160 research outputs found
Synthesis of a new bowl-shaped polyarene aiming
Efficient hydrogen storage is one of the major hurdles towards a potential hydrogen economy. Curved molecules are very interesting for this purpose because of their permanent electrical dipole moment, which can induce a dipole moment on H2 molecules increasing therefore the dipole-dipole interaction and so their adsorption. This work presents the synthesis of a new bowl-shaped polyarene based on curved corannuleneâs motive. Since corannulene is known for its ability to adsorb hydrogen, the greater surface and curvature of our target molecule is assumed to increase the hydrogen adsorption. The plan was to start from phenanthrene-9,10-dione and 1-phenylpropan-2-one to obtain a planar polycyclic aromatic hydrocarbon (PAH) containing a five-membered ring. Then, via a crosscoupling reaction and a classical Scholl reaction under Kovacic conditions, it would have been possible to obtain the bowl-shaped molecule. Unfortunately, the synthesis of the first precursor presented obstacles and, from three proposed strategies, only one allowed the obtainment of the planar PAH in acceptable yield. Moreover, only one attempt for the coupling reaction was made and, because of the small amount and the impurity of the obtained product, no Scholl reaction was performed. Therefore, the desired bowl-shaped polyaromatic compound has not been obtained and the efficacy of the Scholl reaction for this synthesis has not been tested
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Dialoging A Successful Pedagogy for Embedded Tutors
Over the past three years, Rider Universityâs Student Success Center Writing Lab has implemented an embedded tutor program for composition courses. Tutors attend class, participate in class discussions, facilitate writing workshops in class, and hold drop-in hours for students (in addition to tutorsâ Writing Lab hours). The Embedded Tutor (ET) program, facilitated by Jenny Scudder (who is also the Writing Lab Director), has been successful in helping students complete skills-based courses and connect to academic support services. Initial assessment of the ET program supports the inclusion of the tutor in a skills-based course. While an ETâs training is similar to a tutor who works solely in the Writing Lab, there are key additions that are vital to the tutorsââand the programâsâsuccesUniversity Writing Cente
Development of iron catalysts for hydrogenation and polymerization
Im Rahmen der vorliegenden Arbeit wurden eine Reihe von neuen, einfach herzustellenden Eisenhydrierkatalysatoren eingefĂŒhrt. Verschiedenste Aspekte dieser neuen Hydrierkatalysatoren wie Eisenquelle, Aktivierungsmittel, Substrate und Effizienz wurden untersucht. Ein ligandfreier Katalysator, hergestellt aus einer Eisen(II)chlorid-Suspension aktiviert mit Diisobutylaluminiumhydrid (DIBAH), weist die grösste AktivitĂ€t auf. Alle Arten von C-C-Doppelbindungen wie mono-, di- oder trisubstituierte, acyclische oder cyclische, isolierte oder konjugierte Doppelbindungen sowie Alkine werden von diesem Katalysator unter milden Bedingungen (3 bar Wasserstoffdruck, Raumtemperatur) in kurzer Zeit quantitativ hydriert. Sowohl TON wie auch TOF steigen mit zunehmender Menge Aktivierungsmittel, bis bei einem VerhĂ€ltnis FeCl2/DIBAH 1:8 mit TON = 1900 und TOF = 125 h-1 der effizienteste Katalysator erhalten wird. Mit Ausnahme von Ethern und Aminen verhindert die Verwendung eines starken Reduktionsmittels zur Aktivierung die Hydrierung von funktionalisierten Olefinen. In Abwesenheit von Wasserstoff H2 konnte katalytische AktivitĂ€t fĂŒr Alkinpolymerisierungs- und Alkincyclotrimerisierungsreaktionen nachgewiesen werden. Ferner kann dieser Katalysator zur Polymerisierung von Acetylen eingesetzt werden. Bei dem Versuch, die in diesen FĂ€llen katalytisch aktive Spezies zu