An additional potential donor-bearing alkylidene-containing latent NHC–ruthenium-based catalyst for olefin metathesis polymerization†
Latent metathesis catalysts are very important in ring-opening metathesis polymerization (ROMP) because they provide access to high-tech thermoset polymers from dicyclopentadiene (DCPD). The discovery of new latent catalysts is very challenging because they need to be inactive at room temperature and upon activation they must completely convert the starting materials into the desired product. Herein, we report the synthesis of a series of novel complexes 1–4 bearing an additional potential donor, substituted pyridine, which can form a coordination bond with the metal center of an alkylidene-containing NHC–Ru-based complex. Then, their latent catalytic behavior in the ROMP of DCPD is studied. We found that complexes 1 and 2 were inactive at 30 °C and were only active when the temperature was increased to 60 °C, which initiated the ROMP of DCPD. The absence of a sixth coordination bond in the 4-substituted pyridine ligand in 3 and the presence of a potential donor ligand in 4 lead to the ROMP of DCPD at 30 °C after 20 and 2 min for 3 and 4, respectively. For the ROMP of DCPD performed at 80 °C with complexes 1 and 2, the complete conversion of DCPD was observed, and the glass transition temperature (Tg) and TGA data of the poly-DCPD product suggest that the additional donors in 1 and 2 only increase the initiation temperature, i.e. they increase the initiation temperature without affecting the inherent activity of the catalyst.