ic3011822_si_002.cif (103.03 kB)
Synthesis and X‑ray Structures of Novel Macrocycles and Macrobicycles Containing N,N-Di(pyrrolylmethyl)‑N‑methylamine Moiety: Preliminary Anion Binding Study
dataset
posted on 2016-02-20, 14:11 authored by Rajnish Kumar, Tapas Guchhait, Ganesan ManiThe [2 + 2] Schiff base condensation reactions between
the newly
synthesized dialdehyde, N,N-di(α-formylpyrrolyl-α-methyl)-N-methylamine), and ethylenediamine or p-phenylenediamine dihydrochloride readily afforded the 30- and 34-membered
large size macrocycles in very high yields. Subsequent reduction reactions
of these macrocycles with NaBH4 gave the corresponding
saturated macrocyclic hexaamines in good yields. The analogous reaction
of the new dialdehyde with a triamine molecule afforded the [3 + 2]
Schiff base macrobicycle in high yield, which was then reduced by
reaction with NaBH4 to give the saturated macrobicycle.
All these compounds were characterized by spectroscopic methods. The
anion binding properties of the saturated macrocycles having the ethylene
and the phenylene linkers in CDCl3 were studied by NMR
titration methods. Although they have similar pyrrolic and amine NH
groups their binding properties are different and interesting, owing
to the conformational flexibility or rigidness rendered by the ethylene
or phenylene groups, respectively. The macrocycle having the ethylene
linkers binds anions in a 1:1 fashion, while the other receptor having
the phenylene linkers prefers to bind anions in a sequential 1:2 fashion
and has a multiple equilibria between a 1:1 and a 1:2 complexes, as
shown by their binding constants, curve fittings by EQNMR, and Job
plots. The X-ray structures of the 1:2 methanol, the aqua and the
benzoate anion complexes of the macrocycles show two cavities in which
the guests are bound, correlating with the high affinity found for
the formation of stable 1:2 complexes in solution. The X-ray structure
showed that the macrobicycle Schiff base adopts an eclipsed paddle-wheel
shaped conformation and exhibits an out-out configuration
at the bridgehead nitrogen atoms.