Gold-Clip-Assisted Self-Assembly and Proton-Coupled Expansion-Contraction of a Cofacial Fe III -Porphyrin Cage.

A molecular cage {Au-8(mu-PAnP)(4)[Fe(H2O)(2)(TPyP)](2)(OTf)(2)}(OTf)(8) (1) composed of two cofacial Fe-III-porphyrin can be self-assembled from the gold clip [Au-2(PAnP)Cl-2] and Fe3+(H2O)(2)(TPyP)(+) (PAnP=9,10-bis(diphenylphosphino)anthracene, TPyP=meso-tetra(4-pyridyl)porphyrinato). The height of the cage is 8.579(3) angstrom. The addition of a base to a solution of the cage leads to a contracted and twisted cage {[Au-8(mu-PAnP)(4)[Fe-2(mu-O)(TPyP)(2)]}(OTf)(8) (2), which has a height of approximate to 4.4 angstrom and porphyrin-porphyrin torsional angle of approximate to 20 degrees. The contracted cage can be synthesized independently from the gold clip and Fe-2(mu-O)(TPyP)(2). The spectroscopy and crystal structure of an unclipped analog of the contracted cage, {[AuPPh3)(8)[Fe-2(mu-O)(TPyP)(2)]}(OTf)(8) (3), supports the DFT-calculated structure of 2. NMR and UV/Vis titrations show that the expansion-untwisting and contraction-twisting of the cage is reversible.