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, [BBIPYBIXYCY] 4+ from bipyridine (BP) and 1,4‐bis(bromomethyl)benzene (BBB) , directed by the template, 1,5–bis[2(2–hydroxyethoxy)ethoxy]naphthalene (1/5BHEEN) 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 1 H NMR spectroscopy in D 7 ‐DMF solution. On the basis of this spectroscopic evidence and supporting chemical data, the formation of {[2]‐[BPP34C10]‐[BBIPYBIXYCY] catenane} 4+ 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, [BBIPYXY] 2+ , which has been isolated and shown to be an intermediate in the self‐assembly process leading to the [2]catenane, presumably via the [BXYBBIPYXY] 3+ trication — the final intermediate which again has not been isolated.