In just four steps from ferrocene, macrocyclic ferrocenyl bispalladacyles have been synthesized by using a diastereoselective biscyclopalladation reaction as the key step. The complexes not only possess a fascinating structure but are also the first highly active catalysts for the title reaction (see scheme), requiring as little as 0.1 mol % of catalyst for most of the substrates. Ts=toluene-4-sulfonyl. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2007/z603568_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.
Understanding water behaviour on 2D materials is crucial for sensing, microfluidics, and tribology. While water/graphene interactions are well studied, water on hexagonal boron nitride (h-BN) remains largely unexplored. Despite structural similarity to graphene, h-BN's slightly polar B-N bonds impart a large band gap, high thermal conductivity, and chemical stability, making it promising for electronics, lubricants, and coatings. Moreover, existing water studies often focus on multilayer water dynamics, overlooking single-molecular details. We bridge this gap by studying single-molecular water friction and diffusion on h-BN, comparing it with graphene using helium spin-echo experiments and ab initio calculations. Our findings show that water diffusion on h-BN/Ni follows a complex rotational-translational dynamic, unlike graphene. While conventional views treat water motion as discrete jumps between equivalent adsorption sites, we demonstrate that on h-BN, water molecules rotate freely around their centre of mass. Although the binding energies of water on h-BN and graphene are similar, the activation energy for water dynamics on h-BN is 2.5 times lower than on graphene, implying a much lower barrier for molecular mobility. The fundamentally different diffusion characteristics which classical models cannot capture, underscores the need to rethink how we model water on polar 2D materials. Moreover, our analysis reveals that the metal substrate strongly influences water friction, with h-BN/Ni showing a markedly lower friction than graphene/Ni, in stark contrast to the free-standing materials. These findings challenge assumptions about 2D material-water interactions, highlighting the crucial role of substrate effects in chemistry and material science and offer insights for designing next-generation microfluidic devices that require precise water mobility control.
The cover picture shows the X-ray crystal structure of an expanded [6]radialene which adopts a chair-like conformation. Expanded radialenes exhibit remarkable electronic properties owing to a considerable degree of macrocyclic cross-conjugation. In the upper left corner is shown the “radiating” solar disk of the old Egyptian Sun-god Aton. The study on the synthesis and properties of different radialenes is described in more detail by F. Diederich et al. on p. 3263 ff.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Tetraphenyltetraethynylethene and the π-acceptors 2,4,7-trinitrofluoren-9-one and (2,4,7-trinitro-9-fluoroenylidene)malononitrile from highly ordered donor–acceptor π-complexes having 1 : 2 stoichiometry in the solid state; in solution, relatively weak 1 : 1 complexes are formed whose stabilities are related to the spatial disposition of the donor phenyl rings.
Abstract A new route via intermediate pseudoenantiomers was developed to synthesize racemic and enantiomerically pure new non‐peptidic inhibitors of thrombin, a key serine protease in the blood‐coagulation cascade. These ligands feature a conformationally rigid tricyclic core and are decorated with substituents to fill the major binding pockets (distal (D), proximal (P), selectivity (S1), and oxyanion hole) at the thrombin active site ( Fig. 1 ). The key step in the preparation of the new inhibitors is the 1,3‐dipolar cycloaddition between an optically active azomethine ylide, prepared in situ from L ‐(4 R )‐hydroxyproline and 4‐bromobenzaldehyde, and N ‐piperonylmaleimide ( Scheme 1 ). According to this protocol, tricyclic imide (compounds (±)‐ 15 ‐(±)‐ 18 and (+)‐ 21 ) and lactam (compound (+)‐ 2 ) inhibitors with OH or ether substituents at C(7) in the proline‐derived pyrrolidine ring were synthesized to specifically explore the binding features of the oxyanion hole ( Schemes 2–4 ). Biological assays ( Table ) showed that the polar oxyanion hole in thrombin is not suitable for the accommodation of bulky substituents of low polarity, thereby confirming previous findings. In contrast, tricyclic lactam (+)‐ 2 ( K i =9 n M , K i (trypsin)/ K i (thrombin)=1055) and tricyclic imide (+)‐ 21 ( K i =36 n M , K i (trypsin)/ K i (thrombin)=50) with OH‐substituents at the ( R )‐configured C(7)‐atom are among the most‐potent and most‐selective thrombin inhibitors in their respective classes, prepared today. While initial modeling predicted H‐bonding between the OH group at C(7) in (+)‐ 2 and (+)‐ 21 with the H 2 O molecule bound in the oxyanion hole ( Fig. 2 ), the X‐ray crystal structure of the complex of (+)‐ 21 ( Fig. 7 , b ) revealed a different interaction for this group. The propionate side chain of Glu192 undergoes a conformational change, thereby re‐orienting towards the OH group at C(7) under formation of a very short ionic H‐bond (OH⋅⋅⋅ − OOC; d (O⋅⋅⋅O)=2.4 Å). The energetic contribution of this H‐bond, however, is negligible, due to its location on the surface of the protein and the unfavorable conformation of the H‐bonded propionate side chain.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Abstract The X‐ray structures of fifteen 1, 3‐imidazolidine, 1, 3‐oxazolidine, 1, 3‐dioxan‐4‐one, and hydropyrimidine‐4(1 H )‐one derivatives are described ( Table 2 ) and compared with known structures of similar compounds ( Figs. 1–20 ). The differences between structures containing exocyclic N ‐acyl groups and those lacking this structural element arise from the A 1,3 effect of the amide moieties. Even t ‐Bu groups are forced into axial positions of six‐ring half‐chair or into flag‐pole positions of six‐ring twist‐boat conformers by this effect ( Figs. 16–20 ). In the N ‐acylated five‐membered heterocycles, a combination of ring strain and A 1, 3 strain leads to strong pyramidalizations of the amide N‐atoms ( Table 1 ) such that the acyl groups wind up on one side and the other substituents on the opposite side of the rings ( Figs. 4–9 and Scheme 3 ). Thus, the acyl (protecting!) groups strongly contribute to the steric bias between the two faces of the rings. Observed, at first glance surprizing stereoselectivities of reactions of these heterocycles ( Schemes 1 and 2 ) are interpreted ( Scheme 3 ) as an indirect consequence of the amide A 1, 3 strain effect. The conclusions drawn are considered relvant for a better understanding of the ever increasing role which amide groups play in stereoselective syntheses.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
