19 research outputs found

    Acceptor-Substituted Cyclopentadienyl Compounds

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    Efficient methodologies for the synthesis of acceptor-substituted perfunctionalized cyclopentadienyl (Cp) compounds were investigated. A facile multigram, one-pot synthesis of [FeC10(HgO2CC3H7)10] from ferrocene and Hg(O2CC3H7)2 is reported. In the corresponding compound, the Hg-C bonds are inert towards oxygen, moisture and even strong Brønsted acids like trifluoroacetic acid and [C5F5NH][SbF6]. Instead, protonation of the carboxylic groups is observed yielding [FeC10(HgO2CCF3)10] and [FeC10Hg10(C5F5N)n][SbF6]10. In the compound [FeC10Hg10(C5F5N)n][SbF6]10, the labile C5F5N ligands are readily displaced by MeCN or tetrahydrothiophene (THT) to afford rare examples of organometallic decacations [FeC10(HgL)10][SbF6]10 (L = MeCN, THT). Electrochemical investigations on the (soluble) permercurated compounds reveal increasing redox potentials of the corresponding Fe(II)/Fe(III) redox couples with increasing Lewis acidity of the Hg-sites. The isolation of the oxidized forms was realized by reaction with [NO]+ or [NO2]+ salts or MoF6. Furthermore, the first crystallographic characterization of permetalated aromatic compounds [FeC10(HgX)10] (X = Cl, O2CCF3, O2CCCl3), [FeC10(HgTHT)10][SbF6]10 and [FeC10(HgMeCN)10][SbF6]10[MoF6] is presented. Complete halodemercuration is observed in the reaction of [FeC10(HgO2CC3H7)10] with K[Br3] followed by halogenation with FeBr3 and elemental Br2. An oxidation potential of E1/2 = 1.1V renders the corresponding ferrocenium cation as potent oxidizing agent. The isolation is realized by reaction of [FeC10Br10] with AsF5. Further functionalization of [FeC10Br10] is achieved by metalation with elemental Mg or by lithium-halogen-exchange with tBuLi. Quenching experiments with dimethylsilylchloride (DMSCl) yielded polysilylated compounds. Full functionalization was achieved after multiple metalation-silylation sequences. The resulting product [FeC10DMS10] displays the first example of a persilylated metallocene. A series of polysilylated derivatives [FeC10DMSnH10-n] (n = 7, 8, 9, 10) is analyzed by CV, single-crystal XRD, NMR and UV/VIS spectroscopy to evaluate the effect of silylation on the electronic properties of metallocenes. The obtained data are supported by quantum-chemical calculations. In the context of perhalogenated Cp compounds, the reaction of C5X6 (X = Cl, Br) with AsF5 and SbF5 is investigated. Here, the formation of unprecedented [2+2]-cycloaddition products of two Cp cations [C5X5]+ is observed. The obtained dications [C10X10]2+ are analyzed by XRD and NMR spectroscopy. DFT calculations reveal that the dimerzation to [2+2]- instead of [2+4]-products is thermodynamically preferred due to the formation of two allylic p-electron systems. Furthermore, in cooperation with the group of Prof. Dr. Schulz the electrochemical properties of [C5(C6F5)5]+ are presented

    Investigation of Halogenate Complexes Stabilized by Fluorido, Chlorine Monofluoride, and Perfluoro-tert-Butoxy Ligands