identifizieren fand man einen homogenen PrĂ€katalysator, welcher erstaunliche Effizienz aufweist (TOF > 340 h-1). Abgeleitet von der angenommenen Struktur dieses PrĂ€katalysators wurden eine Reihe von Allylbenzylether synthetisiert, welche als Liganden getestet wurden. Die entsprechenden Katalysatoren, erhalten durch Aktivierung mit Alkyllithiumreagenzien, weisen Alkenhydrier- und EthylenoligomerisierungsaktivitĂ€t auf.In the scope of this work, a series of new, easy to prepare iron hydrogenation catalysts have been introduced. Different aspects of this new hydrogenation catalysts such as iron source, activation reagent, substrates and efficiency were investigated. A ligand-free catalyst, prepared from an iron(II) chloride suspension activated with diisobutylaluminiumhydride (DIBAH), showed the highest activity. With this catalyst all kind of C-C double bonds like mono-, di- or trisubstituted, acyclic or cyclic, isolated or conjugated double bonds as well as alkynes were hydrogenated quantitatively under mild conditions (3 bar hydrogen pressure, room temperature) within short time. Both TON and TOF scale with the added amount of activation reagent up to a 1:8 FeCl2/DIBAH ratio furnishing the most active catalyst with TON = 1900 and TOF = 125 in this case. With the exception of ethers and amines, the use of strong reducing agents as activators prevents the hydrogenation of functionalized olefins. In absence of hydrogen H2, catalytic activity for alkyne polymerization and cyclotrimerization was observed. Furthermore, this catalyst is able to promote the polymerization of acetylene. Attempts to identify the catalytic active species led to the development of a homogeneous precatalyst showing an amazing efficiency (TOF > 340 h-1). Derived from the assumed structure of this precatalyst, a series of allylbenzylethers were synthesized and tested as ligands. The corresponding catalysts, obtained by activation with alkyllithium reagents, display alkene hydrogenation and ethylene oligomerization activity
Hexa-peri-hexabenzocoronenes â Controlling their Self-Assembly by Engineering the Lateral Substituents
Polycondensed aromatic hydrocarbons (PAH), which can be regarded as two-dimensional subsections of graphite, have begun to attract increasing interest in supramolecular chemistry. Substituted hexa-peri-hexabenzocoronenes (HBC), an outstanding class of PAH, are well-known to self-organize
in solution into highly ordered columnar molecular stacks. The formed structures are very sensitive to any variation of the medium as well as the lateral substituents of the HBC derivatives. Various perfluoroalkylated HBC compounds have been prepared and investigated by powder XRD, DSC, fluorescence
and cryo-SEM in order to gain certain control over the self-assembling behavior of this class of compounds
Reactivity of Allenes towards Iron Carbonyl Complexes
A series of monosubstituted allenes was reacted with Fe2(CO)9 to give dinuclear iron-carbonyl complexes containing organic ligands derived either from monomeric or dimerized allene. A mechanism of formation is proposed based on isolated intermediates. These intermediates point to an allene dimerization via addition of a reactive allene iron complex to free allene. Unusual chemical shifts were observed for many resonances in the 1H- and 13C-NMR spectra of the new compounds
Synthesis of perfluoroalkylated bulky triarylamines
The synthesis of two new triarylamine compounds bearing perfluoroalkylated side chains is described. Good thermal stabilities combined with a blue emission make these compounds promising candidates for materials applications
Crystal structures of <i>trans</i>-diÂchloridoÂtetraÂkisÂ[1-(2,6-diisoÂpropylÂphenÂyl)-1<i>H</i>-imidazole-Î<i>N</i>Âł]iron(II), <i>trans</i>-diÂbromidoÂtetraÂkisÂ[1-(2,6-diisoÂpropylÂphenÂyl)-1<i>H</i>-imidazole-Î<i>N</i>Âł]iron(II) and <i>trans</i>-diÂbromidoÂtetraÂkisÂ[1-(2,6-diisoÂpropylÂphenÂyl)-1<i>H</i>-imidazole-Î<i>N</i>Âł]iron(II) diethyl ether disolvate
