^{Me}\) with SnH\(_{2}\)Me\(_{2}\) gave the NHC‐stabilized stannylene Me\(_{2}\)Im\(^{Me}\)⋅SnMe\(_{2}\) (4). If the sterically more demanding NHCs Me\(_{2}\)Im\(^{Me}\), 1,3‐di‐isopropyl‐4,5‐dimethyl‐imidazolin‐2‐ylidene (iPr\(_{2}\)Im\(^{Me}\)) and 1,3‐bis‐(2,6‐di‐isopropylphenyl)‐imidazolin‐2‐ylidene (Dipp\(_{2}\)Im) were employed, selective formation of cyclic oligomers (SnMe\(_{2}\))\(_{n}\) (5; n=5–8) in high yield was observed. These cyclic oligomers were also obtained from the controlled decomposition of cAAC\(^{Me}\)H−SnHMe\(_{2}\) (3). KW - cyclic alkyl(amino)carbenes KW - germanium KW - hydrides KW - N-heterocyclic carbenes KW - tin Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-311929 VL - 29 IS - 3 ER - TY - JOUR A1 - Jos, Swetha A1 - Szwetkowski, Connor A1 - Slebodnick, Carla A1 - Ricker, Robert A1 - Chan, Ka Lok A1 - Chan, Wing Chun A1 - Radius, Udo A1 - Lin, Zhenyang A1 - Marder, Todd B. A1 - Santos, Webster L. T1 - Transition Metal‐Free Regio‐ and Stereo‐Selective trans Hydroboration of 1,3‐Diynes: A Phosphine‐Catalyzed Access to (E)‐1‐Boryl‐1,3‐Enynes JF - Chemistry – A European Journal N2 - We report a transition metal‐free, regio‐ and stereo‐selective, phosphine‐catalyzed method for the trans hydroboration of 1,3‐diynes with pinacolborane that affords (E)‐1‐boryl‐1,3‐enynes. The reaction proceeds with excellent selectivity for boron addition to the external carbon of the 1,3‐diyne framework as unambiguously established by NMR and X‐ray crystallographic studies. The reaction displays a broad substrate scope including unsymmetrical diynes to generate products in high yield (up to 95 %). Experimental and theoretical studies suggest that phosphine attack on the alkyne is a key process in the catalytic cycle. KW - enediyne KW - enyne KW - hydroboration KW - organocatalytic KW - stereoselective Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-293784 VL - 28 IS - 63 ER - TY - JOUR A1 - Föhrenbacher, Steffen A. A1 - Krahfuss, Mirjam J. A1 - Zapf, Ludwig A1 - Friedrich, Alexandra A1 - Ignat'ev, Nikolai V. A1 - Finze, Maik A1 - Radius, Udo T1 - Tris(pentafluoroethyl)difluorophosphorane: a versatile fluoride acceptor for transition metal chemistry JF - Chemistry Europe N2 - Fluoride abstraction from different types of transition metal fluoride complexes [L\(_n\)MF] (M=Ti, Ni, Cu) by the Lewis acid tris(pentafluoroethyl)difluorophosphorane (C\(_2\)F\(_5\))\(_3\)PF\(_2\) to yield cationic transition metal complexes with the tris(pentafluoroethyl)trifluorophosphate counterion (FAP anion, [(C\(_2\)F\(_5\))\(_3\)PF\(_3\)]\(^-\)) is reported. (C\(_2\)F\(_5\))\(_3\)PF\(_2\) reacted with trans-[Ni(iPr\(_2\)Im)\(_2\)(Ar\(^F\))F] (iPr2Im=1,3-diisopropylimidazolin-2-ylidene; Ar\(^F\)=C\(_6\)F\(_5\), 1 a; 4-CF\(_3\)-C\(_6\)F\(_4\), 1 b; 4-C\(_6\)F\(_5\)-C\(_6\)F\(_4\), 1 c) through fluoride transfer to form the complex salts trans-[Ni(iPr\(_2\)Im)\(_2\)(solv)(Ar\(^F\))]FAP (2 a-c[solv]; solv=Et\(_2\)O, CH\(_2\)Cl\(_2\), THF) depending on the reaction medium. In the presence of stronger Lewis bases such as carbenes or PPh\(_3\), solvent coordination was suppressed and the complexes trans-[Ni(iPr\(_2\)Im)\(_2\)(PPh\(_3\))(C\(_6\)F\(_5\))]FAP (trans-2 