Macrocyclic Receptor Molecules for Guanidinium Cations. Preparation, X-ray Structures, and Kinetic Stabilities of 1:1 Complexes of Guanidinium Perchlorate with Benzo-27-crown-9, Dibenzo-27-crown-9, and Dibenzo-30-crown-10

Abstract

The complexation of guanidinium perchlorate with crown ethers of different ring size (18-33 ring atoms) and with different subunits, e.g., catechol and 1,3-xylyl moieties, has been studied by using two-phase extraction experiments. The results demonstrate that the 18-crown ethers are able to form perching complexes, whereas crown ethers with <27 ring atoms have a suitable ring size to form encapsulated complexes with guanidinium perchlorate. Aromatic, catechol, and especially 1,3-xylyl moieties have a destabilizing effect on the complex formation. The crystal and the molecular structures of the 1:1 complexes of guanidinium perchlorate with benzo-27-crown-9 (7), dibenzo-27-crown-9 (8), and dibenzo-30-crown-10 (11) have been determined by X-ray crystallography. In these encapsulated complexes all hydrogen atoms of the guanidinium cation are used in hydrogen bonds to the macrocyclic host. The 27-crown ethers show an optimal fit between cation and the macrocyclic host with a complementary binding scheme. Dynamic 500-MHz 1H NMR spectroscopy gave the kinetic stabilities of these complexes with ΔGd‡ values of 11.5, 11.2, and 12.0 kcal mo1-1 for the complexes with benzo-27-crown-9, dibenzo-27-crown-9, and dibenzo-30-crown-10, respectively. © 1983, American Chemical Society. All rights reserved.