ChemistryEurope最新文献

An oligo(iminoborane), depicted on the cover as the dinosaur, was synthesized as part of a series of monodisperse oligo(iminoborane)s with increasing number of B=N units in the chain. Herein, the number of backbone atoms could be extended to 7 boron and 8 nitrogen atoms. This oligomer represents the longest well-defined molecular [>B=N<]_x chain reported so far. The structures of the oligomers were studied by X-ray diffractometry, also providing insight into the microstructure of poly(iminoborane)s (PIBs). In their Research Article, H. Helten and co-workers describe PIBs with increased aromatic content, including the PIB with the highest molecular weight known to date. The meteorite collision visualizes TGA measurements of the polymers which lead to the formation of boron nitride. The authors would like to thank Tina Schneider for creating the cover artwork.

Pt-Pt interactions are able to fold a flexible dinucleotide chain, promoting nucleobase stacking. In their Research Article, M. Gómez-Gallego, M. A. Sierra, and co-workers report the molecular structures of cyclometallated Pt^II purine dinucleotides as chiral helices sustained by Pt−Pt intramolecular interactions. These interactions force the purine nucleobases to stand parallel, as parallel are the four towers of Madrid city, in which the reported compounds have been made. The Pt−Pt interactions can be detected in solution by the appearance of the characteristic MMLCT transitions in the UV/Vis spectra. The authors would like to thank Pablo García-Álvarez for creating the cover artwork.

The carbonyl group is arguably the most versatile functional group for synthetic purposes. Here, a series of N,N’-bis(pyridylideneamide) (bisPYA) complexes of ruthenium(II), [Ru(cym)(bisPYA)Cl]⁺ (cym=cymene), were synthesized and applied as catalysts for Lemieux-Johnson oxidation of alkenes to access carbonyl functionalities. Complexes bearing para- and ortho-bisPYA ligands induce higher activity and selectivity than their mesoionic meta-bisPYA analogues. The non-coordinating counterion of the cationic complexes affects the catalytic performance markedly, with PF₆⁻ enhancing the activity compared to trifluoromethanesulfonate, OTf⁻. Likewise, replacing the anionic ancillary chloride ligand by a neutral and more labile MeCN ligand led to increased activity. Electrochemical and solubility measurements revealed no direct correlation of ligand donor strength to catalytic performance. Variation of the solvent mixture and the ratio of its components provided access to high-performance catalysts. In H₂O/MeCN/CH₂Cl₂ at 3 : 1:0.5 (v/v) ratio, turnover frequencies up to 10,000 h⁻¹ were obtained for the Lemieux-Johnson oxidation of styrene with these Ru(bisPYA) complexes, allowing quantitative conversions within 30 min at 0.1 mol % catalyst loadings and corresponding to a 5 times faster reaction than the best catalyst known to date for this transformation.

L-shape N-Heterocyclic Carbenes (NHCs) based on the imidazo[1,5-a]pyridine (ImPy) scaffold have recently gained considerable interest as the true carbene ligand analogues of the popular dialkylbiarylphosphines, better known as Buchwald phosphines. Nevertheless, the substitution pattern of ImPy ligands is still rather limited due to synthetic access issues. We report herein an efficient and versatile visible light photocatalytic strategy to access L-shape bifunctional ImPy ligands laterally-functionalized by a phenol group. Mechanistic investigations supported by density functional theory (DFT) reveal that the excited state of the iridium photocatalyst undergoes either a reductive quenching (SET process) or an energy-transfer quenching (EnT process) depending on the nature of the counterion of the 5-bromoimidazo[1,5-a]pyridinium substrate salt. Moreover, the bifunctional character of these new family of L-shape ImPy ligands is demonstrated by the preparation of a gold(I) complex exhibiting a free OH function capable of intermolecular hydrogen bonding. This work highlights the advantage of visible light photocatalysis in the synthesis of advanced NHC ligand structures, a strategy that has not yet been considered despite its potential benefits in terms of versatility, diversity and practicability.

While certain inorganic main-group polymers such as silicones (polysiloxanes) are ubiquitous in our everyday life, poly(iminoborane)s have been elusive for a long time. Incorporation of heterocyclic building blocks into their backbone has recently enabled access to the first derivatives of this inorganic-polymer class, as this approach effectively prevents undesired side-reactions to borazines. Information about the microstructure of these cyclolinear macromolecules, however, has been scarce. Herein, we present the synthesis of a series of monodisperse oligomers with up to 7 boron and 8 nitrogen atoms, representing the longest well-defined molecular [>B=N<]_x chain to date. We accomplished to characterize six of them structurally in the solid state by single-crystal X-ray diffraction, thus providing valuable insight into the microstructure of poly(iminoborane)s. In addition, we report on the synthesis of new poly(iminoborane) derivatives featuring aryl side groups, with an increased content of unsubstituted phenyl groups. The p-(n-butyl)phenyl-substituted species 13 represents the highest-molecular-weight sample of this class of inorganic polymers to date.

Mechanically active [c2]daisy chain rotaxanes were functionalized with mesogens to display liquid-crystalline properties. It was shown that the mechanical actuation of such bistable rotaxanes (between their contracted and extended states) modifies the transition temperature between their isotropic and smectic phases. In addition, small angle X-ray scattering (SAXS) experiments revealed a modification of the smectic phase corresponding to the modification of the interlayer distance as controlled by the mechanical bond. The work described by N. Giuseppone and co-workers in their Research Article opens new opportunities to implement [c2]daisy chain rotaxanes in responsive materials.

Peroxo-zirconium-/hafnium-containing polyoxometalates as 3-in-1 catalysts were prepared and studied for homogeneous, heterogeneous, and biphasic oxidation catalysis with H₂O₂ as oxidant. In their Research Article, U. Kortz and co-workers evaluate the catalysts in terms of activity and product selectivity and exhibited unique profiles. Most interestingly, the catalytic results proved to be highly relevant for applications in the chemical industry, possibly paving the way for green chemical processes. The authors would like to thank Mr. Adhiraj Sundar for creating the cover artwork.

Subtle chemical modifications of an intermediate can have significant impacts, since they usually considered to control the reactivity. In their Research Article, J. Zagranyarski, D. Lungerich, C. Cabanetos, and co-workers report the preparation of aza derivatives of the benzothixanthene imide. The intramolecular radical cyclization can be controlled by means of a simple methylation to either afford the thermodynamically favored six-membered or its kinetically favored five-membered ring regioisomers, exhibiting significant photophysical properties.

This article reports the use of metal–metal interactions as a way to induce nucleobase stacking in a dinucleotide chain. We synthetized and study a series of C,N-cyclometallated platinum(II) binuclear complexes derived from 6-phenylpurine dinucleotide 1 as proligand, and β-diketonates, 2,2'-bipyridines and 1,10-phenanthroline as ancillary ligands. The X-ray diffraction analysis revealed that the diketonate derivatives 7 and 8 are chiral helixes sustained by Pt−Pt intramolecular interactions that allow the nucleobase stacking. The folded helical structures are maintained in solution, as demonstrated by the appearance of metal–metal-to-ligand charge-transfer (MMLCT) transitions in the UV-vis spectra. The influence of the ancillary ligand in the molecular structure was evidenced by the absence of bands derived from M−M interactions in the absorption spectra of 2,2’-bipyridine and and 1,10-phenanthroline derivatives 12–14. The existence of Pt−Pt in the complexes of this study can be also detected by electrochemistry.