DOSY study on dynamic catenation: Self-assembly of a [3]catenane as a meta-stable compound from twelve simple components

Synthesis of [2]catenane 6 has been successfully achieved by the combinatio n of Pd complex I and pyridines 2 and 3 at a molar ratio of 2:1:1 in D2O. A mixture of square molecule 4 (prepared from 1 and 2) and macrocycle 5 (obt ained from 1 and 3). in which the final ratio of 1, 2, and 3 was kept 2:1:1 reorganizes in D2O/CD3OD (1:1) to form 6 within one day. However, the same mixture in DO shows the formation of novel [3]catenane 7 along with the [2 ]catenane. In order to make 7, the theoretical ratio of components 1, 2. an d 3 should be 3:1:2. Thus, deliberately maintaining such ratio of the above - mentioned molecules. a higher proportion of the [3]catenane is observed i n D2O as found from H-1 NMR spectra of the system. Reorganization of the tw elve components to form [3]catenane is supported by studies with the DOSY m ethod. This method is a first attempt to separate. from a mixture. either c atenanes or any other supramolecular self-assembly structures. CSI-MS studi es further support the assigned catenane super structures 6 and 7 All the r esults indicate that the [2]catenane is thermodynamically the most stable s tructure, while the [3]catenane is a meta-stable self-assembly.