Cover Feature: “Catch‐Store‐Release” Strategy for the Stabilization of 4,4′‐Methylene Diphenyl Diisocyanate (4,4′‐MDI) (Chem. Eur. J. 30/2023)

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.