Unprecedented Selectivity of Ruthenium Iodide Benzylidenes in Olefin Metathesis Reactions

Abstract

The development of selective olefin metathesis catalysts is crucial to achieving new synthetic pathways. Herein, we show that cis‐diiodo/sulfur‐chelated ruthenium benzylidenes do not react with strained cycloalkenes and internal olefins, but can effectively catalyze metathesis reactions of terminal dienes. Surprisingly, internal olefins may partake in olefin metathesis reactions once the ruthenium methylidene intermediate has been generated. This unexpected behavior allows the facile formation of strained cis‐cyclooctene by the RCM reaction of 1,9‐undecadiene. Moreover, cis‐1,4‐polybutadiene may be transformed into small cyclic molecules, including its smallest precursor, 1,5‐cyclooctadiene, by the use of this novel sequence. Norbornenes, including the reactive dicyclopentadiene (DCPD), remain unscathed even in the presence of terminal olefin substrates as they are too bulky to approach the diiodo ruthenium methylidene. The experimental results are accompanied by thorough DFT calculations.

Reactivity and Selectivity in Ruthenium Sulfur‐Chelated Diiodo Catalysts

“…However, when DEDAM was mixed with DCPD in the presence of 0.5 mol % catalysts, their similar reactivity diverged. Thus, while a solution of DEDAM and DCPD with Ru‐S‐Ph‐I in hot toluene efficiently ring‐closed DEDAM leaving DCPD intact, [11] the use of Ru‐S‐CF 3 ‐I resulted in the reaction of both starting materials, even though no polymer could be detected [13] …”

Sulfur-Chelated Ruthenium Olefin Metathesis Catalysts

“…The fact that 23 could easily catalyze RCM but could not initiate ROMP of a reactive monomer led us to investigate this unique reactivity. 25 In fact, this reactivity is so unusual that it took many repetitions of the experiments by Noy Nechmad to actually convince her supervisor that this was truly happening! Thus, other ROMP monomers were also investigated and found to be completely inert (COE, COD, DCPD, norbornene dicarboxylate, and norbornene anhydride) when mixed with 23.…”

Reactivity and Selectivity in Ruthenium Sulfur‐Chelated Diiodo Catalysts

“…We previously reported that addition of a chloride salt to a mixture of DCPD and Ru-S-Ph-I initiated an anionic ligand exchange that induced fast polymerization. [11] Hence, a photochemical induced anion exchange could be very attractive in this case to expand photochemical prospects. An efficient chloride photocage molecule, 8-(chloromethyl)-4,4-difluoro-1, 3,5,7-tetramethyl-4-bora-3a,4a diaza-s-indacene (Cl-BODIPY), has been developed by Winter and co-workers.…”

“…As expected, both Ru-S-Ph-I and Ru-S-CF 3 -I could efficiently catalyze ring-closing metathesis (RCM) reactions of diethyl diallylmalonate (DEDAM) when heated but were completely inert towards dicyclopentadiene [*] N. B. Nechmad, [+] V. Kobernik, [+] (DCPD) (see SI and ref. [11]). However, when DEDAM was mixed with DCPD in the presence of 0.5 mol % catalysts, their similar reactivity diverged.…”