Construction of π-Surface-Metalated Pillar[5]arenes which Bind Anions via Anion-π Interactions

The development of novel and functional macrocyclic host molecules has always been one of the central subjects within supramolecular chemistry. In this study, by simple ligand exchange of the complexes [(Cp*)M(acetone)3](OTf)2 (Cp* = pentamethylcyclopentadienyl and M = Ir or Rh) with pillar[5]arene, mono- and polymetallic pillar[5]arenes, a new class of metalated host molecules, have been successfully prepared. Single-crystal analysis revealed that the charged transition metal cations were directly bound to the outer π-surface of aromatic rings of pillar[5]arene. Interestingly, one of the triflate anions was deeply embedded within the cavity of trimetallic pillar[5]arenes, which is obviously different from the host-guest behavior of the most known pillar[5]arenes. The DFT calculation of the electrostatic potential revealed that the metalated pillar[5]arenes featured an electron-deficient cavity, thus allowing for encapsulating electron-rich guests mainly driven by anion-π interactions.