posted on 2003-07-31, 00:00authored byAlexander Shivanyuk, Jan C. Friese, Steve Döring, Julius Rebek
Pyrrogallolarenes 2 were prepared by acid-catalyzed condensation of pyrrogallol with aldehydes.
Compound 2a crystallizes from a methanol solution of quinuclidine hydrochloride to give a dimeric
molecular capsule surrounding one disordered quinuclidinium cation. The molecules of 2a are
connected by direct hydrogen bonds and by bridging methanol and water molecules. The chloride
anion is positioned outside the capsule and is hydrogen bonded to the hydroxy groups of 2a. The
shortest distance between the cation and anion was found to be 6.7 Å. Crystallization of 2b from
aqueous acetonitrile resulted in a dimeric capsule linked by a polar belt of 16 hydrogen bonding
water molecules. Four acetonitrile molecules occupy the cavity of this dimeric capsule and assume
two binding sites that differ in hydrogen bonding and electronic environment. Compounds 2 also
form hydrogen-bonded dimeric molecular capsules in alcohols and aqueous acetonitrile solutions.
These assemblies readily encapsulate tetramethylammonium, tetramethylphosphonium, quinuclidinium, and tropylium cations to give complexes stable on the NMR time scale at 233 K.