Getting Harder: Cobalt(III)-Template Synthesis of Catenanes and Rotaxanes

Abstract

The synthesis of catenanes and rotaxanes using the hard trivalent transition metal ion cobalt(III) as a template is reported. Tridentate dianionic pyridine-2,6-dicarboxamido ligands, each with two terminal alkene groups, coordinate Co(III) in a mutually orthogonal arrangement such that entwined or interlocked molecular architectures are produced by ring-closing olefin metathesis. Double macrocyclization of two such ligands bound to Co(III) afford a non-interlocked "figure-of-eight" complex in 42% yield, the structure determined by X-ray crystallography. Preforming one macrocycle and carrying out a single macrocyclization of the second bis-olefin with both ligands attached to the Co(III) template led to the isomeric [2]catenate in 69% yield. The mechanically interlocked structure was confirmed by X-ray crystallography of both the Co(III) catenate and the metal-free catenand. A Co(III)-template [2]rotaxane was assembled in 61% yield by macrocyclization of the bis-olefin ligand about an appropriate dianionic thread. For both catenanes and rotaxanes, removal of the metal ion via reduction under acidic conditions to the more labile Co(II) gave neutral interlocked molecules with well-defined co-conformations stabilized by intercomponent hydrogen bonding.

Metal ions in the synthesis of interlocked molecules and materials

“…More directly, Sauvage's seminal work inspired the development of a plethora of transition metal ion-ligand combinations of varying coordination geometry as templates in PT syntheses of MIMs (Fig 3a), 7 including linear Au I , 8 square planar Pd II , 9 a variety of octahedral metal ions, 10,11 as well as more kinetically inert templates including Ru II12 and Co III . 13 Furthermore, it has proved possible to use the metal ion itself to drive formation of the ligand motif by subcomponent selfassembly as well as directing the formation of the threaded structure (Fig 3b).…”

“…Inspired by the many sophisticated examples of molecular switches and machines based on interlocked molecules that operate beautifully in solution and to some extent in soft materials and on surfaces, it was further demonstrated that the fundamental to and fro motion of a degenerate molecular shuttle could be accomplished in the solid-state inside a MOF material. Using a 13 C enriched sample of a Zn II MOF constructed using a rigid H-shaped linker (Fig 25), it was demonstrated by VT 13 …”

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

“…Durch die Verwendung zweier verschiedener acyclischer Liganden mit ähnlichen Bindungsarten für die Metallionen (Schema 6 a) kçnnen drei unterschiedliche Präcatenankomplexe gebildet werden, die durch einen Ringschluss [2]Catenane ergeben, ebenso wie nichtverschlungene achterfçrmige und Ring-an-Ring-Komplexe sowie Oligomere und Polymere hçherer Ordnung. [75] In vielen Fällen bedeutet die Vorbildung nur eines Makrocyclus (Schema 6 b) allerdings, dass aus sterischen Gründen eine maximale Besetzung der Bindungsstellen nur über einen eingefädelten Komplex erreicht werden kann, aus dem nur ein [2] [76] Die Vorteile dieses Ansatzes sind noch stärker ausgeprägt im Falle der Synthesen heterozirkularer Catenane und Rotaxane, für die gemischte Ligandenkomplexe tatsächlich erforderlich sind. Aus diesem Grund kommen beim Aufbau solcher verschlungener Strukturen oftmals Methoden der "Einfädelung" zum Einsatz.…”

“…[167] [163] Für eine ähnliche [2]Catenatsynthese siehe Schema 7. [76] Schema 29. [165] Ein ähnliches [2]Catenan, das über einen Ringschluss durch eine zweifache RCM gebildet wurde, entstand in 46 % Ausbeute.…”

Metallomacrocycles with a Difference: Macrocyclic Complexes with Exocyclic Ruthenium(II)‐Containing Domains

“…13 An elegant synthetic route devised by Sauvage first introduced the concept of using a tetrahedral {Cu(bpy) 2 } + domain coupled with Grubbs’ RCM to template the formation of a catenane 14–16. Since this breakthrough, metal‐ion‐templated syntheses have been applied to control a variety of ring‐closing steps, thus allowing the assembly of catenanes, knots and rotaxanes 17. Several recent examples have focused on the formation of large organic macrocycles,18–21 and, notably, Sauvage has made use of octahedral ruthenium(II) as the templating metal centre 22–25.…”