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CO 2 and Sn II Adducts of N‐Heterocyclic Carbenes as Delayed‐Action Catalysts for Polyurethane Synthesis
Author(s) -
Bantu Bhasker,
Pawar Gajanan Manohar,
Decker Ulrich,
Wurst Klaus,
Schmidt Axel M.,
Buchmeiser Michael R.
Publication year - 2009
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200802670
Subject(s) - catalysis , polyurethane , adduct , chemistry , polymer chemistry , decomposition , polymer , medicinal chemistry , organic chemistry
Catalytic rivals : Both CO 2 ‐protected tetrahydropyrimidin‐2‐ylidene‐based N‐heterocyclic carbenes (NHCs) and Sn II ‐1,3‐dimesitylimidazol‐2‐ylidene, as well as Sn II ‐1,3‐dimesitylimidazolin‐2‐ylidene complexes (example displayed), have been identified as truly latent catalysts for polyurethane (PUR) synthesis rivaling all existing systems both in activity and latency.A series of CO 2 ‐protected pyrimidin‐2‐ylidenes as well as 1,3‐dimesitylimidazol‐2‐ylidene and dimesitylimidazolin‐2‐ylidene complexes of Sn II have been prepared. Selected single‐crystal X‐ray structures are reported. The new compounds were investigated for their catalytic behavior in polyurethane (PUR) synthesis. All compounds investigated showed excellent catalytic activity, rivaling the industrially most relevant catalyst dibutyltin dilaurate. Even more important, all compounds displayed pronounced latent behavior, in selected cases rivaling and exceeding the industrially relevant latent catalyst phenylmercury neodecanoate both in terms of latency and catalytic activity. This allows for creating one‐component PUR systems with improved pot lifetimes. Pseudo‐second‐order kinetics were found for both CO 2 ‐protected tetrahyropyrimidin‐2‐ylidenes and for [SnCl 2 (1,3‐dimesityldihydroimidazol‐2‐ylidene)], indicating a fast pre‐catalyst decomposition prior to polyurethane formation. 1,3‐Di(2‐propyl)tetrahydropyrimidin‐2‐ylidene was additionally found to be active in the cyclotrimerization of various isocyanates, offering access to a broad variability in polymer structure, that is, creating both urethane and isocyanurate moieties within the same polymer.