Hoveyda–Grubbs 1 ^st and 2 ^nd Generation Precatalysts Modified in the Alkoxybenzylidene Part With Long (Fluorous) Chains: Catalytic Activity and Stability

With the aim to understand the role of the 2‐isopropoxybenzylidene ligand, we synthesized Hoveyda‐Grubbs 1 st and 2 nd generation precatalysts ( HG‐I and HG‐II ) analogs modified in the phenyl ring with 5‐octyloxy, 5‐(3,3,4,4,5,5,6,6,7,7,8,8,8‐tridecafluorooctyloxy), 5‐(2,2,3,3,4,4,5,5,6,6,7,7,7‐tridecafluoroheptyloxy) or 5‐(2,2,4,4,5,5,7,7,7‐nonafluoro‐3,6‐dioxaheptyloxy) ponytails and/or instead of isopropoxy group with longer decan‐2‐yloxy or 5,5,6,6,7,7,8,8,9,9,10,10,10‐tridecafluorodecan‐2‐yloxy groups. To improve the fluorophilicity of the precatalysts, we further modified selected precatalysts by two or four 3,3,4,4,5,5,6,6,7,7,8,8,8‐tridecafluorooctyl ponytails in the NHC ligand. All modified HG‐I analogs were more active than precatalyst HG‐I in the ring‐closing metathesis (RCM) of diethyl allyl(methallyl)malonate ( DEAMM , RCM3). On the other hand, only HG‐II complexes modified with fluorinated chain in the isopropoxy group surpassed commercial HG‐II precatalyst in the RCM3. In the most demanding RCM reaction of diethyl dimethallylmalonate ( DEDMM , RCM4), both precatalysts modified with sec ‐decyloxy group initiated more quickly than HG‐II , but seem to be less stable over long reaction times. Medium fluorous HG‐II analogs bearing two or three polyfluorinated chains in the alkoxybenzylidene ligand were successfully tested in repeated RCM3 using medium fluorous recycle. Release‐return mechanism, essential for medium fluorous recycle, was confirmed by partial exchange of the alkoxybenzylidene moieties in the recycled precatalysts using combinations of precatalysts and styrenes bearing different alkoxy groups.