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    The synthesis and follow-up chemistry of classical and non-classical fluoridochlorates and -bromates is investigated. Here, an efficient synthetic method for the synthesis of soluble di- and tetrafluoridohalogenates(I/III) of bromine and chlorine is presented. Tetraalkylammonium halides are fluorinated with dilute fluorine or chlorine monofluoride (10 % in Ar) in acetonitrile or propionitrile. For the first time, difluoridochlorate(I) and -bromate(I) salts are fully characterized by Raman and NMR spectroscopy as well as by single crystal X-ray diffraction. The data are supported by quantum-chemical calculations. Their potential application as halogenation reagents is studied with different organic and inorganic substrates. These include nitriles and tetracyanoborate which reacted to their corresponding trifluoromethyl compounds, diaryldisulfides were fully fluorinated to pentafluorosulfanyl aryls, noble metals dissolved under formation of fluorido- and bromido metallates and the reaction with carbon monoxide yielded carbonyl fluoride. Furthermore, these compounds are used as substrates in ligand exchange reactions with perfluoro-tert-butyl hypochlorite to install the perfluoro-tert-butoxy ligand on a positively charged halogen atom. The isolation of halogen(I) species with this ligand was possible for chlorine, bromine and iodine, while the oxidation state +III was only reached for bromine and iodine. During the attempted synthesis of a Cl(III) compound, ligand oxidation under formation of perfluoro-tert-butyl hypofluorite and -peroxide was observed. The steric bulk of the ligands in tetrakis(perfluoro-tert-butoxy)iodate(III) effectively shields the iodine center from further oxidation with dilute fluorine. Additionally, the non-classical polyinterhalide [F(ClF)3]– was synthesized from the reaction of tetramethylammonium chloride with an excess of chlorine monofluoride. This compound was thoroughly characterized by Raman spectroscopy and single crystal X-ray diffraction, supported by quantum-chemical calculations. Surprisingly, its calculated global minimum structure is trigonal planar with D3h symmetry instead of the trigonal pyramidal C3v symmetric structure, which is predicted by the VSEPR model and also found in several other polyhalides and -interhalides. The structure giving factor is traced back to the central fluorine atom and its unique electronic properties.Es wird eine effiziente Synthese für organisch lösliche Tetrafluoridohalogenate(I/III) von Brom und Chlor vorgestellt. Dabei werden Tetraalkylammoniumhalogenide mit verdünntem Fluor oder Chlormonofluorid (10 % in Ar) in Acetonitril oder Propionitril fluoriert. Erstmalig wurden Difluoridochlorat(I) und Difluoridobromat(I)-Salze vollständig mittels Raman- und NMR-Spektroskopie sowie Einkristall-Röntenbeugung untersucht. Sämtliche Daten sind durch quantenchemische Berechnungen gestützt. Die Reaktivitäten der Verbindungen wurden anhand von organischen und anorganischen Substraten eruiert. Dabei wurden Nitrile und Tetracyanidoborat in die entsprechenden Trifluoromethylverbindungen überführt, Diaryldisulfide reagierten zu Pentafluorsulfanylarylen, Edelmetalle lösten sich unter Bildung von Fluorido- und Bromidometallaten auf und Kohlenstoffmonoxid reagierte zu Carbonylfluorid. Weiterhin wurden diese Verbindungen als Edukte in Ligandenaustauschreaktionen mit Perfluoro-tert-butylhypochlorit verwendet, um den Perfluoro-tert-butoxyliganden am positiv geladenen Halogenzentrum einzuführen. Mit diesem Liganden konnten Halogen(I)-Verbindungen von Chlor, Brom und Iod isoliert werden, wobei die Oxidationsstufe +III lediglich für Brom und Iod erreicht werden konnte. Während der Syntheseversuche einer Cl(III)-Spezies wurde der Ligand oxidiert unter Bildung von Perfluoro-tert-butylhypofluorit und -peroxid. Der sterische Anspruch des Liganden in Tetrakis(perfluoro-tert-butyl)iodat(III) verhinderte die Oxidation des Iodzentrums mittels verdünntem Fluor. Schlussendlich wurde das nicht-klassische Polyinterhalogenid [F(ClF)3]– ausgehend von Tetramethylammoniumchlorid und einem Überschuss Chlormonofluorid synthetisiert. Die Substanz wurde mittels Raman-Spektroskopie und Röntgenbeugung am Einkristall charakterisiert, sowie quantenchemisch untersucht. Überraschenderweise wurde eine trigonal-planare Struktur mit D3h-Symmetrie als globale Minimumsstruktur berechnet, anstelle der vom VSEPR Modell vorhergesagten und in zahlreichen anderen Poly- und Polyinterhalogeniden gefundenen trigonal-pyramidalen, C3v-symmetrischen Struktur. Das zentrale Fluoratom konnte auf Grund seiner einzigartigen elektronischen Eigenschaften als Ursache für die unterschiedliche Struktur ausgemacht werden

