Metallocene Complexes of Iron and Cobalt Derived from the 4,4‘-Bis(η5-cyclopentadienyl)octafluorobiphenyl Ligand1
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The reaction of decafluorobiphenyl with 10 equiv of sodium cyclopentadienide (NaCp) in THF (65 °C, 2 h) afforded 4,4'-bis(cyclopentadienyl)octafluorobiphenyl (1) as a mixture of double-bond isomers in 72% yield after workup and purification. Subsequent treatment with sodium hydride in THF (25 °C, 6 h) afforded disodium 4,4'-bis(cyclopentadienyl)octafluorobiphenyl (2). Reaction of NaCp, ligand 2, and FeBr2 (21:1:10 mol ratio) in THF afforded mostly ferrocene as well as the diiron complex CpFe(η5-C5H4-4,4'-C6F4C6F4-η5-C5H4)FeCp (3), the linear triiron complex Cp[Fe(η5-C5H4-4,4'-C6F4C6F4-η5-C5H4)]2FeCp (4), and the linear tetrairon complex Cp[Fe(η5-C5H4-4,4'-C6F4C6F4-η5-C5H4)]3FeCp (5), which were isolated by liquid chromatography. Solution voltammetric analysis of 3 showed a single, reversible two-electron oxidation at +200 mV, 4 showed two reversible oxidations (2:1 ratio) at +180 and +372 mV, respectively, and 5 showed two reversible oxidations (2:2 ratio) at +192 and +382 mV, respectively (all vs Cp2Fe|Cp2Fe+). A similar reaction of NaCp, ligand 2, and CoBr2 in THF was worked up with air and dilute aqueous HCl followed by aqueous KPF6 to afford a mixture of cobaltocenium hexafluorophosphates, from which [Cp2Co]+PF6- and the dicobalt complex [CpCo(η5-C5H4-4,4'-C6F4C6F4-η5-C5H4)CoCp]2+[PF6-]2 (6) were isolated by liquid chromatography. CV analysis of 6 showed a single, reversible CoII|CoIII wave at +232 mV relative to Cp2Co|Cp2Co+. These voltammetric data suggest that no significant electronic communication exists between two metals bridged by this conjugated dibasic ligand (2). A crystal structure of diiron complex 3 demonstrated the conformational preferences of the CpC6F4C6F4Cp ligand in the solid state with respective torsional angles of 37.5°, 50.1°, and 32.1°.Keywords:
Cyclopentadienyl complex
Sandwich compound
The crystal structures of [Cp' '2UF]2 and [Cp⧧2UO]2 are reported, where Cp' ' is 1,3-(Me3Si)2C5H3 and Cp⧧ is 1,3-(Me3C)2C5H3. Both complexes have idealized C2h symmetry, and their U···U distances are 3.85 and 3.39 Å, respectively. The X-ray absorption spectra of several uranium metallocene complexes, and the numerical results from fitting the EXAFS spectra, are reported. For [Cp⧧2UF]2, the U···U distance was found by EXAFS to be similar to that in [Cp' '2UF]2, implying that [Cp⧧2UF]2 is dimeric. A structural model is advanced that correlates the U···U distance with the orientation of the cyclopentadienyl rings; the orientation is due to a subtle combination of steric repulsions between ligands on the same metal center and between ligands on adjacent metal centers.
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Ethylene was polymerized with cycloalkylidene-bridged cyclopentadienyl metallocene catalysts 1–9 in the presence of methyl aluminoxane (MAO) as the cocatalyst. Unlike the normal titanocene catalysts, the cycloalkylidene-bridged cyclopentadienyl titanocene catalysts show much higher activities than the corresponding zirconocene and hafnocene catalysts and show the highest activities at higher temperature. This indicates that the cycloalkylidene-bridged cyclopentadienyl titanocene system is very thermally stable and maybe a very promising catalyst system for industrial application.
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The ferrocene compound 1-cyclopentadienyl-8-ferrocenylnaphthalene (5) is readily available from 1,8-diiodonaphthalene and is shown to serve as a useful precursor to stacked trinuclear complexes of general structure 1. Two new complexes of this type, an Fe−Co+−Fe (1b) and an Fe−Ti(Cl2)-Fe (1c) triad, in addition to the Fe−Fe−Fe triad (1a) previously prepared, are reported. The crystal structure of 1c has been determined. Individual molecules are shown to adopt chiral conformations in the racemic crystal. Molecular distortions (Cp ring twisting and splaying), which are associated with electronic charge on the Cp rings, are found to be considerably greater in 1c than in 1a.
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A qualitative approach to the understanding of substituent effects in iron(II) sandwich compounds containing five- and six-membered rings is described. In particular, this approach highlights the differences between the symmetric, bis(arene)- and bis(cyclopentadienyl)-, and the asymmetric, mixed arene–cyclopentadienyl-iron(II) complexes. The results are discussed with respect to their chemical and physical properties and 57 Fe Mössbauer spectra.
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Abstract Bis(/75-cyclopentadienyl)-chloro-selenophenolatotitanium (IV), Bis(?75-cyclopentadienyl)-chloro-selenophenolatozirconium (IV), Bis(//5-cyclopentadienyl)-chloro-selenophenolatohafnium (IV), Bis(^5-cyclopentadienyl)-chloro-selenophenolatotungsten(IV), Mass Spectra The metallocene chloro selenophenolates C p;M Cl(SeChH 5) (Cp = ^5-C5H 5; M = Ti, Z r, Hf, W) were prepared by reaction of Cp2MCl2 with equivalent am ounts of LiSeC6H 5, obtained from phenylselenol and «-butyllithium, and were characterized by 'H NM R, IR and MS data. The fragmentation behaviour of the Ti and W derivatives is elucidated by observing m etastable transi tions in the mass spectra.
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Cyclobutadiene
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ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTComplexes with interactions between metals and aliphatic groups of boron compounds. 1. Synthesis and reactivity of (.eta.5-cyclopentadienyl)cobalt .eta.5-1,3-diborolene complexes, a novel type of sandwich compound with a pentacoordinated carbon atom. Molecular structure of (.eta.5-cyclopentadienyl)cobalt 1,3,4,5-tetraethyl-2-methyl-1,3-diborolene. Extended Hueckel and INDO MO studiesJoseph Edwin, Michael C. Boehm, Nicholas Chester, David M. Hoffman, Roald Hoffmann, Hans Pritzkow, Walter Siebert, Klaus Stumpf, and Hubert WadepohlCite this: Organometallics 1983, 2, 11, 1666–1674Publication Date (Print):November 1, 1983Publication History Published online1 May 2002Published inissue 1 November 1983https://pubs.acs.org/doi/10.1021/om50005a033https://doi.org/10.1021/om50005a033research-articleACS PublicationsRequest reuse permissionsArticle Views128Altmetric-Citations60LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts
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