Catenane

• A Catenane is a mechanically-interlocked molecular architecture consisting of two or more interlocked

macrocycles. They are analogous to bike chains or key rings in which the individual components are not

directly connected, but the components cannot be separated without breaking one of the rings. Catenane is

derived from the Latin catena meaning "chain". They are conceptually related to other

mechanically-interlocked molecular architectures , such as rotaxanes, molecular knots or borromean ring.

The synthesis of such entangled topologies has been made efficient through the combination of

supramolecular chemistry with traditional covalent synthesis, however

mechanically-interlocked molecular architectures have properties that differ from both “supramolecular

assemblies” and “covalently-bonded molecules.” Recently the terminology "mechanical bond" has been

coined to describe the connection between the components of a catenane.

Synthesis

• There two primary approaches to the organic synthesis of catenanes. The first is to simply perform a ring

closing reaction with the hope that some of the rings will form around other rings giving the desired catenane

product. This so-called "statistical approach" lead to the first successful synthesis of a catenane, however the

method suffers from very low yields. The second approach relies on preorganization of the macrocyclic

precursors utilizing hydrogen bonding, metal coordination, hydrophobic forces, or coulombic interactions.

These non-covalent interactions offset some of the entropic cost of association and help position the

components to form the desired catenane upon the final ring-closing. This "template-directed" method has

dramatically increased the yields that can be obtained for catenanes and thus has increased their potential

for application. An example of this approach used bis-bipyridinium salts which form strong complexes

threaded through crown ether bis(para-phenylene)-34-crown-10.

Families of Catenanes

• There are a number of distinct methods of holding the precursors together prior to the ultimate ring-closing

reaction in a template-directed catenane synthesis. Each noncovalent approach to catenane formation

results in what can be considered different families of catenanes.

• Another family of catenanes are called pretzelanes or bridged [2]catenanes after their likeness to pretzels

with a spacer linking the two macrocycles. In one such system [1] one macrocycle is an electron deficient

oligo Bis-bipyridinium ring and the other cycle is crown ether cyclophane based on paraphenylene or

naphthalene. X-ray diffraction shows that due to pi-pi interactions the aromatic group of the cyclophane is

held firmly inside the pyridinium ring. A limited number of (rapidly-interchanging) conformers exist for this type

of compound.

Families of Catenanes

Handcuff shaped catenaneIn handcuff-shaped catenanes [2], two connected rings are threaded through the same ring. The bis-macrocycle (red) contains two phenanthroline units in a crown ether chain. The interlocking ring is self-assembled when two more phenanthroline units with alkene arms coordinate through a copper(I) complex followed by a metathesis ring closing step.

References

• Dynamic Chirality in Donor-Acceptor Pretzelanes Y. Liu, S. A. Vignon, X. Zhang, P. A. Bonvallet, S. I. Khan,

K. N. Houk, and J. F. Stoddart J. Org. Chem.; 2005; 70(23) pp 9334 - 9344; (Article) DOI: 10.1021/jo051430g

• A catenane consisting of a large ring threaded through both cyclic units of a handcuff-like compound Julien

Frey, Tomá Kraus, Valérie Heitz and Jean-Pierre Sauvage Chemical Communications, 2005, (42), 5310 -

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