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 (T
onset) and the temperature of the exotherm maximum
(T
exo,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, T
onset and T
exo,max could be
varied between 52 and 142 °C and between 99 and 174 °C,
respectively.