Metathesis of renewable polyene feedstocks - Indirect evidences of the formation of catalytically active ruthenium allylidene species

Cross-metathesis (CM) of conjugated polyenes, such as 1,6-diphenyl-1,3,5-hexatriene (1) and alpha-eleostearic acid methyl ester (2) with several olefins, including 1-hexene, dimethyl maleate and cis-stilbene as model compounds has been carried out using (1,3-bis-(2,4,6-trimethylphenyl)-2-imidazolidinylidene)dichloro( o-isopropoxyphenylmethylene) ruthenium (Hoveyda-Grubbs 2nd generation, HG2) catalyst. The feasibility of these reactions is demonstrated by the observed high conversions and reasonable yields. Thus, regardless of the relatively low electron density, =CH-CH = conjugated units of molecules, including compound 2 as a sustainable, non-foodstuff source, can be utilized as building blocks for the synthesis of various value-added chemicals via olefin metathesis. DFT-studies and the product spectrum of the self-metathesis of 1,6-diphenyl-1,3,5-hexatriene suggest that a Ru h 1-allylidene complex is the active species in the reaction. (C) 2017 Elsevier B.V. All rights reserved.