Quantitative evaluation of the chloride template effect in the formation of dicationic [1(4)]imidazoliophanes

The formation of macrocycles containing two imidazolium rings such as 1.2X and 2.2X is anion-directed through hydrogen bonding. The template effect exerted by the chloride anion in the ring-closure reaction of the monocationic model intermediate 9+ to yield the 1(4)]imidazoliophane 2(2+) has been evaluated. This effect was quantified following the kinetics of the macrocyclization by using a UV-vis technique. The rate of the ring closure of monocation 9+ is increased up to 10 times, in the presence of Bu4NCl 0.04 M. This finding confirms that the template effect is operative in the macrocyclization leading to dicationic 1(4)]imidazoliophanes.