Highly Selective Olefin Metathesis with CAAC Containing Ruthenium Benzylidenes

Danielle Butilkov butilkov@post.bgu.ac.il Alexander Frenklah N. Gabriel Lemcoff
Chemistry, Ben-Gurion University of the Negev, Beer-Sheva, Israel

Jojoba oil is a diene composed of two monounsaturated hydrocarbon chains linked by an ester moiety. Ruthenium catalysed cross-metathesis reactions (CM) of the oil produced bio-based jet fuel and degradable polyesters under various conditions.1 In our investigation, we noticed a significant double bond migration that led to a broad distribution of the distilled hydrocarbons.

Cyclic alkyl amino carbene (CAAC) ligands are a class of σ-donor ligands which was introduced first by Bertrand et al. in 2005.2 Ruthenium catalysts bearing this type of ligands showed high reactivity towards ethenolysis3 (TON = 340,000) and CM4 (TON = 315,000) reactions. The Bertrand-Grubbs catalyst containing the CAAC ligand showed high selectivity by diminishing isomerization reactions;5 this was especially clear at high temperatures where the more widely used nitrogen heterocyclic carbene (NHC) based catalysts produce significant side reactions. Several olefin metathesis reactions were studied, namely: jojoba oil oligomerization, methyl oleate self-metathesis, ring-closing metathesis (RCM) to form a nitrogen heterocycle, and 1,5-hexadiene acyclic diene metathesis polymerization (ADMET). In addition, Experimental and computational studies determined that it is much more difficult to produce ruthenium hydrides with CAAC, affording a reasonable explanation for the improved observed activity. This finding opens a pathway for the development of even more selective olefin metathesis catalysts for reactions that require harsh conditions.

Reference

  1. Butilkov, and N. G. Lemcoff, Green Chem., 2014, 16, 4728-4733.
  2. Lavallo, Y. Canac, C. Prasang, B. Donnadieu, G. Bertrand, Angew. Chem. Int. Ed., 2005, 44, 5705 – 5709.
  3. M. Marx, A. H. Sullivan, M. Melaimi, S. C. Virgil, B. K. Keitz, D. S. Weinberger, G. Bertrand, and R. H. Grubbs, Angew. Chem. Int. Ed., 2015, 54, 1919-1923.
  4. Gawin, A. Kozakiewicz, P. A. Guńka, P. Dąbrowski, and K. Skowerski, Angew. Chem. Int. Ed., 2016, 56, 981-986.
  5. Butilkov, A. Frenklah, I. Rozenberg., S. Kozuch and, N. G. Lemcoff, ACS Catal., 2017, 7, 7634-7637.








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