CH-π and CF-π Interactions Lead to Structural Changes of N-Heterocyclic Carbene Palladium Complexes

Substitution-Pattern- and Counteranion-Depending Ion-Pairing Assemblies Based on Electron-Deficient Porphyrin-AuIII Complexes

Porphyrin-Au^III complexes, which were partially or totally modified with C₆ F₅ at the meso positions, were synthesized. The highly electron-withdrawing substituents induced electron-deficient states and Lewis acid properties. Single-crystal X-ray analysis of the ion pairs revealed ion-pairing assemblies with characteristics dependent on the number and substitution pattern of the C₆ F₅ units and the geometries of the anions.

The Taming of Redox-Labile Phosphidotitanocene Cations

Tame d⁰ phosphidotitanocene cations stabilized with a pendant tertiary phosphane arm are reported. These compounds were obtained by one-electron oxidation of d¹ precursors with [Cp₂ Fe][BPh₄ ]. The electronic structure of these compounds was studied experimentally (EPR, UV/Vis, and NMR spectroscopy, X-ray diffraction analysis) and through DFT calculations. The theoretical analysis of the bonding situation by using the electron localization function (ELF) shows the presence of π-interactions between the phosphido ligand and Ti in the d⁰ complexes, whereas dπ-pπ repulsion prevents such interactions in the d¹ complexes. In addition, CH-π interactions were observed in several complexes, both in solution and in the solid state, between the phosphido ligand and the phosphane arm. The d⁰ complexes were found to be light sensitive, and decompose through Ti-P bond homolysis to give Ti^III species. A naked d⁰ phosphidotitanocene cation has been trapped by reaction with diphenylacetylene, yielding a Ti/P frustrated Lewis pair (FLP), which was found to be less reactive than a previously reported Zr analog.

Fluoroacetamide Moieties as NMR Spectroscopy Probes for the Molecular Recognition of GlcNAc-Containing Sugars: Modulation of the CH-π Stacking Interactions by Different Fluorination Patterns

We herein propose the use of fluoroacetamide and difluoroacetamide moieties as sensitive tags for the detection of sugar–protein interactions by simple ¹H and/or ¹⁹F NMR spectroscopy methods. In this process, we have chosen the binding of N,N′‐diacetyl chitobiose, a ubiquitous disaccharide fragment in glycoproteins, by wheat‐germ agglutinin (WGA), a model lectin. By using saturation‐transfer difference (STD)‐NMR spectroscopy, we experimentally demonstrate that, under solution conditions, the molecule that contained the CHF₂CONH‐ moiety is the stronger aromatic binder, followed by the analogue with the CH₂FCONH‐ group and the natural molecule (with the CH₃CONH‐ fragment). In contrast, the molecule with the CF₃CONH‐ isoster displayed the weakest intermolecular interaction (one order of magnitude weaker). Because sugar–aromatic CH–π interactions are at the origin of these observations, these results further contribute to the characterization and exploration of these forces and offer an opportunity to use them to unravel complex recognition processes.