Reactivity of Contact Ion Pairs in a Charged Monotopic Receptor

An integrated FT-ICR and computational approach has been employed to investigate the gas phase structure and reactivity of ESI-formed complexes between organic and inorganic acids (HX) and a K+ - containing hexaazamacrocycle (M). Two limiting structures are available to those complexes, either the classical [MK+center dot XH]or the zwitterionic [MH+center dot K+center dot X-]one, with the latter prevailing over the first by increasing the gas-phase acidity of the HX ligand. Both structures undergo the HX displacement when reacting with 2,4-pentanedione (P0) and its 1,1,1-trifluoro (P3) and 1,1,1,5,5,5-hexafluoro (P6) derivatives. The HX displacement efficiency is found to depend not only on the specific structure of the complex, but also on the acid/base properties of the diones. Among them, P3 displays the lowest reactivity towards the [MK+center dot XH] complexes. These findings are consistent with the co-existence of a direct HA-to-HX and a base-catalyzed A(-)-to-HX substitution channels. The PO < P3 更多