The introduction of Grubb’s 2nd generation metathesis catalyst nearly 20 years ago demonstrated the ability of NHC-containing ruthenium catalysts to provide enhanced selectivity and higher turnover numbers (TON) compared to the phosphine-based ligands of Generation 1.1 More recently, a related ligand platform, cyclic alkyl amino carbenes (CAACs), has received significant attention in olefin metathesis. These investigations have shown CAAC-containing catalysts to have enhanced selectivity and unprecedented catalyst lifetimes in several industrially relevant applications.2,3,4
In partnership with Apeiron Synthesis, Strem offers bis- and mono-CAAC Ruthenium- catalysts which have proven to be versatile synthetic tools for use in cross-metathesis, ring-closing metathesis, and ring-opening metathesis polymerization (ROMP).5 The high stability of these systems enables handling in air and remarkably high turnover numbers (TON = 300000 with 1-decene). Scheme 1 shows exceptional performance of the bis-CAAC system UltraCat (cat. #44-0775) in ethenolysis of methyl oleate compared to the NHC-containing Grubbs II catalyst.
Scheme 1. Comparison of catalyst performance in ethenolysis of methyl oleate.
Substitution of ruthenium benzylidene complexes with a judiciously selected CAAC ligand provides a remarkable enhancement in cross metathesis of electron-deficient substrates compared to the related NHC-substituted benzylidene complex, nitro-Grela (scheme 2). UltraNitroCat (cat. #44-0778) also showed a significant advantage in ring-closing metathesis (scheme 3). Importantly, these reactions are likely of interest for application across specialty chemicals, pharmaceutical, and F&F industries (Flagrance and Flavors).
Scheme 2. Performance of mono-CAAC NHC-substituted catalysts in cross-metathesis with acrylonitrile.
Scheme 3. UltraNitroCat outperforms well-known NHC catalysts in ring-closing metathesis.
44-0775 Bis(1-(2,6-diethylphenyl)-3,5,5-trimethyl-3-phenylpyrrolidin-2-ylidene)(3-phenyl-1H-inden-1-ylidene)ruthenium(II) dichloride UltraCat (2055540-61-7)
44-0778 (1-(2,6-Diethylphenyl)-3,5,5-trimethyl-3-phenylpyrrolidin-2-ylidene)(2-isopropoxy-5-nitrobenzylidene)ruthenium(II) dichloride UltraNitroCat (2106819-64-9)
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