Adrian Kremer

Supramolecular Wiring of Benzo-1,3-chalcogenazoles through Programmed Chalcogen Bonding Interactions

The high-yielding synthesis of 2-substituted benzo-1,3-tellurazoles and benzo-1,3-selenazoles through a dehydrative cyclization reaction has been reported, giving access to a large variety of benzo-1,3-chalcogenazoles. Exceptionally, these aromatic heterocycles proved to be very stable and thus very handy to form controlled solid-state organizations in which wire-like polymeric structures are formed through secondary N⋅⋅⋅Y bonding interactions (SBIs) engaging the chalcogen (Y=Se or Te) and nitrogen atoms. In particular, it has been shown that the recognition properties of the chalcogen centre at the solid state could be programmed by selectively barring one of its σ-holes through a combination of electronic and steric effects exerted by the substituent at the 2-position. As predicted by the electrostatic potential surfaces calculated by quantum chemical modelling, the pyridyl groups revealed to be the stronger chalcogen bonding acceptors, and thus the best ligand candidate for programming the molecular organization at the solid state. In contrast, the thiophenyl group is an unsuitable substituent for establishing SBIs in this molecular system as it gives rise to chalcogen-chalcogen repulsion. The weaker chalcogen donor properties of the Se analogues trigger the formation of feeble N⋅⋅⋅Se contacts, which are manifested in similar solid-state polymers featuring longer nitrogen-chalcogen distances.

Walking down the chalcogenic group of the periodic table: from singlet to triplet organic emitters.

The synthesis, X-ray crystal structures, ground- and excited-state UV/Vis absorption spectra, and luminescence properties of chalcogen-doped organic emitters equipped on both extremities with benzoxa-, benzothia-, benzoselena- and benzotellurazole (1X and 2X ) moieties have been reported for the first time. The insertion of the four different chalcogen atoms within the same molecular skeleton enables the investigation of only the chalcogenic effect on the organisation and photophysical properties of the material. Detailed crystal-structure analyses provide evidence of similar packing for 2O -2Se , in which the benzoazoles are engaged in π-π stacking and, for the heavier atoms, in secondary X⋅⋅⋅X and X⋅⋅⋅N bonding interactions. Detailed computational analysis shows that the arrangement is essentially governed by the interplay of van der Waals and secondary bonding interactions. Progressive quenching of the fluorescence and concomitant onset of phosphorescence features with gradually shorter lifetimes are detected as the atomic weight of the chalcogen heteroatom increases, with the tellurium-doped derivatives exhibiting only emission from the lowest triplet excited state. Notably, the phosphorescence spectra of the selenium and tellurium derivatives can be recorded even at room temperature; this is a very rare finding for fully organic emitters.

Versatile Bisethynyl[60]fulleropyrrolidine Scaffolds for Mimicking Artificial Light-Harvesting Photoreaction Centers

Fullerene-based tetrads, triads, and dyads are presented in which [60]fulleropyrrolidine synthons are linked to an oligo(p-phenyleneethynylene) antenna at the nitrogen atom and to electron-donor phenothiazine (PTZ) and/or ferrocene (Fc) moieties at the α carbon of the pyrrolidine cycle through an acetylene spacer. Cyclic voltammetry and UV/ Vis absorption spectra evidence negligible ground-state electronic interactions among the subunits. By contrast, strong excited-state interactions are detected upon selective light irradiation of the antenna (UV) or of the fullerene scaffold (Vis). When only PTZ is present as electron donor, photoinduced electron transfer to the fullerene unit is unambiguously detected in benzonitrile, but this is not the case when Fc is part of the multicomponent system. These results suggest that Fc is a formidable energy transfer quencher and caution should be used in choosing it as electron donor to promote efficient charge separation in multicomponent arrays.

Synthesis of Alkali Metal Carboxylates and Carboxylic Acids Using “Wet” and “Anhydrous” Alkali Metal Hydroxides

Hydroxide ion has been used in a large number of important organic reactions in which it plays the role of either nucleophile or base.1,2 This is inter alias the case of (i) the hydrolysis of esters, amides, nitriles, carbonates, carbamates, and ureas,1-3 (ii) Haller-Bauer-type scission of non enolizable ketones,4 (iii) Favorskii rearrangement,1,5 (iv) Cannizaro disproportion reaction of non enolizable aldehydes,6 (v) carbenes synthesis,7 especially dihalogeno carbenes,7,8 (vi) alkylation reactions8-10 including C alkylations,9 (vii) aldol and related reactions, especially those involving malonates and nitroalkanes,1 (viii) elimination reactions,1 and marginally (ix) fission of unsaturated acid.11

Diastereoselective bromination of compounds bearing a cyclohex-3-enol moiety: application to the enantioselective synthesis of (1R)-cis-deltamethrinic acid.

(1R)-cis-chrysanthemic acid has been prepared in a few steps with complete control of the relative and absolute stereochemistry. Some mechanistic aspect of the addition of bromine to the C,C double bond of 2,2,5,5-tetramethylcyclohex-3-enol is disclosed.

endo-3,3-Dimethyl-4-oxobicyclo­[3.1.0]hexan-2-yl methane­sulfonate

The relative configuration of the endo isomer of the title compound, C9H14O4S, has been established and the conformation of the diastereoisomer is discussed. The five-membered ring adopts an envelope conformation. The conformation of the methanesulfonate substituent is stabilized by intermolecular C—H⋯O hydrogen bonds. The crystal packing results in alternating layers of polar methanesulfonates and stacked bicyclohexanyl rings parallel to ab.