title: Studies on electronic effects in O-, N- and S-chelated ruthenium olefin-metathesis catalysts.
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.
authors.affiliation: Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel.
authors.forename: Eyal
authors.initials: E
authors.lastname: Tzur
authors.forename: Anna
authors.initials: A
authors.lastname: Szadkowska
authors.forename: Amos
authors.initials: A
authors.lastname: Ben-Asuly
authors.forename: Anna
authors.initials: A
authors.lastname: Makal
authors.forename: Israel
authors.initials: I
authors.lastname: Goldberg
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Woźniak
authors.forename: Karol
authors.initials: K
authors.lastname: Grela
authors.forename: N Gabriel
authors.initials: NG
authors.lastname: Lemcoff