Templated Synthesis of a Rotaxane with a [Ru(diimine)₃]²⁺ Core

Abstract

A rotaxane containing a ruthenium bisphenanthroline complex, acting as an axis, and a macrocycle incorporating a 2,2'-bipyridine (bpy) unit, threaded by the axis, has been synthesized. The bisphenanthroline ligand is such that its ruthenium(II) complexes possess a clearly identified axis, making such compounds ideal components of rotaxanes constructed around an octahedral ruthenium(II) center, which serves as a template. The ring is threaded by the axial ruthenium(II) precursor complex, to afford the corresponding pseudorotaxane in moderate yield. The X-ray structure analysis of this compound reveals the threaded nature of the complex. The length of the threaded ring (35 atoms in the periphery) is too short to allow easy threading of the axis through the macrocycle. As a consequence, an isomer is also obtained for which the axial ruthenium complex is attached in an exo fashion. (1)H NMR studies have been carried out, which reveal various conformational equilibria for the pseudorotaxane. Light-induced decoordination of the bpy-containing cyclic fragment was shown to be quantitative and to lead to the free ring and the axial ruthenium(II) complex, regardless of the starting compound (pseudorotaxane or exo isomer). Finally, the real rotaxane could be prepared, although it could not be separated from its exo isomer.

Highly Selective Na+‐Templated Formation of [2]Pseudorotaxanes Exhibiting Significant Optical Outputs

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The diverse range of binding geometries exhibited by metal ions and their relatively stable interactions with ligands can be exploited for the efficient template-directed synthesis of macrocycles,[1] supramolecular architectures, [2] and interlocked molecules.[3] Although the formation of rotaxanes or pseudorotaxanes has been demonstrated using transitionmetal ions coordinated to four (tetrahedral and square planar), [4] five (trigonal bipyramidal and square pyramidal), [5] and six (octahedral) [6] donor atoms, alkali-metal ions, which are useful templates for the synthesis of crown ethers, [7] are rarely used to direct the construction of such complexes. In one example, Li + ions have been used to assist the formation of a unique donor-acceptor pseudorotaxane, [8] but it appears that Na + ions play a similar role in that system.

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“…To determine how the molecular cage 1 coordinates to these two metal ions we grew single crystals suitable for X-ray crystallography by liquid diffusion of diisopropyl ether into solutions of molecular cage 1 and NaBF 4 or KPF 6 (1:2 molar ratio) in CH 3 CN. The solid-state structures reveal that each Na + (Figure 7 A,B) and K + (Figure 7 C,D) ion is bound to all six oxygen atoms of the individual crown ether units of molecular cage 1.…”

Strategien und Taktiken für die metallgesteuerte Synthese von Rotaxanen, Knoten, Catenanen und Verschlingungen höherer Ordnung

“…[166] Ein ähnlicher oktaedrischer "4+2"-Donorligandensatz kam auch bei der Templatsynthese von Rotaxanen zum Einsatz (Schema 30). [167] [163] Für eine ähnliche [2]Catenatsynthese siehe Schema 7. [76] Schema 29.…”

A Simple General Ligand System for Assembling Octahedral Metal–Rotaxane Complexes

“…Efficient synthetic methods have been developed for rotaxanes based on tetrahedral and trigonal-bipyrimidal metal complexes by using the metal-bis-phenanthroline synthon pioneered in Strasbourg. [1a, b, 5] Herein we describe a general ligand system for rotaxane complexes of ions that prefer octahedral coordination-the commonest ligand geometry amongst transition metals, but up to now a rare [6] coordination mode for rotaxanes. Simple mixing of the components at room temperature is sufficient to assemble a broad range of octahedrally coordinated [2]metallorotaxanes in excellent yields.…”