When Self-Assembly Fails: Stepwise Metal-Directed Synthesis of [2]Catenanes

On the attempted synthesis of a series of homo- and heterotrimetallic [2] catenanes by the self-assembly of a 2-(pyridin-4-ylmethyl)-2,7-diazapyrenium ligand, (ethylenediamine) palladium(II) or platinum(II) nitrate, and a dioxoaryl bis(N-monoalkyl-4,4'-bipyridinium) salt as building blocks, both the one-pot direct self-assembly of the components and the so called "magic ring" approach fail to produce the expected trinuclear [2] catenanes under thermodynamically driven conditions. However, one of the target supramolecules is obtained by following a stepwise protocol, consisting of the threading of a dinuclear Pt-II metallacycle and the dioxoaryl bis(N-monoalkyl-4,4'-bipyridinium) axle, followed by kinetically controlled Pt-II-directed cyclization of the corresponding pseudorotaxane.