Tuning the Latent Behavior of Molybdenum Imido Alkylidene N‑Heterocyclic Carbene Complexes in Dicyclopentadiene Polymerization

We report the synthesis of O- and N-chelated hexacoordinated molybdenum imido alkylidene N-heterocyclic carbene (NHC) bistriflate and pentacoordinated molybdenum imido alkylidene NHC monotriflate monoalkoxide complexes and their use as thermally latent and in some cases air-stable precatalysts in the ring-opening metathesis polymerization (ROMP) of dicyclopentadiene (DCPD). Introduction of electron-withdrawing and electron-donating groups at the O-chelated alkylidene ligand allowed for the tuning of both the onset temperature of polymerization (Tonset) and the temperature of the exotherm maximum (Texo,max). In addition, N-chelated complexes were synthesized using easily available 2-vinylpyridine or 2-vinyl-N,N-dimethylaniline to yield five-membered and, for the first time, four-membered molybdenum imido alkylidene NHC chelates. With these precatalysts, Tonset and Texo,max could be varied between 52 and 142 °C and between 99 and 174 °C, respectively.