The Mechanisms of Making Molecules to Order

The mechanisms of formation of a [2]catenane and one of its molecular components have been investigated. While the synthesis of the tetracationic cyclophane, BBIPYBIXYCY⁴⁺ from bipyridine BP and 1,4‐bis(bromomethyl)benzene BBB, directed by the template, 1,5–bis[2(2–hydroxyethoxy)ethoxy]naphthalene1/5BHEEN becomes less efficient (23 to 5%) under ultra‐high pressure reaction conditions (12 kbars), the self‐assembly of {[2]‐[BPP34C10]‐[BBIPYBIXYCY] catenane}⁴⁺ from BP and BBB in the presence of BPP34C10 can be achieved with increased efficiency (18 to 42%) at 12 kbars. This difference in the trends of the yields can be ascribed to the enhanced templating action of BPP34C10 relative to that of 1/5BHEEN when two moles of BP and two moles of BBB are being employed to construct the tetracationic cyclophane. The self‐assembly of the [2]catenane from BP, BBB, and BPP34C10 has been followed by ¹H NMR spectroscopy in D₇‐DMF solution. On the basis of this spectroscopic evidence and supporting chemical data, the formation of [2]‐[BPP34C10]‐[BBIPYBIXYCY] catenane⁴⁺ from two moles of BP, two moles of BBB, and one mole of BPP34C10 is believed to proceed via the monoquatemary intermediate, MBXYBIPY⁺, which has not been isolated, and the dicationic species, BBIPYXY²⁺, which has been isolated and shown to be an intermediate in the self‐assembly process leading to the [2]catenane, presumably via the BXYBBIPYXY³⁺ trication — the final intermediate which again has not been isolated.