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$^{-1}$

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

From weakly coordinating to non-coordinating anions? A simple preparation of the silver salt of the least coordinating anion and its application to determine the ground state structure of the Ag(η2-P4)2+ cation

The unexpected but facile prepn. of the Ag salt of the least coordinating [(RO)3Al-F-Al(OR)3]- anion (R = C(CF3)3) by reaction of Ag[Al(OR)4] with one equiv. of PCl3 is described. The mechanism of the formation of Ag[(RO)3Al-F-Al(OR)3] is explained based on the available exptl. data as well as on quantum chem. calcns. with the inclusion of entropy and COSMO solvation enthalpies. The crystal structures of (RO)3Al(OC4H8), Cs[(RO)2(Me)AlFAl(Me)(OR)2], Ag(CH2Cl2)3[(RO)3AlFAl(OR)3] and Ag(h2-P4)2[(RO)3AlFAl(OR)3]- are described. From the collected data the [(RO)3AlFAl(OR)3]- anion is the least coordinating anion currently known. With respect to the F- ion affinity of two parent Lewis acids Al(OR)3 of 685 kJ mol-1, the ligand affinity (441 kJ mol-1), the proton and Cu decompn. reactions (-983 and -297 kJ mol-1) as well as HOMO level and HOMO-LUMO gap and in comparison with [Sb4F21]-, [Sb(OTeF5)6]-, [Al(OR)4]- as well as [B(RF)4]- (RF = CF3 or C6F5) the [(RO)3Al-F-Al(OR)3]- anion is among the best weakly coordinating anions (WCAs) according to each value. In contrast to most of the other cited anions, the [(RO)3AlFAl(OR)3] anion is available by a simple prepn. in conventional inorg. labs. The least coordinating character of this anion was employed to clarify the question of the ground state geometry of the Ag(h2-P4)2+ cation (D2h, D2 or D2d). In agreement with computational data and NMR spectra it could be shown that the rotation along the Ag-(P-P-centroid) vector has no barrier and that the structure adopted in the solid state depends on packing effects which lead to an almost D2h sym. Ag(h2-P4)2+ cation (0 to 10.6 Deg torsion) for the more sym. [Al(OR)4]- anion, but to a D2 sym. Ag(h2-P4)2+ cation with a 44 Deg twist angle of the two AgP2 planes for the less sym. [(RO)3AlFAl(OR)3]- anion. This implies that Ag back bonding, suggested by quantum chem. population analyses to be of importance, is only weak. [on SciFinder (R)