Synthesis, Chiral Resolution, and Absolute Configuration of Dissymmetric 4,15-Difunctionalized [2.2]Paracyclophanes

Despite the fact that functionalized planar chiral [2.2]­paracyclophanes have received a lot of attention, the chemistry of pseudo-<i>meta</i> 4,15-distubstituted [2.2]­paracyclophanes is largely unexplored. This is mainly due to the fact that the 4,5-dibromo-functionalized [2.2]­paracyclophane is much less prone to halogen-metal exchange reactions than its constitutional pseudo-<i>ortho</i> or pseudo-<i>para</i> isomers. Here, we give an account of an efficient protocol to achieve this, which allows the synthesis of a broad variety of 4,15-disubstituted [2.2]­paracyclophanes. Furthermore, we were able to resolve several of the racemic compounds via chiral HPLC and assign the absolute configurations of the isolated enantiomers by X-ray diffraction and/or by the comparison of calculated and measured CD-spectra

Stepwise Construction of Heterobimetallic Cages by an Extended Molecular Library Approach

Two novel heterobimetallic complexes, a trigonal-bipyramidal and a cubic one, have been synthesized and characterized using the same <i>C</i>₃-symmetric metalloligand, prepared by a simple subcomponent self-assembly strategy. Adopting the molecular library approach, we chose a mononuclear, preorganized iron­(II) complex as the metallo­ligand capable of self-assembly into a trigonal-bipyramidal or a cubic aggregate upon coordination to cis-protected <i>C</i>₂-symmetric palladium­(II) or unprotected tetravalent palladium­(II) ions, respectively. The trigonal-bipyramidal complex was characterized by NMR and UV–vis spectroscopy, electrospray ionization mass spectrometry (ESI-MS), and single-crystal X-ray diffraction. The cubic structure was characterized by NMR and UV–vis spectroscopy and ESI-MS

Synthesis, Chiral Resolution, and Absolute Configuration of Dissymmetric 4,15-Difunctionalized [2.2]Paracyclophanes

Despite the fact that functionalized planar chiral [2.2]­paracyclophanes have received a lot of attention, the chemistry of pseudo-<i>meta</i> 4,15-distubstituted [2.2]­paracyclophanes is largely unexplored. This is mainly due to the fact that the 4,5-dibromo-functionalized [2.2]­paracyclophane is much less prone to halogen-metal exchange reactions than its constitutional pseudo-<i>ortho</i> or pseudo-<i>para</i> isomers. Here, we give an account of an efficient protocol to achieve this, which allows the synthesis of a broad variety of 4,15-disubstituted [2.2]­paracyclophanes. Furthermore, we were able to resolve several of the racemic compounds via chiral HPLC and assign the absolute configurations of the isolated enantiomers by X-ray diffraction and/or by the comparison of calculated and measured CD-spectra

Spotlight on Excitonic Coupling in Polymorphic and Textured Anilino Squaraine Thin Films

Structural diffraction analysis of an anilino squaraine with <i>branched</i> isobutyl side chains shows crystallization into two polymorphic structures in the bulk and in spin-casted thin films. We observe multipeaked and pleochroic absorption spectra being blue-(red)-shifted for the monoclinic (orthorhombic) polymorph. We understand the packing as Coulombic molecular H-(J)-aggregates supporting Davydov splitting. Pictures of projected Davydov components in oriented thin films fit well to polarization resolved spectro-microscopy and crossed-polarized light microscopy investigations. By comparison with literature on anilino squaraines with <i>linear</i> alkyl side chains, we point out a general trend for steering the thin film excitonic properties by simple side chain and/or processing condition variation. Combined with the ability to locally probe the direction of transition dipole moments, this adds value to the rational design of functional thin films for optoelectronic applications, especially envisioning ultrastrong light–matter interactions

Resolution and Determination of the Absolute Configuration of a Twisted Bis-Lactam Analogue of Tröger’s Base: A Comparative Spectroscopic and Computational Study

The first reported twisted bis-lactam, a racemic Tröger’s base (TB) analogue (<b>2</b>), was resolved into its enantiomers on a chiral stationary phase HPLC column. The absolute configuration of (+)-<b>2</b> was determined to be (<i>R</i>,<i>R</i>)-<b>2</b> by comparing experimental and calculated vibrational circular dichroism (VCD) and electronic circular dichroism (ECD) spectra. The absolute configuration of (−)-<b>2</b> was determined by comparing experimental and calculated electronic circular dichroism (ECD) spectra. The corresponding theoretical spectra were calculated using the lowest energy conformation of (<i>R</i>,<i>R</i>)-<b>2</b> and (<i>S</i>,<i>S</i>)-<b>2</b> at the B3LYP/6-31G­(d,p) level of theory. The absolute configuration of (+)-<b>2</b> was also determined to (<i>R</i>,<i>R</i>)-<b>2</b> by anomalous X-ray diffraction (AXRD) in a chiral space group <i>P</i>2₁2₁2₁ using Cu-irradiation resulting in a very low Flack parameter of −0.06(3), despite the heaviest element being an oxygen atom, thus unambiguously confirming the results from the spectroscopic studies. We conclude that, for the Tröger’s base (TB) analogue (<b>2</b>), we may rank the reliability of the individual methods for AC determination as AXRD ≫ VCD > ECD, while the synergy of all three methods provides very strong confidence in the assigned ACs of (+)-(<i>R</i>,<i>R</i>)-<b>2</b> and (−)-(<i>S</i>,<i>S</i>)-<b>2</b>

Enantiomerically Pure Trinuclear Helicates via Diastereoselective Self-Assembly and Characterization of Their Redox Chemistry

A tris­(bipyridine) ligand <b>1</b> with two BINOL (BINOL = 2,2′-di­hydroxy-1,1′-binaphthyl) groups has been prepared in two enantiomerically pure forms. This ligand undergoes completely diastereo­selective self-assembly into <i>D</i>₂-symmeteric double-stranded trinuclear helicates upon coordination to copper­(I) and silver­(I) ions and to <i>D</i>₃-symmetric triple-stranded trinuclear helicates upon coordination to copper­(II), zinc­(II), and iron­(II) ions as demonstrated by mass spectrometry, NMR and CD spectroscopy in combination with quantum chemical calculations and X-ray diffraction analysis. According to the calculations, the single diastereomers that are formed during the self-assembly process are strongly preferred compared to the next stable diastereomers. Due to this strong preference, the self-assembly of the helicates from racemic <b>1</b> proceeds in a completely narcissistic self-sorting manner with an extraordinary high degree of self-sorting that proves the power and reliability of this approach to achieve high-fidelity diastereo­selective self-assembly via chiral self-sorting to get access to stereo­chemically well-defined nanoscaled objects. Furthermore, mass spectrometric methods including electron capture dissociation MS^<i>n</i> experiments could be used to elucidate the redox behavior of the copper helicates