Studies on Electronic Effects in O‐, N‐ and S‐Chelated Ruthenium Olefin‐Metathesis Catalysts |
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Authors: | Eyal Tzur Anna Szadkowska Amos Ben‐Asuly? Dr Anna Makal Israel Goldberg Prof Krzysztof Wo?niak Prof Karol Grela? Prof N?Gabriel Lemcoff Dr |
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Institution: | 1. Department of Chemistry, Ben‐Gurion University of the Negev, Beer‐Sheva 84105 (Israel), Fax: (+972)?86461740;2. Institute of Organic Chemistry PAS, Kasprzaka 44/52, 01‐224 Warszawa (Poland), Fax: (+48)?22‐343‐2109;3. Achva Academic College, Shikmim 79800 (Israel);4. Department of Chemistry, Warsaw University, Pasteura 1, 02‐093 Warzsawa (Poland);5. Department of Chemistry, Tel‐Aviv University, Tel Aviv 69978 (Israel) |
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Abstract: | A short overview on the structural design of the Hoveyda–Grubbs‐type ruthenium initiators chelated through oxygen, nitrogen or sulfur atoms is presented. Our aim was to compare and contrast O‐, N‐ and S‐chelated ruthenium complexes to better understand the impact of electron‐withdrawing and ‐donating substituents on the geometry and activity of the ruthenium complexes and to gain further insight into the trans–cis isomerisation process of the S‐chelated complexes. To evaluate the different effects of chelating heteroatoms and to probe electronic effects on sulfur‐ and nitrogen‐chelated latent catalysts, we synthesised a series of novel complexes. These catalysts were compared against two well‐known oxygen‐chelated initiators and a sulfoxide‐chelated complex. The structures of the new complexes have been determined by single‐crystal X‐ray diffraction and analysed to search for correlations between the structural features and activity. The replacement of the oxygen‐chelating atom by a sulfur or nitrogen atom resulted in catalysts that were inert at room temperature for typical ring‐closing metathesis (RCM) and cross‐metathesis reactions and showed catalytic activity only at higher temperatures. Furthermore, one nitrogen‐chelated initiator demonstrated thermo‐switchable behaviour in RCM reactions, similar to its sulfur‐chelated counterparts. |
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Keywords: | carbenes chelates ligand design metathesis ruthenium |
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