Unraveling the Compounded Interplay of Weakly and Strongly Coordinating Ligands in G3-Catalyzed Living Metathesis Polymerization: toward Well-Defined Polynorbornene at Ambient Temperature
Tiantian Wang, Yajuan Shi, Shen Li, Zheng‐Hong Luo, Yin‐Ning Zhou
Abstract
Ambient temperature ring-opening metathesis polymerization (ROMP) of unhindered cycloolefins is crucial for industrial applications from a sustainable perspective. However, balancing the reactivity of propagating species and polymer molecular structure remains a challenge due to competing secondary metathesis at ambient temperature. We report a facile ligand-competition strategy for achieving excellent control over 3-bromopyridine-coordinated Grubbs’ third-generation catalyst ( 3-bropyr-G3 )-catalyzed ROMP of unsubstituted norbornene ( NB ). The addition of external pyridine with a strong coordinating affinity to regulate the catalytic metathesis activity is capable of tuning polymerization rates. Importantly, our strategy allows well-controlled ROMP of NB at both low (i.e., −20 °C) and ambient (i.e., 20 °C) temperatures, yielding P NB with quantitative M n and low D̵ (≤1.07). Synergetic experimental and computational investigations suggest that stably coordinated pyridine can prevent the Ru center from attacking the backbone C═C double bonds by breaking the interaction between the original weakly coordinating ligand and Ru carbene and thus mitigates the intermolecular chain transfer. This study guides the design of new G3 -catalyzed ROMP systems to regulate the balance of metathesis reactivity and polymer molecular structures.