a[PPh\(_3\)]) and cis-[Ni(iPr\(_2\)Im)\(_2\)(Dipp\(_2\)Im)(C\(_6\)F\(_5\))]FAP (cis-2 a[Dipp\(_2\)Im]) (Dipp\(_2\)Im=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) were isolated. Fluoride abstraction from [(Dipp\(_2\)Im)CuF] (3) in CH\(_2\)Cl\(_2\) or 1,2-difluorobenzene led to the isolation of [{(Dipp\(_2\)Im)Cu}\(_2\)]\(^2\)\(^+\)2 FAP\(^-\) (4). Subsequent reaction of 4 with PPh\(_3\) and different carbenes resulted in the complexes [(Dipp\(_2\)Im)Cu(LB)]FAP (5 a–e, LB=Lewis base). In the presence of C6Me6, fluoride transfer afforded [(Dipp\(_2\)Im)Cu(C\(_6\)Me\(_6\))]FAP (5 f), which serves as a source of [(Dipp\(_2\)Im)Cu)]\(^+\). Fluoride abstraction of [Cp\(_2\)TiF\(_2\)] (7) resulted in the formation of dinuclear [FCp\(_2\)Ti(μ-F)TiCp\(_2\)F]FAP (8) (Cp=η\(^5\)-C\(_5\)H\(_5\)) with one terminal fluoride ligand at each titanium atom and an additional bridging fluoride ligand. KW - inorganic chemistry KW - copper KW - nickel KW - phosphoranes KW - titanium KW - weakly coordinating anions Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256665 VL - 27 IS - 10 ER - TY - JOUR A1 - Zapf, Ludwig A1 - Peters, Sven A1 - Bertermann, Rüdiger A1 - Radius, Udo A1 - Finze, Maik T1 - Tricyanoborane‐Functionalized Anionic N‐Heterocyclic Carbenes: Adjustment of Charge and Stereo‐Electronic Properties JF - Chemistry – A European Journal N2 - The 1‐methyl‐3‐(tricyanoborane)imidazolin‐2‐ylidenate anion (2) was obtained in high yield by deprotonation of the B(CN)3‐methylimidazole adduct 1. Regarding charge and stereo‐electronic properties, anion 2 closes the gap between well‐known neutral NHCs and the ditopic dianionic NHC, the 1,3‐bis(tricyanoborane)imidazolin‐2‐ylidenate dianion (IIb). The influence of the number of N‐bonded tricyanoborane moieties on the σ‐donating and π‐accepting properties of NHCs was assessed by quantum chemical calculations and verified by experimental data on 2, IIb, and 1,3‐dimethylimidazolin‐2‐ylidene (IMe, IIa). Therefore NHC 2, which acts as a ditopic ligand via the carbene center and the cyano groups, was reacted with alkyl iodides, selenium, and [Ni(CO)\(_{4}\)] yielding alkylated imidazoles 3 and 4, the anionic selenium adduct 5, and the anionic nickel tricarbonyl complex 8, respectively. The results of this study prove that charge, number of coordination sites, buried volume (%V\(_{bur}\)) and σ‐donor and π‐acceptor abilities of NHCs can be effectively fine‐tuned via the number of tricyanoborane substituents. KW - N-heterocyclic carbene KW - anionic carbene KW - boron KW - cyanoborate KW - imidazolate Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-287200 VL - 28 IS - 39 ER - TY - JOUR A1 - Krämer, Felix A1 - Luff, Martin S. A1 - Radius, Udo A1 - Weigend, Florian A1 - Breher, Frank T1 - NON‐Ligated N‐Heterocyclic Tetrylenes JF - European Journal of Inorganic Chemistry N2 - We report on the synthesis of N‐heterocyclic tetrylenes ligated by the NON‐donor framework 4,5‐bis(2,6‐diisopropylphenyl‐amino)‐2,7‐di‐tert‐butyl‐9,9‐dimethylxanthene. The molecular structures of the germylene (3), stannylene (4) and plumbylene (5) where determined by X‐ray diffraction studies. Furthermore, we present quantum chemical studies on