COMPLEXATION OF CROWN-ETHERS AND PODANDS WITH TROPYLIUM CATIONS - DETERMINATION OF STABILITY-CONSTANTS AND CRYSTAL-STRUCTURE OF THE DIBENZO-24-CROWN-8-TROPYLIUM CATION COMPLEX

The host-guest complexation of macrocyclic hosts and aromatic carbeniu m cations has been studied. Three different tropylium tetrafluoroborat e compounds were prepared in order to study the interaction between po sitively charged guests and crown ether hosts. The stability constants of complexes were measured by H-1 NMR and UV/Vis spectroscopic method s. Fast atom bombardment mass spectroscopy (FABMS) was used to screen the stoichiometry of complexes. The main interaction force was pi-pi-s tacking and cation-pi interaction between aromatic units in benzene-su bstituted crown ethers and aromatic guests. Additionally, two diphenox yalkane ligands were prepared to investigate the importance of the mac rocyclic ring in the complexation between host and guest. The X-ray cr ystal structure of dibenzo-24-crown-8 (2B24C8) with tropylium tetraflu oroborate inclusion complex was determined, giving the following cryst al data: 2B24C8-TrBF4 (C31H39O8 . 0.5 CH3CN . BF4), monoclinic, space group P2(1)/n (no. 14), a = 14.158(2), b = 14.791(2), c = 16.384(2) An gstrom, beta = 93.90(1), Z = 4. The crystal structure showed that the tropylium ion guest formed an inclusion complex with benzene-substitut ed crown ethers, and its plane is orientated nearly parallel to the pl anes of the aromatic nucleus of the host.