Stereoselective Cyclopolymerization of Polar 1,6-Heptadiynes by Novel, Tailor-Made Ruthenium-Based Metathesis Catalysts

The cyclopolymerization of 4,4‐bis(hydroxymethyl)‐1,6‐heptadiyne (M1), 4‐(carboxyethyl)‐1,6‐heptadiyne (M2), 4‐(hydroxymethyl)‐1,6‐heptadiyne (M3), and 4‐carboxy‐1,6‐heptadiyne (M4) using five different well‐defined metathesis initiators was investigated. Control of molar mass was achieved with catalysts bearing trifluoroacetate ligands. 13C NMR experiments showed that poly‐M2, prepared by the action of any catalyst consisted solely of five‐membered ring structures, i.e., 1,2‐(cyclopent‐1‐enylene)vinylene units. Effective conjugation lengths of all polymers were calculated from the corresponding UV‐Vis absorption maxima, which varied reversibly with temperature.