Merrifield resin-assisted routes to second-generation catalysts for olefin metathesis. Issue 6 (14th February 2018)

• Record Type: Journal Article
• Authors: Nascimento, Daniel L.; Davy, Emma C.; Fogg, Deryn E.
• Is Part Of: Catalysis science & technology. Volume 8:Issue 6(2018)
• Page Start: 1535
• Page End: 1544
• Publication Date: 2018-02-14
• Subjects: Catalysis -- Periodicals; 541.395
• DOI: 10.1039/c7cy02278f
• Languages: English
• ISSNs: 2044-4753

Abstract

Abstract : Phosphine-scavenging Merrifield resins can significantly facilitate the synthesis of highly active Ru metathesis catalysts, including the second-generation Grubbs, Hoveyda, and indenylidene catalysts (GII, HII, InII ). Abstract : Phosphine-scavenging resins can significantly facilitate the synthesis of highly active Ru metathesis catalysts, including the second-generation Grubbs, Hoveyda, and indenylidene catalysts (GII, HII, InII ). These catalysts are customarily prepared by ligand exchange of the corresponding first-generation catalysts with the N-heterocyclic carbene (NHC) H2 IMes. The PCy3 coproduct is conventionally removed by pentane extraction, but the partial solubility of the desired Ru products can cause product losses of over 20%. Sequestration of the PCy3 coproduct with CuCl is more efficient, but is undesirable given the potential for non-innocent copper residues. Use of the arylsulfonic acid resin Amberlyst-15 delivers near-quantitative catalyst yields, but the high acidity of the resin leads to problems with reproducibility and decomposition. An alternative approach is described, in which a neutral Merrifield resin (crosslinked polystyrene with pendant p -C6 H4 CH2 I groups;MF-I ) is used to sequester PCy3 as the covalently-tethered benzylphosphonium salt. Addition ofMF-I following complete ligand exchange effects quantitative uptake of free PCy3 (and any residual free NHC) within 45 min at RT: the clean products are isolated by filtration, in ca. 95% yield. These yields compare well with those obtained via the Amberlyst-15 route, without the challenges due to resin acidity. The efficacy of this methodology is demonstrated in the synthesis of isotopically-labelled derivatives ofHII, in which the H2 IMes ligand bears a 13 C-label at the carbene carbon, or perdeuterated mesityl rings.