Di- and Trinuclear Initiators for 1,6-Heptadiyne Polymerization

Significance

The synthesis of bi- and trinuclear Hoveyda-Schrock-type metathesis initiators, and their application to the polymerization of 1,6-heptadiynes, is reported. Treatment of 1-3 with heptadiynes (R = R′ = CO₂CH₃, CO₂ t-Bu, CH₂OH; or R′ = H) led to the highly selective formation of polymers bearing cyclopentenevinylene repeat units, with moderate yields (17-86%), molecular weights ranging from 4,400-23,300 g/mol, and polydispersities of 1.3-2.0. Cleavage of the siloxane linker in a polymer derived from 2 resulted in a twofold decrease in molecular weight and no change in polydispersity, confirming the formation of a homogeneous A _n XA _n block copolymer.