Buten und binnen – wagen und winnen

Editorial zum Tagungsband für den 109. Deutschen Bibliothekartag in Bremen 202

Das Sokoto-Kalifat und seine ethnischen Grundlagen : eine Untersuchung zum Aufstand des ʿAbd as-Salām

von Rainer OsswaldDie Vorlage enth. insgesamt 2 WerkeLiteraturverz. S. 159 - 164Text teilw. dt., teilw. arab.O

Katalog der arabischen Handschriften in Mauretanien

bearb. von U. Rebstock, R. Osswald und A. Wuld-ʿAbdalqādirText dt. und arab

Buten un binnen - wagen un winnen: 109. Deutscher Bibliothekartag, Bremen 2021

Sammelband mit ausgearbeiteten Kongressbeiträgen vom 109. Deutschen Bibliothekartag, Bremen 202

Extremely Electron-Poor Bis(diarylmethylium)-Substituted Ferrocenes and the First Peroxoferrocenophane

We have prepared and studied extremely electron‐poor, deeply colored dicationic 1,1'‐bis(diarylmethylium)‐substituted ferrocenes [(η5‐C5H4‐CAr2)2Fe]2+ with various aryl substituents as their [B{C6H3(CF3)2‐3,5}4]– salts. Due to the strong acceptor substitution, the redox potential for the ferrocene‐based oxidation of the anisyl‐ or 2‐methylanisyl‐substituted congeners 1b2+ and 1c2+ is close to or even surpasses that of the second oxidation of parent ferrocene, i.e. the Cp2Fe+/2+ couple. The strongly Lewis‐acidic character of these complexes is manifest through strong interactions with donor solvents, which lead to a significant reduction of the intensities of the charge‐transfer bands in their electronic spectra and to solvatochromism. The reduced forms of the complexes tend to dimerize or oligomerize as revealed by EPR spectroscopy. Direduced 1b selectively reacts with molecular oxygen to form a peroxo‐bis(diarylmethyl)[4]ferrocenophane, which was also characterized by X‐ray crystallography.publishe

A Stable Planar-Chiral <i>N</i>‑Heterocyclic Carbene with a 1,1′-Ferrocenediyl Backbone

This paper focuses on the stable, ferrocene-based <i>N</i>-heterocyclic carbene (NHC) <i>rac</i>-[Fe­{(η⁵-<i>t-</i>BuC₅H₃)­NpN}₂C:] (<b>A′-Np</b>, Np = neopentyl), which is planar-chiral due to the two <i>tert</i>-butyl substituents in 3,3′-positions. <b>A′-Np</b> was synthesized in nine steps starting from 1,1′-di-<i>tert</i>-butylferrocene (<b>1</b>), the first step being its 3,3′-dilithiation to afford <i>rac</i>-[Fe­(η⁵-<i>t</i>-BuC₅H₃Li)₂] (<i>rac</i>-fc′Li₂, <b>2</b>). The structures of <i>rac</i>-fc′(SiMe₃)₂ (<b>3</b>), <i>rac</i>-fc′Br₂ (<b>4</b>), <i>rac</i>-fc′(N₃)₂ (<b>5</b>), and the immediate carbene precursor [<b>A′-Np</b>H]­BF₄ were determined by single-crystal X-ray diffraction (XRD). The chemical properties of <b>A′-Np</b> were found to be very similar to those of its <i>tert</i>-butyl-free congener <b>A-Np</b>, both being ambiphilic NHCs with rather high calculated HOMO energies (ca. −4.0 eV) and low singlet–triplet gaps (ca. 35 kcal/mol). A Tolman electronic parameter value of 2050 cm^–1 was derived from IR data of <i>cis</i>-[RhCl­(<b>A′-Np</b>)­(CO)₂], indicating the high donicity of <b>A′-Np</b> as a ligand. Consistent with its ambiphilic nature, <b>A′-Np</b> was found to react readily with carbon monoxide, affording the betainic enolate (<b>A′-Np</b>)₂CO as four stereoisomers, viz. (<i>R</i>_p<i>R</i>_p-<b>A′-Np</b>)C­(O^–)­(<i>R</i>_p<i>R</i>_p-<b>A′-Np</b>⁺), (<i>S</i>_p<i>S</i>_p-<b>A′-Np</b>)C­(O^–)­(<i>S</i>_p<i>S</i>_p-<b>A′-Np</b>⁺), (<i>R</i>_p<i>R</i>_p-<b>A′-Np</b>)C­(O^–)­(<i>S</i>_p<i>S</i>_p-<b>A′-Np</b>⁺), and (<i>S</i>_p<i>S</i>_p-<b>A′-Np</b>)C­(O^–)­(<i>R</i>_p<i>R</i>_p-<b>A′-Np</b>⁺). The former two isomers were structurally characterized as a racemic compound by single-crystal XRD. <b>A′-Np</b> was found to react swiftly with dichloromethane, affording the addition product <b>A′-Np</b>H–CHCl₂ in a reaction that is unprecedented for diaminocarbenes. <b>A-Np</b>H–CHCl₂ was obtained analogously. Both compounds were structurally characterized by single-crystal XRD. An electrochemical investigation of <b>A′-Np</b> by cyclic and square wave voltammetry revealed a reversible oxidation of the carbene at a half-wave potential of −0.310 vs ferrocene/ferrocenium (THF/NBu₄PF₆). The electrochemical data previously published for <b>A-Np</b> were identified to be incorrect, since unnoticed hydrolysis of the NHC had taken place, affording <b>A-Np</b>(H₂O). The hydrolysis products of <b>A-Np</b> and <b>A′-Np</b> were found to be reversibly oxidized at half-wave potentials of −0.418 and −0.437 V, respectively