4,4'-Methylene diphenyl diisocyanate (MDI) is an industrially crucial compound, being one of the most utilized linkers in the polyurethane industry. However, its long-term stability is limited due to dimerization to form insoluble uretdione. Herein we demonstrate an organometallic "catchstore-release" concept aiming at improving the long-term chemical stability of MDI. Treatment of MDI with two equivalents of selected N-heterocyclic carbenes (NHC) forms stable MDIÀ NHC adducts. Treatment of the adducts with CuCl forms metastable di-Cu I complexes that undergo decomposi-tion to re-form MDI (up to 85 %), along with CuÀ NHC complexes. The yield of re-formed MDI can be improved (up to 95 %) by the release of the NHC ligands in the form of thiourea; this prevents subsequent MDI dimerization/polymerization by the carbenes. Furthermore, the need to separate MDI from the reaction mixture can be eliminated by the direct reaction of MDIÀ NHC complexes with alcohols (as models for diols), that form dicarbamate (as a model for polyurethane) quantitatively.
4,4’‐Methylene diphenyl diisocyanate (4,4’‐MDI) is a key diisocyanate linker in the production of polyurethanes. 4,4’‐MDI is thermally unstable, undergoing dimerization to unreactive and insoluble uretdione. The “catch–store–release” strategy presented in the Research Article by S. Groysman and co‐workers (DOI: 10.1002/chem.202300924) allows 4,4’‐MDI to be stabilized in the form of an imidazolium amidate that is produced by the coordination of two equivalents of N‐heterocyclic carbene. The complex can be released by heating with CuCl (with or without sulfur); this forms a CuI carbene/urea complex and restores MDI. Artwork by the authors with help from Mary Iverson.
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