Thermally Stable, Latent Olefin Metathesis Catalysts

Abstract

Highly thermally stable N-aryl,N-alkyl N-heterocyclic carbene (NHC) ruthenium catalysts were designed and synthesized for latent olefin metathesis. These catalysts showed excellent latent behavior toward metathesis reactions, whereby the complexes were inactive at ambient temperature and initiated at elevated temperatures, a challenging property to achieve with second generation catalysts. A sterically hindered N-tert-butyl substituent on the NHC ligand of the ruthenium complex was found to induce latent behavior toward cross-metathesis reactions, and exchange of the chloride ligands for iodide ligands was necessary to attain latent behavior during ring-opening metathesis polymerization (ROMP). Iodide-based catalysts showed no reactivity toward ROMP of norbornene-derived monomers at 25 °C, and upon heating to 85 °C gave complete conversion of monomer to polymer in less than 2 hours. All of the complexes were very stable to air, moisture, and elevated temperatures up to at least 90 °C, and exhibited a long catalyst lifetime in solution at elevated temperatures.

In a Quest for Selectivity Paired with Activity: A Ruthenium Olefin Metathesis Catalyst Bearing an Unsymmetrical Phenanthrene‐Based N‐Heterocyclic Carbene

“…In contrast, under our reactions conditions (40 °C, CD 2 Cl 2 , C=0.1 m ), Ru‐2 has a very low rate of initiation. It is known that the N ‐alkyl‐substituted Hoveyda‐type complexes, require higher temperatures to initiate . This clearly shows that Ru‐3 shows deviation in reactivity from previously published N ‐benzyl‐substituted catalysts, exhibiting initiation rates equal to commercially available catalyst Ru‐1 .…”

Ruthenium Complexes Bearing Thiophene‐Based Unsymmetrical N‐Heterocyclic Carbene Ligands as Selective Catalysts for Olefin Metathesis in Toluene and Environmentally Friendly 2‐Methyltetrahydrofuran

“…This activity is still much lower than standard, SIPr-bearing 3c and 4c,aphenomenon already noted forc omplexes bearing other uNHC ligands, and used as "latent" catalysts in some applications. [23] The relative activity of differently substituted catalysts 10 a-c was distinguishable and only the EWG-activated 10 c resulted in full conversion of 11,w hereas 10 a-b were slightly less reactive (Figure 3).…”

Unprecedented Selectivity of Ruthenium Iodide Benzylidenes in Olefin Metathesis Reactions

“…Previous literature reports with ruthenium diiodo olefin metathesis catalysts revealed that ring opening at room temperature occurred only when the reaction was carried out in a chlorinated solvent, hinting that a partial halogen exchange was in effect . Moreover, ROMP initiated by another diiodo derivative had to be carried out at high temperatures, but RCM could not be achieved in this case . Notably, when norbornenes and diethyl diallylmalonate (DEDAM) were mixed together, all the norbornene derivatives (DCPD, dimethyl cis , endo ‐5‐norbornene‐2,3‐dicarboxylate (NDC), and cis ‐5‐norbornene‐ endo ‐2,3‐dicarboxylic anhydride (Nan)) remained unaffected, even though RCM was efficiently achieved (Table , entries 7–9).…”