2. Increasing catalysts stability

Challenge: Ring closing metathesis (RCM) reactions of terminal olefins evolve ethylene as a byproduct. The released ethylene generally needs to be eliminated from the reaction mixture to enable optimum efficiency and product yield. If not eliminated, ethylene may take part in unproductive metathesis by entering the catalytic cycle in place of the substrate olefin. This competition can dramatically impact the catalyst’s maximum turn-over-number and induce faster decomposition of the catalyst. Large scale, batch olefin metathesis processes often suffer reduced process efficiency due to inefficient removal of ethylene from the reactor – a potentially serious problem that can force a work-around effort in commercial applications.

Apeiron’s Solution: The hallmark of Apeiron’s nitro-Grela catalyst family is a very fast initiator of olefin metathesis. Replacing the chloride anionic ligands with much bulkier iodide anions (nitro-Grela-SIMesI2, AS2053) results in a ruthenium methylidene species having significantly increased selectivity and stability. With typical metathesis catalysts, insertion of larger anionic ligands has little effect on catalyst activity, or may even reduce its activity. In contrast, nitro-Grela complexes containing iodides stand out as efficient catalysts that are more stable than the parent catalyst and relatively tolerant to the presence of ethylene (and other impurities/by-products) during metathesis of terminal dienes.

Exchange of chlorides to iodides results in more stable ruthenium methylidene species and increased catalyst selectivity

Reference:

  1. M. S. Sanford, J. A. Love, R. H. Grubbs “Mechanism and Activity of Ruthenium Olefin Metathesis Catalysts” J. Am. Chem. Soc., 123, 6543 – 6554, (2001).
  2. J. Wappel, C. A. Urbina-Blanco, M. Abbas, J. H. Albering, R. Saf, S. P. Nolan, C. Slugovc “Halide exchanged Hoveyda-type complexes in olefin metathesis” Beilstein J. Org. Chem., 6, 1091 – 1098, (2010).
  3. A. Tracz, M. Matczak, K. Urbaniak, K. Skowerski “Nitro-Grela-type complexes containing iodides – robust and selective catalysts for olefin metathesis under challenging conditions” Beilstein J. Org. Chem., 11, 1823 – 1832, (2015).