Synthesis and X?ray Structures of Novel Macrocycles and Macrobicycles Containing N,N-Di(pyrrolylmethyl)?N?methylamine Moiety: Preliminary Anion Binding Study

摘要

The [2 + 2] Schiff base condensation reactionsnbetween the newly synthesized dialdehyde, N,N-di(α-formylpyrrolyl-nα-methyl)-N-methylamine), and ethylenediaminenor p-phenylenediamine dihydrochloride readily afforded then30- and 34-membered large size macrocycles in very highnyields. Subsequent reduction reactions of these macrocyclesnwith NaBH4 gave the corresponding saturated macrocyclicnhexaamines in good yields. The analogous reaction of the newndialdehyde with a triamine molecule afforded the [3 + 2] Schiffnbase macrobicycle in high yield, which was then reduced bynreaction with NaBH4 to give the saturated macrobicycle. Allnthese compounds were characterized by spectroscopicnmethods. The anion binding properties of the saturatednmacrocycles having the ethylene and the phenylene linkers innCDCl3 were studied by NMR titration methods. Although they have similar pyrrolic and amine NH groups their bindingnproperties are different and interesting, owing to the conformational flexibility or rigidness rendered by the ethylene or phenylenengroups, respectively. The macrocycle having the ethylene linkers binds anions in a 1:1 fashion, while the other receptor havingnthe phenylene linkers prefers to bind anions in a sequential 1:2 fashion and has a multiple equilibria between a 1:1 and a 1:2ncomplexes, as shown by their binding constants, curve fittings by EQNMR, and Job plots. The X-ray structures of the 1:2nmethanol, the aqua and the benzoate anion complexes of the macrocycles show two cavities in which the guests are bound,ncorrelating with the high affinity found for the formation of stable 1:2 complexes in solution. The X-ray structure showed that thenmacrobicycle Schiff base adopts an eclipsed paddle-wheel shaped conformation and exhibits an out-out configuration at thenbridgehead nitrogen atoms.