Host-Guest Complexation. 40. Synthesis and Complexation of Macrocyclic Hosts Containing Cyclic Ureas, Anisyls, and Steric Barriers

Article abstract of DOI:10.1021/jo00373a001

The synthesis and complexing properties of eight new macrocyclic hosts are described.These hosts contain three cyclic urea and two anisyl units as binding sites combined with one of the following: a m-xylylene, an aryl bromide, an aryl ester, or biphenyl units substituted to provide potential steric barriers to complexation with bulky guests.The association constants and free energies of complexation of alkali metal cations and ammonium and alkylammonium ions in CDCl3 saturated with H2O were determinated by the extraction method.Substitution for the hydrogen in the X-position of 3 with Br or CO2CH3 groups generally decreased the binding of alkali metal cations by 0 to 2 kcal mol^-1.A crystal structure of the Na⁺ complex of macrocycle 5 containing the aryl ester bridging unit shows that the carbonyl of the ester hydrogen-bonds a water molecule, which in turn ligates Na⁺.Incorporation of steric barriers into the bridging m-xylylene units provides hosts which discriminate in binding MeNH3⁺ and (CH3)3CNH3⁺ by up to 2.5 kcal mol^-1.