Convergent synthesis of isomeric pairs of metallocene-containing polyether macrocycles

A general method for rapid construction of metallocene-based hosts is described. Treatment of polyether bridged bis(diphenylacetylenes) with a source of cyclopentadienyl cobalt at high temperature leads, via macrocyclization and capture of the intermediate cyclobutadiene, to macrocyclic systems tethered to an integral metallocene platform. Equal yields of the two possible structural isomers, the products of parallel or antiparallel cycloaddition of the precursor, are obtained. A combination of X-ray crystallography and NMR is employed to assign structures to the individual isomers and to assess the strength of lithium ion binding by the individual macrocycles.