Olefin metathesis reaction has been utilized in a wide research area of synthetic organic chemistry. Its contribution to the polymer chemistry is remarkable either, especially in terms of a living polymerization. Now the metathesis polymerization of olefin monomers is one of the most common ways to construct numerous polymer architectures and nanostructures. On the other hand, only a few study reported the polymerization of alkyne-containing molecules, which can efficiently produce conjugated backbone.
We studied the cyclopolymerization of 1,6-heptadiyne derivatives, which is another olefin metathesis polymerization, using Ru-based Grubbs catalysts. In the history of cyclopolymerization of diynes, these catalysts had shown poor activity and resulted in no polymer, whereas Mo-alkylidenes had achieved the efficient cyclopolymerization. We focused on the control of reaction conditions to improve the efficiency of polymerization utilizing common Grubbs catalysts, instead of the catalyst engineering. As a result, it was disclosed that severe dependence on various factors, such as the solvent, temperature, dissociative ligands, and even steric effect, could alter the efficiency of polymerization. Furthermore, sometimes the polymerization suffered from a [2+2+2] cycloaddition reaction, which generated dimers of 1,6-heptadiyne derivatives as side products. With an emphasis on mechanistic aspects, these understandings enabled us to explain why Grubbs catalysts could not catalyze the cyclopolymerization in the previous work and design highly efficient polymerization system.