The title compounds, [FeClâ(Cââ
HââNâ)â], (I), [FeBrâ(Cââ
HââNâ)â], (II), and [FeBrâ(Cââ
HââNâ)â]·2CâHââO, (IIb), respectively, all have triclinic symmetry, with (I) and (II) being isotypic. The FeII atoms in each of the structures are located on an inversion center. They have octaÂhedral FeXâNâ (X = Cl and Br, respectively) coordination spheres with the FeII atom coordinated by two halide ions in a trans arrangement and by the tertiary N atom of four arylÂimidazole ligands [1-(2,6-diisoÂpropylÂphenÂyl)-1H-imidazole] in the equatorial plane. In the two independent ligands, the benzene and imidazole rings are almost normal to one another, with dihedral angles of 88.19 (15) and 79.26 (14)° in (I), 87.0 (3) and 79.2 (3)° in (II), and 84.71 (11) and 80.58 (13)° in (IIb). The imidazole rings of the two independent ligand molÂecules are inclined to one another by 70.04 (15), 69.3 (3) and 61.55 (12)° in (I), (II) and (IIb), respectively, while the benzene rings are inclined to one another by 82.83 (13), 83.0 (2) and 88.16 (12)°, respectively. The various dihedral angles involving (IIb) differ slightly from those in (I) and (II), probably due to the close proximity of the diethyl ether solvent molÂecule. There are a number of C-H***Missing image substitution***halide hydrogen bonds in each molÂecule involving the CH groups of the imidazole units. In the structures of compounds (I) and (II), molÂecules are linked via pairs of C-H...halogen hydrogen bonds, forming chains along the a axis that enclose RâÂČ(12) ring motifs. The chains are linked by C-H...Ï interÂactions, forming sheets parallel to (001). In the structure of compound (IIb), molÂecules are linked via pairs of C-H...halogen hydrogen bonds, forming chains along the b axis, and the diethyl ether solvent molÂecules are attached to the chains via C-H...O hydrogen bonds. The chains are linked by C-H...Ï interÂactions, forming sheets parallel to (001). In (I) and (II), the methyl groups of an isopropyl group are disordered over two positions [occupancy ratio = 0.727 (13):0.273 (13) and 0.5:0.5, respectively]. In (IIb), one of the ethyl groups of the diethyl ether solvent molÂecule is disordered over two positions (occupancy ratio = 0.5:0.5)
Novel iron tweezers complexes for hydrogenation and polymerization of olefins
Lâutilisation des complexes organomĂ©talliques comme catalyseurs est devenu un domaine trĂšs important de la chimie des matĂ©riaux. Cependant et malgrĂ© ce dĂ©veloppement, les catalyseurs Ă base de fer(II) sont peu employĂ©s dans la polymĂ©risation dâolĂ©fines. Un de rares catalyseur utilisĂ© dans ce contexte est le complexe tridentĂ© diimine pyridine dĂ©veloppĂ© par Gibson et Brookhart. Cependant ce modĂšle souffre par son manque de tolĂ©rance envers le moindre changement effectuĂ© dans son enveloppe, rĂ©sultant par une diminution drastique de son activitĂ© catalytique. Le but de ce travail est de synthĂ©tiser des catalyseurs de fer(II) contenant des ligands chelates et dâĂ©tudier leur utilisation dans la polymĂ©risation dâolĂ©fines. Il est important de signaler que des travaux prĂ©cĂ©dents dans notre groupe on montrĂ© une trĂšs bonne corrĂ©lation entre la polymĂ©risation et lâhydrogĂ©nation dâolĂ©fines. Ainsi nous avons aussi exploitĂ© lâhabilitĂ© de nos complexes dans lâhydrogĂ©nation. Deux projets ont Ă©tĂ© menĂ©s en parallĂšle : il sâagit de la synthĂšse de complexes de fer(II) contenant dâun cĂŽtĂ© le ligand benzylĂ©therfurane et de lâautre cĂŽtĂ© les ligands carbenes bisimidazol-2-ylidene. Le complexe de fer(II) benzyletherfurane a Ă©tĂ© employĂ© avec succĂšs dans lâhydrogĂ©nation dâolĂ©fines sous des conditions trĂšs douces (1-3 bar dâhydrogĂšne et Ă tempĂ©rature ambiante), cependant son emploi