Entropy Versus Enthalpy Controlled Temperature/Redox Dual-Triggered Cages for Selective Anion Encapsulation and Release.

Abstract

New C3 -symmetric imidazole ligands were designed with phosphine and phosphine oxide linkers (LP and LPO , respectively) to demonstrate a dual-triggered dynamic closed coordination cage. Both LP and LPO form discrete Zn4 L4 -closed cages (1P and 1PO , respectively) with excellent selectively for BPh4 - , whereas 1P and 1PO encapsulate neither a slightly larger size anion [B(C6 H4 CH3 )4 - ] nor smaller size anions (BF4 - , PF6 - , SbF6 - , and OSO2 CF3 - ). 1PO exhibits more negative enthalpy and entropy changes upon anion encapsulation, thus releasing almost all of the encapsulated anions at high temperature (343 K) (trigger 1: BPh4 - ⊂1PO 1PO +BPh4 - ). In contrast 1P has less negative enthalpy and entropy changes, thus preserving the captured anion over a wide range of temperatures (298 K to 343 K). The 1P cage can be quantitatively oxidized to the 1PO cage by a mild oxidant (Ox.=H2 O2 ), and therefore the captured anion can be released by a redox triggering event (trigger 2: BPh4 - ⊂1P +Ox.→1PO +BPh4 - ).