Synthesis, Complexation Behaviors, and Crystal Structures of Azamacrocycles Having Tropon-2-yl Groups

Azamacrocycles 1-3, having one to three tropon-2-yl groups, were found to display unique absorption spectral changes in the presence of guest cations. Aza-15crown-5 1, 1,7-diaza-12-crown-4 2a, 1,7-diaza-15-crown-5 2b, 1,10-diaza-18-crown-6 2c, and 1,5,9-triazacyclododecane 3 derivatives showed Ba^2+, Zn^2+, Ca^2 +, Ba^2+, and Zn^2+ selectivities, respectively. The crystal structures of free hosts 2a and 2c, the calcium thiocyanate complexes of 1 and 2c, the barium thiocyanate complex of 1, and the zinc thiocyanate complex of 2a were elucidated by X-ray analysis. The 2a·zinc and 2c·calcium thiocyanate complexes consist of an ion pair with a zinc tetrathiocyanate anion and a 2a·zinc cation and with a calcium hexathiocyanate anion and a 2c·H2O·calcium cation, respectively. The aminotropone moiety of 2a and 2c forms a conjugated 10-electron system. Complexation gave rise to deconjugation between the tropone ring and the nonbonding electron pair of the nitrogen atom to cause absorption spectral changes.