Hydrogen Bonded Rotaxanes and Catenanes

and Leigh, D. A., Hydrogen bond-assembled synthetic molecular motors and machines , Top. Curr. Chem. 2005, 262, 133-177. 

5 Metal and Auxiliary Linkage Approaches to Catenanes and Rotaxanes 

The existence of interlocked molecules such as 10.95 can be established by a variety of spectroscopic techniques. Most importantly, mass spectrometry provides very characteristic patterns for catenanes. The mass spectra for catenated species are very different from those of covalently linked precursors (such as 10.94) but are more than the sum of their two individual components. Catenane mass spectra are characterised by the appearance of peaks at high miz corresponding to the parent species as well as fragments corresponding to the transfer of hydrogen atoms from one macrocycle to the functional 

Attempts have also been made to carry out multiple sterically directed cyclisations on closely related systems with a view to generating multiply interlocked materials. Compound 10.97 was prepared and subjected to a triple ring closure reaction. Unfortunately, the inherent low yields of the crucial reaction steps resulted in immense difficulty in characterising the reaction products. Compound 10.97 is prepared in nine steps, and following multiple cyclisation, a total of only 1.7 % of product was obtained, which proved to be an isomeric mixture of three different interlocked species. 

The yield of 10.103 is improved further by adopting a stepwise approach in which the preformed corand 10.104 is reacted with [Cu(MeCN)4]+ and one eqnivalent of the deprotected 10.102 to give an intermediate pseudorotaxane. Cyclisation as before gives the catenate 10.105 in an impressive 42 % yield. 

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