1,4-Additions of tricyclic 1,4-diphosphinines – a novel system to study pi-bond activation and dispersion interactions

The dienic nature of the aromatic π-system in 1,4-diphosphinines remained largely unexplored to this day due to a lack of facile and efficient synthetic protocols. Recently reported stable, tricyclic 1,4-diphosphinines were used to explore the thermal reactivity of the π-system towards an array of dienophiles in [4π+2π]- and, for the first time, in [4π+2σ]-type cycloaddition reactions

Spotlight on Charge-Transfer Excitons in Crystalline Textured n-Alkyl Anilino Squaraine Thin Films

Prototypical n-alkyl terminated anilino squaraines for photovoltaic applications show characteristic double-hump absorption features peaking in the green and deep-red spectral range. These signatures result from coupling of an intramolecular Frenkel exciton and an intermolecular charge transfer exciton. Crystalline, textured thin films suitable for polarized spectro-microscopy have been obtained for compounds with n-hexyl (nHSQ) and n-octyl (nOSQ) terminal alkyl chains. The here released triclinic crystal structure of nOSQ is similar to the known nHSQ crystal structure. Consequently, crystallites from both compounds show equal pronounced linear dichroism with two distinct polarization directions. The difference in polarization angle between the two absorbance maxima cannot be derived by spatial considerations from the crystal structure alone but requires theoretical modeling. Using an essential state model, the observed polarization behavior was discovered to depend on the relative contributions of the intramolecular Frenkel exciton and the intermolecular charge transfer exciton to the total transition dipole moment. For both nHSQ and nOSQ, the contribution of the charge transfer exciton to the total transition dipole moment was found to be small compared to the intramolecular Frenkel exciton. Therefore, the net transition dipole moment is largely determined by the intramolecular component resulting in a relatively small mutual difference between the polarization angles. Ultimately, the molecular alignment within the micro-textured crystallites can be deduced and, with that, the excited state transitions can be spotted.Comment: 12 pages, 8 figure

Expanding the chemistry of ring-fused 1,4-diphosphinines by stable mono anion formation

A new sulfur-enriched tricyclic 1,4-diphosphinine (2) was synthesized and novel reactivity studies on the phosphorus heterocycle was performed: A weak anionic nucleophile (KHMDS) adds selectively thus forming a stable anionic 1,4-diphosphinine derivative (3b) which was fully characterized. The substitution potential of 3b was demonstrated using Ph2PCl to give 4b, while oxidation of 3b using elemental iodine furnished cleanly the P-P coupling product 5

Crystal structure of 4′-{[4-(2,2′:6′,2′′-terpyridyl-4′-yl)phenyl]ethynyl}biphenyl-4-yl (2,2,5,5-tetramethyl-1-oxyl-3-pyrrolin-3-yl)formate benzene 2.5-solvate

The title compound, C44H35N4O3·2.5C6H6 (1), consists of a terpyridine and a N-oxylpyrroline-3-formate group separated by an aromatic spacer, viz. 4-(phenylethynyl)-1,1′-biphenyl. It crystallized in the triclinic space group P-1 with two and a half benzene solvate molecules (one benzene molecule is located about an inversion center), while the dichloromethane solvate (2) of the same molecule [Ackermann et al. (2015). Chem. Commun. 51, 5257–5260] crystallized in the tetragonal space group P42/n, with considerable disorder in the molecule. In (1), the terpyridine (terpy) group assumes an all-trans conformation typical for terpyridines. It is essentially planar with the two outer pyridine rings (B and C) inclined to the central pyridine ring (A) by 8.70 (15) and 14.55 (14)°, respectively. The planes of the aromatic spacer (D, E and F) are nearly coplanar with dihedral angles D/E, D/F and E/F being 3.42 (15), 5.80 (15) and 4.00 (16)°, respectively. It is twisted with respect to the terpy group with, for example, dihedral angle A/D being 24.48 (14)°. The mean plane of the N-oxylpyrroline is almost normal to the biphenyl ring F, making a dihedral angle of 86.57 (16)°, and it is inclined to pyridine ring A by 72.61 (15)°. The intramolecular separation between the O atom of the nitroxyl group and the N atom of the central pyridine ring of the terpyridine group is 25.044 (3) Å. In the crystal, molecules are linked by pairs of C—H...O hydrogen bonds, forming inversion dimers. The dimers stack along the c axis forming columns. Within and between the columns, the spaces are occupied by benzene molecules. The shortest oxygen–oxygen separation between nitroxyl groups is 4.004 (4) Å. The details of the title compound are compared with those of the dichloromethane solvate (2) and with the structure of a related molecule, 4′-{4-[(2,2,5,5-tetramethyl-N-oxyl-3-pyrrolin-3-yl)ethynyl]phenyl}-2,2′:6′,2′′-terpyridine (3), which has an ethynylphenyl spacer [Meyer et al. (2015). Acta Cryst. E71, 870–874]

Towards allosteric receptors – synthesis of β-cyclodextrin-functionalised 2,2’-bipyridines and their metal complexes

Herein, we present three new 2,2’-bipyridines that carry two β-cyclodextrin moieties in different substitution patterns. When coordinated by zinc(II) or copper(I) ions (or their complexes), these compounds undergo conformational changes and switch between “open” and “closed” forms and thereby bringing together or separating the cyclodextrin moieties from each other

The enzyme mechanism of patchoulol synthase

Different mechanisms for the cyclisation of farnesyl pyrophosphate to patchoulol by the patchoulol synthase are discussed in the literature. They are based on isotopic labelling experiments, but the results from these experiments are contradictory. The present work reports on a reinvestigation of patchoulol biosynthesis by isotopic labelling experiments and computational chemistry. The results are in favour of a pathway through the neutral intermediates germacrene A and alpha-bulnesene that are both reactivated by protonation for further cyclisation steps, while previously discussed intra- and intermolecular hydrogen transfers are not supported. Furthermore, the isolation of the new natural product (2S,3S,7S,10R)-guaia-1,11-dien-10-ol from patchouli oil is reported

Tris[2,2,6,6-tetramethyl-8-(trimethylsilyl)benzo[1,2-d;4,5-d′]bis(1,3-dithiol)-4-yl]methanol diethyl ether monosolvate

The title compound, a triarylmethanol, C46H64OS12Si3 1, was synthesized via lithiation of tris-2,2,6,6-tetramethylbenzo[1,2-d;4,5-d′]bis[1,3]dithiol-4-yl-methanol, 2, and electrophilic quenching with trimethylsilyl chloride. The current crystal structure reveals information about the reactivity of this compound and compares well with the structure reported for the unsubstituted parent compound 2 [Driesschaert et al. (2012). Eur. J. Org. Chem. 33, 6517–6525]. The title compound 1 forms molecular propellers and crystallizes in P\overline{1}, featuring an unusually long Si—Car bond of 1.910 (3) Å. Moreover, the geometry at the central quaternary carbon is rather trigonal-pyramidal than tetrahedral due to vast intramolecular stress. One trimethylsilyl group is disordered over two positions in a 0.504 (4):0.496 (4) ratio and one S atom is disordered over two positions in a 0.509 (7):0.491 (7) ratio. The contribution of disordered diethyl ether solvent molecule(s) was removed using the PLATON SQUEEZE (Spek, 2015) solvent masking procedure. These solvent molecules are not considered in the given chemical formula and other crystal data