Two series of aza macrocycles containing the phenyldinaphthomethane subunit (a three bladed propeller); crystal structures and dynamic NMR spectroscopy

Abstract

Two new series of azapropeller crowns have been synthesised and investigated. The aza-propeller crowns 7,10-ditosylaza-1,4,13,16-tetraoxacyclooctadecane, (9a) and 4,7,10-tritosylaza-1,13-dioxacyclo-pentadecane, (11) have been shown by X-ray structure determination to have the propeller conformation matching that of the common isomer found previously in the polyether propeller crowns 1. The N-tosyl substituents, used as a probe of the movement of attached ring segments on the macrocyclic ring, rendered observable (in ¹H NMR studies) the flipping of these segments, for which the calculated free energy of activation was typical of that for an unsubstituted propeller, ΔG^‡₂₁₇= 10.54 kcal mol^–1 at the coalescence temperature for 9a, ΔG^‡₂₁₅= 10.74 kcal mol^–1 for the analogous ring compound 10 with one additional methylene residue, and ΔG^‡= 12.5 ± 0.4 kcal mol^–1(at 230–240 K) for the tritosyl compound 11. These results and other NMR data show that the relatively slow switch of the propeller is the movement which mainly controls the observable process. Successful detosylation of 9a is reported. Two examples of a second series of propeller crowns having amide links in the macrocyclic ring have been prepared by two routes. Their selectivity for transport of silver and lead cations is described.