A trifluoromethyl sulfur‐chelated ruthenium benzylidene, Ru‐S‐CF3‐I, was synthesized and characterized. This latent precatalyst provides a distinct activity and selectivity profiles for olefin metathesis reactions depending on the substrate. For example, 1,3‐divinyl‐hexahydropentalene derivatives were efficiently obtained by ring‐opening metathesis (ROM) of dicyclopentadiene (DCPD). Ru‐S‐CF3‐I also presented a much more effective photoisomerization process from the inactive cis‐diiodo to the active trans‐diiodo configuration after exposure to 510 nm (green light), allowing for a wide scope of photoinduced olefin metathesis reactions. DFT calculations suggest a faster formation and enhanced stability of the active trans‐diiodo species of Ru‐S‐CF3‐I compared with Ru‐S‐Ph‐I, explaining its higher reactivity. In addition, the photochemical release of chloride anions by irradiation of Cl‐BODIPY in the presence of DCPD derivatives with diiodo Ru benzylidenes, led to in situ generation of chloride complexes, which quickly produced the corresponding cross‐linked polymers. Thus, novel selective pathways that use visible light to guide olefin metathesis based synthetic sequences is presented.
The ruthenium alkylidene catalyzed ring‐closing metathesis (RCM) of 5‐membered rings is an intramolecular reaction that is highly favored due to entropic and enthalpic contributions. Counterintuitively, by using trifluoromethyl sulfur‐chelated ruthenium benzylidene (Ru−SCF3−I), RCM of a diene with a hindered dimethyl terminus, diethyl 2‐allyl‐2‐(3‐methylbut‐2‐en‐1‐yl) malonate (S1), could be achieved at high concentrations but not at low concentrations. This finding led to the discovery that several additives, including ethyl acetate, significantly enhance the latent catalyst's activity. DFT computations and NMR control experiments suggest that additive coordination influences the catalytic cycle. Moreover, the “ethyl acetate effect” was studied in ring‐opening metathesis polymerizations (ROMP), providing a more efficient initiation when the reactions are run in environmentally friendly ethyl acetate as the solvent. The strong influence of simple coordinating additives (sometimes present in the substrate itself) on the activation of latent catalysts provides important insights into the reaction mechanism and opens a doorway towards improving the efficiency of these types of catalysts.
A trifluoromethyl sulfur‐chelated ruthenium benzylidene, Ru‐S‐CF3‐I, was synthesized and characterized. This latent precatalyst provides a distinct activity and selectivity profiles for olefin metathesis reactions depending on the substrate. For example, 1,3‐divinyl‐hexahydropentalene derivatives were efficiently obtained by ring‐opening metathesis (ROM) of dicyclopentadiene (DCPD). Ru‐S‐CF3‐I also presented a much more effective photoisomerization process from the inactive cis‐diiodo to the active trans‐diiodo configuration after exposure to 510 nm (green light), allowing for a wide scope of photoinduced olefin metathesis reactions. DFT calculations suggest a faster formation and enhanced stability of the active trans‐diiodo species of Ru‐S‐CF3‐I compared with Ru‐S‐Ph‐I, explaining its higher reactivity. In addition, the photochemical release of chloride anions by irradiation of Cl‐BODIPY in the presence of DCPD derivatives with diiodo Ru benzylidenes, led to in situ generation of chloride complexes, which quickly produced the corresponding cross‐linked polymers. Thus, novel selective pathways that use visible light to guide olefin metathesis based synthetic sequences is presented.
Chemical communication between macromolecules was studied by observing the controlled single chain collapse that ensues the exchange of am etal cross-linker between two polymer chains. The rhodium(I) organometallic cross-linker transfer from al ow molecular weight collapsed polybutadienet oal arger polymerw as followed using size exclusionc hromatography.T he increased effective molarity in the larger polymer seemstobethe driving force for the metal migration. Thus, we demonstrate here as trategy for transferring am olecular signalt hat induces chain collapse of ap olymer chain based on non-covalent interactions, mimicking biological behaviors reminiscent of signal transductions in proteins.
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