Synthesis of macrocycles and an unusually asymmetric [2]catenane via templated acetylenic couplings

An unusually asymmetric [2]catenane has been prepared by interlocking a hybrid crown macrocycle (containing one polyether and one butadiyne linker) with a diimide-derived macrocycle itself constructed with a pair of rigid butadiyne links. This system of complementary building blocks and connectors has proved a versatile vehicle for demonstration of a number of templating effects. Synthesis of the hybrid crown monomer by intramolecular cyclisation is promoted by the presence of a benzene diimide, acting as a positive template, but a sufficiently different effect is exerted by a naphthalene diimide derivative that intermolecular dimerisation becomes significant. Templating the hybrid crown synthesis with an 'active' benzene diimide, itself bearing acetylene functions, allows the first tandem synthesis of a catenane comprising two different rings: the diimide first acts as a template for the formation of the hybrid crown, which itself in turn acts as a template for cyclodimerisation of the acetylenic diimide. Remarkably, the yield of catenane is essentially independent of the initial cyclisation state of the crown component. No significant production of covalently linked donor-acceptor species is observed from these reactions, supporting the presence of an intermediate complex pre-organised to catenane formation. In contrast, oxidative coupling of an alkyl solubilised diimide gave no interlocked products and yielded only small amounts of cyclic poly-imide macrocyles.