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Influence of Anionic Ligand Exchange in Latent Sulfur-Chelated Ruthenium Precatalysts

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journal contribution
posted on 2018-12-04, 00:00 authored by Elisa Ivry, Noy B. Nechmad, Mark Baranov, Israel Goldberg, N. Gabriel Lemcoff
Four new cis-dianionic S-chelated ruthenium benzylidenes were synthesized by chloride ligand exchange. The special cis-dianionic conformation of these complexes contributed to a particularly facile anion exchange process, producing room-temperature-latent precatalysts. Their catalytic activity was strongly influenced by the solvent used. The latent iodide complex very efficiently promoted ring-closing metathesis by heating in toluene. Conversely, carboxylate ligands produced quite poor catalysts, but could abstract chlorides from chlorinated solvents to transform into active precatalysts. In tetrahydrofuran (THF), the S-chelated dichloro complex was shown to promote cycloisomerization instead of metathesis; however, the metathesis activity in THF could be recovered in the presence of phenylacetylene as a cocatalyst. Under the same conditions, all the other complexes required addition of LiCl to mimic this dichotomous behavior.