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

By simple ligand exchange of the cationic transition-metal complexes [(Cp*) M(acetone)(3)](OTf)(2) (Cp* = pentamethylcyclopentadienyl and M = Ir or Rh) with pillar[5] arene, mono-and polynuclear pillar[5] arenes, a new class of metalated host molecules, is prepared. Single-crystal X-ray analysis shows that the charged transition-metal cations are directly bound to the outer pi-surface of aromatic rings of pillar[5] arene. One of the triflate anions is deeply embedded within the cavity of the trinuclear pillar[5] arenes, which is different to the host-guest behavior of most pillar[5] arenes. DFT calculation of the electrostatic potential revealed that the metalated pillar[5] arenes featured an electron-deficient cavity due to the presence of the electron-withdrawing transition metals, thus allowing encapsulation of electron-rich guests mainly driven by anion-pi interactions.