A study of the complexation of bis(m-phenylene) crown ethers and secondary ammonium ions

Two macrocycles, bis(m-phenylene)-26-crown-8 (1) and bis(m-phenylene)-32-crown-10 (2), were combined with several linear components, dibenzyl- (3 . PF6), di-n-butyl- (4 . PF6), and diphenethyl-(5 . PF6) ammonium hexafluorophosphate salts. The smaller macrocycle 1 was shown not to complex effectively with any of the ammonium salts in solution by H-1 NMR, but 1:1 complexes were shown to exist in the "gas phase" as [1:3], [1:4], and [1:5] by high-resolution fast atom bombardment mass spectrometry (HRFABMS) and electrospray ionization mass spectrometry (ESIMS). The X-ray crystal structure of macrocycle 1 is reported. The larger macrocycle 2 did form 1:2 complexes with the ammonium salts in solution, which were observed as well in the solid and gas phases. X-ray crystal structures of the pseudorotaxanes [2:(3)(2)]. 2PF(6) and [2:(5)(2)]. 2PF(6) were determined and are discussed. The pseudorotaxanes are stabilized by hydrogen bonding between the ammonium hydrogens of the linear salt unit and the oxygens of the crown ether macrocycle. Secondary stabilization also occurs by edge-to-face pi stacking.