Chiral bis-porphyrins are currently the subject of intense interest as chiral receptors and as probes in the determination of structure and stereochemistry. To provide an improved framework for interpreting the circular dichroism (CD) spectra of bis-porphyrins, we have calculated the CD spectra of chiral bis-porphyrins from three classes: I, where porphyrins can adopt a relatively wide range of orientations relative to each other; II, porphyrins have a fixed relative orientation; III, porphyrins undergo pi-stacking. The calculations primarily utilized the classical polarizability theory of DeVoe, but were supplemented by the quantum mechanical matrix method. Class I was represented by three isomers of the diester of 5alpha-cholestane-3,17-diol with 5-(4'-carboxyphenyl)-10,15,20-triphenylporphin (2-alphabeta, 2-betaalpha, 2-betabeta). Careful analysis of the torsional degrees of freedom led to two to four minimum-energy conformers for each isomer, in each of which the phenyl-porphyrin bonds had torsional angles near 90 degrees. Libration about these bonds is relatively unrestricted over a range of +/-45 degrees. CD spectra in the Soret region were calculated as Boltzmann-weighted averages over the low-energy conformers for each isomer. Three models were used: the effective transition moment model, in which only one of the degenerate Soret components is considered, along the 5-15 direction; the circular oscillator model, in which both Soret components are given equal weight; and the hybrid model, in which the 10-20 oscillator is given half the weight of the 5-15 oscillator, to mimic the effect of extensive librational averaging about the 5-15 direction. All three models predict Soret exciton couplets with signs in agreement with experiment. Quantitatively, the best results are given by the hybrid and circular oscillator models. These results validate the widely used effective transition moment model for qualitative assignments of bis-porphyrin chirality and thus permit application of the exciton chirality model. However, for quantitative studies, the circular oscillator or hybrid models should be used. The simplified effective transition moment and hybrid models are justified by the librational averaging in the class I bis-porphyrins and should only be used with such systems. Two class II bis-porphyrins were also studied by DeVoe method calculations in the circular oscillator model, which yielded good agreement with experiment. Class III bis-porphyrins were represented by 2-alphaalpha, for which the calculations gave qualitative agreement. However, limitations in the conformational analysis with the close contacts and dynamic effects in these pi-stacked systems preclude quantitative results.

No abstract

Keywords: Natural products / Canthin-6-ones / Indole alkaloids / Chiral sulfoxides / Quantum chemical calculations A unique set of thiomethylated canthin-6-one derivatives was isolated from Boletus curtisii. The bright yellow color of this mushroom is caused by two optically active canthin-6-one sulfoxides for which the names curtisin and 9-deoxycurtisin are proposed. The structures of the new compounds were established by MS and NMR methods and the absolute con-

Tetraphenylethylene (TPE) and its derivatives are the typical aggregation-induced emission (AIE) compounds with helical chirality, and they have enormous applications potential in chiral sensor, asymmetric catalyst, optoelectronic materials, and so on. The aggregation-induced helical chirality of TPE and its derivatives can only be observed in condensed phase such as crystalline or film state. The accurate determination of absolute configuration (AC) of TPE core compounds is complicated and difficult, especially when there is no heavy atoms exist in their structures. Herein, we demonstrate a powerful and convenient method to quickly determine the helical chirality of these stereochemically labile TPE core compounds through the combination of comprehensive solid-state chiroptical spectroscopy and theoretical calculation. Our study reveals that from lower to higher energy of the fingerprint region, the first electronic circular dichroism (ECD) band in the 300−450 nm or the first most intensive vibrational circular dichroism (VCD) peak in the 875−730 cm −1 can be used as the diagnostic bands for the AC determination of the TPE core with the fixed chirality. If these diagnostic bands cannot be observed in ECD or VCD spectra, the helical chirality of the atropisomers of TPE derivatives is not fixed. The explicit AC determination of TPE core contributes to the study of the helical chirality of supramolecular TPE core derivatives and allows for the further fabrication of novel chiral AIE functional materials.

The enantiomers of complex 1 (1a and 1b) have been obtained by spontaneous resolution upon crystallization in the absence of a chiral source. The enantiomeric nature of 1a and 1b was confirmed by circular dichroism (CD) spectra and theoretical investigation.

Via a simple adsorption, the second generation Hoveyda-Grubbs catalyst was successfully immobilized on a mesoporous material SBA-1, leading to a highly recyclable solid catalyst for olefin metathesis.

No abstract

Inspired by the recent discovery of the metal-centered tubular molecular rotor C B-Ta@B with the record coordination number of CN = 20 and based on extensive first-principles theory calculations, we present herein the possibility of the largest tubular molecular rotors C B-Ta@B (1) and C B-Ta@B (2) and smallest axially chiral endohedral metalloborospherenes D Ta@B (3 and 3'), unveiling a tubular-to-cage-like structural transition in metal-centered boron clusters at Ta@Bvia effective spherical coordination interactions. The highly stable Ta@B (3) as an elegant superatom, which features two equivalent corner-sharing B boron double chains interconnected by two B units with four equivalent B heptagons evenly distributed on the cage surface, conforms to the 18-electron configuration with a bonding pattern of σ + π double delocalization and follows the 2(n + 1) electron counting rule for spherical aromaticity (n = 2). Its calculated adiabatic detachment energy of ADE = 3.88 eV represents the electron affinity of the cage-like neutral D Ta@B which can be viewed as a superhalogen. The infrared, Raman, VCD, and UV-vis spectra of the concerned species are computationally simulated to facilitate their spectral characterizations.