Complexation of C-methyl pyrogallarene with small quaternary and tertiary alkyl ammonium cations

Abstract

Complexation properties of pyrogallarene 1 towards small quaternary and tertiary alkyl ammonium cations were studied in gas phase, solution and in solid state. In gas phase both dimeric capsules and monomeric 1 : 1 complexes of all cations 2a+–d+ are detected but only in the case of 2a+ is the abundance of the capsule form higher than the monomeric 1 : 1 complex. A similar trend is observed in NMR experiments, which reveal a favourable dimeric complex for 2a+ and a weaker dimeric complex for 2b+ but only monomeric complexes for 2c+ and 2d+. Also in solid state, 2a+ and 2b+ form capsules when crystallized from MeOH while 2c+ and 2d+ form dimeric 1 : 1 complexes. As a reference, hetero-conformational dimeric capsule EtOH@12 obtained from the crystallization without any guest, is reported. The capsule consists of two directly hydrogen-bonded pyrogallarenes 1, one in boat conformation and the other in crown conformation, and encloses a molecule of ethanol.