Reactivity and Selectivity in Ruthenium Sulfur‐Chelated Diiodo Catalysts

Abstract

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.

Coordinating Additives as Activity Modulators in Diiodo Latent Olefin Metathesis Catalysts

“…Thus, in principle, either the five‐membered RCM product or self‐dimerization through CM of the terminal alkenes can be obtained. Under the conditions noted (100 mM S1 , 1 mol% catalyst, at 80 °C in benzene‐d 6 for 1 h), Ru−SCF 3 −I exclusively promoted the intramolecular RCM of S1 [9] . We attributed this pathway to a significant Thorpe‐Ingold effect that favors cyclization and the relatively large steric hindrance that lowers affinity for dimerization.…”

“…Anionic ligands have shown a crucial influence on the efficiency and selectivity of the olefin metathesis reaction [6] . Given the remarkable ease by which anionic ligands may be replaced in complexes with cis‐ dihalo configurations, we have broadly studied this permutation for S‐chelated complexes; in particular, the effect of iodides as anionic ligands in Ru−SPh−I [7,8] and Ru−SCF 3 −I [9] (Figure 1). These special complexes displayed unique olefin metathesis reactivity and selectivity [10] .…”