A SWITCHABLE HYBRID [2]-CATENANE BASED ON TRANSITION-METAL COMPLEXATION AND PI-ELECTRON DONOR-ACCEPTOR INTERACTIONS

A bimodal [2]-catenane has been synthesized via a copper(I) templated synthesis. The compound contains both a transition metal coordination site and a set of pi-electron rich and pi-electron deficient aromatic units suitable for the formation of acceptor-donor complexes. Each con stituent ring is thus different from the other, and the organic backbo ne can adopt two favored contrasting orientations by circumrotation of one ring within the other: (i) in the metal complex mode, each dpp un it (dpp = 2,9-diphenyl-1,10-phenanthroline) is entwined about the othe r, while a cationic species is complexed in the coordination site thus created; (ii) in the organic pi-electron acceptor-donor complex mode, the dpp fragments are remote from one another, and the pi-electron ri ch and pi-electron deficient units stack to form a complex. The conver sion of one binding mode to the other implies complete topographical r earrangement of the molecule. It can be triggered by adding or removin g the cation center (Cu+, Li+, or H+), bonded to the dpp-containing co mplexing site. Interestingly, this switching process can be easily mon itored by H-1 NMR, since it involves drastic relative orientational ch anges. It can also be evidenced by electronic spectroscopy. In particu lar, the proton-driven rearrangement reactions lead to significant cha nges in the absorption spectrum, which correspond to the appearance (b y deprotonation) and disappearance (by protonation of the dpp) of a ch arge transfer band (around 470 nm) resulting from the pi-electron dono r-acceptor noncovalent interaction.