comme catalyseur de polymĂ©risation dâolĂ©fines nâa pas donnĂ© les rĂ©sultats escomptĂ©s. Compte tenu de ceci, ce projet Ă Ă©tĂ© mis Ă cĂŽtĂ© au profit des complexes de fer(II) bisimidazol-2-ylidene qui eux ont montrĂ© une bonne activitĂ© dans les deux rĂ©actions, polymĂ©risation et hydrogĂ©nation des olĂ©fines sous des conditions douces. Durant la prĂ©paration de ces prĂ©catalyseurs, plusieurs autres complexes de fer(II) et fer(III) ont Ă©tĂ© isolĂ© comme Ă©tant des produits secondaires de la rĂ©action. Dans le but de caractĂ©riser les produits obtenus, nous avons aussi prĂ©parĂ© plusieurs dĂ©rivĂ©s en introduisant des ligands supplĂ©mentaires dans la sphĂšre de coordination; câest ainsi que des dĂ©rivĂ©s formiate, carboxylate, triflate et cyclopentadiĂ©nyle ont Ă©tĂ© synthĂ©tisĂ©s. Plusieurs voies ont Ă©tĂ© exploitĂ©es pour synthĂ©tiser les complexes fer(II) bisimidazol-2-ylidene, une dâelles, la transmetallation, nous a conduit Ă prĂ©parer des nouveaux complexes dâargent; ces complexes ont Ă©tĂ© caractĂ©risĂ©s entre autre par diffraction de rayons â X. Enfin dans une dĂ©marche purement comparative, deux complexes nickel bisimidazol-2-ylidene ont Ă©tĂ© prĂ©parĂ©s et leur activitĂ© catalytique dans la polymĂ©risation dâĂ©thylĂšne a Ă©tĂ© sommairement Ă©tudiĂ©e, donnant de trĂšs bons rĂ©sultats.The use of organometallic complexes as catalysts became a very significant topic in the field of material chemistry. However, despite of this development, only few of them contain iron(II), except the tridentate complex diimine pyridine developed by Gibson and Brookhart and employed in the olefin polymerization. Unfortunately, this model suffers by its lack of tolerance towards the minor changes carried out in its envelope, resulting by a drastic reduction from its catalytic activity. The goal of this work is to synthesize iron(II) complexes containing pincer ligands and to study their use as catalyst for polymerization of olefins. It has to be noted that previous work in our group showed a very good correlation between the polymerization and the hydrogenation of olefin. Thus, we have also exploited the ability of our news complexes in hydrogenation. Two projects were carried out in parallel: one was the synthesis of iron(II) complexes containing benzyletherfuran ligand and the second one was the preparation of iron(II) bisimidazol-2-ylidene complexes. First project : The prepared iron(II) benzyletherfuran complex was successfully tested in the hydrogenation of olefin under very mild conditions (1-3 bar of hydrogen at room temperature); however, its employment as catalyst for olefin polymerization did not give the expected results. Thus, this project was left aside with the profit of the second one. Second project : The prepared iron(II) bisimidazol-2-ylidene complexes showed a good activity in both reactions, polymerization and hydrogenation of olefins under mild conditions. During the preparation of these complexes, several other complexes of iron(II) and iron(III) were isolated as secondary products from the reaction. With the purpose of characterizing the obtained products, we also prepared several derivatives by introducing additional ligands into the coordination sphere of iron(II) bisimidazol-2- ylidene complexes. Thus, formiate, carboxylate, triflate and cyclopentadienyl derivatives were synthesized. Several ways were exploited to synthesize the iron(II) bisimidazol-2-ylidenes complexes, one of them was the transmetallation which led us to prepare new silver complexes. These complexes were characterized amongst other analytical tools by X-ray diffraction. Finally, in a purely comparative approach, two nickel bisimidazol-2-ylidene complexes were prepared and their catalytic activity in the ethylene polymerization was studied, giving very good results
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