Mechanistic Investigation into the Acetate-Initiated Catalytic Trimerization of Aliphatic Isocyanates: A Bicyclic Ride

The
acetate-initiated aliphatic isocyanate trimerization to isocyanurate
was investigated by state-of-the-art analytical and computational
methods. Although the common cyclotrimerization mechanism assumes
the consecutive addition of three equivalents of isocyanate to acetate
prior to product formation, we found that the underlying mechanism
is more complex. In this work, we demonstrate that the product, in
fact, is formed via the connection of two unexpected catalytic cycles,
with acetate being only the precatalyst. The initial discovery of
a precatalyst activation by quantum chemical computations and the
resulting first catalysis cycle were corroborated by mass spectrometric
and NMR experiments, thereby additionally revealing a catalyst migration
to the second catalytic cycle. These results were further confirmed
by computations, completing the full mechanistic understanding of
this catalytic system. Identification of a side product with undesired
properties for final coating applications allows for process optimization
in the chemical industry.