Dichtefunktionaluntersuchungen zur Reaktivität von non-IPR-Fullerenen

Kleine Fullerene stellen ein wichtiges Teilgebiet der Forschung an nanostrukturierten Kohlenstoffmaterialien dar. Sie sind jedoch sehr reaktiv, da sie die Regel der isolierten Fünfringe (IPR) verletzen. Experimentell können non-IPR-Fullerene mit Wasserstoff- oder Halogenatomen stabilisiert und als Derivate isoliert werden. Die vorliegende Arbeit befasst sich mit der quantenchemischen Untersuchung möglicher Produkte mit dem Ziel, die Stabilität der experimentell beobachteten Strukturen zu erklären und darüberhinaus weitere besonders stabile Strukturen vorherzusagen

Asymmetric organocatalytic synthesis of 4,6-bis-(1H-indole-3-yl)-piperidine-2 carboxylates

Peer reviewe

Impact of Heterocycle Annulation on NIR Absorbance in Quinoid Thioacene Derivatives

The synthesis and characterisation of a homologous series of quinoid sulfur-containing imidazolyl-substituted heteroacenes is described. The optoelectronic and magnetic properties were investigated by UV/vis, fluorescence and EPR spectroscopy as well as quantum-chemical calculations, and were compared to those of the corresponding benzo congener. The room-temperature and atmospherically stable quinoids display strong absorption in the NIR region between 678 and 819 nm. The dithieno[3,2-b:2′,3′-d]thiophene and the thieno[2′,3′:4,5]thieno[3,2-b]thieno[2,3-d]thiophene derivatives were EPR active at room temperature. For the latter, variable-temperature EPR spectroscopy revealed the presence of a thermally accessible triplet state, with a singlet-triplet separation of 14.1 kJ mol$^{-1}$

Star-shaped triarylamines - One-step metal-free synthesis and optoelectronic properties

Triarylamine derivatives are often implemented in organic optoelectronic devices due to their excellent hole-transport properties and their versatile structural tuneability. Common synthetic routes to obtain functionalized triarylamines follow multi-step procedures utilizing transition metal catalysts. Here, we investigate the synthesis of a series of star-shaped tris(biphenylamines) by a one-step base-promoted homolytic aromatic substitution (BHAS), simultaneously attaching three peripheral arenes to the triarylamine core. We demonstrate the versatility of this synthetic route by coupling four different functionalized arenes to the core and study their influence on the optoelectronic properties. BHAS as a metal-free synthetic route produces pure organic semiconductors without transition metal residues.Peer reviewe

Radical exchange reaction of multi-spin isoindoline nitroxides followed by EPR spectroscopy

The synthesis of a rigid, isoindoline-functionalized tetraphenylmethane multi-spin system is described. The isoindoline nitroxide groups are used in a nitroxide exchange reaction with a TEMPO containing alkoxyamine. Using EPR spectroscopy it is possible to follow the exchange process and thereby find the optimal experimental conditions to have the maximum yield. The presented approach could be used to study the nitroxide exchange process of various systems and to determine the kinetics of the exchange process. The presented molecular components can be used as tectons in the construction of covalently linked organic networks or as model systems for EPR distance measurements

Metastable Se6 as a ligand for Ag+: from isolated molecular to polymeric 1D and 2D structures

