Macrotricycles ammonium complexes

A relative of the latter class of compounds are the macrotricyclic quaternary ammonium salts which have been reported by Schmidtchen. The bridges may contain either methylenes or ethyleneoxy units and the nitrogens are quaternarized. The underlying principle is to provide a cavity suitable for solvating or at least trapping anions. Schmidtchen presents evidence which suggests the formation of halide inclusion complexes. The synthesis of these molecules is accomplished along more or less traditional lines Such a species is illustrated above as compound 19. 

A system exhibiting chiral recognition. The chiral macrotricyclic tet-raamide (250) (Lehn, Simon Moradpour, 1978) has been used for the complexation, extraction and transport of primary ammonium salts. The tetraamide was used rather than the corresponding tetraamine because of the lower basicity of the nitrogens in the former ligand. This avoids the possibility of proton transfer occurring from the primary ammonium substrates R-NH3+ used as guests. In a typical experiment, a solution of a primary ammonium salt, such as naphthylethyl ammonium or phenylalanine methylester hydrochloride in hydrochloric acid was... 

A theoretical (AMI molecular orbital) treatment of boron analogues of the katapinand series as well as macrotricyclic compounds related to 16 has also recently appeared. As with the ammonium-based host molecules the macrotricyclic hosts containing four boron atoms exhibited a greater degree of anion specificity as a consequence of the rigidity of their binding sites. In all cases, size selective complexation of halide anions was observed with accompanying decreases in B - B distances and partial sp -> sp rehybridization. ... 

Enolase type activity is displayed in the efficient supramolecular catalysis of H/D exchange in malonate and pyruvate bound to macrocyclic polyamines [5.32]. Other processes that have been studied comprise for instance the catalysis of nucleophilic aromatic substitution by macrotricyclic quaternary ammonium receptors of type 21 [5.33], the asymmetric catalysis of Michael additions [5.34], the selective functionalization of doubly bound dicarboxylic acids [5.35] or the activation of reactions on substituted crown ethers by complexed metal ions [5.36]. 

Metz, B., Rosalky, J. M., Weiss, R., [3] Cryptates - X-ray crystal-structures of chloride and ammonium ion complexes of a spheroidal macrotricyclic ligand. J. Chem. Soc., Chem. Commun. 1976, 533-534. 

MD simulations of halide anions [X]- and their inclusion complexes [X] c [L4+] with a macrotricyclic tetrahedral host built from four quaternary ammonium sites dissolved in [C4mim][PF6] were carried out [118]. In the dry IL the uncomplexed halides were surrounded by four to five [C4mim]+ cations which bond via hydrogen bonding to facial coordination. The first solvation shell of [Cl]-, [Br], and [I] comprised of three to four cations next to four H20 molecules for the humid system. The solvation of the [L4+] host and of its [X]-1 [L4+] complex mainly involved anions in the dry IL, and additional H20 molecules in the humid IL. Free energy perturbation calculations predicted that in the dry liquid [F] is preferred over [Cl] , [Br] and [I]- in contrast to the aqueous solution where [L4+] was selective for [Cl]-. In the humid liquid no [F] /[C1] discrimination was observed, showing the importance of small amounts of water on the complexation selectivity [118]. 

Figure 72 A basket-shaped macrotricyclic receptor for the complexation of quaternary ammonium cations [98]...

Ballardini et al. have reported detailed photophysical studies with a cylindrical macrotricyclic receptor (Figure 77) and its complexes with protons, ammonium ions and [Pt(NH3)2(bipy)]2+ [103],... 

---