    Exploring sustainability in fluorine methodologies

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    The fluorination of organic compounds is extremely important to the modern world, especially within the chemical sciences, however as we transition to a more sustainable future, current industrial fluorination methodologies grow increasingly unsuitable towards the preparation of these fluorinated molecules, especially from an energy and materials perspective. To address this new fluorination, defluorination and fluorine transfer methodologies have been developed with a focus on improved sustainability over traditional fluorination techniques. This thesis explores new methodologies to control the reactivity of fluorine: from the enhancement of reactivity of metal fluoride salts, one of the more sustainable sources of fluorine available, through the treatment with organometallic complexes; to the activation of fluorine within perfluorinated organic moieties, enabling the selective transfer of fluorine between two organic substrates, providing the potential of utilising waste sources of fluorine as feedstocks in the future. A series of group 9 organometallic complexes were targeted and synthesised, to investigate their catalytic fluorination potential upon treatment with metal fluoride salts. Treatment of these complexes bearing fluorinated ligands with silver oxide resulted in the formation of a new class of cyclometallated and orthometallated rhodium and iridium complexes, providing new catalytic targets for the fluorination of organic electrophiles. The fluorination potential of transition metal fluoride complexes upon treatment with acyl chlorides was examined, providing first evidence of nucleophilic fluorination from [RhF(CO)(PPh3)2]. The catalytic fluorination of acyl chlorides with [(η5,κ2C-C5Me4CH2C6F5CH2NC3H2NMe)- RhCl] was investigated, utilising metal fluoride salts as the fluorine source, affording the quantitative fluorination of a range of electron deficient and electron rich acyl chlorides under mild conditions. A procedure for catalyst recovery, regeneration and reuse was established. In-situ FTIR analysis and variable time normalised analysis of this catalytic fluorination procedure gave further insights into this catalytic reaction enabling a plausible mechanism to be proposed. A transfer fluorination reaction was developed through the treatment of [(η5,κ2C-C5Me4CH2C6F5CH2NC3H2NMe)-RhCl] 22, and organic electrophiles in the absence of an external fluorine source, resulting in the formation of a bimetallic rhodacycle and a new fluorinated product. Multi-spectral analysis provided an understanding of the environment required to generate nucleophilic fluorine within the perfluorinated ligand, enabling the transfer of fluorine to occur between the perfluorinated group and an organic electrophile via C−F bond activation. The transfer of fluorine was tracked in real time using in-situ IR analysis The synthesis of functionalised partially fluorinated heteroarenes was investigated through the defluorination of pentafluoropyridine. A catalytic transfer fluorination protocol was adapted enabling fluorine transfer from pentafluoropyridine to benzoic anhydride. Additionally, the catalytic selective mono-defluorination and hydrodefluorination of pentafluoro-pyridine was achieved using commercially available group 8 and 9 catalysts

    SYNTHESIS AND STUDY OF THE REACTIVITY OF CAGE MOLECULES WITH ENFORCED SHORT CONTACTS BETWEEN VARIED FUNCTIONAL GROUPS

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    Cage molecules have long been employed to trap reactive or fleeting species, as their rigid nature allows them to enforce situations that otherwise would not persist. We have employed rigid cage structures to investigate the close noncovalent interactions of fluorine and oxygen with other functional groups and determine how mutual proximity affects both physical properties and chemical reactivity. Interaction of fluorine and an arene ring induces unexpected anisotropic deshielding of the fluorine nucleus, and dramatically increases the rate of reaction of the perturbed ring to electrophilic aromatic substitution. This effect is even stronger when the fluorine is replaced with a hydroxyl group, capable of overriding the effects of strong deactivating groups covalently bound to the ring. Interaction of fluorine and a ketone results in unusual electronic distortions about the fluorine atom and a blue-shift of the carbonyl stretch. When a hydroxyl group is placed in proximity of a nonconjugated alkene, a very strong red-shift in the OH stretching frequency is observed, and the hydrogen atom becomes ‘trapped’ in the molecule and will not exchange. Unusual covalent interactions of fluorine are also explored: the cage can close to form the first solution-phase C-F-C fluoronium ion, which is first investigated as a reactive intermediate and later observed as a stable entity

