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

The acetate-catalyzed aliphatic isocyanate trimerization to isocyanurate was investigated by state-of-the-art analyti-cal and computational methods. Whereas the common cyclotrimerization mechanism assumes the consecutive addi-tion 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 unex-pected catalytic cycles, with acetate only being the pre-catalyst. The initial discovery of a pre-catalyst 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. Identifica-tion of a side-product with undesired properties for final coating applications allows for process optimization in the chemical industry.