Zinc(II)-templated synthesis of a [2]-catenane 2,2′,6′,2"-terpyridine-incorporating cycle and a 1,10-phenanthroline-containing ring

A nonsymmetrical [2]-catenane has been synthesized, with a 5-coordinated metal center (Zn2+) as template. One of the two rings contains a terdentate ligand (2,2',6',2"-terpyridine) and the other one incorporates a bidentate chelate (1,10-phenanthroline). The first ring was prepared separately and, subsequently, Zn2+ was used as the gathering and threading element to pass the stringlike component through the ring. This open-chain species bears two terminal olefins, which were reacted with Grubbs first-generation catalyst (ring-closing metathesis) to afford the desired catenane. Hydrogenation of the double bond and removal of the zinc(II) template afforded the final free [2]-catenane in 40% yield from the terdentate ligand-containing cycle and the diolefinic compound. Complexation studies on this new pentacoordinating catenane were carried out with Fe(II) or Cu(II). The most interesting observation is that the 5-coordinated complexes obtained are strongly stabilized. Their electrochemical reduction occurs at negative potentials.