Attempts to prepare the hitherto unknown Se6 2+ cation by the reaction of elemental selenium and Ag[A] ([A]- = [Sb(OTeF5)6]-, [Al(OC(CF3)3)4]-) in SO2 led to the formation of [(OSO)Ag(Se6)Ag(OSO)][Sb(OTeF5)6]2 1 and [(OSO)2Ag(Se6)Ag(OSO)2][Al(OC(CF3)3)4]2 2a. 1 could only be prepared by using bromine as co-oxidant, however, bulk 2b (2a with loss of SO2) was accessible from Ag[Al(OC(CF3)3)4] and grey Se in SO2 (chem. analysis). The reactions of Ag[MF6] (M= As, Sb) and elemental selenium led to crystals of 1/∞{[Ag(Se6)]∞[Ag2(SbF6)3]∞} 3 and {1/∞[Ag(Se6)Ag]∞}[AsF6]2 4. Pure bulk 4 was best prepared by the reaction of Se4[AsF6]2, silver metal and elemental selenium. Attempts to prepare bulk 1 and 3 were unsuccessful. 1–4 were characterized by single-crystal X-ray structure determinations, 2b and 4 additionally by chemical analysis and 4 also by X-ray powder diffraction, FT-Raman and FT-IR pectroscopy. Application of the PRESTO III sequence allowed for the first time 109Ag MAS NMR investigations of 4 as well as AgF, AgF2, AgMF6 and {1/∞[Ag(I2)]∞}[MF6] (M= As, Sb). Compounds 1 and 2a/b, with the very large counter ions, contain isolated [Ag(Se6)Ag]2+ heterocubane units consisting of a Se6 molecule bicapped by two silver cations (local D3d sym). 3 and 4, with the smaller anions, contain close packed stacked arrays of Se6 rings with Ag+ residing in octahedral holes. Each Ag+ ion coordinates to three selenium atoms of each adjacent Se6 ring. 4 contains [Ag(Se6)+]∞ stacks additionally linked by Ag(2)+ into a two dimensional network. 3 features a remarkable 3-dimensional [Ag2(SbF6)3]- anion held together by strong Sb–F … Ag contacts between the component Ag+ and [SbF6]- ions. The hexagonal channels formed by the [Ag2(SbF6)3]- anions are filled by stacks of [Ag(Se6)+]∞ cations. Overall 1–4 are new members of the rare class of metal complexes of neutral main group elemental clusters, in which the main group element is positively polarized due to coordination to a metal ion. Notably, 1 to 4 include the commonly metastable Se6 molecule as a ligand. The structure, bonding and thermodynamics of 1 to 4 were investigated with the help of quantum chemical calculations (PBE0/TZVPP and (RI-)MP2/TZVPP, in part including COSMO solvation) and Born–Fajans–Haber-cycle calculations. From an analysis of all the available data it appears that the formation of the usually metastable Se6 molecule from grey selenium is thermodynamically driven by the coordination to the Ag+ ions

Dichtefunktionaluntersuchungen zur Reaktivität von non-IPR-Fullerenen

Kleine Fullerene stellen ein wichtiges Teilgebiet der Forschung an nanostrukturierten Kohlenstoffmaterialien dar. Sie sind jedoch sehr reaktiv, da sie die Regel der isolierten Fünfringe (IPR) verletzen. Experimentell können non-IPR-Fullerene mit Wasserstoff- oder Halogenatomen stabilisiert und als Derivate isoliert werden.Die vorliegende Arbeit befasst sich mit der quantenchemischen Untersuchung möglicher Produkte mit dem Ziel, die Stabilität der experimentell beobachteten Strukturen zu erklären und darüberhinaus weitere besonders stabile Strukturen vorherzusagen

Structure and characterization of CI3+[Al{OC(CF3)3}4]-; Lewis acidities of CX3+ and BX3

Prepn. of the title compd. (I) from starting materials CI4 and Ag[Al{OC(CF3)3}4](II) was performed with the complete exclusion of light and with carefully purified diiodine-free CI4, since CI4 decomps. within minutes in soln. in light with formation of I2 and other carbon iodides, and II reacts immediately with I2 to give yet unidentified decompn. products. With these precautions I was prepd. in quant. yield. According to calcns. at the MP2/TZVPP level and estn. of the sublimation and lattice enthalpies in a suitable cycle, we est. that the reaction is exothermic by -33 kJmol-1 in the gas phase and by -127 kJmol-1 in the solid state. In CH2Cl2 soln., I is dark blood red and in situ NMR reactions show only resonance signals for the CI3+ ion (d(13C)= 97 ppm; in SO2ClF: d(13C) = 95 ppm; calcd. value: d(13C) = 106 ppm) and the anion (d(13C) = 121.5 ppm (q); d(27A1)= 38.0 ppm). A CH2Cl2 soln. of I is stable for about 8 to 12 h at ambient temp. and much longer if stored at -30 or -78 DegC. Single crystals that appeared yellow as thin plates but black when thicker were grown at -78 DegC from cooled concd. CH2Cl2 solns. of I. The crystal structure detn. of a dark orthorhombic block of I showed that it contained isolated trigonal-planar CI3+ ions with a sum of I-C-I bond angles of 360.0 Deg (range: 118.8-122.1 Deg0) and Al{OC(CF3)3}4 ions. [on SciFinder (R)

Tethering for Selective Synthesis of 2,2′-Biphenols : the Acetal Method

2,2'-Biphenols are a large and diverse group of compounds with exceptional properties both as ligands and bioactive agents. Traditional methods for their synthesis by oxidative dimerisation are often problematic and lead to mixtures of ortho- and para-connected regioisomers. To compound these issues, an intermolecular dimerisation strategy is often inappropriate for the synthesis of heterodimers. The ‘acetal method’ provides a solution for these problems: stepwise tethering of two monomeric phenols enables heterodimer synthesis, enforces ortho regioselectivity and allows relatively facile and selective intramolecular reactions to take place. The resulting dibenzo[1,3]dioxepines have been analysed by quantum chemical calculations to obtain information about the activation barrier for ring flip between the enantiomers. Hydrolytic removal of the dioxepine acetal unit revealed the 2,2′-biphenol target