Two [2]pseudorotaxane-like complexes and their corresponding [2]rotaxanes stabilized via interactions on opposite ends of the same macrocycle

Crystal structure of 2,6-bis(3-hydroxy-3-methylbut-1-yn-1-yl)pyridine monohydrate

In the crystal, the hydrogen bonds between the pyridine mol­ecule and the water mol­ecule, viz. O_hy­droxy—H⋯O_water, O_hy­droxy—H⋯O_hy­droxy, O_water—H⋯O_hy­droxy, and O_water—H⋯N_pyridine, result in the formation of a ribbon structure running along [01].

In the title pyridine derivative, C₁₅H₁₇NO₂·H₂O, the two OH groups are oriented in directions opposite to each other with respect to the plane of the pyridine ring. In the crystal, hydrogen bonds between the pyridine mol­ecule and the water mol­ecule, viz. O_hy­droxy—H⋯O_water, O_hy­droxy—H⋯O_hy­droxy, O_water—H⋯O_hy­droxy and O_water—H···N_pyridine, result in the formation of a ribbon-like structure running along [011].

Design of [2]rotaxane through image threshold segmentation of electrostatic potential image

An electrostatic potential (ESP)-based image segmentation method has been used to estimate the ability of proton donation and acceptance involved in ring-rod recognition. The relative binding strength of [2]rotaxane has also been further estimated from the difference of the characteristic image-segmentation derived ESP between proton donor and proton acceptor. The size and electrostatic compatibility criteria are introduced to guide the design of interlocked [2]rotaxane. A library of 75 thermodynamically stable [2]rotaxane candidates has been generated, including 16 experimentally known systems. The theoretical results for 16 experimentally known [2]rotaxanes are in good agreement with both the experimental association constants and density functional theory-calculated binding energies. Our ESP-based image segmentation model is also applicable to the tristable [2]rotaxane molecular shuttle as well as [1]rotaxane with self-inclusion function, indicating this simple method is generic in the field of constructing other supramolecular architectures formed with donor/acceptor molecular recognition. © 2016 Wiley Periodicals, Inc.

Toward metal complexes that can directionally walk along tracks: controlled stepping of a molecular biped with a palladium(II) foot

We report on the design, synthesis, and operation of a bimetallic molecular biped on a three-foothold track. The "walker" features a palladium(II) complex "foot" that can be selectively stepped between 4-dimethylaminopyridine and pyridine ligand sites on the track via reversible protonation while the walker remains attached to the track throughout by means of a kinetically inert platinum(II) complex foot. The substitution pattern of the three ligand binding sites, together with the kinetic stability of the metal-ligand coordination bonds, affords the two positional isomers a high degree of metastability, meaning that altering the chemical state of the track does not automatically instigate stepping in the absence of an additional stimulus (heat in the presence of a coordinating solvent). The use of metastable metal complexes for foot-track interactions offers a promising alternative to dynamic covalent chemistry for the design of small-molecule synthetic molecular walkers.

Strategies and tactics for the metal-directed synthesis of rotaxanes, knots, catenanes, and higher order links

More than a quarter of a century after the first metal template synthesis of a [2]catenane in Strasbourg, there now exists a plethora of strategies available for the construction of mechanically bonded and entwined molecular level structures. Catenanes, rotaxanes, knots and Borromean rings have all been successfully accessed by methods in which metal ions play a pivotal role. Originally metal ions were used solely for their coordination chemistry; acting either to gather and position the building blocks such that subsequent reactions generated the interlocked products or by being an integral part of the rings or "stoppers" of the interlocked assembly. Recently the role of the metal has evolved to encompass catalysis: the metal ions not only organize the building blocks in an entwined or threaded arrangement but also actively promote the reaction that covalently captures the interlocked structure. This Review outlines the diverse strategies that currently exist for forming mechanically bonded molecular structures with metal ions and details the tactics that the chemist can utilize for creating cross-over points, maximizing the yield of interlocked over non-interlocked products, and the reactions-of-choice for the covalent capture of threaded and entwined intermediates.

Successive catalytic reactions specific to Pd-based rotaxane complexes as a result of wheel translation along the axle

Rotaxane-structure-specific Pd-catalyzed rearrangement of propargyl urethane or allyl urethane groups to 2-oxazolidone or oxazolidinone moieties proceeded efficiently.