Helvetica Chimica Acta最新文献

Atropisomeric scaffolds offer the possibility to predictably position donor and acceptor groups in specific spatial relationships. Herein, a configurationally stable 1,2’-binaphthyl linkage was employed to place a ruthenium(II) tris-(2,2’-bipyridine) complex in proximity to an anthracene moiety to explore how photoinduced triplet-triplet energy transfer can proceed across this type of molecular bridge. An efficient synthesis provided the ruthenium(II)-anthracene dyad with high yields, which allowed to determine characteristic features for the intramolecular energy transfer.

4-Aryl-1,4-dihydropyridines are prevalent pharmacophores and versatile building blocks in medicinal and synthetic chemistry. Herein, we demonstrated a mechanistically distinct radical-radical cross-coupling approach to 4-aryl-1,4-dihydropyridines, via direct C4−H arylation of 1,4-dihydropyridines with readily available cyanoarenes. This mild protocol is initiated by the direct photoexcitation of 1,4-dihydropyridines, eliminating the need for expensive photocatalysts and enabling operation under ambient air conditions.

A recurring misconception in some textbooks and research papers has led to an abandonment of fundamental physical laws when describing a subset of acid-base equilibria, especially regarding the role of the solvent. In the specific case of the autoprotolysis of water, experiments and theoretical calculations prove that the K_w of water at 25 °C, 1.00×10⁻¹⁴, is identical to its acid ionization constant, K_a. Nevertheless, several articles have been published erroneously purporting to give theoretical proof that the K_a of water is 10^−15.743 (1.81×10⁻¹⁶) and that the K_a of the aqueous proton (hydronium ion) is 55.3 rather than 1.00. Here we argue that using the incorrect numbers has pedagogical implications beyond those of a simple error. Arguments for the incorrect K_a and pK_a values require a misapplication of Henry's law and violate long-standing methods that use Raoult's law and the conservation of matter to describe the behavior of solutions. As a result, chemistry students may be asked to accept one set of physical principles in one course and another set in another course. Here we argue for adherence to fundamental physical laws governing solution equilibria as applied to the autoprotolysis of water and all aqueous acid base equilibria.

Chiral polycyclic aromatic hydrocarbons with monkey saddle topology are a fascinating class of negatively curved compounds. To make the monkey-saddles valuable building blocks for chirality-assisted synthesis (CAS) approaches, the inversion barriers between the two possible enantiomers need to be high enough to prevent interconversion under CAS conditions. By molecular editing, aza monkey saddles were converted to the corresponding chromene monkey saddles that are configurationally stable even at temperatures of 220 °C over a period of 47 days. Their structures were studied by single X-ray diffraction and enantiomers were separated to study the chiroptical properties. Furthermore, mechanistic assumptions of the formation of the chromene monkey saddles by DFT calculations are discussed.

Herein, we detail an extension of our research on the synthesis of a small library of furanoheliangolides and the characterization of the covalent interaction between goyazensolide and IPO5. Using a build-couple-pair strategy, we assembled a small library of germacrene-type lactones and diversified them into eight groups of structurally different analogues. The germacrene lactones were synthesized using Sonogashira coupling and Barbier-type macrocyclization, while the furanoheliangolides were further elaborated through gold-catalyzed transannulation followed by esterification. This synthetic approach enabled the generation of a goyazensolide alkyne-tagged cellular probe, which was used to identify the selective binding between goyazensolide and the oncoprotein importin-5 (IPO5). Mass spectrometry analysis of the proteolytic digest from the reaction between the goyazensolide probe and a recombinant IPO5 indicated a covalent engagement at Cys560 of IPO5, which was confirmed by site-directed mutagenesis.

Imido ligand is a ubiquitous motif in organometallic chemistry, serving roles spanning from ancillary ligands to reactive sites. The nature of M=N bond is highly depended on the metal centres and their d-electron configuration, with late transition metal (TM) imido complexes exhibiting contrasting features when compared to their early TM analogues. Envisioning to uncover general electronic descriptor for the nature of imido ligands, we computationally investigate the solid-state ¹⁵N NMR signatures of late TM imido complexes with various central metals, geometries and d-electron counts, and compare them against these of the corresponding early TM systems. The spectroscopic signatures are mostly driven by the presence of filled, π-symmetry orbitals in late TM imido complexes, suggesting the development of high-lying π(M=N) and low-lying σ/σ^*(M=N) orbitals. This contrasts with what is observed for the reported early TM systems, for which high-lying σ-type orbitals determine the NMR signature. Noteworthily, Ni- and Pd-imido complexes with formal d¹⁰ configurations exhibit highly asymmetric nitrogen-15 NMR signature with extremely deshielded principal components, because of the presence of filled, high-lying antibonding π^*(M=N) orbitals, consistent with their high reactivity. The sensitive response of ¹⁵N NMR signature to the nature of metal sites further highlights that chemical shift is a useful reactivity descriptor.

Supported catalysts are central to industrial catalytic processes. While traditional synthesis methods often yield poorly defined materials, thus complicating structural elucidation, Surface Organometallic Chemistry (SOMC) offers a solution, producing well-defined structures. Recent advances in SOMC precursor development have shown that amidinate-based complexes are a privileged class of precursors to generate supported metallic nanoparticles. In that context, this study investigates the grafting mechanism of a prototypical amidinate precursor, Ir(COD)(DIA) (1-Ir), onto SiO₂. Unique to amidinate complexes, grafting is shown to occur without ligand release, creating a reversible covalent bond. Using tris(tert-butoxy)silanol as a molecular analogue for a silanol group on SiO₂, the structure of the grafted species is elucidated by single X-Ray diffraction, comparison of IR spectroscopy, and X-Ray absorption spectroscopy (XAS) data. The reversibility of the reaction with O−H groups is demonstrated using variable-temperature NMR spectroscopy, IR spectroscopy, and is supported by DFT calculations. Notably, we show that a partial degrafting is also possible at elevated temperatures under vacuum.

Multi-resonant thermally activated delayed fluorescence (MR-TADF) helicenes show great potential as chiral emitters due to their typically high photoluminescence quantum yield and that they emit circularly polarized luminescence. Here, a new propeller-shaped chiral MR-TADF helicene DiKTa3, integrating three DiKTa moieties, was designed and synthesized aiming to achieve co-parallel electronic and magnitude transition dipole moments that would lead to a high dissymmetry factor, g. It emits at λ_PL of 491 nm, with a full width at half maximum of 52 nm and has a moderate ΔE_ST value of 0.24 eV in toluene. The separated (P,P,P) enantiomer shows an absorption dissymmetry factor |g_abs| of 6.8×10⁻⁴ at 450 nm, which results from a lower symmetry conformation adopted by the compound in solution than the C₃-symmetric optimized structure. This work highlights the strong influence that geometry can have on the chiroptical properties of the emitter.