Snapshot of cyclooctyne ring-opening to a tethered alkylidene cyclic polymer catalyst.

Cyclooctyne reacts with the trianionic pincer ligand supported alkylidyne [ BuOCO]WCC(CH)(THF) (1) to yield tungstacyclopropene (3) and tungstacyclopentadiene (4) complexes. The ratio of 3 and 4 in the reaction mixture depends on the stoichiometry of the reaction. The maximum concentration of 3 occurs with one equiv. of cyclooctyne and 4 is the exclusive product of the reaction above three equivalents. Both complexes 3 and 4 convert to the cyclooctyne ring-opened product 5 upon heating. While the conversion of 4 to 5 is accompanied by formation of polycyclooctyne as a white precipitate during the reaction, conversion of 3 to 5 is homogeneous. Exhibiting Ring Expansion Polymerization (REP), complexes 4 and 5 initiate the polymerization of phenylacetylene to generate cyclic poly(phenylacetylene) (c-PPA).