the σ‐donor and π‐acceptor properties of 3–5. Additionally, we report on the reactivity of the tetrylenes towards the transition metal carbonyls [Rh(CO)\(_{2}\)Cl]\(_{2}\), [W(CO)\(_{6}\)] and [Ni(CO)\(_{4}\)]. The isolated complexes (6 and 7) show the differing reactivity of NHTs compared to NHCs. Instead of just forming the anticipated complex [(NON)Sn−Rh(CO)\(_{2}\)Cl], 4 inserts into the Rh−Cl bond to afford [(NON)Sn(Cl)Rh(CO)(C\(_{6}\)H\(_{6}\))] (6, additional CO/C6H6 exchange) and [(NON)Sn(Cl)Rh\(_{2}\)(CO)\(_{4}\)Cl] (7). By avoiding halogenated transition metal precursors in order to prevent insertion reactions, germylene 3 shows “classical” coordination chemistry towards {Ni(CO)3} forming the complex [(NON)Ge−Ni(CO)\(_{3}\)] (8). KW - Germylenes KW - heterocyclic tetrylenes KW - hetrocyclic tetrylene complexes KW - Plumbylenes KW - Stannylenes Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-262586 VL - 2021 IS - 35 SP - 3591 EP - 3600 ER - TY - JOUR A1 - Luis, Werner A1 - Horrer, Günther A1 - Philipp, Michael A1 - Lubitz, Katharina A1 - Kuntze‐Fechner, Maximilian W. A1 - Radius, Udo T1 - A General Synthetic Route to NHC‐Phosphinidenes: NHC‐mediated Dehydrogenation of Primary Phosphines JF - Zeitschrift für anorganische und allgemeine Chemie N2 - The dehydrocoupling of primary phosphines with N-heterocyclic carbenes (NHCs) to yield NHC-phosphinidenes is reported. The reaction of two equivalents of the NHCs Me\(_2\)Im (1,3-dimethylimidazolin-2-ylidene), Me\(_4\)Im (1,3,4,5-tetramethylimidazolin-2-ylidene), iPr\(_2\)Im (1,3-di-iso-propylimidazolin-2-ylidene) and Mes\(_2\)Im (2,4,6-trimethylphenylimidazolin-2-ylidene) with PhPH\(_2\) and MesPH\(_2\) led to the NHC stabilized phosphinidenes (NHC)PAr: (iPr\(_2\)Im)PPh (1), (Mes\(_2\)Im)PPh (2), (Me\(_4\)Im)PPh (3), (Mes\(_2\)Im)PMes (4), (Me\(_2\)Im)PMes (5), (Me\(_4\)Im)PMes (6) and (iPr\(_2\)Im)PMes (7). The reaction of tBuPH\(_2\) with two equivalents of the NHCs afforded the corresponding NHC stabilized parent phosphinidenes (NHC)PH: (iPr\(_2\)Im)PH (8), (Mes\(_2\)Im)PH (9) and (Me\(_4\)Im)PH (10). Reaction of 1 with oxygen and sulfur led to isolation of iPr\(_2\)Im-P(O)\(_2\)Ph (11) and iPr\(_2\)Im-P(S)\(_2\)Ph (12), whereas the reaction with elemental selenium and tellurium gave (NHC)PPh cleavage with formation of (iPr\(_2\)Im)Se (13), iPr\(_2\)ImTe (14) and different cyclo-oligophosphines. Furthermore, the complexes [{(iPr\(_2\)Im)PPh}W(CO)\(_5\)] (15), [Co(CO)\(_2\)(NO){(iPr\(_2\)Im)PPh}] (16) and [(η\(^5\)-C\(_5\)Me\(_2\))Co(η\(^2\)-C\(_2\)H\(_4\)){(iPr\(_2\)Im)PPh}] (17) have been prepared starting from 1 and a suitable transition metal complex precursor. The complexes 16 and 17 decompose in solution upon heating to ca. 80 °C to yield the NHC complexes [Co(iPr\(_2\)Im)(CO)\(_2\)(NO)] and [(η\(^5\)-C\(_5\)Me\(_5\))Co(iPr\(_2\)Im)(η\(^2\)-C\(_2\)H\(_4\))] with formation of cyclo-oligophosphines. The reaction of 1 with [Ni(COD)\(_2\)] afforded the diphosphene complex [Ni(iPr\(_2\)Im)\(_2\)(trans-PhP=PPh)] 18. KW - transition metal complexes KW - N-heterocyclic carbenes KW - phosphinidenes KW - dehydrocoupling Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-258016 VL - 647 IS - 8 ER -