Iron chains: The highly soluble, ferrocene‐containing polymer [‐fc‐B(Mes)‐]n (fc=Fe(C5H4)2, Mes=mesityl), with an average chain length of about 16 repeat units (n=16), is readily accessible by a novel polycondensation reaction starting from fc(BBr2)2 and HSiEt3 (see scheme). The polymer contains three‐coordinate boron centers, which are well‐suited for the promotion of electron delocalization along the polymer chain.

Dinuclear and trinuclear ferrocene complexes {[Fc2BMe2]Li, [Fc-BMe2-fc-BMe2-Fc]Li2, Fc2B(pyind), [Fc2B(bipy)]PF6, [Fc-B(bipy)-fc-B(bipy)-Fc](PF6)2} bearing anionic, uncharged, and cationic four-coordinate boron bridges have been synthesized (Fc: ferrocenyl; fc: 1,1'-ferrocenylene; pyind: 5-fluoro-2-(2'-pyridyl)indolyl; bipy: 2,2'-bipyridyl). The molecular structures of [Fc2BMe2]Li(12-crown-4)2, [Fc-BMe2-fc-BMe2-Fc](Li(12-crown-4)2)2, Fc2B(pyind), and [Fc2B(bipy)]PF6 were determined by X-ray crystallography. The anionic aggregates [Fc2BMe2]- and [Fc-BMe2-fc-BMe2-Fc]2- are very sensitive to air and moisture whereas bromide salts of their cationic counterparts [Fc(2)B(bipy)]+ and [Fc-B(bipy)-fc-B(bipy)-Fc]2+ may be dissolved in water without decomposition. Cyclic voltammograms of the diferrocene species show two well-resolved one-electron transitions separated by 0.21 V ([Fc2BMe2]Li; Eo' = -0.43 V, -0.64 V; vs. FcH/FcH+), 0.18 V (Fc2B(pyind); Eo' = -0.03 V, -0.21 V), and 0.16 V ([Fc2B(bipy)]PF6; Eo' = +0.23 V, +0.07 V), which indicates electronic interactions between the two ferrocenyl substituents. Two redox waves with an intensity ratio of 1:2 are observed in the cyclic voltammograms of the trinuclear derivatives [Fc-BMe2-fc-BMe2-Fc]Li2 and [Fc-B(bipy)-fc-B(bipy)-Fc](PF6)2. In the case of the BMe(2)-bridged species, the electrochemically unique central ferrocenylene unit is oxidized at a much more cathodic potential value (Eo' = -1.21 V) than the two terminal ferrocenyl substituents (Eo' = -0.51 V). The opposite is true in the case of the B(bipy)-bridged trimer where oxidation of the terminal ferrocenyl groups (Eo' = +0.03 V) precedes oxidation of the internal iron atom (Eo' = +0.26 V). The Fe(II)/Fe(III) redox potentials of the mono- and dianionic species differ to a much larger extent from the redox potential of parent ferrocene (Eo' = 0 V) than the Eo' values of the corresponding mono- and dicationic derivatives. Apart from electrostatic interactions, the electrochemical properties of BMe2- and B(bipy)-bridged oligoferrocenes are determined by the pronounced positive inductive effect of triorganoborate substituents together with positive sigma/pi* hyperconjugation on the one hand and ferrocene-to-B(bipy) charge transfer on the other.

No abstract

Optimised synthesis procedures and results of X-ray single crystal structure analyses for 4-(dibromoboryl)toluene, 1,3bis(dibromoboryl)benzene, 1,4-bis(dibromoboryl)benzene, and 1,3,5-tris(dibromoboryl)benzene are reported. These compounds have also been studied by Hartree-Fock (HF), density functional theory (DFT), and Møller-Plesset second-order perturbation (MP2) methods in combination with the polarized double-ζ valence (SVP) and polarized triple-ζ valence (TZVP) basis sets of Ahlrichs and coworkers. A comparison of the quantum chemical results for optimised geometries and computed NMR chemical shifts with experiment is presented to test the quality of the various methods Mehrfach borylierte Arene: Kristallstrukturanalysen and quantenchemische RechnungenInhaltsübersicht. Wir berichten über optimierte Synthesevorschriften und die Ergebnisse der Kristallstrukturanalysen von 4-(Dibromoboryl)toluol, 1,3-Bis(dibromoboryl)benzol, 1,4-Bis(dibromoboryl)benzol und 1,3,5-Tris(dibromoboryl)benzol. Diese Verbindungen wurden weiterhin mittels Hartree-Fock (HF), Dichtefunktionaltheorie (DFT) und Møller-Plesset-Störungstheorie (MP2) in Kombination mit dem polarisierten Double-ζ Valenz-(SVP) und dem polarisierten Triple-ζ Valenzbasissatz (TZVP) von Ahlrichs et al. untersucht. Ein Vergleich der optimierten Geometrien und berechneten NMR-Verschiebungen mit den entsprechenden experimentellen Daten dient als Test für die Qualität der unterschiedli-

Eisenketten: Das leicht lösliche Ferrocen‐haltige Polymer [‐fc‐B(Mes)‐]n (fc=Fe(C5H4)2, Mes=Mesityl) mit einer mittleren Kettenlänge von ca. 16 Wiederholungseinheiten (n=16) lässt sich einfach durch eine neuartige Polykondensation ausgehend von fc(BBr2)2 und HSiEt3 erhalten (siehe Schema). Das Polymer enthält dreifach koordinierte Borzentren, die sich gut für die Elektronendelokalisierung entlang der Polymerkette eignen.