    Azidoperfluoroalkany: Syntéza a Aplikace

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    Zavedení trifluormethylové a perfluoralkylové skupiny do organických molekul představuje jedno z hlavních témat syntetické organofluorové chemie. Existuje řada metod pro zavedení CF3 skupiny na atom uhlíku, kyslíku a síry. Naopak metody pro syntézu N-trifluor-methylovaných a N-perfluoralkylovaných sloučenin jsou velmi omezené a vývoj nových přístupů k jejich syntéze je vysoce žádaný. Nedostatek těchto sloučenin nás vedl k vývoji činidel schopných přenosu perfluoralkylové skupiny na atom dusíku, kde jsme jako vhodná činidla zvolili azidoperfluoralkany. Tato práce se zabývá syntézou a aplikací perfluoralkylazidů. První část popisuje přípravu azidoperfluoralkanů. Po aktivaci fluoridem cesným může TMSCF3 přenést trifluormethylovou skupinu na elektrofilní azid za vzniku žádaného azidotrifluormethanu. Azidoperfluoralkany s delším uhlíkatým řetězcem byly připraveny podobným způsobem vycházejícím z příslušného organosilanu. Rozdílný syntetický přístup byl použit pro přípravu azidoperfluorethanu, kde byl při reakci pentafluorethanu s n BuLi generován perfluorethylový anion, k němuž byl následně přidán tosylazid. Fluorované azidy byly izolovány pomocí destilace s vhodným rozpouštědlem. Druhá část se zabývá syntetickým potenciálem azidoperfluoralkanů. Tyto azidy vykazovaly velkou reaktivitu v azido-alkynových...The incorporation of the trifluoromethyl and perfluoroalkyl motifs into organic compounds has been a hot topic in synthetic organofluorine chemistry. There is a plethora of methods for the introduction of the CF3 moiety at carbon, oxygen and sulfur centers. In sharp contrast, methods for synthesizing N-trifluoromethyl and N-perfluoroalkyl compounds are very limited and new approaches are highly sought-after. The scarcity of these compounds prompted us to develop reagents capable of transferring the perfluoroalkyl unit to nitrogen atom. To fulfil this purpose, we have regarded azidoperfluoroalkanes as ideal reagents, therefore, this thesis is concerned with the synthesis and applications of these azides. The first part describes the preparation of azidoperfluoroalkanes. Upon activation by cesium fluoride, TMSCF3 transfers the trifluoromethyl group to an electrophilic azide to produce the desired azidotrifluoromethane. Longer carbon chain azidoperfluoroalkanes were prepared in a similar way, starting from the corresponding organosilane. A different synthetic strategy was applied for the preparation of azidopentafluoroethane where the perfluoroalkyl anion was generated from pentafluoroethane with n BuLi, followed by the addition of tosyl azide. The isolation of these fluorinated azides was...Department of Organic ChemistryKatedra organické chemieFaculty of SciencePřírodovědecká fakult

    Recognition processes based on molecular cages and tripodal receptors

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    Questa tesi di dottorato riguarda la sintesi e lo studio di nuovi sistemi molecolari, tripodali e a forma di gabbia, adatti per il riconoscimento di specie ioniche in soluzione. Questi leganti, dotati di un’elevata preorganizzazione, presentano una maggiore selettività nel riconoscimento molecolare rispetto ai sistemi lineari. Il riconoscimento host:guest è basato su una sinergia di interazioni: elettrostatiche, legame a idrogeno e ad alogeno e coordinazione a centri metallici

    A New Dimension in Fluorine Chemistry: Fluorine in Close Interactions

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    This work attempts to shed some light on some of the fundamental chemistry utilized by C-F bonds in organofluorine compounds, with special care to noncovalent interactions. A fluorinated sesquinorbornane scaffold was the template for the majority of the studies owing to its rigid conformation and ability to be modified. Thanks to those two attributes, the properties of C-F bonds were observed under various conditions in a multitude of different conformations. Through that work, the C-F bond was observed to take part in SN1 reactions through anchimeric assistance. Even more interesting is the anchimeric assistance is facilitated through a positively charged fluoronium intermediate. In addition, the conformation of the scaffold, allows other functional groups to be placed in close proximity to the C-F bond. After making a series of molecules with different functional groups, the through-space interaction of the C-F bond with the proximal C-H was investigated. A correlation between proton-fluorine coupling constants and the interaction’s strength was observed. The positioning also allowed the observation of a strong hydrogen bonding interaction between the fluorine and an alcohol. While the hydrogen bond appears strong by most spectroscopic methods, IR spectroscopy shows little to no shift when compared to a control molecule. This appears to be a rare case of bond compression from steric strain cancelling out bond relaxation from hydrogen bonding, a so called “no-shift” bond. In an attempt to be sure our system can be used to generate hydrogen bonds, a hydrogen bond between an alcohol and a nonconjugated pi-system was investigated. Owing to the reduction of steric strain in the molecule a strong hydrogen bond was observed accompanied by a characteristic red shift in the IR spectrum. Interestingly the red shift was nearly 189 cm-1, which is much larger than other observed examples of this type of interaction. In order to bolster our claims about a fluoronium ion intermediate, an in depth investigation into the reactivity of the fluoronium system was reported. This was done through several rate studies, control reactions and isotopic labeling experiments. All of which indicate that the fluoronium is the most likely intermediate. Finally another example of fluorine acting as a directing group was investigated. Specifically, a C-F bond was found to influence a Diels-Alder reaction between a fluorinated dienophile and a borole so that one product was favored to a substantial degree

    The Halogen Bond

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    The halogen bond occurs when there is evidence of a net attractive interaction between an electrophilic region associated with a halogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. In this fairly extensive review, after a brief history of the interaction, we will provide the reader with a snapshot of where the research on the halogen bond is now, and, perhaps, where it is going. The specific advantages brought up by a design based on the use of the halogen bond will be demonstrated in quite different fields spanning from material sciences to biomolecular recognition and drug design

    Wechselwirkungen kleiner fluorhaltiger Moleküle unter kryogenen Bedingungen

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