Entropy Versus Enthalpy Controlled Temperature/Redox Dual‐Triggered Cages for Selective Anion Encapsulation and Release
Kyosuke Hamashima, Junpei Yuasa
Abstract
Abstract New C 3 ‐symmetric imidazole ligands were designed with phosphine and phosphine oxide linkers ( L P and L PO , respectively) to demonstrate a dual‐triggered dynamic closed coordination cage. Both L P and L PO form discrete Zn 4 L 4 ‐closed cages ( 1 P and 1 PO , respectively) with excellent selectively for BPh 4 − , whereas 1 P and 1 PO encapsulate neither a slightly larger size anion [B(C 6 H 4 CH 3 ) 4 − ] nor smaller size anions (BF 4 − , PF 6 − , SbF 6 − , and OSO 2 CF 3 − ). 1 PO 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: BPh 4 − ⊂ 1 PO 1 PO +BPh 4 − ). In contrast 1 P has less negative enthalpy and entropy changes, thus preserving the captured anion over a wide range of temperatures (298 K to 343 K). The 1 P cage can be quantitatively oxidized to the 1 PO cage by a mild oxidant (Ox.=H 2 O 2 ), and therefore the captured anion can be released by a redox triggering event (trigger 2: BPh 4 − ⊂ 1 P +Ox.→ 1 PO +BPh 4 − ).