Ring Expansion Metathesis Polymerization (REMP) Initiators with an Unusual Ancillary Ligand

Tethered tungsten-alkylidenes bearing azoimido ligands (M≡Nγ-Nβ=NαR) are synthesized, characterized, and tested as initiators for ring expansion metathesis polymerization (REMP). While these ligands are typically unstable and prone to dinitrogen loss, this work demonstrates that tethered alkylidene complexes bearing azoimido ligands are stable enough to be REMP initiators. Moreover, they are more efficient, long-lived, and stereoselective than their corresponding imido derivatives (M≡NR). Density Functional Theory (DFT) analysis of the azoimido complexes provides insight into their unusual stability.