Olefin Metathesis with Grubbs and Hoveyda–Grubbs Second-Generation Catalysts

May 22, 2026 Methodology, Science metathesis, Grubbs, Hoveyda-Grubbs, ruthenium, ring-closing, cross-metathesis

Olefin metathesis, recognized by the 2005 Nobel Prize awarded to Chauvin, Grubbs, and Schrock, has become a routine C–C bond-forming reaction in medicinal and process chemistry. Among the many catalysts developed, the second-generation Grubbs and Hoveyda–Grubbs ruthenium complexes are the most widely used due to their balance of activity, functional group tolerance, and air stability.

Catalyst Comparison

The Grubbs 2nd-generation catalyst (SIMes)(PCy₃)Cl₂Ru=CHPh features an N-heterocyclic carbene (NHC) ligand that dramatically increases activity relative to the first-generation bis-phosphine system. The Hoveyda–Grubbs 2nd-generation catalyst replaces the benzylidene with a chelating isopropoxybenzylidene; this boosts latency (the catalyst is slow to initiate until heated or activated), which is valuable in industrial settings where premature initiation causes side reactions.

Dominant Reaction Classes

  • Ring-closing metathesis (RCM) — formation of 5–8 membered carbocycles and heterocycles; the single most common application.
  • Cross-metathesis (CM) — coupling of two terminal olefins; selective with sterically or electronically biased partners.
  • Enyne metathesis — constructs 1,3-dienes, useful in natural product synthesis.
  • Ring-opening metathesis polymerization (ROMP) — materials science applications.

Process Considerations

  • Catalyst loading: 0.5–5 mol% typical; lower in flow with immobilized variants.
  • Solvent: Toluene, DCM, and THF are standard; ethyl acetate tolerates some catalysts.
  • Oxygen/moisture sensitivity: Work under inert atmosphere; catalysts tolerate brief air exposure.
  • Ru removal: Post-reaction, silica treatment or phosphine scavengers reduce residual Ru to <10 ppm.

Metathesis has expanded into late-stage functionalization, macrocyclization of peptide and macrocyclic APIs, and stereoselective Z-selective variants using cyclometalated Ru catalysts. The reliability of the 2nd-generation catalysts continues to make them the default choice for route scouting in drug discovery.

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