Switching of molecular insertion in a cyclic molecule via photo- and thermal isomerization

Two new cyclic ligands were synthesized: a ligand with two trans-azobenzene moieties and one bipyridine moiety, trans(2)-oAB-O13, and a ligand with two trans-azobenzene moieties and two bipyridine moieties, trans(2)-oAB-bpy. Both ligands underwent reversible trans-cis isomerization at the azobenzene moieties. The mole ratios of the trans(2) form:trans-cis form:cis(2) form, evaluated by (1)H NMR spectroscopy of the photostationary states prepared by 1 h illumination, were 0.13:0.27:0.60 (365 nm irradiation) and 0.41:0.47:0.12 (436 nm irradiation) for oAB-O13, and 0.18:0.12:0.70 (365 nm irradiation) and 0.36:0.43:0.21 (436 nm irradiation) for oAB-bpy. When trans(2)-oAB-O13 was mixed with Cu(I), both the bipyridine units and the polyether chains coordinated to the copper center. Addition of a noncyclic bipyridine ligand, trans(2)-oAB-2OH, afforded a bis(bipyridine)copper(I) complex, Cu(trans(2)-oAB-O13)(trans(2)-oAB-2OH)]BF(4). The bis(bipyridine) ligand, trans(2)-oAB-bpy, formed a 1:1 complex with Cu(I), Cu(trans(2)-oAB-bpy)]BF(4). Cu(cis(2)-oAB-bpy)]BF(4) did not undergo the ligand substitution reaction with a noncyclic ligand with two azobenzene moieties and one bipyridine moiety, oAB, whereas its thermal isomerization in the presence of oAB caused the formation of Cu(trans(2)-oAB-bpy)(trans(2)-oAB)]BF(4), indicating that the isomerization and ligand exchange reactions synchronized via a conformational change of the cyclic ligand.